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Cormorants and the European Environment

Exploring ecology on a continental scale Photo — Shutterstock

Cormorants and the European Environment

Exploring Cormorant ecology on a continental scale Photographs — INTERCAFE

Mennobart van Eerden, Stef van Rijn, Stefano Volponi, Jean-Yves Paquet & Dave Carss intercafe – cormorants and the european environment

Acknowledgements

This publication has been produced Cormorant Research Group and experts — and, ultimately, by INTERCAFE’s Work Group 1, (WI-CRG). Through them we to new data. Mervyn Roos, the ‘Ecological Databases and would like to warmly thank the Jean-Yves Paquet and Marijan Analyses’ group, which comprised thousands of counters, mostly Govedic carried out the GIS tasks 24 researchers from 22 countries volunteers, for undertaking the and Simon Delany of Wetlands across and beyond (for full breeding and winter counts. International kindly put the IWC details of WG1 participants, please Coordinators of the Pan-European data at our disposal. see Appendix). winter counts were Loïc Marion and Rosemarie Parz-Gollner. Photographs in this publication In addition, data on management Thomas Bregnballe, Stef van Rijn by courtesy of INTERCAFE actions taken against Cormorants and Stefano Volponi coordinated participants and others, at the ‘European’ scale (see 6.4) the breeding census. National and individual sources are were collected and collated by coordinators were responsible acknowledged under each picture INTERCAFE’s Work Group for the management of the local wherever possible. 2, the ‘Conflict Resolution and networks. The breeding counts Management’ group, under the (although carried out and owned by Information on actions taken dedicated guidance of Thomas WI-CRG) were facilitated by the against Cormorants (presented Keller. COST programme’s INTERCAFE in section 10.3) was collated by network. As such, this allowed Thomas Keller through the work of Cormorant counts were organised WI-CRG to coordinate activities INTERCAFE’s WG2 (‘Conflict under the responsibility of the better than before but it also gave Resolution and Management’). IUCN/Wetlands International them access to new countries

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Contents

1 PREFACE 6 8 CORMORANTS WINTERING IN EUROPE: EXPLANATORY FACTORS 51 2 INTRODUCTION 9 8.1 Choice of the study area 51 8.2 Exploring the water surface area/climatic 3 METHODOLOGICAL APPROACHES 11 patterns in the study area 51 3.1 INTERCAFE meetings and Case Studies 11 3.2 Additional Work Group 1 meetings 11 9 THE WATER SYSTEMS DATABASE 57 3.3 INTERCAFE Water System Database 13 9.1 Introduction 57 3.4 Access to international Cormorant census 9.2 Water surface area and Cormorant density 59 data 15 9.3 Water quality 61 3.5 Environmental and GIS datasets 16 9.4 biomass 61 9.5 Abundance and consumption of fish 62 4 AQUATIC AND USE BY CORMORANTS IN EUROPE 19 4.1 Landscape and ecosystem descriptions 19 10 CORMORANT CONFLICTS 67 10.1 Ecological conflicts: protected fish 4.2 Cormorants and water systems 27 and Cormorants 67 10.2 Economic aspects: distribution of cases 68 5 CASE STUDIES FROM THE MAIN TYPES OF 10.3 Management actions taken against WATER SYSTEMS 29 cormorants at the ‘European’ scale 71 5.1 Gulf of 29 5.2 Delta 31 5.3 Delta (, ) 32 11 CASE STUDIES OF CONFLICTS: ECOLOGICAL 5.4 IJsselmeer, The 33 ASPECTS AT A LOCAL LEVEL 78 5.5 The Lagoon, Baltic , 11.1 (category: open sea) 78 34 11.2 Lake IJsselmeer and Markermeer, The 5.6 Slovenian & Austrian pre-Alpine rivers and Netherlands (category: inland sea) 79 streams 35 11.3 The Vistula Lagoon, Poland (category: 5.7 South , 36 inland sea) 81 5.8 Upper , Saxony, 37 11.4 Po Delta (category: complex 5.9 and Lake Kinneret (Sea of and lagoon system) 82 ), 39 11.5 (category: small rivers and pre-Alpine streams) 83 6 CORMORANTS ON A WIDER EUROPEAN 11.6 (category: small rivers) 84 SCALE 41 11.7 South Bohemia, Czech Republic 6.1 Ecology, flyways and countries involved 41 (category: medium sized rivers, fishpond 6.2 Breeding numbers and distribution 42 areas) 86 6.3 Winter distribution 44 11.8 Saxony, Germany (category: complex of artificial and reservoirs, small 7 CORMORANTS BREED75ING IN EUROPE: lowland rivers and fish pond areas) 87 EXPLANATORY FACTORS 46 11.9 Hula Valley and Bet Shean Valley, Israel 7.1 Climatic aspects 46 (category: fishfarms) 90

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12 DISCUSSION 93 12.2.4 What future ecological studies are 12.1 The number of Cormorants 93 needed? 102 12.1.1 What is ‘Europe’ and which populations are we talking 13 SUMMARY AND SYNTHESIS 104 about? 93 13.1 The -Cormorants-Human 12.1.2 How comparable are the Fisheries triptych 104 population data? 94 13.1.1 Cormorant 104 12.1.3 How many Cormorants do we 13.1.2 Fishes 107 have in total? 94 13.1.3 Human fisheries 108 12.1.4 Counting effort and numerical 13.2 Epilogue: towards a solution of ‘the assessment during summer and Cormorant problem’ from an ecological winter 95 perspective? 111 12.1.5 What future census work is needed? 97 14 References 115 12.2 Cormorant ecology 98 12.2.1 Distribution and environmental 15 APPENDIX: WORK GROUP 1 factors 98 MEMBERSHIP 124 12.2.2 Food and feeding ecology 99 12.2.3 Stocking management, ecological research and monitoring of fish 101

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As well as compiling ecological Starting from discussions like this, Ma: ‘Cormorants just changed the data, WG1 devoted quite some WG1 worked with the available steepness of the decline — it was effort to discussing relevant topics data and tried to quantify relevant happening anyway.’ and perspectives. This publication parameters and explore apparent only summarises the main relationships. Mt: ‘We have seen no recoveries in findings of WG1. There follows fish populations after the arrival of an illustration of the detailed J: ‘Nase populations are going Cormorants — and the spawning recordings undertaken, a small down everywhere, for instance in stock has declined. No population exposé of part of a discussion the Danube catchment — so it’s structure data are available. We at a WG1 meeting in Bohinj, not just a Slovenian issue. The only have annual catches — but Slovenia in October 2006. Such Nase was declining before the the population has become older discussions — down to regional Cormorants came’. and older — all the juveniles are level and local, site-specific missing. We now breed fish and try levels were apparent throughout M: ‘That is the question. Were the to repopulate parts of the upper INTERCAFE’s work and refer the cause of the decline or river . Here the population is to the basic questions behind were the fish vulnerable because now in a better state and 2–4 - Cormorant-fisheries interactions: is they were already at low numbers?’ old fish are present now.’ there an effect of the birds on the fish and, if so, can we explain it?

Photo courtesy of Florian Möllers

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1 PREFACE

This publication is supported by of human-wildlife conflicts at Action. INTERCAFE held a series COST. It is one of the outputs of the local to international levels across of eight meetings, each themed INTERCAFE COST Action (635). Europe. It also aimed at delivering around a topic particularly relevant COST (European Cooperation in a coordinated information exchange to the host country: Science and Technology) is the system and improved communication longest-running intergovernmental between stakeholders. To this end, 1. Gdansk, Poland, April network for cooperation in research INTERCAFE attempted to address:- 2005 — ‘Cormorant ecology, across Europe. commercial fishing and i. The fundamental distrust stakeholder interaction’ INTERCAFE — ‘Conserving between the main stakeholder 2. Saxony, Germany, September biodiversity: interdisciplinary groups which was compounded 2005 — ‘Commercial initiative to reduce pan-European by the disparate and aquaculture’ Cormorant-fishery conflicts’ — was uncoordinated nature of 3. Hula Valley, Israel, January awarded funding for four available sources of information, 2006 — ‘Cormorant-fishery (2004–2008). COST Actions are ii. The necessity of applying an conflict management in the Hula charged with directing European integrated interdisciplinary Valley, Israel’ science and do not pay for research approach (biological, 4. Bohinj, Slovenia, October 2006 — researchers’ time. Instead, funding social, legal) to Cormorant-fishery ‘Angling and EU legislation’ was available for INTERCAFE conflicts (as these are as much a 5. Hanko, Finland, April to organise and run a series of matter of human interests as they 2007 — ‘What to do when the international meetings, drawing are of biology or ecology), thus Cormorant comes’ together researchers from a number recognising the need for different 6. Po Delta, , September of disciplines (-related and perspectives in the development 2007 — ‘Extensive aquaculture broader ecology, fisheries science of collaborative strategies, and systems and relationships and management, sociology, social iii. The lack of an integrated between stakeholder anthropology and international understanding of the perspectives and different law) and other experts (very often interdisciplinary factors at the spatial and institutional levels’ connected with fisheries production, heart of Cormorant-fisheries 7. South Bohemia, harvest and management, or conflicts that precludes the Czech Republic, April to regional/national policy provision of useful and practical 2008 — ‘Management practices and decision-making). Under information and advice to all in a complex mosaic and INTERCAFE’s coordination, interested/affected parties. at local, regional and national interested parties, from local levels’ stakeholders to international policy- The INTERCAFE network 8. , , September makers, were thus offered a unique comprised almost seventy 2008 — ‘The management of opportunity to address European researchers from all 27 EU Member Cormorant-fisheries conflicts in Cormorant-fisheries issues. States (except Luxemburg, France and the wider European and ) and other countries context’ The main objective of INTERCAFE in continental Europe (, was to improve European scientific , ) and the Middle At each meeting, INTERCAFE knowledge of Cormorant-fisheries East (Israel). In addition to these participants worked in one of three interactions in the context of the 28 countries, Ukraine and Work Groups, covering the broad interdisciplinary management were also associated with the aims of the Action:

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▪▪ Work Group One — Ecological ▪▪ Cormorant-fisheries conflicts Nowadays, the Databases and Analyses at Carp ponds in Europe and carbo constitutes ▪▪ Work Group Two — Conflict Israel — an INTERCAFE a prominent top predator in many Resolution and Management overview. (ISBN 978-1-906698- diverse aquatic habitats across ▪▪ Work Group Three — Linking 10-2) Europe. Having successfully Science with Policy and Best ▪▪ Essential social, cultural recovered from a greatly reduced Practice and legal perspectives on population numbering some Cormorant-fisheries conflicts. 600 pairs in two colonies in The Most meetings included a field (ISBN 978-1-906698-11-9) Netherlands in the late 1960s, the visit to allow participants to see species is no longer threatened Cormorant-fishery conflicts at Highlights from these publications from a conservation perspective. first-hand. In addition, wherever will be available in INTERCAFE: The spectacular increase in the possible the INTERCAFE an integrated synthesis (ISBN population of the ‘continental’ budget was also used to invite 978-1-906698-065) at http://www. race (P. c. sinensis) is considered appropriate local, regional, intercafeproject.net a success story in terms of nature national or international experts conservation. A top predator has to these meetings. Through these Drawing on INTERCAFE’s ability been reinstated through the joint discussions and interactions, to develop a network of researchers efforts of protective measures INTERCAFE participants tried to and the Action’s privileged and improving conditions in the understand the diverse Cormorant- opportunity to see and hear about aquatic environment (van Eerden fishery conflicts in Europe and Cormorant-fishery issues across et al. 2003). As such, the nature beyond. Europe and beyond, ‘Cormorants conservation goal for the species and the European environment’ has been met, parallel with those This publication is one of a series is an exploration of Cormorant of other wetland species like of INTERCAFE outputs aimed ecology, particularly in relation Great White Egret (Egretta alba), at providing readers with an to interactions with fish, on a Spoonbill (Platalea leucorodia), overview of European Cormorant- continental scale. White-tailed (Haliaeetus fishery conflicts and associated albicilla) and others. The fact that issues, which is as comprehensive Cormorants are now relatively as possible given the budgetary numerous across their former and time constraints on all of geographical range and in many INTERCAFE’s participants. places where they were formerly absent, that the species often The INTERCAFE publications are: operates in large flocks, is highly mobile, and a versatile forager ▪▪ Cormorants and the European across a bewildering diversity of Environment: exploring fresh, brackish and coastal waters Cormorant ecology on a forms the biological basis for continental scale. conflict with fisheries’ interests (ISBN 978-1-906698-07-2) (e.g. van Eerden et al. 2003, Carss ▪▪ The INTERCAFE Field & Marzano 2005, Carss et al. Manual: research methods for 2009). Cormorant ecology and Cormorants, fishes, and the population dynamics have been interactions between them. studied for decades and few, if (ISBN 978-1-906698-08-9) any, other waterbirds in Europe ▪▪ The INTERCAFE Cormorant have been investigated in such Management Toolbox: methods Adult male Cormorant (Phalacrocorax quantitative biological detail (van for reducing Cormorant carbo sinensis), Oostvaardersplassen, Eerden et al. 2003). Nevertheless, problems at European fisheries. The Netherlands. there is much still to learn about the (ISBN 978-1-906698-09-6) Photo courtesy of Mervyn Roos. ecology of Great Cormorants and

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their relationship with European knowledge on an EU-27, and even ▪▪ (2) how this is related to the wetland environments. on a pan-European, scale and this is abundance and availability of undoubtedly a unique strength of the fish species, and This publication is the result work of the INTERCAFE Action. ▪▪ (3) how the conflicts which of the joint efforts of a number fisheries interests fit into this of researchers during the One of the main tasks of framework. INTERCAFE Action. ‘Cormorants INTERCAFE’s WorkGroup 1 was and the European environment’ takes to come up with a coherent view on INTERCAFE’s Work Group 1 an integrative approach, bringing the population status of Cormorants, produced two main outputs, this together ecological knowledge and the distribution of the species and publication being the result of the data relating to both Cormorants its ecology. With regard to the latter, main analysis of ecological aspects and their fish prey but also relating the Work Group concentrated on in relation to European Cormorants, to wider European environments. the issue of fish and the and ‘The INTERCAFE Field The aggregation of information was position of this fish-eating bird Manual: research methods for possible both in the field by meeting in the various aquatic habitats. Cormorants, fishes, and the local and national experts from a Emphasis was placed on the interactions between them’ (Carss, diverse range of sites across Europe ecological factors that determine Parz-Gollner & Trauttmansdorff during INTERCAFE meetings the occurrence and availability of 2012), which provides an (see page 6), as well as from the fish. By using this approach the overview of common methods and literature and unpublished data. Work Group attempted to collate a techniques used in Cormorant-fish This has led to considerable new coherent picture of: studies and which form the basis insights into Cormorant ecology at a of much of the quantitative data large geographic scale. Of particular ▪▪ (1) the ecological circumstances collated and discussed here. benefit was the opportunity to under which Cormorants use integrate information from numerous their habitat, different sources and to provide

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2 INTRODUCTION

Within INTERCAFE’s timeframe fish, as well as with respect to the This massive area stretches from (2004–2008), Work Group 1 dealt timing and site-specific (and site- , and with ‘ecology’ with the aim of dependent) aspects of the conflicts. in the west to the , describing relationships between and in the east, and the living world and the abiotic Part of the ecological work from and the Barents (non-living, usually physical and described here was begun on Sea in the north to , chemical) environment. With a European scale during the and Saudi Arabia in the south. respect to the Cormorant-fisheries REDCAFE EU-Concerted Action However, the ultimate focus of issue, this meant unravelling (Carss 2003). However, through INTERCAFE’s work was on the what could be termed ‘the Fishes- INTERCAFE, it was possible to ‘European’ situation, particularly Cormorants-Human fisheries extend the original database by that pertaining to the EU-27 . triptych’ and both its environmental adding more relevant information and geographical variation across from across the This publication details the Europe. Therefore emphasis was and beyond. Additional information occurrence of two subspecies (or placed not only on Cormorants but was also obtained from non-EU races) of Cormorants in Europe. also on numerous species of fishes countries like Israel, Georgia and The first, Phalacrocorax carbo and their mutual dependence in , as well as by combining carbo, the so-called ‘carbo’ or water systems at the continental information from the IUCN- ‘Atlantic’ race has its main breeding scale. Using quantitative food Wetlands International Cormorant distribution on the rocky of web analysis as a basis, this Research Group (WI-CRG) on a Ireland, the UK, northwest France, triptych approach has previously much larger geographical scale, Iceland and Norway. The second, been successfully formulated and that of the Western Palaearctic. P. c. sinensis, the so-called ‘sinensis’ applied in the IJsselmeer system in the Netherlands, a long-established foraging and breeding area for Cormorants (van Rijn & van Eerden 2002). The rationale behind this approach is that by quantifying ecological relationships between Cormorants and fish, as well as those between fish and human fisheries, the mutual bonds between Cormorants and fisheries can be better understood. As such it was also possible to relate ecological research findings to the issue of ‘conflict’ (see also van Eerden et al. 2003, Carss & Marzano 2005, Carss et al. 2009). INTERCAFE addressed this issue by comparing different water systems with respect Colony of ground-breeding Cormorants (Ph.c.sinensis) in a reed bed to the occurrence of Cormorants along the shore of Lake IJsselmeer, . in relation to the ‘availability’ of Photo courtesy of Florian Möllers.

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or ‘continental’ race breeds inland, Group. In terms of data collection, throughout the breeding (chapter 7) often in trees but also on the ground, synthesis and analysis, this and wintering (chapter 8) periods. across a wide area from France publication includes five related Analysis and interpretation are and Italy in the south to the Low sections, which explore Cormorants carried out within a GIS framework, Countries, Germany and Poland and and the European environment at a incorporating independent north into the countries bordering number of different scales, moving environmental datasets. Chapter the Baltic. This subspecies is also between the continental and the 6 also includes information on widely spread throughout central and site-specific, as follows: management actions taken against from the countries Cormorants at a European scale. along the Danube catchment area (i) Eight broad aquatic habitat and and extending into types used by Cormorants (iv) The relationships between , Ukraine, Turkey, and the throughout Europe are described, Cormorants and their food Russian Federation and beyond. with emphasis on their general requirements at specific water Although ‘carbo’ birds breed and ecological characteristics and scale. bodies are investigated through generally winter on rocky coasts, Descriptions are based on expert analysis of 179 site-specific cases there is an increasing trend for inland knowledge and published sources across Europe where quantitative breeding and these birds can spend (chapter 4). (or at least semi-quantitative) prolonged periods inland during data are available for both birds the winter. By contrast, ‘sinensis’ (ii) Within these aquatic habitat and fishes. This exploration is birds are more generally confined to types, detailed ecological done under the framework of brackish and fresh waters. descriptions are given of nine INTERCAFE’s Water Systems representative areas (most were Database (chapter 9), which also Being a migratory species, the chosen as case study locations for contains information relating to Cormorant clearly exploits INTERCAFE meetings) at a site- Cormorant conflicts with fisheries different areas in winter and specific level (chapter 5). interests (chapter 10). summer. Therefore, a key element of the work reported here was to (iii) Cormorant numbers and (v) Finally, the exploration document these seasonal changes distribution across Europe and returns to the site-specific level by in distribution and numbers across beyond are described — often examining some key ecological Europe. This was greatly assisted at a very large geographic scale perspectives of these conflicts by access to data collected and (chapter 6), and these data are (chapter 11) from many of the held by members of Wetland explored in relation to prevailing representative water systems types International’s Cormorant Research environmental conditions described previously (chapter 5).

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3 METHODOLOGICAL APPROACHES

The main methods used here (1) INTERCAFE meetings and fisheries, but each also allowed relied on gathering existing Case Studies (see Preface). Work Group 1 to explore a specific data through contact with local ecological issue (see Table 3.1). scientists and stakeholders during (2) Additional Work Group 1 Work Group 1 addressed the INTERCAFE’s international meetings. ecological description of each area meetings. Such information and tried to add the key data from made a vital contribution to the (3) INTERCAFE’s Water Systems that region to INTERCAFE’s compilation of the final datasets Database, including enquiries for database. Contacts with local explored here. Additionally, relevant data from researchers stakeholders were useful in terms enquiries were made to numerous across Europe. of access to local ecological researchers in an attempt to collate information but also helped (4) Cormorant census data for the best available information about participants to understand the status and distribution (breeding Cormorants in relation to fish in perception of the conflict as well and wintering), provided by IUCN- specific waters throughout Europe. as explore the economic and social Wetlands International Cormorant As it was commonly felt that the factors affecting the local community Research Group (WI-CRG). situation across Europe differed (see Marzano & Carss 2012). considerably, an attempt was (5) Integration of Cormorant Specific information is discussed made to describe these observed data with environmental and GIS through each of the INTERCAFE patterns independently by using datasets, including ESRI, CORINE meeting reports (it is planned that a geographic information system and World Climate Data. these will be available at http://www. (GIS). As such, the data gathered intercafeproject.net), while the main during INTERCAFE meetings conclusions are fully integrated and from enquiries (see below) were 3.1 INTERCAFE meetings and reflected in this publication. Table integrated by working with Case Studies 3.1 gives the location, date, theme, commonly available EU-wide major habitat type, and more specific datasets. Thus information from INTERCAFE meetings and Case ecological issues explored in each INTERCAFE’s Water Systems Studies were organised in specific INTERCAFE meeting and Case Database could be explored more carefully chosen areas where the Study. deeply and projected to a much Cormorant-fishery issues were wider geographic scale. considered ‘typical’ of several other places throughout Europe (see also 3.2 Additional Work Group 1 The remainder of this chapter chapter 13 of ‘Essential social, meetings provides an outline of the cultural and legal perspectives main set-up for the collation on Cormorant-fisheries conflicts’ Several additional Work Group 1 of INTERCAFE’s ecological [Marzano & Carss 2012]). Each of meetings were organised during the databases and subsequent analyses the nine INTERCAFE meetings Action. These small meetings (see at the European scale. Essentially, thus explored both a major wetland Table 3.2) were directed towards data collation was undertaken in habitat type on a pan-European data analysis and the transfer of five integrated modules: scale in relation to Cormorants and techniques (standardised methods),

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Table 3.1 INTERCAFE meetings and Case Studies: location, date, theme, major habitat type, and more specific ecological issues explored.

Meeting location Date Specific theme Major habitat Ecological issue(s) type Lisbon (Portugal) Jan 2005 Interdisciplinary integration of Atlantic coast, Important wintering area of Cormorants, natural and social science estuary both carbo and sinensis races Gdansk, Vistula Apr 2005 Cormorant ecology, commercial Lagoon, Baltic Largest colony in Europe, feeding lagoon (Poland) fishing and stakeholder Sea strategy (lagoon versus sea), potential interaction competition with commercial fishery Saxony (Germany) Oct 2005 Commercial carp aquaculture Carp fish ponds Biosphere reserve with carp ponds and (semi-extensive) alternative water bodies used by large number of Cormorants Hula Valley (Israel) Jan 2006 Cormorant-fishery conflict man- Carp fish ponds Major wintering area for agement (intensive), Cormorants, important area for wetlands aquaculture and other water birds Bohinj Lake Oct 2006 Angling and EU legislation Alpine rivers and Small number of wintering Cormorant in (Slovenia) lakes an apparently pristine river environment with high conservation value for endangered and/or scarce fish species and widespread stocking for recreational angling Hanko Apr 2007 What to do when the Baltic coast Rapidly increasing breeding population (Finland) Cormorant comes of Cormorants in a coastal environment Po Delta Sept 2007 Extensive aquaculture systems Large wetland Large coastal lagoon system used as (Italy) and relationships between complex extensive fish ponds, very important stakeholder perspectives and area for biodiversity used in winter by different spatial and institutional Cormorant (and ) levels South Bohemia Apr 2008 Management practices in a Carp fish ponds Carp ponds used by wintering (Czech Republic) complex habitat mosaic and and large rivers cormorant, complex wetland mosaic at local, regional and national with water turbidity issues levels Paris Sept 2008 The management of Cormorant- Water bodies at Impact of shooting large number of birds (France) fisheries conflicts in France and a large country on both Cormorant distribution and that the wider European context level of associated conflicts others were wrap-up sessions These additional meetings were of the coverage of countries and between local specialists and also used to produce an overview during the pan-European included data analysis and reporting. of the process and structure for Cormorant breeding colony count The main aims of these meetings data management of the pan- was constructed and used as means were to (a) discuss how best to European counts of Cormorant of trying to retrieve data from organise and analyse data provided roosts and colonies made available countries where no data had been from counts of breeding colonies to INTERCAFE. The database received so far. Decisions were and roosting sites, (b) retrieve data structures of the pan-European also taken about rules for future from countries from which no roost and breeding colony access to the data collated. Letters information had been received, and databases were also discussed and concerning the protocols for data (c) analyse some of the data by use documented. A quality check of the handling and decisions about future of a Geographic Information System pan-European Cormorant roost data access to data were written during (GIS, see section 3.5). was also conducted. An overview these meetings and later mailed

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Ringing young Cormorants during an Colour-ringed young Cormorants for studying migration movements, additional Work Group 1 meeting, Kivilaid, , June 2007). Kivilaid, Estonia, June 2007. Photo courtesy of Karlis Millers. Photo courtesy of Karlis Millers. to the national coordinators of the (bird ringing, taking biometrical data, to water bodies throughout Europe. Cormorant census. food analysis and aerial counting) Standardised information on fish, in relation to parameterising these fisheries, and Cormorants were Two additional meetings were complex habitats in relation to Work acquired as well as background directed to areas where a big Group 1’s broad aims. water chemistry (i.e. nutrient status) expansion of Cormorants had and topographic information. occured recently, the Finnish Gulf in the eastern Baltic and 3.3 INTERCAFE Water Systems An extensive inquiry, based on a the Danube Delta in the area of Database standard Excel spreadsheet (see the Black Sea, another important Table 3.3) was sent out to numerous European focal point. Both meetings The main aim of this module was to researchers and to representatives were specifically designed and obtain relevant data (from published of the different countries implemented to transfer methods and unpublished sources) relating participating in the INTERCAFE Action. By grouping different water bodies into different types, Table 3.2 Additonal meetings organised within Work Group 1. the aim was to collect information Additional meeting location Date Main Goal on the full array of European water , Kälø February 2007 Water Systems body types whilst taking into Database account their geographic position and distribution across Europe. Romania, Tulcea, Danube Delta May 2007 Methodology transfer This information was then made Estonia, Finland, Finish Gulf June 2007 Methodology transfer available for further analysis in Austria, Vienna June 2007 Water Systems relation to eight water body types: Database

Belgium, Liege December 2007 Reporting ▪▪ Open sea/shore ▪▪ /river deltas The Netherlands, June 2008 GIS analysis ▪▪ Inland sea/large lagoon , Edinburgh December 2008 Writing-up session ▪▪ Large lakes

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Table 3.3 Example of the spreadsheet used to obtain structured data on different water bodies used by Cormorants for INTERCAFE’s Water Systems Database. Both hydrological and ecological data were requested according to a fixed format. Some cells remained blank if the respondent was unable to provide relevant information.

Name of respondent Stef van Rijn Country The Netherlands Name of site Markermeer

Issue Specification Data Habitat-type see README 3 Location Greenwich coordinates 52.35N,5.1E reference(s) of study peer/non-peer reviewed/anecdotal* peer Period of study (give range) year(s) 1996–2000 Sub-species carbo-sinensis* sinensis Number of Cormorants involved maximum 15,000 Number of Cormorants involved bird days per year 680,000 Status of Cormorants breeding/non-breeding breeding Flock size at times of fishing average number of Cormorants 1,000 Occurrance of mass fishing yes/no yes Juveniles % of number 12 Size of fishing water Km2 700 Water body natural/semi-natural/artificial semi-natural Depth m 3.5 Trophic status oligotrophic/mesotrophic/eutrophic* eutrophic Turbidity (Secchi depth) m 0.5 Fish species in area number 36 Fish species/group most abundant (rank 1) name Abramis brama Fish species/group most abundant (rank 2) latin name Osmerus eperlanus Fish species/group most abundant (rank 3) latin name Gymnocephalus cernuus Overall fish biomass Kg/ha 115 Density of most abundant species (rank 1) Kg/ha 50 Density of most abundant species (rank 2) Kg/ha 40 Density of most abundant species (rank 3) Kg/ha 15 Fish species in diet number 14 Fish species/group eaten most (rank 1) latin name Gymnocephalus cernuus Fish species/group eaten most (rank 2) latin name Perca fluviatilis Fish species/group eaten most (rank 3) latin name Rutilis rutilis Density of most eaten speciess (rank 1) Kg/ha 15 Density of most eaten speciess (rank 2) Kg/ha 5 Density of most eaten speciess (rank 3) Kg/ha 3 Overall consumption (all fish species) % taken from available (Kg/ha) 4.4 Consumption of most eaten species (1-3) % taken from available (Kg/ha) 16.5 Distance of colony or roost to fishing water Km 3 Distance to nearest colony or roost Km 14 Distance to nearest alternative fishing water Km 7 Colony/roost existence number of years 23 Colony/roost habitat willow/poplar willow alder/birch ash///birch/lime coniferous ground nesting other Population increase or decrease % average last 5 years (-=decrease, +=increase

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▪▪ Large rivers a useful way to express Cormorant The preparation of the WI-CRG ▪▪ Streams/small rivers use of an area in relation to the count was carried out by a small ▪▪ Reservoirs/small lakes, sandpits potential impact on a certain water group of researchers experienced ▪▪ Fish ponds body (for detailed discussion on in counting Cormorant colonies. integrating Cormorant and fish data A technical description of how to In total, 179 water bodies were in relation to ‘impact’ at fisheries, count nests and how to enter data characterised during this process see chapter 9 of Carss et al. 2012). into an electronic database was from 26 INTERCAFE countries prepared. National coordinators and the responses of a further total were selected, and contacted by of 65 experts. As well as water 3.4 Access to international letter and e-mail, prior to the 2006 systems within the European Union Cormorant census data breeding season. In the field, territory, additional information was counts of colonies were generally obtained from Norway, , Cormorants breed in colonies in conducted as counts of Apparently Croatia and Georgia. These summer, where they construct nests Occupied Nests, defined as nests in complemented the dataset because either in trees, bushes, or on the use and sufficiently finished to hold they represented specific examples ground in reed beds and on bare one or more . Following Carss of water quality, management and/ rock or sand. Colonies occur in the et al. (2012), a colony was defined or use by Cormorants. vicinity of larger water bodies in a as a group or groups of nests that variety of habitats, often in wetlands, are within 2,000 m of each other. In the spreadsheet, common riverine woodlands, coastal forests, Such neighbouring groups were characteristics like water body remote or rocky seashores. referred to as ‘sub-colonies’ (for size, location and depth were Furthermore, artificial structures full information on the standard requested, plus biotic data on fish such as high lighthouses or remote methodologies for counting (total number of fish species, peak platforms and shipwrecks may also breeding Cormorants see section standing stock of fish in summer, be used. Cormorant colonies can 2.2 of Carss et al. 2012). top three ranking of most important vary enormously in size with some fish species) as well as data on comprising only a few nests whilst the trophic level and secchi depth the largest ones may contain up to In winter, Cormorants disperse (a standardised measure of water several thousand nests. over large areas in both freshwater clarity). Cormorant abundance and and shallow marine waters. Birds use was requested, as were peak In 2006 the most recent Pan- aggregate at night in roosts, situated numbers, total number of bird days European breeding census of on islands, in trees and bushes in spent at the site per year, flock size Cormorants was organised under the wetlands, on river banks or artificial and data on diet (top three ranking responsibility of the IUCN Wetlands constructions like high tension of the most important fish species International Cormorant Research poles, lighthouses, ship wrecks, and according to dietary studies). Group. The organisation of the dikes. Although winter and summer The presence of Cormorants was breeding counts was facilitated areas overlap, most birds breed expressed in ‘bird days’, that is by INTERCAFE through its at northern latitudes and winter the product of the average number meetings and the extensive research more to the south. During daytime, of Cormorants and the number of network established by the Action. foraging flights occur between days that this number is present (for INTERCAFE meetings offered colonies or roosts and feeding areas a detailed discussion, see section unique opportunities for the and may range between 5–25 km 2.4 of the INTERCAFE Field Cormorant Research Group to (max. 40–60 km) in each direction. Manual [Carss et al. 2012]). For discuss and coordinate its activities. In Europe counts outside the example, if 200 Cormorants were INTERCAFE was also an breeding season are best undertaken present for three weeks on a lake, extremely valuable platform through at night roosts. However, in some this results in a total of 200 birds which WI-CRG could build contacts areas only daytime counts exist, and x 21 days = 4,200 bird days. The with new countries and local experts these were included to complete same number is obtained when 600 which otherwise would have been the picture of winter status and birds stay one week. Bird days are difficult to communicate with. distribution.

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Cormorant counts in winter ‘Lambert Azimuthal Equal Area’ from www.worldclim.org (data require coordinated action by projection was used for making Version 1.4 [release 3]) were used, skilled persons, using binoculars, charts in the coordinate system specifically the mean, minimum telescopes and other techniques ETRS 1989. A 50 km x 50 km grid and maximum temperatures (1950– such as aerial photography was applied to all layers. For each 2000) for each month, averaged per and ship-based counts in large, 50 x 50 km cell of the grid, several grid cell. The available temperature inaccessible areas. Roost counts calculations were made, based on grid data had a resolution of 30-arc are carried out using standardised the climatic or water information d, often referred to as 1 km spatial methodology, over a specific dataset (see below), but also on the resolution (Hijmans et al. 2005). allocated time period for counting number of Cormorants counted All analyses were done with Excel and using pre-printed forms (for during either the 2003 winter roost (Microsoft), ArcView 3.3 (ESRI), further information on the standard counts or the 2006 colony count. ArcGis 9.1 (ESRI) using different methodologies for counting The following environmental extensions (Spatial Analyst, Get roosting Cormorants in winter, see variables were calculated for each Grid values) and Scripts (clipgrid) section 2.3 of Carss et al., 2012). grid cell: where necessary.

Thus two datasets were ultimately ▪▪ average minimal temperature in From the original database of made available to INTERCAFE, January (°C) Cormorant colonies, a shape both being the most up-to-date ▪▪ surface area of shallow sea file was produced. In ArcView and geographically widespread water (ha) temperature values from grid available — a breeding count at ▪▪ surface area of freshwater lakes climatic data were added to colonies colonies in summer 2006, and (ha) as attributes. The ‘Map query’ a winter roost count undertaken ▪▪ surface area of each Strahler tool was then used to explore the in 2003. Data from both counts type river section (ha) temperature grid files. In to were transformed during the investigate how different climatic INTERCAFE Action into a Along with these variables, latitude conditions across Europe might uniform 50 x 50 km grid across and longitude were also used as predict the suitability of a region Europe (see section 3.5) in order ‘spatial variables’ and as a proxy to for Cormorant colonies, the start of to relate the data to environmental geographical situation (i.e. distance breeding activity in a colony was parameters. A basic ‘layer’ was to main breeding area). assumed to be related to average produced with 885 geo-referenced spring temperature. Temperature colonies from all European This GIS-module aimed to explore changes for each colony site were countries (plus Turkey and Iran) geographically the ecology then determined for a time, three for further multi-layer GIS analysis of Cormorants in Europe by months after the potential start of (conflict cases, climatic conditions combining two ecological datasets breeding, which was assumed to be and geographical location). For (the distribution of Cormorant the time at which young Cormorants the winter 2003 roost count, a colonies and winter roosts) with leave the colony. The broad geo-referenced database (and climatic data and data on the rationale behind this approach was corresponding maps) were produced type and spatial distribution of the relationship between ambient from more than 2,500 roosts across waterbodies across the . temperature, water temperature Europe. This work was divided into four and its oxygen content, and the blocks, focusing on the following swimming speed of fishes, which in subjects. turn determine the suitability of a 3.5 Environmental and GIS region for Cormorants based on the datasets 1. Climatic data availability of their prey. Cormorant distribution across All the spatial information Europe was explored through 2. European Water Chart layers were processed using the a spatial and temporal analysis Cormorant distribution across Geographic Information System of general climatic patterns. For Europe was further explored software ArcGis 9.1 (ESRI). The this analysis temperature data through comparison with

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a compilation of existing Table 3.4 Number of countries where conflicts were reported during geographical information from INTERCAFE and REDCAFE projects, as well as the total number of conflicts. As some CORINE and ESRI on the countries and conflicts were reported in both projects, there is overlap between occurrence of different water datasets and so figures cannot be totalled across rows. bodies in Europe. With the Conflict details REDCAFE Concerted INTERCAFE COST emphasis within these datasets Action Action on rivers and lakes, additional information was also included on No. of countries 23 15 other water bodies such as shallow Total No. of conflicts reported 238 200 coastal systems. Validation of the database for specific areas showed considerable deviation for coastal conflict data file from REDCAFE were used to arrive at a grid of water bodies (deltas, lowland lakes, and, subsequently, a spatial analysis 50 km x 50 km across Europe. This oxbows and backwaters). These of conflict cases was performed grid (RASTER50000) was then topographic aberrations have been in relation to the distribution and used as basis for calculations and repaired where possible, using abundance of water bodies and the GIS presentations. satellite images obtained from the distribution of Cormorants in both Internet (e.g. Google™ ). summer and winter. Rivers and lakes For rivers and lakes, the ‘River and 3. Cormorant ecology data Table 3.4 above shows the total Catchment Database for Europe, The 2003 winter count data and number of conflict cases used Version 2.0 (CCM2) — 2007 the 2006 colony count data were in this study, as well as the (Joint Research Centre)’ was explored in relation to datasets of number originally obtained by the used. See also website: (http:// both climatic variables and the REDCAFE project. In some regions/ ccm.jrc.ec.europa.eu/php/index. availability of water bodies (rivers, countries there were no new conflict php?action=view&id=24). The lakes, coasts etc). Based on the cases and so only one source is CCM2 database covers the 50 x 50 km2 gridcell information, shown on the resulting map. entire pan-European continent, Cormorant distribution was including the Atlantic islands, correlated with environmental factors 5. Analysis Iceland and Turkey. It also at the same level, thus allowing Countries includes a hierarchical set of river analysis of multiple factor effects. With respect to country borders, segments and catchments based the shape file COUNTRY from on the ‘Strahler order’ system (see 4. Conflict cases ESRIDATA_EUROPE was used Table 3.5) for different tributaries The REDCAFE EU-Concerted initially. However, as this file was of a river system, a lake layer and Action attempted to produce a incomplete, especially for Northern structured hydrological feature broad-brush picture of the distribution , the and , codes based on the Pfafstetter and scale of reported conflicts with more recent files were obtained from system. This allowed calculations on Cormorants. Whilst there were ESRIDATA. The coastline of North the quantitative presence of different certain limitations to this approach, Africa and specific areas such as water bodies at a continental scale. the resulting picture was considered large interior lakes and the deltas of the best available at the time (see large rivers were incorporated from This database was available as a Carss 2003, pp.78–102, particularly Google™ Earth satellite images. Geodatabase only and because sections 4.1 and 4.9). This dataset was INTERCAFE’s analyses were updated during INTERCAFE and Raster in ArcGis 9.1, all individual files the distribution of reported fisheries In order to arrive at a rectangled were downloaded and transformed conflicts with Cormorants was also grid system we used the Lambert into shapefiles, ‘CCM2-rivers’ and included in INTERCAFE’s GIS Azimuthal Equal Area Projection, ‘CCM2-lakes’. Using the adjusted analyses, firstly in relation to the WI- ETRS 1989. Minimum and dataset COUNTRY, the layers CRG database of breeding colonies. maximum X and Y coordinates of CCM2-rivers and CCM2-lakes Quality checks were made of the the adjusted COUNTRY shapefile were clipped and stored again. This

www.intercafeproject.net [17] intercafe – cormorants and the european environment

The Danube in Serbia is one of the few large rivers of the category ‘Strahler 10’ in Europe. Photo courtesy of Daliborka Stankovic. resulted in a greater reliability of different areas in Europe, an average the unique nature of this analysis, the areas in Eastern Europe. value for river width was given to this was the first European-wide each Strahler category within the estimation of this ‘shallow coastal Procedure system as shown in Table 3.5. water’ parameter. In the file CCM2-rivers, river sections were coded according to Values for river length and width, Total water the Strahler system. Type 1 is most and thus surface area, were computed A chart WATER_HA was upstream and thus the smallest; type for each river section and added to constructed using data from 10 is used rarely in Europe, only each grid cell in RASTER50000. CCM2-rivers, CCM2-lakes and occurring in the largest catchment Using an ID number in the output SHALLOW COAST. For each areas such as the River Danube. table, the calculated data could then grid cell, the total surface area The Strahler system counts with be presented graphically on a map. of water suitable for foraging all confluences in a logic order. The same procedure was followed Cormorants (i.e freshwater and According to the general knowledge for lakes in CCM2-lakes, using total shallow coastal waters) was of INTERCAFE participants from lake size for each grid cell. calculated. The smallest river sections, categorised as Strahler-1, Shallow coast were excluded from this calculation Table 3.5 River sections according For shallow coasts no basic charts as they were assumed from the to different categories of the Strahler system, with standardised width based were available for all areas in Europe. literature to be unsuitable as on local observation in the field (Strahler Consequently, bathymetric data with Cormorant foraging waters. category 10 was provisionally given the larger intervals in class width were same width as Strahler category 9). used to arrive at a best estimate for Statistical analysis each grid cell. By using topographic Statistical analyses were performed Strahler Average width (m) atlases and digital maps of smaller on the raw or modified data in the category areas the availability of shallow databases. Common procedures 1 3 water was assessed. The focus was included calculation of means, on shallow water because this is standard deviations, ranges and 2 7 most suitable as feeding areas for frequency distribution of various 3 15 Cormorants. Based on published parameters. Variation was presented 4 30 research, ‘shallow water’ in relation as 95% confidence limits around 5 60 to foraging Cormorants was defined the mean. Standard statistics were as that up to 25 m deep. Using the performed in Excel, SAS a.o., and 6 125 files RASTER50000 and COUNTRY multivariate statistics were performed 7 200 the surface area of coastal water using SPSS. Principal Component 8 500 could be calculated. The derived file Analyses were conducted in Minitab SHALLOW COAST combines 12.2, and where appropriate, values 9 1,250 depth class (i.e. less than 25 m) and were log-transformed to obtain 10 1,250 surface area for each grid cell. Given normal distributions.

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4 AQUATIC HABITATS AND USE BY CORMORANTS IN EUROPE

Cormorants use a variety of Open sea/shore many birds make extensive winter water types as foraging sites (see This habitat category includes movements to freshwaters inland. reviews in Cramp & Simmons large-scale, open shallow waters Sinensis birds also use coasts 1977, Johnsgard 1993, Nelson and coastal areas. Areas comprise throughout the year, generally the 2005). Research experience and in excess of 10–1,000 km2 more sheltered continental coasts information from INTERCAFE of similar habitat, which is of the , Kattegat and participants was used to describe considerably larger than any other Skagerrak, and the eastern North the major pattern of water types water habitat type. Cormorants use Sea in summer and the western across Europe and beyond. As coatal waters throughout the year, Baltic, Kattegat, Mediterranean, the variation in landscapes and particularly the carbo race whose Adriatic, Aegean and Black in aquatic habitats is huge, a basic breeding distribution is mainly winter. system was used to distinguish restricted to the northwestern coasts between the most important of Europe. This race also forages Coastal water clarity (and hence water types. This approach is not off coasts in winter but is probably visibility for foraging Cormorants) exhaustive but merely provides a somewhat limited by both the in the sea can be highly variable, simple overall view of the existing movement of fishes into deeper being clear, turbid or extremely variation within and between basic water and poor weather conditions murky under certain conditions. water types occurring in Europe. at this time of year — and so However, as a rule, most seawater Furthermore, it also emphasises ‘scale’ as an important factor/ variable associated with these habitats. A description of how Cormorants use these habitat types, both in summer and in winter, follows. Again, this is based on available published sources collated through the INTERCAFE network.

4.1 Landscape and ecosystem descriptions The following brief description includes each of the main categories of water systems types. Emphasis is placed on the general characteristics and scale of the system, including biological data, Coastal habitat along large open sea, nests constructed of bladder wrack particularly with respect to the (Fucus spp.), Horsens Fjord, Denmark. The breeding adults are used to regular occurrence of fishes. visits to the colony by researchers. Photo courtesy of Thomas Bregnballe.

www.intercafeproject.net [19] intercafe – cormorants and the european environment

is clearer than freshwater systems. gives rise to a complex underwater in some regions, fish populations In some cases brackish (or even habitat, providing diverse habitats, and communities in regions like fresh) water dominates at the large food and shelter (cover) for the Baltic Sea have been strongly scale within this habitat category. In numerous fishes. This rocky-algal affected by human activities such Europe this is the case in the Baltic community includes Eelpout as nutrient enrichment and heavy Sea, where a declining salinity (Zoarces viviparus), Gobies and exploitation (e.g. see chapter 13). influence occurs from west to Sculpins (Cottidae), and east, leading to almost freshwater (Labridae) in more exposed places. Estuaries/river deltas conditions in the eastern regions On sandy bottoms analogous Estuaries are dynamic ecosystems, (Gdansk-Turku) as well as the top habitats are often provided by being semi-enclosed coastal water of the . Similarly Eelgrass (Zostera spp.) beds and bodies where the mouth of a river in the Black Sea area, extensive these habitats are frequented by (usually surrounded by expanses of brackish waters occur in the Sea of similar species to rocky areas with flat land) has a free connection to the Azov regions in the Northern part algal cover. Finally, over both rocky open sea and within which there is a of this system. and soft substrates, a third broad constantly changing mixture of fish community comprises several and . Because of the high Around seas, coasts may either be ‘pelagic’ fish species that live in the sediment load from rivers, many rocky (in summer many of these water column (as opposed to close estuaries are characterised by large are often cliffs), as is the to the bottom). These are often areas of intertidal flats and muds. case along the Atlantic coasts of juvenile individuals exploiting the Europe, at many places along the relatively sheltered shallow coastal River deltas form when a river Mediterranean coasts and along waters and include Herring (Clupea meets the sea and water flow is the southern shores of the Black harengus), several members of no longer confined to its channel Sea and occasionally in the Baltic. the Cod (Gadidae), and and the river expands in width. Sometimes, the rocks are relatively Capelin (Mallotus villosus) in the This causes a reduction in flow low, often rounded boulders with . Evidence suggests that velocity and sediment drops out numerous low stony outcrops and islets shaped by land ice (e.g. in the Baltic). Coasts also may also include beaches, sand spits, dunes, mudflats and foreshores. Across Europe, the main prey of Cormorants on the coast fall into three broad categories, each associated with a different habitat. As a result of differences in geomorphology, the coastal seafloor is sandy or muddy and sometimes contains extensive aggregations of stones or bare rocks. On soft substrates (sand and mud) lacking cover, the first fish community tends to comprise benthic (bottom-living) species such as (particularly Pleuronectidae), Gobies (), and (Anguilla The delta of the River Danube is one of the most complete estuarine habitats anguilla). In rocky situations, in Europe. Besides Cormorants, the area hosts the major European part of the the dense underwater growth of Great White (Pelecanus onocratulus) population. macro-algae (large seaweeds) Photo courtesy of Botond Kiss.

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and deposits. Over time, this single channel will build up pushing the mouth further into the standing water. As this happens, the slope of the river channel decreases and it becomes unstable and the river can breach banks and cut new channels, ultimately resulting in a mature delta with a distributary network of channels. A similar network can also be achieved if a river deposits mid-channel sand/gravel bars at its mouth and is ultimately split into several distributary channels. Lagoon in the Po Delta, Italy: an example of large-scale shallow water with Estuaries vary greatly in size but numerous oyster racks, often used by Cormorants as roosting place. are generally in the region of Photo courtesy of Stefano Volponi. 1–10 km2, although the from Texel in the Netherlands to Esbjerg in Denmark is the largest (Salix spp.) bushes and forests on under human pressure for a long estuarine area in Europe at about the higher . However, the time, factors include building 10,000 km2. Some estuaries can slow-flowing, and often relatively and urbanisation, the disposal of also form into huge deltas. For warm water of estuaries, often industrial and domestic waste, or example, the Po Delta in northeast coupled with nutrient-rich waters the reclamation of land for industry Italy covers over 520 km2 whilst and substrates means that aquatic and agriculture. These factors have the Danube Delta in Romania and plants usually flourish in estuaries inevitably also affected both fish Ukraine covers some 5,800 km2. and deltas. populations and the composition of Whilst not all of the delta territory estuarine fish communities. is open water (much of it is Fish species composition in reedbeds, woodland, shrubs and estuaries is often very diverse Inland sea/large lagoons meadows), the areas of surface and the distribution of many Some freshwater lakes are so huge water can amount to , if not species changes with season. in surface area that they are often 1,000s, of hectares. Being located Apart from the species commonly called ‘inland seas’. Very large in lowland areas close to the sea, associated with either fresh or salt lakes in this category were often estuaries very often connect several water habitats (e.g. Cyprinids, isolated from the sea because of different water systems. Riverine Pike (Esox lucius), Perch (Perca geological processes as is the case freshwater mixes with seawater fluviatilis) and Herring, Gobies, with lakes Peipsi (3,500 km2) giving rise to brackish water zones Gadidae, respectively), many between Estonia and the Russian that vary in size depending on river brackish water species also inhabit Federation), Ladoga (17,981 km2), discharge and tidal movement. estuaries. These include Flounder and Onega (9,894 km2) both in Lakes, coastal waters, isolated (Pleuronectes platessa), Eel, the Russian Federation. Other tributaries and oxbow lakes all Smelt (Osmerus eperlanus), Grey inland seas were actually cut form different elements, making Mullets (Mugilidae) and Sea Bass off from the sea by man, such many estuarine habitats very (Dicentrarchus labrax). At certain as the IJsselmeer/Markermeer diverse. Terrestrial vegetation times of year, migratory fish such (1,800 km2) in The Netherlands. cover in estuaries is mostly low, as Brown Trout (Salmo trutta) and These lakes are rather shallow consisting of marsh vegetation such Atlantic Salmon (S. salar) will also for the greater part, being around as Reeds (Phragmites australis), pass through estuaries on migration 10 m (but up to 120 m) deep. By Sedges (Carex spp.) and Reedmace to (in spring) or from (in autumn) contrast, others like (Typha spp.), with scattered Willow the sea. Many estuaries have been (582 km2) between Switzerland and

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France is a deepwater lake (372 m (some 1,800 km2 in total) in The waters are often brackish but can average depth), are in mountainous Netherlands have been well studied occasionally be fresh water as landscapes. Deepwater lakes in and here Perch and Pikeperch have is the case on the Baltic coast of rarely freeze over, been harvested intensively. The Poland and . Lagoon fish which makes them attractive fish community has shifted as a communities are often dominated wintering habitat for water birds, result and become dominated by by Sand-smelts (Atherinidae), including Cormorants. Smelt, and small Cyprinids. Mullets and Gobies, depending by Modelling suggests that with the salinity, sediment and turbidity. Many of the shallow large lakes absence of commercial fishing, the Fish distribution changes have generally similar fish amount of predatory fish would seasonally in an annual cycle of communities. For instance lakes increase strongly and the amount resident species (which move into Peipsi, Ladoga, and Onega have of small (prey) fish decrease by deeper waters in autumn/winter) around 30–60 fish species which 40–50% (van Nes et al. 2002). and the spring/summer migration include shoaling Cyprinids such However, such broad predictions of juveniles between coastal areas as Roach (Rutilus rutilus), Bream must be treated with caution, and lagoons. Lagoons are important (Abramis brama), predatory species as knowledge of the density- nursery areas for many species. such as Perch, Pike and Pikeperch dependent mechanisms regulating Like estuaries, lagoons are highly (Sander lucioperca), Salmonids and fish numbers is far from complete. sensitive to anthropogenic pressures close relatives (including Brown such as commercial fisheries. Trout, Charr (Salvelinus Coastal lagoons are areas of alpinus), Whitefish (Coregonus shallow, coastal salt water, wholly Large lakes spp.), Grayling (Thymallus or partially separated from the sea Large lakes are generally thymallus), and other species by sandbanks, shingle or rocks. somewhere up to around 100– such as Burbot (Lota lota), Ruffe Lagoons show a wide range of 1,000 km2 in area and their depths (Gymnocephalus cernuus) and geographical and ecological can be highly variable, changes in Smelt. Deeper large lakes often variation and the water in them water level occurring naturally. In contain communities of coldwater can vary in salinity from brackish general, this means the lowest levels fishes including Brown Trout and (owing to dilution of seawater by occur in summer and autumn and Whitefish, with predatory fishes freshwater) to hypersaline (i.e. highest ones in late spring. Lake such as Pike and Perch. Where more salty than seawater as a result morphology is highly dependent waters are warmer (usually at of evaporation). Lagoons vary in on surrounding landscape. In lower altitudes), fish communities size but may be around 30–100 km2 mountainous terrain, lakes are will also include Cyprinid in for example and often relatively small and deep species like Roach and Bream. are invariably shallow with a mean (commonly up to 100 m) whilst in Both eutrophication (nutrient depth of no more than around 10 m riverine habitats at lower altitudes enrichment) and acidification have (and often considerably less). they tend to be larger and shallower drastically changed the fish species (commonly less than 30 m and composition and biomass in many The plant and communities often considerable shallower). very large lakes. Furthermore, there of lagoons vary according to site- These surrounding landscapes are commercial fisheries for many specific physical characteristics also often determine the general fish species here, often operating and the salinity regime. Although, nutrient status of lakes, upland for many decades, which have also compared to other marine habitats, lakes tending to be oligotrophic altered the community structure lagoons hold only a limited (nutrient poor) and lowland ones of fish stocks in many places. As range of fish species, many are eutrophic (nutrient rich). Islands in a result, several lake restoration adapted to the varying salinity lakes are often afforested because programmes have been initiated, regimes of lagoons and some they are not grazed and they also including fisheries management are unique to these habitats. In usually lack carnivorous predators measures and re-stocking projects. coastal regions, large lagoons and are relatively undisturbed Fish communities in the large share similar aspects with some by man. This makes these sites IJsselmeer and Markermeer lakes large shallow inland seas. Lagoon particularly attractive to both

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often present. Riverbanks consist of Willow forests but often levees and floodplain areas are often cultivated in grassland or arable land. Typically, such large river sections contain islands, often (former) levees of the main stream, which hold softwood forests. During summer, low water conditions give rise to extensive sandbanks and isolated hollows and pools within these rivers.

Fish communities in river sections Lake Kinneret or , Israel with extensive reed beds tend to vary with altitude and and Cormorant roost in winter. Photo courtesy of Stef van Rijn. river width. Wide sections of large rivers are often characterised by breeding Cormorants and for massive fish kills (caused by the ‘Barbel Zone’, which has a the establishment of roosts. The anoxia, disease or overpopulation), gentle gradient, moderate water shallowest lakes (2–15 m deep) and exploitation by fisheries. This flow and temperature, with a good freeze easily during winter and is particularly true if the species oxygen content and mixed silt and populations of waterbirds are then harvested are top predators (see gravel substrates. It is characterised forced to move. example of IJsselmeer on previous by some ‘upstream’ species (see page). Streams/small rivers) plus Barbel (Barbus barbus), Roach, Rudd Lake fish communities are similarly (Scardinius erythrophthalmus), influenced by the morphology, and Large rivers Perch, Pike and Eel. These rivers ultimately the location, of lakes. River sections of the largest then enter the ‘Bream Zone’, Thus, Salmonids and Coregonids category are very wide, slow the true lowland zone, where the tend to dominate in oligotrophic running waters. These river sections gradient is very gentle and the (upland, colder, deeper) lakes, fall within Strahler types 7, 8, 9 water slow moving. Although Cyprinids in eutrophic (lowland, and 10, with corresponding widths oxygen content is usually good, warmer, shallower) lakes, and of 200–1,250 m or more. These temperature is more variable than Perch (and sometimes Pike) are water bodies are extremely open, in other zones and the substrate is commonly found in both types. If and several deeper channels are connected to a river system, fish stocks (particularly Salmonids) may migrate further upstream in order to and/or migrate to the lake to over-winter. As a response to cooling water temperatures in autumn, many fish will move down to the deeper parts of the lake as the season progresses. The shallow fringes of lakes are often important spawning areas for fish as are the seasonally flooded lake margins. Lake fish communities can change rapidly River Danube, one of Europe’s largest river systems, Serbia. as a result of species introductions, Photo courtesy of Daliborka Stankovic.

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often silty and the water clarity low. consists of a network of smaller Few upland species can survive channels separated by little, and here and only a few upstream often temporary, islands called species (Roach, Rudd, Perch, braid bars. These channels and Pike) inhabit this zone that is also braid bars are usually highly mobile characterised by Bream, Tench and the river course can often (Tinca tinca) and Carp (Cyprinis change significantly during flood carpio). events. Channels move sideways because of their differential Impounded river sections of this velocity, on the outside of a curve, size resemble medium-sized lakes, deeper, fast-flowing water picks up and sometimes have similar fish sediment (usually gravel or larger communities to these habitats. stones) which is re-deposited in The dams, weirs and sluices slow-moving water on the inside of associated with impoundment a bend. Braided channels may flow often hamper the movements of within an area defined by relatively riverine fish. In winter, fish tend stable banks or may occupy an to concentrate in the deeper river entire valley floor. These systems sections, or migrate downstream. If are often associated with numerous spring flooding occurs, important oxbow lakes and partially habitat for spawning and nursery connected backwaters. Small rivers: Lowland (left) and areas for juvenile fish are created sub-Alpine (right). Photos courtesy of in temporary riparian lakes and In upland areas, the smallest INTERCAFE. pools. Large rivers are often used (Strahler 1) river sections occur in as navigation routes for shipping the uppermost fringes of catchment and the course of the river has areas. Given their width of no more poorer in terms of species numbers. often been altered and the riverbed than a few meters, river sections of At the far west (the UK, Ireland regularly deepened by dredging, this size are normally not visited by and Norway) the native freshwater such habitat modification usually Cormorants and they have therefore species are actually only those has negative effects on local fish been excluded from further analysis that became isolated there as sea communities. here. In similar uplands, Strahler 2 levels rose after the last Ice Age or and 3 category tributaries are often gained access from the sea during Streams, small rivers fast flowing waters with extensive this period. Much of the current River sections of the smaller pebble beds. These sections may fish fauna is present entirely as a categories fall within Strahler or may not be surrounded by trees result of translocation by humans categories 2, 3, 4, 5 and 6, with depending on altitude. The sub-alpine (e.g. Maitland & Campbell 1992). corresponding widths of between sections of such rivers rarely freeze Overlaid on this for rivers, there 7 m (Strahler 2) and 125 m due to the relatively high water flows. is often a continuous increase in (Strahler 6). Riverbanks are mostly species richness (i.e. total number surrounded by trees, woodlots or Fish communities in small rivers of species) with progression forests but sometimes rivers also and streams are diverse, depending downstream. Thus, typical streams run through intensive agricultural on altitude and geographical and small rivers start with a zone land. If natural water regimes position within Europe. As with (the ‘Trout Zone’) characterised by prevail, summer low flow levels all freshwaters, broad scale fish steep gradients, fast flowing water to the presence of sand and distribution is chiefly controlled and cool temperatures and holds pebble banks. The downstream by climatic, topographical and Brown Trout, Atlantic Salmon, (and hence wider) sections of rivers hydrological differences. Within Bullhead (Cottus gobio) and Stone often become ‘braided’, the high Europe, as one moves westwards Loach (Barbatula barbatula). This sediment loads being deposited and from the Danube, the freshwater is followed by the ‘Grayling Zone’ the river forming a channel that fish fauna gradually becomes that tends to be slightly warmer

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influenced by hydrological management. The size of these waterbodies is highly variable, from a few hectares to ‘small’ lakes of some 10’s of km2 and to reservoirs that may be a few 100’s of km2. Not only is the water table set but the way that shorelines develop depends largely on management decision-making. Water depth varies according to the use of the waterbody, former gravel and sandpits being the deepest (10–30 m). Commonly, little vegetation grows around these relatively small standing waters and, in the case of deep waters, little or no aquatic vegetation grows. In reservoirs, fish populations are often isolated and small lakes and ponds are often stocked in order to provide quarry and can hold all the above species (through changes in water flow) and for recreational angling. Fish with the addition of Grayling, thus reducing the amount of suitable stocks in many of these waters (Phoxinus phoxinus), spawning area available to them. are thus often enhanced or exist Chub ( cephalus) and only because of the release of Dace ( leuciscus). Farther Reservoirs, small lakes and hatchery-reared fish. The most downstream, rivers can contain sandpits extreme type of waters are the other zones with characteristic fish Water bodies in this habitat so-called ‘put-and-take’ fisheries communities (described above). category are very often heavily where fish of appropriate size are

Many coldwater species occur in small rivers and streams and water clarity here is generally high, due to low levels of algal production. Small streams and rivers in this habitat category can be disconnected from the downstream sections by dams (for water storage and the generation of hydro-electricity) and these barriers can cause serious problems for fish (particularly migratory species, including Salmonids) as they alter hydrological conditions and prevent the passage of fish. This can have severe effects on fish through physically restricting their access to upstream spawning sites and/or Reservoir in Spain during a winter period of low water showing altering the substrate characteristics the remains of a former village. Photo courtesy of Mennobart van Eerden.

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put into the water by fisheries Fishponds The water clarity (and hence, managers for them to be taken Fishponds are artificially underwater visibility) of fishponds out again (often very quickly) constructed water bodies, made by is generally low because the by anglers. Such fisheries may either damming off parts of a small bottom-dwelling fish species stock fish into their waters with a river and/or by excavating new tend to stir-up the mud there. frequency of a few weeks or even basins. Fishponds are often situated Furthermore, algal blooms often days. The reproduction capacity in areas that have relatively few occur because of the absence of of waters in this habitat category natural water bodies and for many water plants and the relatively large often depends on extra shelter or centuries people have used them to inputs of nutrients. structural measures being provided provide fish as an additional food to increase fish production. source. Through intensification it Fish are often reared at very high has also been possible to export densities in fishponds, depending The level of fish stocking depends, fish beyond purely local markets. on the intensity of fish farming. ultimately, on the type of stillwater. Although some fishponds may be Production in fishponds is generally In the UK, recommended stocking only a few hectares, many are much considerably higher than in density (biomass) for natural larger. For example, pond surface similarly-sized natural waters, upland lakes is 100 kg/ha, for area in the Czech Republic ranges largely because of the additional recently created lakes and gravel from about 140 ha to 7,500 ha. food supplied to the fish. Standing pits is 150 kg/ha, for mature gravel The existence of such large areas stock in ponds in central Europe pits is 250 kg/ha, for mature of shallow water in relatively dry tends to vary between 200 kg/ lowland lakes is 350 kg/ha, and for habitat attracts various wildlife, ha (almost natural) and 600 kg/ rich farm ponds is 500 kg/ha. especially in the more extensively ha (occasionally 1,000 kg/ha). operated systems, and so many However, in Israel there are some A wide diversity of fish may be fishponds are also associated with very intensive aquaculture systems used in stocking, often dependent high biodiversity value. Similarly, (for species and Carp), on the potential angling market. many pond farms also have high with stocking densities of more Thus many fisheries are stocked historical, cultural and social value, than 10,000 kg of fish per ha. Fish with Salmonid fish, very often the as well as economic value through production is generally directed to North American Rainbow Trout the production of fish. one, or a few, core species and pond (Oncorhynchus mykiss) but also the native Brown Trout. These fish are stocked in a variety of sizes, often between 0.5–7.0 kg), and on capture are often removed by the anglers. Other fisheries can be stocked with a mixture of Cyprinid fishes, and traditionally, these fish are returned alive to the water after capture. At these fisheries, stocked fish may often include Roach, Bream, Crucian Carp (Carassius carassius), Rudd, and Tench. These fish are often stocked from around 8 cm but more commonly at 20–25 cm. Some fisheries specialise in large, so-called ‘specimen’ fish, of particular species, particularly Carp which are often stocked at around 1.5–2.0 kg and can grow to an average of about 16 kg The Nagli fish pond area in , reed burning in progress. (but up to 20 kg) within ten years. Photo courtesy of Karlis Millers.

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farms in core central European areas tend to produce predominantly Carp, and to a much lesser extent Tench, Pike, Pikeperch and Wels (Silurus glanis). Other species of ‘wild’ fish enter these systems, and fish communities can be quite diverse but dominated by a few commercially produced species. In central Europe, fishponds are drained every second or third year and, during these periods of harvest, fish stocks may be particularly vulnerable to predators such as Cormorants and many other fish-eating birds and sometimes mammals, like Eurasian Otter (Lutra lutra), in the resulting shallow waters. Most sinensis Cormorants in Europe breed in trees usually associated with wetlands such as willow (Salix), alder (Alnus) and birch (Betula). In some cases, 4.2 Cormorants and water tall old-growth forest is used such as these (Quercus) in Braendegård, Denmark. Photo courtesy of Florian Möllers. systems Cormorants feed almost exclusively their time in the water. Besides the foraging grounds are generally on fish caught underwater the foraging period that totals 1–4 10–15 km in each direction but can whilst usually diving 2–5 m but hours per day on average, birds range from less than 1km to over occasionally up to 20 m or more. also aggregate at roosts to rest and 40 km. Whilst underwater visibility is preen (sometimes referred to as very important for capturing fish, ‘loafing’) or at colonies to breed. Birds spend about 3–4 months Cormorants tend to avoid both Cormorants are so-called ‘Central in colonies, from arrival, pair- really clear water and extremely Place Foragers’, that is they use forming and -laying to the turbid water. Prey fish species their foraging area from a single time when young birds have are exceptionally diverse and can point — the central place — to fledged, left the nest and become include shoaling species in the which they return (i.e. the roost or independent but, if conditions middle or upper parts of the water the breeding colony). As well as are favourable, birds may stay column and also demersal fish suitable foraging areas, Cormorants longer at colonies or nearby, living close to, or on, the bottom. thus also require suitable nesting using the area as a night roost. Birds may congregate in large and roosting habitats. However, the Generally speaking, birds move flocks in order to prey on shoals species is remarkably flexible in its to other post-breeding gatherings of fish or make fish move up requirements for these sites, being after the breeding period. In towards the clearer top layers of the able to breed in most relatively autumn, typically from mid- water column where they can be undisturbed areas — on cliffs, October onwards, birds perform more easily captured. Underwater rocky coastal outcrops, trees and, longer migrations towards their vision is therefore considered a where ground predators are absent, wintering sites. This migration key parameter for describing the on the ground. Similarly, roost sites differs between individuals with suitability of particular waters as can be established on riverbanks some birds flying directly to their feeding grounds for Cormorants. or lakeshores in bushes, woods or wintering site whilst others adopt single trees, or even on artificial a hopping strategy, visiting several In both winter and summer, structures. The distances flown to locations en route. Some birds fly Cormorants spend only part of and from the roost or colony to as far as northern Africa to spend

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the winter, but others may also area of ‘Europe’ considered here. Russian Federation and beyond. In be almost resident and move very The ‘carbo’ or ‘Atlantic’ race has winter carbo birds largely remain limited distances throughout the its main breeding distribution on along the coasts but also partly year. In spring (from early March), the rocky coasts of Ireland, the move inland (e.g. in the UK) and a major northerly migration UK, northwest France, Iceland and migrate to the south (to Denmark, begins. However, many birds again Norway, and also in Greenland and France, Spain and Portugal) where show intermediate patterns with through the Russian Federation they mix with sinensis birds. smaller movements between areas along the . The Because of their habit of using and some birds moving very little. ‘sinensis’ or ‘Continental’ race exposed (often inaccessible) areas As such, the Cormorant adopts breeds inland across a wide area as breeding places, this part of the full array of avian migration from France and Italy in the south the overall ‘European’ population strategies. to the , Germany cannot easily be monitored at and Poland and north into the the subspecies level and so there Subspecies: the carbo and countries bordering the Baltic and is less detailed geographical sinensis races is widespread throughout central information on the carbo race As mentioned in chapter 2, there and eastern Europe, extending compared with that available for are two races of Cormorants in the into Belarus, Ukraine, Turkey, the sinensis birds.

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5 CASE STUDIES FROM THE MAIN TYPES OF WATER SYSTEMS

INTERCAFE’s Case Studies fisheries make of them for each literature, regular INTERCAFE were identified so as to provide location. Information collected meetings, and work undertaken at specific information about the during INTERCAFE’s Case additional Work Group meetings. relationship between Cormorants Study meetings (see Part Three Table 5.1 gives an outline of Cases and their habitats. This chapter of Marzano & Carss 2012) is included here. This chapter focuses provides summary information complemented with information on the key ecological aspects whilst about Cormorant habitat use, the obtained from other sources pertinent Cormorant-fisheries general status and trends in fish including participant’s knowledge conflict issues are dealt with in populations, as well as the use that of particular systems, the published chapter 10 (Europe-wide) and 11 (regional- and local-scales). Table 5.1 INTERCAFE Case Study examples of Cormorant ecology in different water systems across Europe and Israel. 5.1 Gulf of Finland WG1 Case Study Section in Primary information Habitat category location chapter source(s) Introduction The Gulf of Finland is a large- Gulf of Finland, 5.1 Regular INTERCAFE Open sea and scale coastal area in the northern Estonia & Finland meeting and coastal area additional WG1 European Baltic Sea, bordering meeting Finland, Estonia and the Russian Federation. The salinity of the Po Delta, Italy 5.2 INTERCAFE Case Estuary, complex Baltic has been decreasing since Study river delta the last century and the sea is Danube Delta, 5.3 Additional WG1 Estuary, Large River becoming brackish and slowly Romania meeting and expert and complex river being transformed into a fresh knowledge exchange delta water systems. This is generally IJsselmeer, 5.4 Expert knowledge Inland Sea considered to be due to climate Netherlands exchange change with increased rain (fresh) Vistula Lagoon, 5.5 Regular INTERCAFE Inland Sea water inflow from the surrounding Poland meeting river systems, and increasingly irregular inundations of sea water Pre-Alpine 5.6 Regular INTERCAFE Small River and streams, Slovenia meeting, additional streams from the western approaches to & Austria WG1 meeting and the Baltic. The area is isolated expert knowledge from influence so there exchange is almost no tide. In spring and early summer, clear waters still South Bohemia, 5.7 Regular INTERCAFE Fish Pond, complex Czech Republic meeting wetland dominate the coastal areas in the Gulf of Finland. In June 2007 Saxony, Germany 5.8 Regular INTERCAFE Fish Pond, complex Secchi depths (a measure of water meeting wetland clarity) recorded at Finnish coastal Hula Valley, Israel 5.9 INTERCAFE Case Fish Pond, complex sites varied between 2.5–4 m (van Study wetland Eerden et al. 2007). Nutrient loads

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to the Baltic Sea have increased sedimentation of organic matter since the early 20th century. Total mainly arises from the spring nitrogen load has increased by a production of green algae, which is factor of 4 and phosphorus load by nitrogen limited. There is thus the a factor of 8. The internal loading danger of a vicious circle in which of phosphorus is an especially the nitrogen-based spring bloom serious problem, and will continue increases the phosphorus input in to be so in the future, even though the water phase from the sediment. there has been some decrease in the This, in turn, intensifies the growth external nutrient loads in the . of nitrogen-fixating Cyanobacteria Increased nutrient levels have speeding up the nitrogen caused intensified algae blooms, accumulation of the water mass, decreased water clarity and reduced thus enabling an increased spring oxygen conditions in the deeper production of plankton (Harri areas of the Baltic. Kuosa pers. comm., Tvärminne Zoological Station, Hanko). The productivity of the Baltic Sea is based on the quantity of Fish communities available nutrients entering it and The water quality changes nutrient concentrations here have described above, among others, increased considerably, especially have both direct and indirect because of the strong increase effects on fish communities in the in human populations during the Baltic. Total fish catches here have Baltic Sea coast and rocky islets off last century. Blue green algae increased tenfold since the early the Hanko Peninsula, Finland. (Cyanobacteria) now dominate 20th century. There are two reasons Photo courtesy of INTERCAFE. the system in summer. The water for this: (1) open sea fishing has residence time in the Baltic is intensified, and (2) fish production in their spawning areas. Changes around 20 years and the increased has increased, being correlated in salinity conditions have also nutrient inputs have thus changed with nutrient enrichment leading affected the food supply of Herring the Baltic considerably. Primary to the state of eutrophication and Sprat. production is limited by both P (Meri Härmä: Finnish Game and (phosphate) and N (nitrogen). Fisheries Research Institute). Nowadays freshwater fish species Blue-green algae are able to fix dominate in the northern Baltic molecular nitrogen from the air The pelagic fish community in the Sea. Roach (Rutilus rutilus) is and use the available phosphorus Baltic Sea (those fish species that now the most abundant species in for growth. As both nutrients are live in the water column as opposed the northern coast of the Gulf of limiting productivity, the additions to close to the bottom) is dominated Finland and in the Archipelago of either will therefore increase by four species: Baltic Herring Sea. During the 1990s, the species biological production. Phosphorus (Clupea harengus membras), Sprat spread out even to the outer levels in the Baltic remain high due (Sprattus sprattus), Cod (Gadus archipelago. The abundance of other to input to the water column from morhua) and the anadromous (i.e. Cyprinids, like Bream (Abramis the benthic (bottom) substrates breeds in freshwater, matures in the brama) and Bream (Blicca under low oxygen conditions. sea) Atlantic salmon (Salmo salar). bjoerkna) has also increased. The only way to decrease There was a regime shift from Eutrophication and climate change phosphorus availability would a Herring- and Cod-dominated (increased amount of nutrients and thus be to decrease the amount community to one dominanted by more rainfall, and hence freshwater of sedimentation of organic Sprat during the 1990s. There were run-off, decreasing the salinity of material, and as a consequence, several reasons for this. Cod stocks waters in the region) have resulted enhance oxygen conditions on collapsed due to over-fishing and in improved reproductive conditions the sea bottom. In the Baltic, deteriorating oxygen conditions for Cyprinids in the innermost

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The general situation in the study establishing nature reserves and area at present is one of low fish through the proper implementation stocks or the absence of large of nature management and predatory fish. Stocks of large Cod, inventory tasks. The changing Pikeperch, Eel, Atlantic Salmon society and the current greater and migratory Brown Trout, role of is a common so-called Sea Trout (to name but development in the region (van some key species) have greatly Eerden et al. 2007). decreased in recent decades (1980– 1995). The decreasing salinity, combined with increased inflow 5.2 Po Delta of nutrients and a high fishing effort by the commercial fishery Introduction has lead to marked changes in fish The Po Delta (NE Italy) can be composition. It is therefore highly defined as the 80 km of coastal likely that the absence of large belt from the River Adige and predatory fish has led to an increase the wetlands north of the town of small prey fish. It is well known of Ravenna, including both the that species like Eelpout (Zoarces present (Veneto region) and the viviparus), Butterfish (Pholis historical river delta (Emilia- gunnellus) and Gobies (Gobidae) Romagna region). Typically for formed important prey for Cod large estuarine areas, the Po Delta in the past but these species (and is a complex ecological system possibly others) may now be including a mosaic of more than experiencing considerably reduced 38,000 ha of highly productive predation pressure from piscivorous eutrophic wetlands. Shallow (fish-eating) fish species. The coastal sea bays (6,200 ha), recent expansion of Cormorants brackish lagoons (25,000 ha), into Baltic Sea waters may thus be freshwater marshes (800 ha) and facilitated by the low number of a complex web of canals and river large predatory fish species. branches lie in a continuum with Extensive coastal lagoon system, the lagoon of Venice and Caorle Po Delta, Italy. Photo courtesy of Role of Cormorants (57,000 ha) and wetlands of the INTERCAFE. The recent expansion of Gulf of (30,000 ha). The Cormorants in is vertebrate fauna comprises some archipelago and are the main particularly evident in the eastern 374 species, plus more than 300 reasons for the recent increase in Baltic area, the Gulf of Finland bird species reported during the Cyprinid abundance. Some other and the Gulf of Bothnia. Generally last few decades. Most of the Delta species like Pikeperch (Sander speaking, fewer commercial fish is protected as regional parks lucioperca) have also benefited are being caught here, whereas the and included in the Natura 2000 from changes in the coastal Cormorant population is expanding network as SPA/SCI, while many environment. It is expected that in greatly, a situation of great concern wetlands are on the Ramsar list of the next 100 years climate change to many local people (see also protected sites for the conservation will probably further decrease the Marzano & Carss, 2012). However, and wise use of wetlands and their salinity of the Baltic Sea (e.g. by on the Finish side, coastal fisheries resources. increased rainfall in winter leading largely stopped around 1960, well to increased run-off) and the before the arrival of Cormorants. Fish communities decreasing salinity in spring will Estonian and Finnish governments The fish fauna of the Po Delta most likely benefit the reproduction have implemented European comprises over 60 species conditions of Roach. environmental legislation by including freshwater, brackish

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water and coastal sea species and Big-scale dominate typical for the areas close to the (Gandolfi et al. 1985). Fishes by number and biomass during Black Sea. adapted to eutrophic waters with autumn, while Gobies (Black low oxygen content dominate in Goby Gobius , Grass Goby Since the construction (in 1972 riverine habitats and freshwater Zosterisessor ophiocephalus) and and 1984) of the Iron Gates dams marshes. Here the most abundant Flounder (Platichthys flesus) are and associated power stations in species are Cyprinids, such as taken especially in spring (Volponi the Danube (near the Romanian- Crucian carp (Carassius carassius), & Callegarini 1997). Predation Serbian border), water movements Ruffe (Gymnocephalus cernuus) on the most valuable commercial in the system tend to be less than and (Cyprinus species (Eel, Sea Bass and Sea before. Lack of dredging in recent carpio), but several exotic species Bream) occurs mainly in lagoons years has resulted in increased are common (e.g. Wels (Silurus used for ‘vallicoltura’, where they siltation and water ‘stagnation’ glanis), Black Bullhead (Ameiurus may cause important economic loss in many places. Nevertheless, melas), Mosquito Fish (Gambusia (Volponi & Rossi 1995). floods still occur in late spring affinis) and play an important role and large parts of the delta remain in the fish community. Estuarine subject to fluctuating water levels. and brackish waters account over 5.3 Danube Delta (Romania, Shipping is mainly through the 30 species. Among those, five Ukraine) deeper canals, but fishing boats species of Grey Mullet (Mugilidae), may enter many of the different Sea Bream (Sparus aurata), Sea Introduction water bodies. The area is of the Bass (Dicentrarchus labrax), Eel This is one of the largest river highest international importance (Anguilla anguilla) and Big-scale deltas in Europe (5,800 km2). The in relation to its biodiversity value, Sand Smelt ( boyeri) are area consists of extended areas the size of the area and the sheer the fishes of highest commercial of shallow (1.5 m) eutrophic and diversity of habitat types supporting interest. partially mesotrophic waters. This a wealth of species. For example, huge area has peat, clay and sandy with respect to fish-eating birds all Role of Cormorants areas in combination with a wide European and egrets nest in Since the early 1980s, Cormorant array of water bodies (large and the area, together with two species numbers have increased small lakes, pools, backwaters, of pelican and both Cormorant and considerably in the Po Delta so that inundated meadows and brackish Pygmy Cormorant (P. pygmaeus). the delta can now be considered transitional waters including The latter species has its European a ‘honey pot’ area for the species. lagoons). stronghold in this single area (see Recoveries of ringed birds have Platteeuw et al. 2004). shown that Cormorants visiting Large parts of the water systems the Po Delta originate mainly are turbid (with visibility of around Fish communities from the Baltic countries and The 0.75 m or less), but some lakes The Danube Delta waters support Netherlands. Nowadays, about and isolated backwaters maintain a up to 125 fish species. Cyprinids 6,500 Cormorants, with occasional clear water state for longer periods, and Gobiids are most abundant peaks up to 10,000 individuals, often into the summer. During high (overall biomass is high and can regularly winter in the whole water flows a large sediment load be around 250 kg/ha). Many Delta, whilst about 1,000 pairs is typical for these waters and it species also migrate through the breed in the largest Italian colony can extend more than 10 km into area, including the Pontic Shad located in the Southern Delta. the Black Sea. Water plants are (Allosa pontica, see Navodaru, Stomach and analysis has an important component of the 2001) and several species of shown that Cormorants here prey system if nutrient conditions are Sturgeons (Acipenseridae). Fish on a diverse range of fish species. modest and shore-based vegetation species composition differs with However, there is large variation comprises meadows, marshes, respect to the different water in the proportions of different and forests but may also consist bodies. Backwaters and lakes fish prey taken according to both of sandy levees with little, or no, further from the main stream season and foraging site. Mullets vegetation at all. The latter is comprise less eutrophicated and

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thus more waterplant-rich systems. 5.4 Lake IJsselmeer, The form the greater part of the Brackish waters occur at the Netherlands target of the commercial fishery. coastal areas of the Delta. The Another important part of the fish huge Lake Razelm (45,000 ha) is Introduction community comprises Roach and turbid and comprises entirely of Lake IJsselmeer is a former inland large Bream. Due to the heavy freshwater. Here, Pikeperch is the sea situated in the Netherlands. fishing pressure on Pikeperch and dominant predatory fish, whereas After closing it with a large dam Perch, stocks of these species in the more clear water areas of in 1932 it became a fresh water have decreased. Recently, due to the Delta the Pike (Esox lucius) lake. After 1932, large parts selective fishing for Bream and has this role. (around 2,000 km2) were reclaimed Roach, the smaller Ruffe has and cultivated as polders. The experienced reduced competition Role of Cormorants remaining part was split in two and has increased substantially to The Danube Delta is home to in 1975 forming the present Lake form the biggest part of the fish about 16,000 breeding pairs of Markermeer (700 km2) and the stock nowadays. Cormorants in the Cormorants, and up to 40,000 IJsselmeer (1,150 km2). These area feed largely on Ruffe, recently birds may be present in the area in fresh, water lakes are shallow recorded at up to 70% of their diet total. Colonies are dispersed over (4–6 m depth) and stagnant. The (van Eerden & van Rijn in prep.). the area, but mainly occur in the water is turbid with visibility inner part of the delta. Birds fly to depths of less than 1 m (often Role of Cormorants the larger lakes to forage, often in only 0.2–0.5 m). The water is Cormorants have been protected combination with . The eutrophic with a strong tendency of in the Netherlands since 1965. main channels of the river are used lowered nutrient loads of N and P This country, with a significant as foraging sites in early spring since 1980. The lakes are heavily breeding population, was the and again in late autumn. Coastal used by humans for transport, first in to ban lagoons and lakes (Sinoie, Razelm) sand extraction, spoil deposition interference in colonies. At that form typical post-breeding habitat and recreational boating (both time, the species was rare due to and sometimes excursions range motorised and sailing craft) and poor water quality (the effect of into the shallow parts of the Black they also support commercial pesticides), drainage of wetlands Sea. Post-breeding concentrations fisheries. The lakes are both and continual persecution of the typically form along the shores of Ramsar sites protected for the birds. However, protection and the Black Sea. During frost periods conservation and wise use of enhanced water quality caused an most Cormorants leave the area, but wetlands and their resources and increase of the Dutch population in in mild winters several thousands were included in the Natura 2000 the 1970s and 1980s. Numerically, stay behind, near the mouth of network (SPA/SCI) in 2003. growth started in the IJsselmeer the main channels (Chilia, Sulina, area and levelled off in the 1990s. and Sf Gheorghe). Cormorants Fish communities Since 1995, some 10–12,000 prey on a variety of species, much Altogether, 40 species of fish pairs of Cormorants have bred depending on season and foraging- inhabit the system (Lammens et annually in the Lake IJsselmeer site location. The large scale of the al. 2007). Initially the lakes had system (55–67% of the total Dutch delta complex and the occurrence a semi-natural fish community population, in seven colonies). of many different habitat types with good stocks of predatory Although in more colonies, imply the buffering of individual fish species like Pikeperch and this is fewer birds than at the water bodies with regard to Perch. Eel was also a common beginning of the 1990s when the predation pressure. Moreover, the fish species in the early 1980s. number reached more than 15,000 occurrence of natural protection Furthermore the lakes held an breeding pairs under temporary for fish (water plants, debris, important population of Smelt favourable circumstances. A overhanging trees, deep channels (Osmerus eperlanus), situated natural stabilisation of Cormorant and turbid waters) is likely to limit at the southwesterly edge of numbers took place after a dramatic the effect that birds might have on its distribution range in North decrease in 1994 and for almost the ecosystem. West Europe. These four species two decades the total population

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has remained stable. As this surges may increase to 4% and Role of Cormorants natural stabilisation suggests, the 6%, respectively. Waves, which Cormorants inhabit the Vistula maximum level of exploitation of can reach a height of 1.2 m, cause Lagoon mainly during the breeding the area has probably been reached. the quick mixing of the water in period (April to July) and only Furthermore, production of young the Lagoon. The influx of fresh a few individuals remain during in the colonies is now at a low level water from the River Nogat, other winter. Cormorants often breed in most years, often being less than tributaries of the Vistula and the in mixed colonies with Grey one young fledged per nest (van rivers flowing down from the Herons ( cinerea) in the Rijn & van Eerden 2002). As well Elblag Heights, have negligible dry forest of Ka˛ty Rybackie, as the breeding population, there effects on water levels and salinity. on the Vistula Spit. The colony are also staging birds in winter. The here has increased significantly wintering numbers were low in the Fish communities during the last few decades from 1980s and 1990s with only several The fish community of this over 3,500 pairs in 1990 (Przybył hundred birds at most, but they eutrophic lagoon is dominated by 1994) to almost 6,000 pairs in have increased in the last 10 years Cyprinid fishes, mainly Roach 1996, becoming (in 2004–2006) up to 5–8,000 birds are present in and Bream. Ruffe, a commercial the largest European Cormorant mid-winter. species here, is also abundant. Most colony with 11,500 pairs. Studies important commercial species fish carried out on regurgitations and are Pikeperch, Atlantic Salmon, Sea pellets since the mid-1990s have 5.5 The Vistula Lagoon, Baltic Trout (Salmo trutta), and Eel. In the shown that Cormorants feed mostly Sea coast, Poland most recent years, the Round Goby on Ruffe (58–75% by number), (Neogobius melanostomus) has Roach (5–12%) and Round Goby Introduction become one of the most abundant (Martyniak et al. 1997, 2003; The Vistula Lagoon is a large species both in the fish community Stempniewicz et al. 2003a, b). shallow eutrophic water body and the diet of Cormorants. This Pikeperch and Eel represented located on the southern shore of bottom-dwelling, aggressive fish 1.2% and 2.9% respectively, the Baltic Sea. The Lagoon is arrived from the Black and Caspian of Cormorant prey during the about 80 km long and 6–10 km Sea region and, as an invasive breeding season. Cormorants feed wide, and stretches over 838 km2 species, has rapidly colonised the in both in the Lagoon and also at of which 328 km2 is situated in lagoon. sea along the Vistula spit. Poland and the remainder in the Russian Federation (Kaliningrad region). The Lagoon is separated from the Gulf of Gdansk by a long sand spit, the Mierzeja Wislana and the only connection with open sea is through the Baltijsk Channel. The average depth in the Polish part of the Lagoon is 2.4 m and the maximum is 4.4m. Wind direction and strength are the key factors driving the lagoon environment. Influxes of seawater from the Baltic can cause considerable fluctuations in the water level, sometimes exceeding 1 m in 24 hours, and also lead to changes in salinity. This normally ranges from 0.5% in the SW area to 3% Small-scale commercial fishery operating in the Vistula Lagoon, Poland. in the centre, but during Photo courtesy of INTERCAFE.

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5.6 Slovenian & Austrian pre- The Netherlands, Germany and Alpine rivers and streams Croatia (Govedicˇ 2001).

Introduction As in the whole of Slovenia, The fish populations of most there are no Cormorant breeding Austrian rivers have been carefully colonies in the Socˇa valley and bird investigated whilst in Slovenia, the presence is limited to relatively and Sava Bohinjka are well- small numbers during winter and studied pre-Alpine river sections. migration periods. There was a Water quality is extremely good as general agreement on the need for effluents from settlements generally basic information on Cormorant do not occur. In these waters, those Typical small sub-Alpine river, ecology from a wide geographical stretches in the ‘Barbel-zone’ (see Slovenia. Photo courtesy of INTERCAFE. range to be able to elaborate a section 4.1) are particularly rich local management policy for the in species. These river stretches Cormorant problem. So far, the are slow-flowing with increasing area in the Balkan countries. In situation in (westernmost Alpine) amounts of silt compared to the upstream parts the Salmonids Slovenia has still not produced a lot those further upstream, and have represent a significant and, from of Cormorant damage cases. considerable aquatic vegetation the perspective of biological cover. Stretches of fast-flowing diversity, a highly valuable part of The diet of Cormorants wintering water occur further upstream and the aquatic fauna and these values on the Sava River between these are typically inhabited by are internationally recognised and and Zagorje in the winter salmonids like Brown Trout (Salmo protected under the EC Habitat of 1998–1999 (Sava River and its trutta) and also Grayling (Thymallus Directive. For example, the tributary, Ljubljanica) consisted of thymallus). These waters are Marbled Trout (Salmo marmoratus) 23 fish species, by far more than is generally characterised by high is now considered a separate regularly found elsewehere (4–10 fish species diversity that is also species and much effort has been species): (Brown Trout, Rainbow reflected in the diet of Cormorants. directed to the reconstruction of Trout (Oncorhynchus mykiss), Construction of hydro-dams the original genotype. In Slovenia, (Hucho hucho), Grayling, has disconnected the migratory a genetic breeding programme Chub (Squalius cephalus), Nase pathways for fishes and has also runs parallel with measures to (Chondrostoma nasus), Danube impacted the discharge patterns, and reduce the occurrence of foreign Roach (Rutilus pigus), Roach, locally the flow speeds, of rivers. species/races of fishes and an Blageon/Soufie ( souffia), awareness programme amongst Prussian/Gibel Carp (Carrassius Fish communities anglers to develop a framework for gibelio/C. auratus), Barbel (Barbus Given the special mountainous sustainable recreational fishing. barbus), Bream, Pike, Perch, Rudd river conditions that prevail in (Scardinius erythrophthalmus), the lower Alpine range, in both Role of Cormorants Carp, Tench, Schneider Slovenia and Austria, the fish In the 1970s, Cormorants were ( bipunctatus), Zährte community is rather unique and rare visitors to Slovenia and (Vimba vimba), Streber (Zingel differs considerably from many they were still uncommon in the streber), Bullhead (Cottus gobio), other mountainous parts in Europe. early-1980s but the first flocks Burbot (Lota lota) and Weather Also for the lower parts these river appeared in 1984. It was estimated Fish (Misgurnus fossilis). In the sections hold fish populations that that in 1993–1994 about 1,000 river Ljubljanica, 27 fish species are diverse and comprise many Cormorants wintered on large were documented, including 8 not more species than elsewhere in lowland rivers in Slovenia, and a recorded in the Sava; Crucian Carp north-west Europe. In Slovenia for few thousand have done so in more (Carassius carassius), Gudgeon instance, over 90 species of fish recent years. On the basis of ringed (), Minnow (Phoxinus occur and many are endemic to the Cormorants, these birds breed in phoxinus), the Cyprinid Barbus country or to a relatively confined Denmark, , Poland, Estonia, petenyi, Pikeperch, Wels (Siluris

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glanis), Bleak (Alburnus alburnus) class was 70–170 mm (50% by of pond farms, extensive ‘natural’ and Golden Loach (Cobitis aurata) number and 19% by mass), but ones and more intensive systems (see Govedicˇ et al. 2002). large individuals (>170 mm) were where the fish are fed with wheat common (25% by number and 80% and manure is used as a fertiliser. Cormorants from the night roost at by mass) in the diet of Cormorants. There are no commercial fisheries Hotic consumed between 16,071 The respective numbers of on Czech reservoirs, except for and 32,143 kg of fish or between Cyprinids, Percids, and Salmonids a very poor Eel fishery. In South 44.8 and 89.6 kg/hectare in winter varied significantly between months Bohemia the majority of the water (1998/99). From the same section while the number of specimens surface area (about 85%) consists of water 8,812 kg of fish (31.6 kg/ did not. It was concluded that the of isolated ponds and lakes, the ha) was taken by anglers in 1998. differences in fish species caught remaining surface area is made However, since the productivity of by Cormorants in the study area up of rivers. This compares to the this stretch of river was not known depended on random detection of a Czech Republic as a whole where it was impossible to evaluate the particular fish species and was not rivers and lakes each comprise effect of Cormorant predation the result of selective hunting. Chub about a third of the water surface on fish stocks there. Among 473 and Nase are shoaling fishes and are area, the remainder comprising pellets, 70 % contained the remains probably more easily detected by lakes and ponds connected to larger of fish but they also contained Cormorants than the non-shoaling rivers, often with dams. worms and tapeworms, species. the remains of caddisflies, snails Fish communities (largely remains of diet of fish At a European scale, the Czech species eaten) and a single frog. 5.7 South Bohemia, Czech Republic is at the centre of the In individual pellets, the remains Republic major European watersheds, of between 1–69 fish (median = 2, those running towards the Black average = 3.9) were found: most Introduction Sea and those to the Baltic-North (93.6%) contained the remains of up The Czech Republic includes Sea. Rivers can be categorised as to 10 fish. Altogether, the remains several water systems types that are (1) small/upstream or (2) large/ of 1,279 fish were found. The total used by anglers or by commercial downstream. In both types, the weight of these fish was estimated fisheries. Large rivers, small rivers fish communities are rather at 57 kg. The diet consisted of and reservoirs are mostly stocked diverse, with some 25–30 species. 12 fish species: Brown Trout, with fish species to be used for Small rivers are dominated by Grayling, Chub, Nase, Danube angling. Large- and medium-sized Brown Trout, Rainbow Trout Roach, Roach, Barbel, Bream, fishponds, which have existed since and Grayling. More downstream Bleak, Pike, Perch, and Ruffe. Most the , are traditionally rivers are dominated by Roach and of the diet consisted of cyprinids used by Carp (Cyprinus carpio) Chub; the remaining species being (88% by number, 90% by biomass) farmers. For a long period, man has a considerably less significant although Grayling and Brown Trout managed the water resources in this part of the fish stock. Pike occurs represented 6% by number and 4% region by increasing the amount of everywhere but in very low by mass and Pike, Perch and Ruffe still waters. As in Germany, parts numbers (no more than 2% of represented 7% by number and 4% of France and further in Eastern stock). Wels is present in reservoirs by mass. Among the Cyprinids, Europe, these artificial lakes and and lowland rivers, again in very Chub (16% by number and 39% by ponds are used for fish farming. low numbers. mass) and Nase (4% by number and Nowadays, about 20 million kg of 16% by mass) were most common. fish are produced annually in the Table 5.2 shows the fish species and The proportion of unidentified Czech Republic, of which about the approximate productivity for Cyprinids was 57% by number and 420 kg per hectare come from the different Czech water bodies on an 28% by mass. south Bohemian Carp region. Since annual basis. The lowest production 1995 this production has slowly occurs in small running waters Prey size ranged from 23 to 345 increased. Production is divided where Trout and Grayling occur, mm. The most frequent length about equally between two kinds with an annual production of some

[36] INTERCAFE Toolbox intercafe – cormorants and the european environment

Table 5.2 Simplified overview of the major fish species and scale of fish form a biologically comparable production in different water systems in the Czech Republic. predator, in terms of the amounts of fish taken in the region. Water body type Main fish species Annual production (kg/ha) Table 5.3 illustrates how the water Small river Trout, Grayling 50 surface area of the Czech Republic Large river Roach, Chub 300 is distributed and how Cormorant numbers are distributed between Reservoir Bream, Roach, Bleak, 250 waters, both in winter and summer. Perch Wintering numbers of Cormorants Pond Carp (Grass Carp, Silver 500 (but up to 1,000) are higher than those in summer Carp) and wintering birds appear to make preferential use of the river Table 5.3 Estimated percentage share of different water bodies in Czech Republic systems. In summer, birds mainly and estimated percentage share of use by Cormorants, and absolute estimated forage specifically in pond areas number of birds. where they also breed.

Water % % share % share Estimated Estimated body share of birds of birds bird bird 5.8 Upper Lusatia, Saxony, type of total (winter) (summer) numbers numbers water (winter) (summer) Germany

River 30 80 - 8,000 - Introduction

Pond 30 5 100 500 1,000 The Upper Lusatia region covers about 950 km2 and the area is Reservoir 30 15 - 1,500 - the centre of Carp (Cyprinus carpio) production in Saxony, 50kg/ha. In both reservoirs and are allowed to breed in a few holding a large concentration large river sections, fish production strictly protected nature reserves. of fish ponds — many of which is higher (250 and 300kg/ha, Wintering Cormorants are present are intensively managed. Local respectively) and the fish species in increasing numbers and these Carp production is a 500-years- also differ. In reservoirs, Bream, birds have most interactions with old tradition and considered a Roach, Bleak and Perch are usually fisheries’ interests. However, most good example of sustainable fish the dominant species, whereas fishponds freeze in winter and some production. Water for the fish ponds Roach and Chub predominate in are left drained after the fish are is sourced from impounded river larger river sections. The highest harvested and so these are not used sections. Ponds range in size from annual fish production is recorded in by wintering Cormorants. Otters several hectares up to over 100 ha ponds where an average of 500kg/ha each; they are about 1.5 m deep, is fairly representative for large extremely turbid and stocked with areas, but occasionally the more abundant small fish. Ponds look intensively farmed areas may yield semi-natural, and are surrounded by up to 1,000 kg/ha/year. In contrast trees and bush growth, resulting in to the other (more natural) systems, a semi-closed landscape. Sparsely Carp is by far the commonest inhabited and large forested species held in fishponds. areas surround many of these water bodies. Smaller or wider Role of Cormorants stretches of Reed, Bulrush or other Management measures have macrophytes border the small lakes resulted in a comparatively low Extensive naturalised Carp pond and, in some places, the water table number of breeding Cormorants in farm system, South Bohemia, Czech is maintained artificially. At the time the Czech Republic. Cormorants Republic. Photo courtesy of INTERCAFE. of fish harvest, the pond system is

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Dense aquatic vegetation on the banks of extensive, naturalised Carp pond farm system, Saxony. Photo courtesy of INTERCAFE. drained and fish are collected from (Talsperre Quitzdorf) was created the deepest part of the basin. by a dam installed on a tributary of the River Spree on a flood Larger water bodies in the area only 3 m deep. Its main function include reservoirs, river sections is to supply water for industry but and recently developed water bodies also for aquaculture and to provide resulting from restoration activities flood protection. The reservoir is in former open cast mining also used for recreation, angling and areas. The system is also considered nature conservation. Water is now important for biodiversity. Former being taken from the reservoir to open-cast coal mines in Upper maintain the level of the river Spree. Lusatia are being converted into artificial lakes, sometimes relatively Fish communities large ones, by stopping the active The total production of Carp in drainage of water from the mines the area is about 900 tonnes, for and by pumping water directly from which some 3,000 tonnes of wheat the River Spree system. Fish are are supplied annually as food for thus transferred from the river Spree the fish. Besides harvestable Carp into the artificial lake as river water (3-year old fish), a further 800 is being used to fill it. One reservoir tonnes of fry (young-of-the-year,

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0+ fish) and young (1+ group) fish 5.9 Hula Valley and Lake products are produced, including are produced each year. Other, Kinneret (Sea of Galilee), peanuts. more recently Israel include , Grass Carp and Fish communities Silver Carp, but Carp remains the Introduction Fish farmers in the Hula Valley main species under cultivation. The Hula Valley is a large area cultivate mostly Carp but also Typical lowland freshwater species with a complex of natural habitats Silver Carp, Chinese Carp and like Bream, Ide (Leuciscus idus), (Lake Agmon area), the large Lake Mullets. The Reservoir produces Roach, Perch, Tench and Rudd Kinneret (Sea of Galilee, 166 km2), over 400 kg/ha/year, mostly Carp occur in the small flowing rivers scattered pond farms and a few but also Grey Mullet and Silver and unmanaged ponds and lakes. reservoirs. One such is the Anan Carp. Intensive fish farming Reservoir with an area of about complexes are located south of Role of Cormorants 40 ha and depth of up to 11 m. It Sea of Galilee, with an average The Cormorants in this area are contains ‘second hand’ water (from production of 10,000 kg of fish/ migratory, exploiting the water the surrounding area) that is used ha/year. These farms hold Carp, bodies from about five main in the lowlands and then pumped Tilapia and other species. Intensive roosts. Cormorants use the area some 800 m into the hills. The Lake Cormorant shooting is undertaken during migration as a stopover site. Agmon area was the first wetland throughout daytime in order to Sometimes they have attempted site to be reinstated in Israel. In protect the area from visiting birds. to establish nests but these have 1992, part of the Hula Valley was been destroyed. In winter when re-flooded after earlier drainage Role of Cormorants waters are often frozen, the birds of the area and the Lake Agmon Cormorants winter in the Hula leave the area. Possible impact of Nature Reserve was formed. In Valley and at the Sea of Galilee. Cormorants on fish stocks has been the rest of the Valley there are Wintering birds in Israel are part little studied so far and there are around 100 km of canals, which of a flyway originating from few data on the diet of birds in the create a unique wetland system. All a large breeding population in region. agriculture has changed and new the Ukrainian river deltas of the

Fish pond area in the Hula Valley, Israel a former natural wetland area. Photo courtesy of Stef van Rijn.

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northern Black Sea. When the Hula ponds closer to the Reserve during ‘protection’ to the fish stocks there. Valley project was started, there the course of the winter. Detailed studies with captive birds were 8–9,000 Cormorants in the have shown many new facts with Hula Reserve — winter visitors Nowadays about 1,500 Cormorants respects to underwater vision and between November and mid-March. winter in the Hula Reserve and fish detection (Strod et al. 2004). About 1,000 of these birds fed on only about 200 appear to forage The protection of Cormorants in surrounding aquaculture ponds each in the surrounding ponds. Some certain areas in combination with day. The flight time from the roost birds make daily foraging trips effective disturbance programmes in the Reserve to the nearest ponds into and some go into in the most sensitive areas has is about 30 seconds, and birds the . Large roosts greatly alleviated the problems would feed at the ponds for about occur on the shoreline of the Sea of with Cormorants. Similar routines 30 minutes at a time. Other birds Galilee, where 12,000 Cormorants with the aim of zoning the use moved out to other fishponds, and may regularly forage. At this of specific habitats/areas that around half of the birds flew the 25– large lake there appeared to be ‘conflicting species’ are allowed to 30 km south to Galilee. By January, few, if any, conflicts with local exploit have also been developed around 90% of the birds were fisheries interests perhaps due for Cranes (Grus grus) and White making foraging trips to the Sea of to the lake’s very large size and/ Pelicans (Pelecanus onocrotalus) Galilee, implying that changes had or the relatively low underwater (Shmueli et al. 2000, Gutman et al. occurred in the availability of fish in visibility offering a degree of 2001).

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6 CORMORANTS ON A WIDER EUROPEAN SCALE

This overview presents the most discussing Cormorant numbers Africa constitute the main area of recent information on the numbers ‘in Europe’, it is important to distribution of two subspecies of and geographic distribution of define the precise geographical the Cormorant: sinensis occurring Cormorants Phalacrocorax carbo. area under consideration. Also the mostly inland and along coasts It is based on two pan-European period during the year is important of non-tidal waters and carbo censuses, carried out for wintering with respect to the numbers and breeding on rocky coasts in more birds in January 2003 and for distribution of Cormorants. exposed, marine habitat. The breeding birds in 2006. Cormorants population and range of distribution show distinct patterns of occurrence extends from Europe into and different populations use this 6.1 Ecology, flyways and as as . ‘Europe’ vast area, which extends partly countries involved can be broadly split into three into the Russian Federation, regions, mainly according to the Northern Africa, Turkey and the In the western Palaearctic Europe, breeding distribution and migratory Middle East. Therefore, when the Middle East and North movements of Cormorants:

A. Atlantic-/western Mediterranean population ranging from Norway, Denmark, UK, Ireland, Low Countries, France, into the western Mediterranean; this group includes the subspecies carbo which is largely confined to coastal marine waters in summer but can move some C distance inland in winter. B. Baltic/central European population ranging from Sweden, Finland, the Baltic countries, Poland, Germany, B all the way south through central and eastern Europe (Danube countries) to the south including Italy and .

A C. Black Sea/ population ranging from Belarus, Ukraine, south to Figure 6.1 Map of Europe and beyond showing the major areas of Turkey, Israel and Egypt and occurrence of Cormorants (regions A, B and C). possibly .

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These three regional groups should Table 6.1 Comparison of Cormorant counts in 47 countries in the western not to be considered as closed Palaearctic, including and the Middle East, in summer 2006. Counts are units operating independently but split into three geographic regions (source: IUCN-Wetland International Cormorant more as ‘meta-populations’ given Research Group). the large geographical area they Regional group Summer 2006 are operating in. A metapopulation consists of a group of spatially Number of nests % separated populations of the same (A) Atlantic-North Sea 121,763 33 species which interact at some (B) Baltic-Central Europe 162,691 44 level. The term metapopulation was coined by Richard Levins (C) Black Sea-East Mediterranean 87,882 24 in 1970 to describe a model of Total 372,336 population dynamics of insect pests in agricultural fields, but the idea has been most broadly European Russia and Turkey, breeding (the so-called ‘floaters’) applied to species in naturally or where some 87,880 breeding was estimated to be between artificially fragmented habitats. pairs were estimated (Table 6.1). 100,000 and 200,000 individuals In Levins’ own words, it consists In order to arrive at a realistic for populations in regions (A) and of ‘a population of populations’ estimate of the number of birds in (B) combined. (www.Wikipedia.org). Notice that this region, estimates for average both regions A and B have strong production of fledged young Thus, from the breeding counts links in winter to countries outside in three categories were used. in regions (A) and (B) in summer the EU, whereas those birds in These production estimates (from 2006, a January 2007 total of region C are largely confined to research undertaken in regions 755,300 Cormorants (sinensis) was non-EU countries throughout the A and B) were derived from estimated. This number includes year. production levels in (i) old, long- the breeding birds plus both young established colonies (1.0 fledgling/ of the year and the non-breeders. nest), (ii) relatively new expanding Mortality factors applied imply 6.2 Breeding numbers and colonies (2.5/nest), and (iii) an that the population in May (prior intermediate category between to hatching) would be lower and distribution these two extremes (at 1.8/nest). By in August (maximum number of Researchers are far less well applying different mortality rates young fledged) higher than this. informed about the Cormorant for different age classes of birds population in region C, a territory through the season until January, How many Cormorants are there that includes Belarus, Ukraine, it is possible to estimate the size in total? of the mid-winter population. Cormorants (P. carbo sinensis) are Mortality rates applied were 0.4 distributed continuously through In 2006, the most recent Pan- for first calendar year birds, 0.3 Europe and Asia.Thus to answer European breeding census of for immature non-breeders and the question above in a meaningful Cormorants was organised and 0.2 for breeding adults in these way, the geographic area under undertaken by WI-CRG (see calculations, adjusted for the consideration must be carefully Figure 6.2). In regions A and B, elapsed time between the end of defined. The division suggested a total of 232,311 breeding pairs the breeding season and January. here into three regions is a first of the sinensis race was assessed January is commonly used as attempt to do this. The analysis of and 52,143 breeding pairs of the month in which numbers of migratory movements of ringed the carbo race, giving a total of waterbirds are counted. Cormorants could be used to almost 284,500 breeding pairs further elaborate and distinguish breeding in the EU-27 region, The number of immature in a more sophisticated way Norway and Switzerland (see Cormorants of one, two and three between different sub-populations. Table 6.1). years old that have yet to start Nevertheless, from the overall

[42] intercafe – cormorants and the european environment



Figure 6.2 Distribution of breeding Cormorants (sinensis) in Europe. Notice the presence of the larger concentrations along the coastal (lowland) regions. Data are presented per 50 x 50 km grid cell, showing clearly the concentrations in the Baltic-North Sea as well as in the NW Black Sea region. Data for Turkey have not been included in this map, due to incomplete information at this grid cell level. number of breeding pairs in regions an estimate of total numbers. The counts in colonies produce data (A), (B) and (C) (including both young birds of the year and the non on breeding success, which is the carbo and sinensis races), it is breeding part of the population also number of fledged young per couple estimated that a total of 372,300 have to be taken into account. In that have started breeding. Applying pairs of Cormorants breed. the westernmost part of the range this conversion factor as derived for we have data to compare summer sinensis birds in regions (A) and However, the number of breeding and winter numbers; ringed birds (B) (i.e. a conversion estimate of pairs is not just doubled to arrive at provide estimates for mortality and 3.25 from the numbers of breeding

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pairs to the number of individuals 755,300 Cormorants were estimated 6.3 Winter distribution in the following January), produces to be present in regions (A) and Cormorants spend their winter in a a tentative estimate for January (B) combined. The latter number wider geographical range than they 2007 of 1.2 million birds in the corresponds essentially to the EU- do during summer: generally more entire pan-European range (i.e the 27 countries plus Switzerland and to the south, mainly because of Western Palearctic extending well Norway estimated for January the freezing-over of the freshwater beyond EU- boundaries). Of these, 2007. habitats they are using most of the

 Figure 6.3 Distribution of Cormorants in Europe in January 2003. Only geo-referenced data are shown, thus excluding most carbo birds in Norway, Iceland and Ireland, as well as birds in Ukraine, Russia and parts of Turkey. The green area depicts regions experiencing an average winter temperature below -5.5°C which largely coincides with areas not used by wintering Cormorants.

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Table 6.2 Comparison of Cormorant counts in 47 countries in the Western Using data from about 2,500 Palaearctic, including North Africa and the Middle East, in January 2003. Counts are roosts, complemented by counts split into three geographic regions, similar to the breeding count. Notice the shift in of Cormorants at water bodies percentage use of zone A compared to B between summer and winter (Table 6.1), made during the International indicating the increased importance of zone A in winter. Census (IWC) in January coordinated by Wetlands Regional group January 2003 International, an overall total Number of birds % number of almost 676,000 Cormorants was assessed in all (A) Atlantic-North Sea 346,524 51 three geographic regions together (B) Baltic-Central Europe 214,413 32 (Table 6.2). Half of this total (C) Black Sea-East Mediterranean 114,898 17 was in the Atlantic-North Sea/ Total 675,835 Western Mediterranean area and one third in the Baltic-Central European area. Regions (A) and winter numbers with counts during majority of Cormorants (51%) (B), including the greater part breeding time. Counting Cormorants winter in Western Europe, with of west and central Europe, thus in winter is more time consuming much lower numbers wintering in held a combined total of 561,000 than a breeding census as birds are central (32%) and eastern (17%) Cormorants. scattered over vast territories. Europe. This is largely due to the fact that many waters in central time. The pan-European attempt The January 2003 count (see and Eastern Europe freeze and thus to count Cormorants in winter Figure 6.3) gave an estimated total become unavailable as feeding was first organised in 2003. The number of 427,000 sinensis birds sites in winter. Please see chapter main aim was to assess the mid- and 134,100 carbo birds, mostly 12 for discussion and further winter distribution of the birds in confined to coastal (lowland) areas. interpretation of these assessments Europe and beyond and to compare As can be seen from Table 6.2 the of Cormorant numbers.

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7 CORMORANTS BREEDING IN EUROPE: EXPLANATORY FACTORS

7.1 Climatic aspects 

 The rationale behind this analysis is that as climatic factors differ  considerably across Europe, this &  R may have a large impact on the  breeding and wintering conditions DWXUH experienced by Cormorants. By  MXQ analysing European climatic WHPSHU PD\  conditions, it might be possible to DSU interpret some of the key driving PDU  forces behind the distributional IHE MDQ patterns of Cormorants at the  continental level. Temperature was Figure 7.1 Average minimum air temperature at Cormorant breeding colonies in considered to be the main factor the Netherlands in different months. March is important here as it is the month with affecting the birds’ distribution. the earliest recorded start of Cormorant breeding in the Netherlands. During this In winter freezing temperatures month such early breeding occurred when median air temperature = 1.8ºC, (average limit the availability of fishing = 1.7ºC, range = 0.7–2.8ºC). X-axis shows the ranking of all data points in March, waters whilst temperature sets from lowest (left) to highest (right), the other months are derived from this.

Figure 7.2 Months in which average minimum temperature 1.5°C is reached across the European continent, ranging from January to June. This illustrates the calculated possible start of Cormorant Cormorants breeding in Europe have more than four months difference in the breeding across Europe, based on temperature-dependent timing of the start of their egg-laying. Displaying temperature development. male bird. Photo courtesy of Florian Möllers.

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Figure 7.3 Months in which an average minimum temperature of 1.5°C is reached in relation to (sinensis) main Cormorant breeding colonies (indicated by blue dots). the biological timing of events used: (1) the time of onset of from The Netherlands, , in spring. The spawning of fish, Cormorant breeding in spring, Italy and Finland. Climatic data their swimming speeds, and also (2) the period when young birds at the time of fledged young was the energetic costs of Cormorant fledge, and (3) during mid-winter. assessed across pan-European and foraging are all related to Spring temperatures (average North African regions by looking temperature. minimum) in relation to the onset at temperature changes at these of Cormorant breeding at various sites 90 days after the start of For analyses, climatic data at places in Europe were explored. breeding, so as to reflect conditions three characteristic periods were For calibration, data were used at the time of fledging. The mid-

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winter distribution of Cormorants start to breeding in January in south during the fledging period would be was considered in relation to the and north-east Italy and of a late important. For this, temperature at average temperature in January, start to breeding in northern parts known breeding sites three months importantly this corresponds to of the Baltic Sea at the end of May. after presumed start of breeding (i.e. the period when Cormorants are On the map there is obviously a vast at or above an average temperature counted at mid-winter roosts. area around the Baltic that would of 1.5°C) was analysed. Because be suitable for Cormorant breeding this fledging period corresponds to Data from detailed observations from this perspective. On the Atlantic summertime, it was not expected that from the Netherlands show that, on side, the month of March covers a minimum temperatures would be average, the majority of Cormorants significant area whereas in Eastern important — rather it would be the start to breed in March. A closer Europe this is not the case. As a maximum temperatures which could look at the minimum temperature whole, the shift in spring temperature have an effect on in March for all colony sites in is more advanced but also slower in of the nestlings and/or conditions in The Netherlands shows an east- the west than in the east, probably the shallow feeding waters. west gradient within this rather related to the effect of the Gulf small territory of almost 2°C. This Stream. Breeding occurs in a SW to Analysis showed that at no breeding temperature gradient (effect of the NE sweep according to the average site in Europe did maximum North Sea) can also be observed minimum temperature threshold of temperature during the fledging from data on the commencement 1.5 degrees. So, it starts as early as period reach, on average, more of breeding, with birds in the January/February in SW Europe, than 30°C. Figure 7.4 shows the southwest breeding earlier than in March in UK, F, NL, in April for distribution of all colonies with those in the northeast of the country. large parts of central/eastern Europe respect to this temperature at the time By taking the minimum March and in May for Northern parts of that the young birds are fledging. temperature at 50% of the colonies Baltic and finally June for northern (quartiles 2–3) as the average start Norway and Finland. As can be seen from Figure 7.4, the of breeding we found a temperature average temperature at Cormorant of 1.5–2.1°C (Figure 7.1). Temperature at breeding sites at colonies three months after the time of fledged young onset of breeding is 20.9°C. The In subsequent analysis, 1.5°C (Q1) Besides minimum temperature in distribution appears to have two was adopted as an estimator of the relation to start of breeding, it was peaks, one at 20–21°C and one average temperature at the start of also tested whether temperature around 24°C. the Cormorant breeding period. The place where and when this temperature is reached was thus assessed in relation to Cormorant colonies throughout Europe.

There is a gradient across Europe with regard to the period at which minimum temperature for breeding (1.5°C) is reached (Figure 7.2). This gradient runs from southwest-northeast Europe and occurs sometime from January to May depending on location. This ‘temperature threshold’ nicely corresponds to the months when Cormorants actually breed in these Figure 7.4 The number of Cormorant colonies in relation to the local maximum regions (for distribution see Figure temperature during the fledging period of young (Q1=19.9°C, Q3=23.3°C, 7.3). There are records of an early Median=20.9°C, min-max: 12–30°C).

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mean maximum temperature at breeding sites 12−19

19.1−22

22.1−25

25.1−30

June

July

Figure 7.5 Mean maximum temperatures at Cormorant breeding colonies (dots) and areas where an average maximum temperature of 24°C is exceeded in June and/or July (black and darkest grey areas), that is at the time of fledging of young birds. Birds from colonies in the warmest temperature range (red dots) are known to move out of these areas towards cooler areas during the summer. This is partly also true for areas where the maximum temperature at time of fledging is greater than 22°C (yellow dots).

Figure 7.5 shows these The Netherlands, Denmark, and temperatures during the fledging temperatures mapped in relation Southern Sweden all the way east period reach more than 25°C, these to the individual colony sites in to the . Although are restricted to the interior parts Europe (for sinensis only). The many colonies occur in the zone of Spain, Italy, along the Danube coolest sites during the fledging just south of this (i.e. central and the northern edge of the Black period occur around the Atlantic France, Germany, Poland and Sea. Temperatures around 25°C and North Sea shores. The majority Belarus), average colony size here are probably ecologically the of all colonies are found in an area is smaller than elsewhere. Few highest the birds can cope with, ranging from central England, colonies occur in the area where and this is corroborated with data

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on post-fledge movements. At area occurring just below of this The important conclusion many colonies young disperse temperature range. According to from these analyses is that well out of the area of actual the analysis, such areas do not the distribution patterns and breeding and almost all birds exist in the greater part of the movements of Cormorants (in move out of the area where the coastal Black Sea and Azov Sea, terms of where and when birds maximum temperature during the as well as for the greater part of breed and where birds may move fledging period is greater than the coasts of the Mediterranean from after breeding/fledging) 24°C. Many even move out of the which seem simply too hot at this correspond with known temperature area when temperatures exceed time of year. Interestingly, some gradients across Europe. These 22°C during this period in the exceptions occur in the river Rhone relationships could thus be used to breeding cycle. The post-fledge and Po Delta, Sardinia and Puglia explore future developments (e.g. staging sites around the North Sea in Italy as well as coastal parts of colonisation patterns and/or effects and Baltic Sea are situated in an in Greece. of global change).

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8 CORMORANTS WINTERING IN EUROPE: EXPLANATORY FACTORS

The rationale behind this analysis is that habitat availability is a vital factor in determining the ecological tolerance of an area for Cormorants in winter. Describing the available space in relation to a temperature gradient and habitat availability will provide a better view of the ecologically based dispersion patterns of Cormorants across Europe.

8.1 Choice of the study area The winter distribution of the Great Cormorant used in this analysis was constructed using the Wetlands International Cormorant Research Group (WI-CRG) coordinated Figure 8.1 Map of Europe showing the sub-set of 1,242 grid cells (50 x 50 km) night roost count of mid-January used for analysis in the present study. 2003. Analysis was concentrated on a large geographic area, count was approximately 370,000, Temperature with homogeneous data quality, which accounted for 65% of the Figure 8.2 shows the average encompassing most of the sinensis estimated European population of minimum temperature in January in wintering population from regional Cormorants at that time, including the study area. A strong southwest groups A and B (see Figure 6.1 the carbo race. to northeast gradient in ambient map). This area covers South- (air) temperature is visible, West Europe (excluding Portugal), clearly showing the effect of the north to southern Scotland and 8.2 Exploring the water continental land mass as well as Denmark, east to Poland and surface area/climatic patterns the influence of the relatively warm , and south to central Italy in the study area Gulf Stream, generally showing (see Figure 8.1). This study area cooler temperatures inland and is approximately 3.1 million km2 In order to describe how the towards the east. Notice the high and includes 1,242 50 x 50 km environmental conditions vary mean temperatures along the coasts grid cells where environmental across the study area, several maps of Sardinia. variables have been calculated were drawn (Figures 8.2 to 8.5) and (note: each grid cell thus represents a multivariate analysis (Principal Depth profiles along the coast 2,500 km2 or 250,000 ha). The Component Analysis) was performed The coastal waters immediately number of birds observed in this in order to understand relationships adjacent to the mainland differ with area during the January 2003 and patterns between the variables. respect to average depth. Figure 8.3

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Figure 8.2 Average minimum temperatures in January for each 50 x 50 km grid cell covering the study area.

Figure 8.3 The sea surface area of shallow waters for each 50 x 50 km grid cell containing shallow water (i.e. surface area for water of less than 25 m deep).

Figure 8.4 The surface area (ha) of small rivers (Strahler category 3, estimated width = 15 m) within 50 x 50 km grid cells. The mountainous areas are clearly visible because of the high density of small streams there.

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shows contrasting differences in pattern between the more shallow coastal areas around the North Sea, Baltic and Atlantic coast of France and the much deeper and steeper coasts along the mountainous parts of the Mediterranean and Adriatic. The Spanish between San Sebastian and Vigo, the SE coast from to Cartagena, the French and Italian Riviera coasts between and La Spezia as well as the coast of the Adriatic in Western are particularly steep.

Water inland Figure 8.5 The surface area (ha) of larger rivers (Strahler category 7, estimated In relation to the ‘availability’ of width = 200 m) within 50 x 50 km grid cells. surface waters on land, Figure 8.4 shows the occurrence of small rivers (Strahler category 3). The mountainous areas in Europe show in these regions. By contrast, the shows the occurrence of Strahler up well in this figure because of presence of large rivers is far less category 7 rivers across this part of the high density of small rivers common. For example, Figure 8.5 Europe. Note the difference in the

Young Cormorants tend to winter under more temperate climate conditions than others. Colour-ringed Dutch-born Cormorant in first winter recorded wintering in France. Photo courtesy of Florian Möllers.

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Table 8.1 Principal Component Analysis showing the correlation between the first The first axis (PC1) accounted three axes and the environmental variables. Significant factors are shown in bold. for 25% of the total variability in wintering Cormorant numbers. PC1 axis PC2 axis PC3 axis PC1 is positively correlated with Variance explained 25.2 % 14.0 % 9.9 % shallow coastal water surface area Average minimum temperature in January 0.27 0.51 0.15 and negatively correlated with all small river surfaces, as well Coastal surface area 0.36 -0.03 0.07 as with the variety of water types Lake surface area -0.08 -0.21 -0.07 (Table 8.1 and Figure 8.6). PC1 Strahler 2 river surface area -0.46 0.14 -0.19 is only poorly correlated with geographical coordinates. Thus, Strahler 3 river surface area -0.43 0.12 -0.19 PC1 separates the coastal, low Strahler 4 river surface area -0.35 0.13 -0.29 altitude areas used by Cormorants Strahler 5 river surface area -0.28 0.08 0.05 in winter from the higher altitude, Strahler 6 river surface area -0.16 -0.11 0.40 smaller river areas. The second axis (PC2) accounted for 14% of the Strahler 7 river surface area -0.11 -0.04 0.40 variability in wintering Cormorant Strahler 8 river surface area -0.06 -0.21 0.43 numbers. PC2 is strongly correlated Strahler 9 river surface area 0.00 -0.11 0.17 with higher average minimum January temperatures, and also with Latitude 0.12 -0.49 -0.26 the north-eastern coordinates, thus Longitude -0.10 -0.58 -0.07 it reflects the strong north-east to Diversity of water types -0.36 -0.01 0.46 south-west gradient in European winter conditions (Figure 8.7). The third axis (PC3) accounted for absolute value of the surface areas the general environmental variation 10% of the variability in wintering involved in these three aquatic across the study area (see Table Cormorant numbers and was habitat maps. Shallow sea surface 8.1). especially positively correlated areas (see Figure 8.3) constitute the largest areas, followed by larger rivers (Figure 8.5) and then small rivers (Figure 8.4). This means that, in relation to habitat type, the total area of water suitable for Cormorants is divided in an unusual way. The water surface area in regions with the highest density of small rivers never reaches the level of water surface area associated with even a single, or a few, large river sections. Moreover, when coastal shallow water is considered, the surface area of this habitat type greatly exceeds that of any freshwaters on a 50 x 50 km grid cell basis.

A PCA was carried out with all 14 Figure 8.6 Spatial representation of the PC1 axis (explaining 25% of variation environmental variables used in the in winter Cormorant numbers), separating potential Cormorant foraging habitat present analysis, in order to explore (available water surface area) in coastal versus high altitude habitats.

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related to these synthetic descriptors?

A plot of the 1,242 grid cells projected along the first two PCA axes is given in Figure 8.9, showing cells with or without Cormorants. There is no clear segregation of Cormorant presence/absence in this two- dimensional space, except that negative values on the PC2 axis (i.e. the northeast-southwest temperature gradient) seem to be more correlated to the absence of Cormorants. This is mainly due to the absence of wintering birds in Figure 8.7 Spatial representation of the PC2 axis (explaining 14% of variation in the northeast corner of the study winter Cormorant numbers), showing a northeast to southwest gradient, primarily the area (e.g. in Poland) during the result of average minimum January temperatures. 2003 census. It is noteworthy that PC1 (coastal versus high altitude) does not seem to be of importance in explaining the presence/absence of Cormorants in winter. This may be a reflection of the very wide environmental adaptability of the species in its winter range, but also of the differing availability of fish in winter relative to the different habitat types present. More specifically the availability of fish (e.g. species, size in relation to water depth, water current velocity, underwater visibility etc.) is not equally distributed across the water bodies but varies independently.

Pearson correlation analysis of Figure 8.8 Spatial representation of the PC3 axis (explaining 10% of variation in the log-transformed value of the winter Cormorant numbers), which fits well with the presence of medium and large number of wintering Cormorants river systems and to an increased diversity of aquatic habitat types. (excluding the cells where no Cormorants were observed), shows with medium to large rivers, as This analysis suggests that it is that Cormorant numbers are neither well as with a high diversity of meaningful to use the the three correlated with PC1 (coastal versus water types (Figure 8.8). On PCA axes as basic ‘synthetic high altitude, R = 0.045, p = 0.231), this map, high values of PC3 are descriptors’ of water and climate nor with PC2 (northeast-south clearly concentrated on major river conditions within the study area west temperature gradient, R = systems (e.g. , Rhône, Po, in relation to the distribution of -0.022, p = 0.552). These two major Danube, ) even at 50 x 50 km wintering Cormorants there. How environmental descriptors thus do resolution. is the Cormorant distribution not explain the overall patterns of

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3URMHFWLRQRIWKHFHOOLQWKH3&$VSDFH Cormorants in winter seem to have a European wintering range  determined by temperature  limits. Within this ‘temperature window’, the birds are widely 

H distributed, showing a strong QF

LD  tendency to be more abundant DU

IY in the regions of the major river R   systems (i.e. large river valleys

    

V and associated floodplains).

LQ  OD Based on the presence of suitable [S

H 

 foraging habitat, there is no

3& clear evidence that, within the  geographical wintering range,

 regions are used to capacity by Cormorants. Except for large  river systems, probably other 3&D[LV H[SODLQVRIYDULDQFH factors (such as fish availability) 3UHVHQFHRIZLQWHULQJ&RUPRUDQW $EVHQFHRIZLQWHULQJ&RUPRUDQW are highly variable and therefore Figure 8.9 Projection of the 1,242 grid cells in the space defined by the first may determine Cormorant and second axes of the PCA in relation to the presence/absence of wintering distribution in greater detail Cormorants. (see chapter 9). However, if the temperature window is modified Cormorant abundance in winter. = 0.347, p <0.001). Within the (e.g. by climate change), it Again, this suggests that, within wintering range, areas with the is highly probable that more the limit of the birds’ winter range highest Cormorant abundance aquatic habitat will become (probably primarily determined by fit with the major river systems, available to Cormorants due the climate), Cormorants in winter regardless of the geographical to the fact that more potential are not simply confined by the context of these systems (i.e. habitat is available in the north- overall surface area of the various southern or northern, continental east of the region than it is in the water types available in Europe. or maritime parts of the range). south-west and southern parts of This GIS-based analysis of Europe. However, the abundance of Cormorant wintering distribution Cormorants in winter is positively across much of Europe is Text Box 8.1 Summary of GIS-based correlated to the ‘major river summarised and interpreted in Text analysis of European Cormorant wintering system’ variable (i.e. PC3, R Box 8.1. distribution.

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9 THE WATER SYSTEMS DATABASE

The rationale behind this data largely depends on the surrounding referenced water bodies were collation and exploration is that land use and the input of phosphorus included in the analysis. These analysis of more detailed data and nitrogen. Furthermore, human waters accounted for approximately on the relationships between management of water bodies 30,000 km2 of sampled water surface Cormorants and their use of has changed fish communities and related to a maximum number feeding habitats, diet and their extensively (see chapter 4). By of about 350,000 Cormorants. For foraging densities at specific water closing off inland seas, lagoons and almost all cases, data on fish species bodies would provide important estuaries, by constructing artificial were provided as a ranking of (i) information about the role of these lakes and diverting rivers, many the three most abundant species avian predators in these water aquatic systems have become in the system and (ii) the three systems. less natural. Fish communities most common species eaten by have been altered and habitats Cormorants there. A total of 90 fish become disconnected. Through species were ultimately included in 9.1 Introduction their relationship with fish as food, the Water Systems Database. Cormorants are likely to react to all Water surface area is considered an these changes in some way. Ultimately, the cases included important variable that accounts for in the Water Systems database the total number of Cormorants or, A Water Systems Database, based represented a large area of the more precisely, the total number of on discrete water bodies, was European continent but tended to bird days (i.e. an index of ‘habitat established in order to broadly be concentrated a little more in use’ calculated as the number of assess the relationship(s) between eastern countries ranging from birds x the number of days the Cormorants and fish, and the the Baltic Sea and Sweden to the birds are present at a specific factors that determine them. Pooled Alpine zone, Italy and Greece. In location). The critically significant knowledge from 65 experts in 26 Western Europe (i.e. Netherlands, factor affecting the density of birds, countries (in total, 179 different Belgium, UK) cases are also well however, is the supply of edible cases, see Table 9.1) of geo- represented but in southern Europe (i.e. relatively small) fish and its ‘availability’. Prey availability is a complicated concept, covering Table 9.1 The number of cases included in the Water Systems Database, more than the abundance of in relation to different water body types. potential prey and encapsulating its ‘ease’ of capture. Thus, besides Water Systems Type Number of Cases (%) the abundance or biomass of edible Open sea/Shore 7 (4) fish, water depth and turbidity will Estuaries/River delta 17 (9) determine the carrying capacity of a water systems (i.e. the number of Inland sea/Large Lagoon 14 ( 8) Cormorants that it can support). Large Lakes 44 (25)

Large Rivers 28 (16) Nutrients and algae are an important food source for micro-organisms Streams/Small Rivers 30 (17) and macro that, in turn, Reservoirs/Small Lakes/Sandpits 21 (12) form the food supplies for fish and Fish Ponds 18 (10) result in subsequent fish biomass. The nutrient balance of a water body Total 179 (100%)

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considerable gaps occured, for is strongly reflected by the absent in the north. Smaller rivers instance in the interior parts of geographical range of waters within and streams are represented in a France and Spain (Figure 9.1). the continent. Open seas, inland wide geographic gradient from high Spain did not actively participate seas and estuaries are situated altitudes to lowland situations, and in the INTERCAFE network but along the coasts of the western reservoirs are distributed similarly. contributed some cases during parts of Europe and outside Europe Fishponds are distributed in a the earlier REDCAFE Concerted at the Black Sea coasts. Large wide area of inland Europe but are Action. Outside Europe, water lakes are situated in the Baltic concentrated in a belt of eastern systems information was also and partly in The Netherlands, the European countries from the Baltic obtained from Israel and Georgia. alpine countries and Italy. Large States and Poland to the Czech rivers are mostly situated in the Republic and France, but also The variety of European water extensive lowlands of western and extending further southeast into the systems types (see section 4.1) Central Europe and are generally Balkan countries.

Figure 9.1 Map showing reported cases used in the Water Systems Database for Europe. Each case has quantitative data on water quality, aquatic biota and Cormorants. Cases from Israel and Georgia are not shown on the map. Eight different types of water system are differentiated.

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The cases included and used in the Water Systems Database represent and describe the major European water bodies. Coastal areas are not so well represented but range from Estonia and Finland to Portugal. Other water systems types in the Database cover a representative portion of their European occurrence. Reservoirs are probably an under-represented habitat type that might account for a larger proportion of European fish-eating birds than is currently known, whilst fishpond cases are mainly from Baltic and central European Figure 9.2 Relationship between total bird days per year for Cormorants countries and not from southern and water surface area (N = 132 reported cases). regions (i.e. France and Spain or the Balkans, see Figure 9.1). indicate that smaller water bodies either large-scale or smaller-scaled are more intensively used than systems in terms of their water Over the whole dataset, there is larger water bodies as the slope surface area (see section 4.1). a clear relationship between the of the regression line is less steep Large-scaled waters are open seas, annual number of ‘bird days’ spent than the 1:1 relationship with water inland seas and lagoons, estuaries by Cormorants at a particular site surface area. and large lakes, smaller-scaled and the surface area of the water ones are the large rivers, streams body concerned (Figure 9.2). In and small rivers, reservoirs and absolute terms, large water bodies 9.2 Water surface area and fishponds (Figure 9.3). A bootstrap have far more Cormorants (i.e. Cormorant density analysis of the data for each water more bird days, and so a heavier body type produced the mean overall ‘use’ by Cormorants) than do The water bodies collated in the values and 95% confidence limits smaller ones. However, corrected for Database can be divided into shown. The water body types surface area, this equates roughly to some 5,000–10,000 Cormorant days per square kilometre of water per ) year for smaller waters and lower 2 at 1,000–5,000 Cormorant days per square kilometre of water per year for large surface areas.

As can be seen from Figure 9.2, the variation in the dataset is size of fishing water (km large with some individual cases diverging by a factor of around 10 (plus or minus) from this general pattern. However, the relationship clearly shows that large numbers of Cormorants and/or the length of their residence time at specific sites Figure 9.3 Mean size (± 95% Confidence Limits) of foraging water for different across Europe are associated with water body types, n = sample size; notice log scale (values based on bootstrap large water bodies. The data also calculation).

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rivers, and this was significantly lower than all other water body types except reservoirs (Figure 9.4).

Cormorant presence, as measured by the average number of bird days spent at a site, is thus largely related to the size of the water body used for foraging (compare Figures 9.3 and 9.4). Streams and small rivers have the smallest average number of bird days, and reservoirs, small lakes and fishponds are similar to each other, having more bird days. By Figure 9.4 Mean number (+/-95% Confidence Limits) of bird days per year for contrast, the largest number of Cormorants at different water body types, n = sample size; notice log scale (values Cormorant days throughout the based on bootstrap calculation). year are recorded on estuaries, followed by inland seas, shallow clearly fall into the two groups values for these three habitat types coasts and large rivers being only mentioned above, according to showed no significant differences slightly less heavily used. The the water surface area available (i.e. overlapping confidence limits) important conclusion from this to foraging Cormorants, the and were much higher than those analysis is that the large-scale water mean surface area (km2) being of other water body types. Large bodies in Europe are used most by approximately 50 times greater for lakes, large rivers, reservoirs Cormorants. open sea, estuary, inland sea and and fishponds also did not differ large lake than for the other four significantly from each other but A different picture of Cormorant water body types. they did have significantly lower use of water systems is apparent if numbers of bird days than did the bird days are examined in relation Cormorant numbers are often large-scale systems. The smallest to water surface area in terms of best expressed as ‘bird days’, the mean value for bird days was bird density (‘Cormorant days per number of Cormorants multiplied calculated for streams and small hectare per year’, see Figure 9.5). by the number of days that they are present at a specific site. The  total number of bird days per year 2SHQ6HD (VWXDULHV ,QODQGVHD shows which habitats are most /DUJHODNHV /DUJHULYHUV heavily used by Cormorants.  6WUHDPVVPDOOULYHUV 5HVHUYRLUVVPDOOODNHVVDQGSLWV

Although the number of cases for D )LVKSRQGV

the different water body types is HDUK  not equally distributed over Europe \V\ and the sample size of open sea ELUGGD and estuary cases is too small to  get reliable results by bootstrap analysis, there are clear differences  in the number of bird days between         water body types. The large VDPSOLQJVL]H Q  Q Q  Q  Q  Q  Q  Q  systems (i.e. open seas, inland seas +DELWDWW\SH and estuaries) carry the largest Figure 9.5 Relationship between Cormorant density (bird days/ha/year) and number of bird days (Figure 9.4, water body type. Box plots showing data range, 95% Confidence Limits and 75% note logarithmic scale). The mean percentiles of values around the median.

[60] intercafe – cormorants and the european environment

Although samples are small (especially for the number of site- specific datasets for open seas and estuaries), there is a trend towards higher average Cormorant densities in the smaller-sized water bodies like the reservoirs and fishponds. To some extent this is also true for the inland seas and lagoons. Almost all median annual density values are less than 100 bird days per ha, and only reservoirs/small lakes/sandpits have a higher density (Figure 9.5). These high Cormorant Figure 9.6 The frequency of Cormorant density classes (bird days/ha/year) for water density water systems all share the bodies of increasing nutrient levels (oligotrophic, mesotrophic and eutrophic) in fact that they are artificial, man- Europe. made waters. The natural waters such as open seas, estuaries, large lakes, large rivers and small rivers clearly have the lowest densities of foraging Cormorants (Figure 9.5).

The analysis thus suggests that artificial water bodies attract Cormorants in higher densities than do other water systems. However, the overall number of birds in relation to their duration of stay is always small at these foraging sites and Cormorants are most numerous in the large natural waters of

Europe. Figure 9.7 The frequency of Cormorant density classes (bird days/ha/year) for increasingly less natural water bodies (natural, semi-natural and artificial) in Europe. 9.3 Water quality water bodies (i.e. those with highest more than 50 bird days/ha/year) are Trophic state (i.e. overall nutrient status). Waters of a higher often associated with semi-natural productivity based on the availability trophic level thus appear to attract and artificial water bodies (Figure of nutrients) can also determine more Cormorants than do other 9.7). Extremely high Cormorant the distribution of Cormorants (see water body types. densities are actually strongly Figure 9.6). The lowest Cormorant related to artificial water systems densities occur in oligotrophic water Another factor to explore is the which clearly implies that more systems (i.e. those with low nutrient effect of the ‘naturalness’ of water ‘unnatural’ waters attract greater levels), whilst intermediate densities bodies on Cormorant numbers. Cormorant numbers. are mostly recorded on waters of Generally, the lowest Cormorant higher nutrient status (i.e. so-called densities occur in natural water 9.4 Fish biomass mesotrophic and eutrophic waters). systems, intermediate Cormorant The highest Cormorant densities densities are mostly recorded on Relatively few quantitative data (more than 50 bird days/ha/year) semi-natural waters, whilst the exist on fish density in absolute are often reported from eutrophic higher Cormorant densities (of terms in many European freshwater

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   seas. These water types with higher  fish biomass values correspond to   those where Cormorant densities  are also relatively high (see Figure   D 9.5), suggesting that the birds are K

 NJ  attracted to systems holding a high  density of fish.      O OO V V UV HD DO HD WV  LH 9.5 Abundance and NH V PD 6 YH 6 RQG DU OD UL 6P 6

 UV S WX QG QGSL HQ H H V UV consumption of fish OD YH VK UJ UJ (V RL 6D

 UL 2S ,Q DP )L V UY /D /D  UH NH VH Many experts provided extensive 6W OD  5H information on fish for the  Q     different cases collated into the Figure 9.8 Reported fish biomass (kg/ha) for different water body types across Water Systems Database. The Europe, n = sample size (means and error bars derived by bootstrap calculation). total number of fish species in a specific water systems was systems. Most data available for lakes (Hanson & Leggett provided to demonstrate the range refer to relative — rather than 1982, Quiros 1990, Jeppesen of biodiversity within European absolute — abundance, used for et al. 1997). Eutrophication of waters. The total number of fish assessing stock trends rather than many surface waters due to the species differs considerably calculating absolute fish density. In discharge of untreated sewage between water systems types but the present analysis, fish biomass waters has taken place in many, if also within them (Figure 9.9). was partly estimated by expert not all, lowland areas in Western Coastal waters and other generally judgement or was determined by Europe. Especially after WW-2 the large-scale areas (i.e. open sea, standardised methods, mostly situation deteriorated, culminating lagoons, estuaries and inland through statistical calculations. The in many countries around 1980. seas) have a higher diversity of 117 cases providing information In the last decades the reverse fish species overall than do most on fish biomass include all eight trend has taken place in many freshwater systems. In estuaries, water systems types, although, as European countries. This process the number of fish species varies in other analyses, the numbers of of nutrient reduction has involved considerably between simply- cases from opens seas and estuaries intense technical efforts to treat structured (often small) areas that is small (Figure 9.8). sewage and a shift to phosphate- support few fish species and the free detergents, (Scheffer 1998). larger, often more natural, areas like Generally speaking, fish biomass The practical effects of this trend the Danube Delta with more than varies between seasons, years, are still the subject of research 120 fish species present (Figure sampling sites and between water but the ‘environmental clean-up’ 9.9). Large freshwater systems (e.g. body types. The biomass of a fish tends to result in a reduction of fish large lakes and large rivers) have an species is the result of recruitment biomass, very often accompanied intermediate number of fish species, size, mortality- and growth-rates, by a shift in species composition. whilst the smallest freshwaters which are influenced by food (e.g. streams, reservoirs and fish and habitat characteristics or by In this study, the reported fish ponds) contain only few fish abiotic parameters like water biomass situation appears to be species, chiefly reflecting unnatural level changes, drought or nutrient fairly similar for most water body situations, or even commercial content. From the scientific types in Europe (Figure 9.8). monoculture of certain species. literature, the correlation between However, the highest reported phosphorous content and fish overall mean fish biomass values In terms of the fish communities biomass has been well documented occur for fishponds and inland within different water systems, a

[62] intercafe – cormorants and the european environment

fishes most commonly eaten by Cormorants in these same places are compared, a strikingly comparable pattern appears (Figure 9.10). The distribution of the most commonly reported fish species in this combined sample is not representative of the entire European situation because some water systems types are under- or over-represented. Nevertheless, the picture shows that only a few species of fish constitute the majority of the most commonly reported — both in Laboratory work at RIZA, The Netherlands: identifying and measuring fish terms of abundance in particular otoliths from Cormorant pellets provides data on the species and size of fish waters and also in their frequency eaten by the birds. Photo courtesy of Florian Möllers. in Cormorant diet at the same location. The general pattern thus indicates that the most common  2SHQVHD fish species in a particular water (VWXDULHV systems are also the most common  ,QODQGVHD /DUJHODNHV Cormorant prey. Nonetheless HV  /DUJHULYHUV 6PDOOULYHUV Cormorants might be more SHFL 5HVHUYRLUV selective for certain fish species  )LVKSRQGV VK V

IIL if more detailed information R  on the availability of these fish HU

PE  to the birds were available. An

1X important factor here is likely to  be the size-distribution of the fish.

 Cormorants clearly feed primarily  on the most abundant fish species V\VWHPW\SH and tend to eat smaller individuals (often young-of-the-year and/or Figure 9.9 The reported number of fish species (and average) for different water body juveniles). Larger fish are often types across Europe. The average value for each system is indicated by the white square. too fast and thus evade capture, or are not numerous enough to be comparison was made between the some 90 species were reported. included as a significant part of ranking of the three most abundant This illustrates the diversity of Cormorant diet. fish species reported in each water water systems in the European body and the three most commonly context. All eleven most common Finally, patterns of fish abundance reported fish species eaten by species present, as reported for the and frequency in Cormorant diet Cormorants at the same site. This Water Systems Database, occur in were explored separately for comparison was meant to show the freshwater systems. This is partly a different European water body most ‘important’ fish species involved result of the greater diversity in salt types (Figure 9.11). and their relationships with both and brackish waters compared to Cormorants and water systems type. that in most freshwater systems. Open sea, inland seas, lagoons and estuaries are considered In ranking the three most abundant If the most abundant fish species together here as ‘coastal areas’. and most commonly eaten fish, at specific locations and the The distribution of the ten most

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Figure 9.10 Frequencies of reported cases of fish species that are the most abundant (N = 465) and the most commonly eaten (N = 309) by Cormorants at locations included in the Water Systems Database. abundant fish species in these Large lakes are clearly dominated of the fish fauna of larger rivers coastal waters is rather even with by Roach and Perch (Perca (see Govedic et al. 2002). no specific species dominating fluviatilis). These species are the community. This is thought also the most commonly reported According to the available to ultimately reflect the high prey of Cormorants here. Other information provided through the diversity of coastal habitats that, Cyprinids, Mullets (Mugilidae) inquiry, small rivers and streams in turn, support a large variety and Whitefish (Coregonus spp.) are are dominated by Salmonid species of fishes with no particularly less abundant but tend to be eaten like Brown Trout (Salmo trutta), dominant species overall. There more often than expected from Rainbow Trout (Oncorhynchus is no clear relationship between their presumed abundance. Species mykiss) and by Grayling (Thymallus the most abundant fish species that are taken by Cormorants less thymallus). Brown Trout and and those most commonly eaten frequently than their abundance Grayling are often reported as being by Cormorants. The tendency would suggest are often predatory commonly taken Cormorant prey appears to be that common near- fish such as Pike (Esox lucius) and in these water systems. However, bottom freshwater species like Pikeperch (Sander lucioperca) or extensive Austrian pellet studies Roach (Rutilus rutilus, in inland larger species like Bream (Abramis have shown that Cormorants in seas and the Baltic for instance) brama). this habitat most commonly ate and Ruffe (Gymnocephalus Nase (Chondrostoma nasus), cernuus, inland seas) are eaten The Cyprinids Chub (Leuciscus Roach and Ruffe (Trauttmansdorff by Cormorants somewhat more cephalus) and Roach dominate & Wassermann 1995). Similarly, frequently than their presumed in large rivers. Experts provided extensive studies in Slovenia have abundance would indicate. The data on the most commonly eaten shown the importance of Chub, more pelagic species (that tend species by Cormorants in only Nase and Barbel (Govedic et al. to live in the water column, often ten cases. This was insufficient to 2002) in these small river habitats. farther offshore) such as the show a clear relationship with the Remarkably, these species did not Sprat (Sprattus sprattus), Smelt most abundant species. However, occur in the top ten most abundant (Osmerus eperlanus) and Herring although not drawn directly from fish species reported from this (Clupea harengus), are taken far the Water Systems Database, habitat type in the present study less commonly; the same is true for cyprinid species are often found to and were seldom reported as being most other, less abundant, species. be the most important constituent commonly eaten by Cormorants

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Figure 9.11 The distribution of fish species reported as being most abundant compared with those reported to be most commonly eaten by Cormorants presented for 6 different habitat/water system types across Europe. Open sea, inland sea and estuaries have been combined as ‘coastal areas’. For large rivers, too few data were provided on the most commonly eaten species for data to be shown.

(in a Bulgarian small river Roach respect to their abundance nor in this habitat type. Cormorants have was reported as the second most to their prevalence in Cormorant a clear preference for Cyprinids in common prey species and Chub diet. See chapter 12 for further this habitat and, to a lesser extent, was reported once each in German, discussion. for Perch. Other, less common Italian, Slovenian and Bulgarian species are reported to be eaten by small river cases). Hardly any Perch tends to dominate the fish Cormorants as might be expected information was available for the community of reservoirs, small from their presumed abundance. many endemic species of fish in the lakes and sandpits, and Roach, Balkan countries, central Romania, Bream and several other Cyprinids Fishponds in Europe are strongly and Greece, neither with are also reported as being abundant dominated by Carp (Cyprinus

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carpio). This species, together be expected from their abundance. freshwater systems and Sea Bass with the introduced Grass Carp Less commonly eaten species (Dicentrarchus labrax) in modified (Ctenopharyngodon idella), is than might be expected are again lagoon systems. eaten more commonly than might the predatory fish such as Pike in

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10 CORMORANT CONFLICTS

The rationale behind this conflicts which occur in the case parts of the Po river basin, areas in exploration of ‘Cormorant areas described in chapter 5. north east Austria, parts of upper conflicts’ is that knowledge of the Slovenia and Croatia, and rivers spatial distribution and ecology discharging into the . of Cormorants and fish is basic to 10.1 Ecological conflicts: understanding of the occurrence protected fish species and At a European scale the area of of these conflicts, and may be of Cormorants northeast Austria and the water help in mitigating possible damage systems surrounding the upper to fisheries interests caused by the Cormorants are an important avian part of the Adriatic Sea appear birds. Furthermore, this exploration predator on fish stocks. In Europe, most important with respect to the includes the most recent (i.e. up many fish species and aquatic diversity of protected freshwater fish to 2007/08) information available habitats are preserved under the species. This area probably extends to INTERCAFE participants EU-Habitat Directive, as well as further southeast into the Balkans in relation to the management by national laws. Data for a large but, due to the lack of grid-based actions taken against cormorants part of Europe (Figure 10.1) show inventory data in these countries, across Europe. Such actions being the widespread distribution of a this situation remains unclear. In taken as a result of Cormorant- number of protected fish species winter, Cormorants in Europe are fishery conflicts, some of which under the EU’s Habitat Directive, distributed rather evenly across are considered here. Generally, these data include material from the array of available inland water these management actions are Slovenia and Croatia collected habitats (see Figure 6.3). As the low- also relevant to INTERCAFE’s through recent investigations (M. altitude larger river systems attract information on Cormorant Govedicˇ). Although this picture is most Cormorants (see chapter 8), population status and distribution far from complete, especially for in a number of cases these are also (see chapter 6). Specifically, the eastern European countries, areas holding the highest numbers of information is collated on six general conclusions can be derived protected fish species. For example, different management actions from the map. First, sites of major the lower and area, carried out across Europe. This importance with respect to the the , Tagus and more recent information on presence of fish species occur in catchments share high Cormorant management actions allows most European countries. However, numbers (in regional group [A], see comparison with similar, earlier at a regional scale, some focal areas chapter 6) and a high presence of information provided by Carss are apparent, for example in areas protected fish species, whilst in the (2003: 106–108). Similarly some where seven or more protected Baltic/central European regional of the information here can be species occur at the level of five group (B), the most important fish compared to the Cormorant status or more neighbouring 50 x 50 km conservation areas are in northeast and distribution information grid cells. These areas comprise Austria and the Po river catchment. presented earlier in chapter 6. the River , and the upper The latter region is known as Rhine area in Germany, the lower an important wintering area for This chapter begins with a broad- Rhine area in The Netherlands, Cormorants. Compared to the brush approach based on conflict and some waters in Wales in the distribution maps of Cormorants (see information provided to the Water UK, major stretches along both chapter 6) there is no clear picture at Systems Database and found in the the upper and lower River Loire all that Cormorants are attracted by published literature. In chapter 11 in France, the Tagus and upper areas of high fish species diversity. we then examine site-specific local Guadiana basin in Spain, major Any overlap in the areas mentioned

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Figure 10.1 50 x 50 km grid cells showing the number of fish species listed under Annex II of the Habitat Directive. Data are from the Natura 2000 database. Note the fact that data for non-EU countries (e.g. Switzerland, Norway) are not presented and that for some countries (e.g. Czech Republic, Romania, parts of former ) data are currently unavailable. above is probably due to factors standard 50 x 50 km grid (see the distribution of conflict areas in other than the presence of diverse chapter 8). The data from the Europe, it is possible to correlate fish species. We may conclude, REDCAFE Concerted Action were the distribution of reported however, that Cormorants do show used and extended with recent conflicts with environmental and up in areas with a high number of information. Several conflicts were socio-economic factors, as well as fish species although this is probably reported to us several times and directly with Cormorant numbers. not the specific reason for their so any duplicates were omitted. appearance there. Thus the overall list of 438 cases As can be seen from Figures 10.2 (see Table 3.4) was condensed to and 10.3 (both show the same 312 cases (Table 10.1). Countries conflict data), the major conflict 10.2 Economic aspects: ranged from 57 conflicts reported in cases reported are not randomly distribution of cases Poland to 1 in Norway and analysis distributed across Europe. Fewer shows that the higher number of conflicts are reported from the Most ‘important’ conflict areas reported conflicts is associated with western part of the continent than in each country in Europe were an increasing amount of small-scale are from the east. Some countries plotted on a map, using the areas. By identifying patterns in like Spain and Portugal (occupied

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Table 10.1 Cormorant-fishery only wintering Cormorants, and to north eastern Italy and to central conflicts reported during the REDCAFE the Baltic States predominantly France. This area is most intensely and INTERCAFE projects for different have breeding Cormorants in the used by Cormorants belonging to countries. Conflict areas are unique with summer. Conflicts are thus not regional group (B) — the Baltic/ respect to geographic location. confined to a specific time of year Central European group — that (see also chapter 3 of Carss, 2003). is currently undergoing rapid Country Cases expansion. Interestingly, the area Poland 57 When compared to the distribution roughly coincides with the main Italy 32 of larger areas of surface water, watershed through Europe that Slovenia 26 no straightforward association divides those river catchments between this and the reported discharging towards the North Austria 20 conflict locations is apparent. In and Baltic Seas as well as to the Germany 20 the breeding period (Figure 10.2), on one hand and Lithuania 17 reported conflicts include areas towards the Adriatic, Mediterranean with larger areas of surface and Black Sea on the other. Spain 14 water like for instance in Poland Romania 13 (Mazurian Lakes), the Baltic States When reported conflicts are France 13 (coasts) and The Netherlands compared to the distribution of

Bulgaria 12 (Lake IJsselmeer). However, main winter roosts, again no clear on the European scale, most pattern is obvious. The majority of Portugal 11 Cormorant-fisheries conflicts are Cormorants winter in areas where UK 9 being reported in an area ranging relatively few conflicts are reported. Finland 9 roughly from the north east Baltic More specifically, conflicts tend via Poland, the Czech Republic, to be reported most at the edges Sweden 9 Austria, and south east Germany of the geographical distribution of Denmark 9  Latvia 8

Greece 6

Czech Republic 5

Georgia 5

Belgium 4

Estonia 3

Israel 3

Netherlands 3

Serbia 3

Norway 1

by wintering sinensis Cormorants), but also Norway (occupied year- round by carbo birds) have few reported conflict cases, whereas  other countries (e.g. Italy, Austria, Figure 10.2 European Cormorant-fisheries conflicts (green dots) reported during the Slovenia, Baltic States) have a REDCAFE Concerted Action and through the INTERCAFE network project, in relation longer list of records. For the latter to the distribution of Cormorants during summer (grid cells 50*50km). Most of the countries, Italy has both breeding conflict cases reported do not coincide with the core breeding areas (as indicated by and wintering Cormorants, Austria red/purple grid cells).

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 finding is probably related to the fact that the highest density classes of Cormorants occur in lowland areas where fisheries’ interests (and hence conflicts) are less prominent.

Many Cormorant-fishery conflicts are reported from the relatively small pre-Alpine region (see Figure 10.5). This is clearly an important area for further investigation. Here, a lot of different water body types are present within a short distance as fast running waters and small lakes at high altitudes merge into larger rivers and lakes. Cormorants migrate through this area to and from the   Mediterranean and as well as there Figure 10.3 European Cormorant-fisheries conflicts (green dots) reported during the being wintering bird concentrations REDCAFE Concerted Action and through the INTERCAFE network project, in relation to there mainly on the larger lakes the distribution of Cormorants during winter (grid cells 50*50 km). Most of the conflict and river systems. During periods cases reported do not coincide with the core wintering areas (as indicated by red/ of severe frost, the birds move purple grid cells). out of such areas or use the more upstream parts of the small river Cormorants. This may be either (i) conflicts are either for the lowest sections. These tend to freeze a seasonal effect, as for instance Cormorant densities or for the later or not at all during frosty when Cormorants migrate from highest density classes. The latter weather. It is this specific habit one area to another, passing across areas where they (at most times) do  not concentrate or (ii) a temporal effect in terms of areas that have become established by Cormorants only recently due to the species’ continued range expansion.

Overall, using data from the area presented in Figure 10.3, reported cases of conflicts with Cormorants were not restricted to areas where winter densities of the birds were highest (Figure 10.4). Indeed, most conflict cases were reported in areas of intermediate densities of Cormorants in winter. At increasing Cormorant density (winter roost  counts), the number of reported conflicts increases. However the Figure 10.4 Map of the southern part of the UK showing sites in England where lower proportions of reported Cormorants were shot under licence, in order to mitigate a specific local problem.

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 East Anglia is remarkable, given the proximity to the continent and the known influx of wintering birds from continental areas, possibly related to the fact that this is a relatively rural area. A similar situation occurs in a country like France; here, many local conflicts have resulted in the acceptance of shooting for which licences are issued and over 30,000 birds are shot each winter (e.g. 31,000 in 2001/08 and up to 33,000 in   2009/10 from a permitted ‘quota’ of  41,800 birds). Licences for killing Figure 10.5 Detail of map showing the distribution of reported conflict cases (green Cormorants are issued according dots) for the area centring on the greater Alpine and sub-Alpine region in Europe. The 50*50 km grid squares depict Cormorant density in winter. to nationally agreed procedures, most often by specialist wildlife biologists, to ensure as consistent that causes most concern, as these reported at regional or local scales. an approach as possible. are the waters holding the most At a finer geographical scale, that vulnerable Salmonid and Grayling of a single country or state, many populations. As can be seen in small conflicts may occur. As 10.3 Management actions Figure 10.5, the concentration an example, Figure 10.4 shows taken against cormorants at of reported conflicts in the pre- the number of licenses issued the ‘European’ scale Alpine region is not correlated recently to kill Cormorants under to the presence of Cormorant derogation in part of the UK. The Earlier work by REDCAFE roosts in winter. There was also map gives an update showing participants (Carss 2003: 103– no correlation with the presence the locations where licences to 130) provided information on of breeding colonies. Also, if shoot Cormorants were issued in management actions taken against compared to the distribution of England over the most recently Cormorants during 2001/02. This protected fish species, the areas available licensing period (winter information was available for only partially overlap. For example, 2010–11). This indicates a pretty 25 countries: Austria, Belgium, most reported cases of Cormorant broad, countrywide distribution of Bulgaria, Czech Republic, damage to fisheries in Slovenia ‘conflicts’, with concentrations in Denmark, Estonia, Finland, France, originate in areas other than those the south and the Midlands, and Germany, Greece, Hungary, with the highest diversity of relatively few licences issued in Ireland, Israel, Italy, Latvia, protected fish species. In the next the far southwest and East Anglia. Lithuania, Netherlands, Norway, chapter the cases of Slovenian Again, this distribution only partly Poland, Portugal, Romania, and Austrian pre-Alpine rivers are reflects Cormorant distribution Slovenia, Spain, Sweden and further explored (see 11.5 and 11.6 in winter, but will merely be the United Kingdom. During the respectively). influenced by the location and work of the INTERCAFE COST management of fishery sites. Most Action it was possible to update Conflicts differ with respect to licences are issued on still waters this information for 2006/07 and their extent. The conflicts listed (the majority being managed also to incorporate information above comprise the major cases recreational fisheries, often with from an additional three countries: that have been mentioned and elevated fish stock densities) and Croatia, Serbia and . reported on a European scale. these are often sited near centres of Wherever possible, information for However, the effects of Cormorant human population. The relatively these countries was also provided predation are also invariably low number of licences issued for retrospectively for the period up

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to 2002 and so, for all countries, pricking of eggs to kill the embryos Information on these four areas is the two time periods (up to 2002, and prevent them hatching), (3) presented in Table 10.2. 2006/07) were broadly comparable. the killing of nestlings, (4) of non- breeding birds (adults and immatures) Specific management actions Information is presented below, and (5) of adult breeding birds, and This section is an exploration of on a country-by-country basis, for (6) the destruction and/or disturbance some of the figures presented in all those countries participating in of night roosts. This information is Table 10.2, and the information REDCAFE and/or INTERCAFE presented for each of the 29 countries discussed from ‘earlier years’ named on previous page. However, participating in INTERCAFE (Table (specifically 1990-2002) was mindful of earlier comments 10.1 parts I-III). originally collated during the (section 6.2) that, when considering EU-funded REDCAFE Concerted Cormorant status and distribution it This information can be further Action and was originally presented is vital to carefully define the specific collated and summarised in relation in Carss (2003: 106–108). area under consideration, information to two ‘politically-relevant’ areas is also presented and discussed here and two ‘biologically-relevant’ The information collated here was on the basis of four geographically ones. The ‘politically-relevant’ derived both from published sources derived datasets. These relate to two areas are (a) all 29 countries and from the informed estimates ‘politically-relevant’ geographic participating in REDCAFE/ of the various experts involved areas and two ‘biologically-relevant’ INTERCAFE and (b) EU-27 in the INTERCAFE Action. As ones (see below). countries (all except , such, these estimates should not be Hungary, , Malta) regarded as an authoritative, official, The basic ‘management actions’ whilst the two ‘biologially-relevant’ nor even a necessarily completely dataset(s) areas are (c) countries in Region A accurate estimate. Nevertheless, Specific information was collated on (see Figure 6.1 but here excluding they provide the most thorough six different Cormorant management Iceland, Luxembourg, Morocco, information available (in both actions carried out across Europe. Algeria, ) and (d) countries specific detail and geographical These are (1) the destruction and/or in Region B (see Figure 6.1 but spread). Thus INTERCAFE’s disturbance of breeding colonies, (2) here excluding Kaliningrad, most recent data (mainly relating to the destruction of nests and/or their Hungary, , Macedonia, information for the year 2006 or the contents (often through the oiling or Bosnia & Herzegovina). winter 2006/07) is thought to provide a reasonable basis for comparison with the REDCAFE data (compiled in a similar way, mostly for 2001/02) and a means for indicating possible trends. Where possible the information on the effects of management actions is compared with that of cormorant status and distribution given earlier in chapter 6.

(i) Breeding colonies destroyed or disturbed In earlier years (1990–2002), 50 Cormorant breeding colonies were reported to have been destroyed or disturbed each year in the 28 countries reviewed here. More The spraying of Cormorant eggs in ground-breeding colonies in Denmark is a recent data suggest such actions management tool to reduce the number of offspring produced. have increased somewhat in the Photo courtesy of Florian Möllers. countries surveyed, with a current

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Table 10.1 Information on the management actions taken against Cormorants in each of the 28 countries participating in INTERCAFE. Countries are grouped according to whether they either fall into the ‘biologically-relevant’ geographic regions A or B (parts I and II of Table, respectively) as described in section 6.1 or whether they occur in the Middle East (i.e Israel, part III of Table).

(I) Region Time No. of No. of nests No. of No. of birds No. of No. of period breeding destroyed nestlings (adults & breeding night roosts A countries colonies killed immatures) adults destroyed destroyed killed in killed or disturbed or the non- disturbed breeding season

1. Belgium 2001/02 0 0 0 0 0 2–3 2006/07 0 0 0 ca. 100 0 Yes

2. Denmark 1994–2002 10 3,000 0 2,700 400 1 2006 23 6,6001 0 3,7002 0 1

3. France 2001/02 2 0 0 20,000 0 200 2006/07 1 0 0 30,861 The majority

4. Ireland 2001/02 0 0 0 <20 <20 0 2006/07 0 0 0 <20 <20 0

5. Netherlands 2001/02 0 0 0 0 0 0 2006/07 0 0 0 0 0 0

6. Norway3 2001/02 0 0 0 10,000 0 0 2006/07 0 0 0 10,000 0 0

7. Portugal 2001/02 0 0 0 0 0 0 2006/07 n/a n/a n/a 0 n/a 0

8. Spain 2001/02 0 0 0 0 0 0 2006/07 0 0 0 >1,000 0 0

9. Switzerland 2001/02 0 0 0 1,300 0 Yes 2006/07 0 0 0 1,000 0 0

10a. UK — 2001/02 0 0 0 200–250 0 <20 England & Wales 2005/06 0 0 0 1,388 0 0

10b. UK — Scotland 1995–2002 0 0 0 300 0 0 2006/07 0 0 0 90 0 0

(2006/07) estimate of at least 63 to have been destroyed annually Nest destruction activities are thus colonies affected. Most of these across the 28 countries, including concentrated in particular countries, colonies were in Sweden (a few nests where eggs were oiled. This and so, overall, this management tens) and Denmark (23). Smaller increased to between 9,845 and action affects relatively low propor- numbers of colonies were destroyed 10,845 nests in the most recent tions of active nests across ‘Europe’. or disturbed in Austria (1), Estonia (2006/07) estimates, mainly as a (5), Finland (3), France (1), consequence of egg oiling. Such In terms of the EU-27 political Germany (6), and Lithuania (4). actions mainly occured in Denmark area, data are available for 23 of (6,600 nests) and Sweden (2,000 to these countries and they can be (ii) Nests destroyed 3,000 nests), with smaller numbers compared with the Cormorant In 2001/02 some 7,094–8,094 in Estonia (650), Finland (403) and breeding population figures given Cormorant nests were reported Germany (192). in section 6.2 which refer to the

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Table 10.1 Continued.

(II) Time period No. of No. of No. of No. of birds No. of No. of breeding nests de- nestlings (adults & breeding night roosts Region B colonies stroyed killed immatures) adults destroyed countries destroyed killed in the killed or disturbed or non-breeding disturbed season

11. Austria 1995–2002 0 0 0 >450 0 >4 2000–2006/07 14 04 04 400–450 0 >6

12. Bulgaria 1998–2002 2 81 0 >1,000 Yes 5 2006/07 0 0 0 <1,000 <100 2–3

13. Croatia5 2001/02 6 n/a n/a n/a n/a n/a 2006/07 0 0 0 >1,000 0 n/a

14. Czech 1990–2002 2 0 0 1,600–2,800 0 Yes Republic 2004–2006 0 0 0 2,100–3,100 Few Yes

15. Estonia 1997–2001 7 1,800 50–100 102 0 0 2006 5 650 0 290 0 0

16. Finland 2001/02 0 0 0 0 0 0 2007 3 403 0 0 0 0

17. Germany 1995–2002 9 113 500 7,131 78 Yes 2006/07 6 192 0 ca. 15,105 0 Yes

18. Greece 2001/02 1 0 >50 250–350 0 1 2007/086 0 0 0 5,000–6,000 0 n/a

19. Italy 2001/02 5 <100 0 2,000–2,500 <100 12 2004/05 0 0 0 4,500–5,000 <550 n/a

20. Latvia 1995–2002 0 0 0 >200 0 0 2006/07 0 0 0 137 0 0

21. Lithuania 2001/02 1 0 0 1,000 0 0 2005–20087 4 0 0 1,009 0 0

22. Poland 2001/02 0 0 0 2,100–2,300 0 0 2006/07 0 0 0 2,000–2,600 0 0

23. Romania8 2001/02 0 0 0 >200 0 0 2006/07 n/a n/a n/a n/a n/a n/a

24. Serbia 2001/02 n/a n/a n/a n/a n/a n/a 2006/07 0 0 0 20–30 5-10 0

25. Slovakia 2001/02 n/a n/a n/a n/a n/a n/a 2006/07 0 0 0 >100 0 0

26. Slovenia 2001/02 0 0 0 >200 0 0 2006/07 0 0 0 2009 0 0

27. Sweden 2000 ca. 510 ? ? 1,000 3,000 No 2006/07 2011 <2,000– 0 <3,500 <3,500 No 3,00012

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Table 10.1 Continued.

(III) Middle Time No. of No. of nests No. of No. of birds No. of No. of period breeding destroyed nestlings (adults & breeding night roosts East colonies killed immatures) adults destroyed destroyed killed in killed or disturbed or the non- disturbed breeding season

28. Israel 2001/02 0 0 0 200 0 2 2006/07 0 0 0 2,000 0 2

1. Mostly oiling of eggs (this is the case for 89% of the nests destroyed). 2. Figure refers to numbers of birds killed in 2005 non-breeding season. 3. P.c.carbo birds only in Norway. 4. There were two breeding colonies in Austria in 2007: partial tree-cuting in one colony to reduce nest numbers and breeding pairs. 5. Colonies on five fishponds (Donji Miholjac, Jelas, Nasice, Grudnjak, Koncanica) were completely destroyed in the 1980’s. Breeeding adults and nestlings in the nest were killed at the Kopacki rit colony in 1989 and there was a 50% reduction in breeding pairs in the following year. There is no procedure for reporting bird numbers killed at fishponds. 6. Numbers are estimated form information provided by fishermen and biologists. All cormorants are illegally shot. 7. Numbers given are the average for the period 2005–2007. 8. Numbers for 2001/02 refer to the Danube Delta area only. 9. The official figure is 23: the number given is a best estimate 10. In total, 63 colonies are known to have been disturbed in the twelve years between 1985–2000 — giving an annual figure of just over 5 colonies. Disturbed colonies ranged in size from very small to quite large and only in a few cases of distrubance was complete breeding failure reported. 11. The number given is a best estimate, the true figure is unknown. Illegal disturbance takes place in a number of colonies every year but it is probable that this only occasionally results in abandonment or complete breeding failure. 12. In 2007 for the whole of Sweden, egg-pricking was undertaken on 10–15,000 eggs, whilst it is impossible to state exactly how many nests were affected, it probably corresponds to the figure given of 2–3,000 nests. Large egg-pricking campaigns have taken place for many years along the coast of Småland and, in recent years, also in the Stockholm archipelago. The practice also takes place along the coast in the province of Östergötland. Up to around 10,000 eggs were pricked in Småland in one season but the figure in 2007 was only 960 eggs. Egg-pricking was intense in the Stockholm archipelago in 2007 (about 8,000 eggs) but was almost zero the following year (for some reason people did not apply to do it in 2008).

EU-27 region plus Norway and Similar comparisons for biologically and 54,003 adult Cormorants Switzerland. Apparently no nest relevant regions A and B in 2006 (including immature birds in destruction took place in either (see Table 6.1) suggest that about their first winter and older ones) of these countries and so, for 5% and 2–3% of active nests were were reportedly shot annually this ‘EU-27 plus’ area, the best destroyed annually in each region, as control measures. This figure estimate is of some 9,845–10,845 respectively. included 10,000 birds of the nests destroyed in 2006/07. This ‘Atlantic’ race (Phalacrocorax compares to an estimated breeding (iii) Nestlings killed carbo carbo) hunted legally in total, for the same area in 2006, About 600 to 700 Cormorant Norway. The remaining 41,953 to of approximately 284,500 pairs of nestlings were reported to have been 44,003 Cormorants thus mostly Cormorants. Assuming each pair killed annually up to 2002, mainly comprised the ‘Continental’ race of birds is associated with a single in Germany (500). No killing of (P. c. sinensis). In the more recent nest, implies that this geographic nestling Cormorants in Europe estimates (2006/07), these numbers area contained around 142,250 was reported to INTERCAFE increased to 86,520–89,680 birds, nests. Current information for (2006/07), and the shooting of again including about 10,000 management actions, suggesting nestlings in Germany has ceased. ‘carbo’ birds hunted legally in about 10,845 nests destroyed here Norway. As in the earlier period, in 2006/07, represented perhaps (iv) Adult and immature birds most Cormorants were shot in 7.6% of active nests overall in ‘EU- killed in the non-breeding season France (30,861 in 2006/07). Other 27 plus’. Up to 2002, between 51,953 countries where relatively large

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Table 10.2 Summary information on the management actions taken against Cormorants in the 29 countries participating in INTERCAFE, summarised for four geographic areas (a-d). Note that these geographic areas are not necessarily mutually exclusive (for full details see text).

* The figures in these three columns are considered to be best estimates, ** The figures in these three columns are considered to be under-estimates 1. Includes 2005/06 information for UK - England & Wales, which also applies to rows (a) and (b). 2. Includes 2000/07 information for Austria, 2004–2006 for the Czech Republic, 2006 for Estonia, 2007 for Finland, 2007/08 for Greece, 2004/05 for Italy, and 2005/08 for Lithuania, which also applies to rows (a) and (b). Totals Time No. of No. of nests No. of No. of birds No. of No. of period breeding destroyed nestlings (adults & breeding night for 4 colonies killed immatures) adults killed roosts different destroyed killed in the destroyed or non-breeding or areas of disturbed* season disturbed Europe (a) All 28 Up to 2002 50 7,094–8,094 600–700 51,953–54,003 3,598 247–248 INTERCAFE countries 2006/07 63 9,845–10,845 0 86,520–89,680 4,175–4,180 509–510

(b) EU-27 Up to 2002 44 7,094–8,094 600–700 40,453–42,503 3,598 245–246

2006/07 63 9,845–10,845 0 72,490–75,650 4,165–4,175 507–508

(c) Region A Up to 2002 12 3,000 0 34,520–34,570 420 223–224 6,600 2006/071 24 0 48,159 20 501

(d) Region B Up to 2002 38 4,094–5,094 600–700 17,233–19,233 3,178 22

2006/072 39 3,245–4,245 0 36,361–39,521 4,155–4,160 8–9

numbers of ‘adult’ Cormorants (the first — and to date — only with the winter count of 2003 have been shot in recent years coordinated count at the (probably a less valid comparison (mainly data for 2006/07) are: continental scale, see Table 6.2), because wintering numbers may Bulgaria (<1,000), Croatia the most valid comparison (given well have increased between (>1,000), Czech Republic (2,100– the different time periods for which 2003 and 2006/07) for regions 3,100), Denmark (3,700), Germany data are available) is, perhaps, with A and B gives proportions of the (15,105), Greece (5,000–6,000), the numbers of Cormorants killed winter population killed under Israel (2,000), Italy (4,500–5,000), outside the breeding season up management actions of 14% and Lithuania (1,009), Poland (2,000– to 2002. During this time period 17–18%, respectively. 2,600), Spain (>1,000), Sweden the available information suggest (>3,500), Switzerland (1,000), and that killed birds represented about (v) Breeding adults killed UK–England & Wales (1,400). 10% of the numbers of Cormorants More than 3,598 adult Cormorants estimated for region A in the were reported to have been killed Killing birds (adults, first-winter winter of 2003 — very similar to annually during the breeding and older immatures) during the the corresponding proportion for season (April to September) for non-breeding season is thus a fairly region B which was 8–9% of the years up to 2002. For the more widespread management action estimated number of wintering recent estimate, this figure has across Europe. Cormorants. increased to at least 4,175–4,180 birds, with most again being killed For the biologically relevant Comparing the estimated numbers in Sweden (<3,500) and Italy regions A and B in January 2003 of Cormorants killed in 2006/07 (<550).

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(vi) Night roosts destroyed or disturbed annually has increased Whilst not directly comparable, disturbed from >248 for the countries section 6.3 mentions the 2,500 Although Cormorants are known covered by REDCAFE to more roosts which formed part of to be disturbed and shot at night than 500 in the present study. As the winter 2003 pan-European roosts in several countries, no before, such actions are believed to Cormorant count. Acknowledging reliable numbers have been take place mostly in France where that this number is almost available for either the REDCAFE a large proportion of the known certainly an underestimate, the COST Action or the more recent 869 roosts in the country are available figure of at least 500 INTERCAFE investigation. believed to be affected. Estimates roosts experiencing destruction or Nevertheless, the reported numbers for other countries were relatively disturbance represents nevertheless of night roosts destroyed or small. 20% of this figure.

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11 CASE STUDIES OF CONFLICTS: ECOLOGICAL ASPECTS AT A LOCAL LEVEL

The ecological background of systems type and by level of habitat 11.1 Gulf of Finland several ‘local’ Cormorant-fisheries scale: Gulf of Finland (coastal (category: open sea) conflicts was explored during some seas), Lake IJsselmeer and Vistula INTERCAFE meetings. Intensive Lagoon (inland seas), Po Delta Cormorants are strongly increasing contacts with local stakeholders (estuaries), Austrian and Slovenian (numerically) and spreading here allowed the situation and rivers (small rivers), Saxony, South (geographically) in this part of environment of the conflicts to be Bohemia and Hula & Bet Shean Europe, mainly during the spring put into some sort of ecological Valleys (complex small scale water and summer months. The area context. Given the time available bodies with fish pond areas). is not typical wintering habitat for this (maximum three days in Case Study meetings), the results Cormorant colony on one of the many islets in the eastern Baltic, Finland. were useful so as to describe Photo courtesy of Stef van Rijn. the major patterns. As a result, explorations tended to focus on a specific important ecological aspect related to each case but from which insight could be applied to other water systems throughout Europe. Needless to say, according to the different settings and attendance by local stakeholders at such meetings, the ecological elements explored varied according to the input. As such, the information presented here is very much input-oriented (i.e ‘bottom-up’) and is therefore considered a reflection of the regional or local situation. We have tried to highlight the specific issues that were derived from the field by local experts. By putting the conflict into the context of the regional ecological situation and possible shifts therein, this was supposed to help to untangle the problem. This section discusses the outcome of these explorations at a regional or local level, again arranged by water

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as many shallow parts of the Although extended research is understanding of such changes Baltic Sea freeze over and fish needed to cover a greater time span is clearly necessary to put the retreat toward deeper water as and to indicate seasonal patterns Cormorant issue into ecological temperatures fall. The concurrent over a larger geographical area, context. The next two cases share negative trend in catches of the picture is that the majority of some similarities with the Gulf commercial fish species is regarded fish taken are bottom-dwelling of Finland situation, exploring as a direct consequence of the Eelpout (Zoarces viviparus), in more detail the effects of increasing Cormorant population Butterfish (Pholis gunnellus), nutrient enrichment and intensive and, locally, measures are taken to Gobies (Cottus spp.) and Sculpins commercial fisheries on fish reduce the population (Timo Asanti (Myoxocephalus spp.), augmented community structure in large pers. comm.). with Sprat (Sprattus sprattus), shallow waters. Herring (Clupea harengus) The role that Cormorants play and, locally, Roach (Rutilus as a fish predator in this region rutilus). It is hypothesised that 11.2 Lake IJsselmeer and does not point to it being a major the Cormorant has reacted to a Markermeer, The Netherlands threat to the fish populations here, major environmental shift in the (category: inland sea) at least not according to recent Baltic, which was first induced investigations (Lehikoinen 2006, by environmental changes (less Cormorants are considered van Eerden et al. 2007). Food saline water entering from the a strong competitor of the items recorded in three colonies west), reinforced by human action commercial fisheries in the Lake in Estonia and three in Finland in through the over-fishing of stocks IJsselmeer area by the local 2007 comprised predominantly of large predatory fish, as well fishermen. There are indications non-commercial prey species. as a concurrent increase in the of potential competition for Perch nutrient load. All three factors have (Perca fluviatilis) but, given a positive effect on the abundance the heavy fishery pressure and (and availability) of the small correspondingly low stocks, this is sedentary brackish and freshwater much less likely for Eel (Anguilla fish species, which in turn provide anguilla) and Pikeperch (Sander ideal foraging conditions for lucioperca). However, the stock Cormorants. assessments show large numbers of young predatory fish which do This wider, longer-term ecological not seem to enter the population. perspective shows the Cormorant- Most of the ‘evidence’ for losses fisheries conflict in a different of commercially important fish light to that of simply Cormorants stocks due to Cormorant predation having direct impact on fisheries. in these large systems is still This complex situation urgently based on indirect observations requires validation by extended and calculations. In a recent study, research. Nevertheless, the extrapolated data from other, conclusion is unavoidable — that smaller-scaled water bodies were the Cormorant prey choice merely used to demonstrate the effect of reflects the fish availability in these Cormorant predation on the yield waters, rather than being the result of Pikeperch (Witteveen & Bos of selective hunting and foraging 2008). These authors hypothesise by the birds themselves. Thus in a severe predation pressure by the Gulf of Finland, Cormorants Cormorants on young Pikeperch as can be considered to be responding they concentrate in deeper waters to drastic environmental changes, in autumn and winter. Selective some at a very large-scale and hunting would exterminate the occurring over a long time. An shoals and aggregations of young

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fish. Current research on the food of the Cormorant outside the breeding period in the IJsselmeer area itself is now underway to elucidate the situation. Another possibility for this loss is the management of discharge water from the lake to the Waddenzee. It has been shown that in a nine month period over 1,000 tonnes of freshwater fish end up in the Waddenzee due to this massive discharge event at low tides. This corresponds to 50% of the estimated gross production of 0+ fish (i.e. young-of-the-year), being roughly 10 kg/ha (Witteveen & Bos Social fishing by Cormorants: an adaptation for foraging in turbid waters 2009). The fish that have no cue (Lake IJsselmeer). Photo courtesy of Mervyn Roos. as to what direction they are taken by the current are washed out and cannot return to the lake. Except the abundance and community season, Cormorants mainly feed in for Smelt, most other species structure of fish species (and also Lake IJsselmeer and only forage die because of salt stress. Again, their length-frequency distribution) in Lake Markermeer on days with Cormorants, but also mergansers, in the lakes are largely reflected little wind and, consequently, less gulls and terns exploit this food in the birds’ diet in similar turbid water. During periods of source which is mainly the result proportions. strong winds, the birds invariably of the lack of a salinity gradient choose to forage in sheltered (less towards the open sea. Ecologically, the influence of turbid) waters of IJsselmeer. turbid water is also important with The key ecological perspective respect to the observed levels of The annual consumption of fish by here is that, on the other hand, Cormorant predation. Cormorants Cormorants in the IJsselmeer area over-fishing in these lakes is always prefer to forage in waters has been estimated at about 10 kg/ plausibly the cause of a relatively with an intermediate underwater ha/year (Van Rijn & Van Eerden large proportion of small fish clarity of 0.4–0.8 m Secchi 2002). This was considered the there. These are mainly Ruffe depth and turbidity is therefore maximum possible exploitation (Gymnocephalus cernuus), a considered important with respect for the current situation on this non-commercial species that to the predation levels that the lake under ‘natural’ conditions (of now constitutes up to 70% of birds can achieve. Lake IJsselmeer current fish biomass and water Cormorant diet (in terms of has a clear water phase in April turbidity). There may be a possible biomass). The conclusion of a and May, caused by effect of Cormorant predation on long-term study into the issue grazing on green algae. Before and commercially harvestable fish is that over-fishing has in fact after this period, turbidity is mainly stocks of Perch but this is unlikely altered fish community structure to caused by algae (diatoms and blue for Eel, Pikeperch and Smelt. favour both these abundant small greens, respectively). This is in The natural mortality of fish has fishes and, consequently, provide strong contrast with the situation not been measured under natural increased foraging opportunities in Lake Markermeer (separated by conditions and so the estimated for Cormorants (van Rijn & van a dike from the northern part since consumption of fish by Cormorants Eerden 2002). It was concluded 1975) that is turbid throughout cannot simply be related to the yield that Cormorants were not selective the year because of erosion of its taken by fishermen in later years. in the prey they took and that muddy clay bottom. In the breeding Assumptions about natural fish

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mortality, in relation to the effect peculiar position that Cormorants the birds can reduce yields of that Cormorants may have, play a have in these modified waters. valuable commercial fish species. central role in the outcome of the Cormorants typically adapt to the However, some local fishermen models applied to this complex man-induced changes and easily use have indicated that over-fishing biological system (van Dam et obstructions such as sluices, dams, is actually the main cause of al. 1995). As long as the question and locks which hamper the passage the reduced sustainability of the of additive versus compensatory and movement of fish. The altered fishery. Thus, this conflict between mortality levels in fish is fish-species composition caused by fishermen and Cormorants has unresolved, this remains the key the heavy fishing of commercial again to be considered within missing element for demonstrating fisheries is reflected in a shift in the a wider socio-economic and whether there is a significant diet of Cormorants. This ecological ecological context. Nevertheless, Cormorant predation effect or not. perspective also bears parallels to the key ecological perspective Essentially this question is: does that explored in the Vistula Lagoon, here is not that Cormorants are predation by Cormorants increase Poland. driving the fisheries system and overall fish mortality (i.e. ‘additive’ are responsible for its changed mortality) or would the individuals status but the reverse — that the eaten by Cormorants merely have 11.3 The Vistula Lagoon, birds are responding to wide-scale died from other causes had they not Poland (category: inland sea) ecological changes, in this case been predated (i.e. ‘compensatory’ overfishing — which has lead to a mortality), thus improving the Local fishermen generally consider super abundance of small fishes in conditions for those uneaten fish by Cormorants to be the main the Lagoon. Cormorants here are providing less competition for food, cause of reduced fish landings also accused of killing the trees in space and other resources. in the Lagoon, believing that which they breed through

Consumption of large amounts of Ruffe by Cormorants may even have a positive effect on the food situation for Eel. Recent over-fishing of large Bream (Abramis brama) in the system has caused further advantages (feeding opportunities) for Ruffe because both species feed on midge (Chironomidae) larvae on the lake bottom. Over-fishing has at least an effect on fish size, shifting it towards a length frequency with much smaller fishes present than would be the case under natural conditions. This too has a positive effect on the exploitation possibilities of Cormorants. High numbers of Cormorants can thus be explained from an ecological perspective by the highly eutrophicated status of the system, combined with the situation of over- fishing by commercial fishermen. For water and fisheries’ managers this example demonstrates the Measuring Cormorant eggs at the Ka¸ty Rybackie colony, Poland, one of the complexity of the situation and the largest colonies in Europe. Photo courtesy of Paolo Volponi.

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deposition and by the removal of large, predatory fish. small branches for nest building. While the local comorant colony expands and moves year after year, 11.4 Po Delta (category: the actual area of destroyed forest complex estuary and lagoon in the Ka˛ty Rybackie Reserve increases annually. system) The Po Delta is a major area It is estimated that a total of for Cormorants in Italy as well 2,200–3,100 tonnes of small fish as for commercial fisheries are removed each year from the and ‘vallicoltura’, a traditional Lagoon, commercial landings and form of low-tech aquaculture Cormorant predation accounting consisting of specific lagoon for about 1,484–2,267 tonnes management and extensive fish and 712–816 tonnes, respectively production (Ardizzone et al. 1988). (Stempniewicz et al. 2003a). Commercial fishing is carried out Commercial fish catches have on a seasonal basis using fyke declined considerably in the last nets and gill nets in open bays and 30 years, except for those of river estuaries, whilst about 30 Herring. However, Cormorants different wetlands (valli) ranging generally select smaller fish between 250–6,500 hectares are than those caught by fishermen. managed for vallicoltura. Both in Indeed, due both to their small open bays and valli, fish catches size and species composition, the show wide annual and site-to-site fish species taken by Cormorants fluctuations, ranging between have been found to be of little 70–112 and 11–84 kg/ha/year, economic value. Cormorants are respectively (Volponi 1997). believed to have a positive effect Cormorant predation here has been on the Lagoon’s fish community by estimated at between 5–10 kg/ha/ reducing dominant species, such as year (Volponi & Rossi 1995). Ruffe, while the negative impact is largely considered to be related Cormorants forage opportunistically to predation on Eel and young in all available habitats but feed Pikeperch, Atlantic Salmon (Salmo more regularly and intensively in salar) and Sea Trout (S. trutta, the fishing-valli in late autumn Martyniak et al. 1997, 2003). and winter in particular — this also being the main fishing and In summary, for these large water fish-stocking period (Boldreghini systems the prognosis for the et al. 1997) and fish availability future very much depends on the and predictability is higher here implementation of measures to than in adjacent river and open reduce over-fishing by commercial coastal waters. This is perhaps the fisheries. Considerable reduction key ecological perspective in this in overall human fishing pressure situation — that birds visit the would probably reduce the fishingvalli seasonally during the Cormorant population because the migration and wintering periods, number of small fish (both species coincidentally the time when the and size-range) would decline in fish there are most vulnerable. Coastal lagoon in the Po Delta, Italy. relation to an increased stock of Further important ecological issues Photo courtesy of Paolo Volponi.

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The Cormorant conflict is thus one factor in a complex system of multiple uses for aquatic resources, fishing being only one of many objectives.

11.5 Slovenia (category: small rivers and pre-Alpine streams) Cormorants exploit small running streams and rivers in Slovenia, mainly on migration and in winter during freezing conditions. As the lowland rivers and lakes become frozen over, the remaining Cormorants tend to concentrate on the faster-running streams where they forage in waters home to a variety of Salmonid species. Here, this region shares some key ecological perspectives (i.e. seasonal Cormorant predation coinciding with the main prey vulnerability period) to other places such as the Po Delta.

Although ‘pristine’ at first sight, the Slovenian environment has undergone some major changes (e.g. damaged/altered river Sub-Alpine rivers are of particular interest for their Salmonid fish populations: courses by human activities, the the Soca River, Slovenia. Photo courtesy of Stef van Rijn. construction of dams). These changes have had a negative effect on the occurrence of the typical relate to the presence of large uses of the Po Delta wetland system anadromous fish species (i.e. numbers of other waterfowl here make the management of the those that spawn in freshwater and to the general complexity of Cormorant conflict a complex task. but migrate to sea for most of this wetland system. Other than fishing and fish farming, their adult lives). However, from wildfowl hunting may represent a biodiversity perspective, many Different management an ecologically and economically threatened or endangered fish programmes for the Cormorant- important resource for most fishing species still occur in this region vallicoltura conflict are carried valli, providing large incomes often (e.g. Atlantic Salmon, Marbled out by landowners in the two higher than those from aquaculture. Trout S. marmoratus, Grayling administrative regions of the Delta. Nature tourism is based on Thymallus thymallus, Nase This involves the use of non- the great diversity of habitat Chondrostoma nasus), sometimes lethal techniques, shooting, and and waterbirds in the area and actively managed by stocking partial financial reimbursement for represents a fast-growing economic programmes. These fish species and damage. However the conflict is far resource, especially valuable their populations deserve at least as from being solved and the multiple outside the summer holiday season. much protection as do fish-eating

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birds and many have been protected (commonly available) Cyprinid predation pressure is key to under the EC-Habitat Directive. prey (Govedicˇ 2001). As such, the explaining Cormorant conflicts situation described indicates the in regions like Slovenia (see Most Slovenian case studies do not sensitivity of the system, at least previously) and also in other demonstrate categorically a negative as seen by the managers. Although regions such as Austria where effect of Cormorant predation on most Cormorants prey on larger- angling for migratory Salmonids either fish stocks or angling catches. scale water bodies (this is also and Grayling is a highly valued However, Cormorants (first reported where the main roosts occur at sport. Cormorants visit smaller arriving in the winter of 1997/98) times of migration), smaller parts streams in the upper catchments are claimed to affect angling of the migrating population cause of pre-Alpine rivers mainly in catches of Grayling in the Socˇa interference to fisheries interests winter, mostly from roosts in trees River as demonstrated by fishing in the high altitude streams. along rivers further downstream. statistics of Fishing Club Tolmin. Although predation levels are The ecological principle of saving This observation could be alarming difficult to quantify scientifically energy by minimising travelling for two reasons. First, Grayling in here, examples from similar river distances to the following the Socˇa belongs to a genetically systems in Austria allow a more hypothesis: that Cormorants will unique Adriatic line (Susnik et al. in-depth exploration of Cormorant forage more intensely close to the 2001) and thus deserves particular impact in such systems. roost than in more distant areas attention. Second, it has been and thus predation pressure will estimated that angling tourism decrease as a function of distance contributes 2.3 million to 11.6 Austria (category: small from the roost. the local economy (Post et al. rivers) 2002). Likewise FC Novo Mesto In order to examine this has presented evidence of how Considering the interaction hypothesis, three Cormorant roosts Cormorants would affect angling between Cormorants and fishes in Austria were identified for catches even for a species like Nase, in small streams it is important further analysis according to their which is locally very abundant. to consider how possible impact location and the local abundance might be measured. This potential of fishes. Radial distances of 10, Twenty-two Cormorant conflicts cases were reported from Slovenia, on 19 rivers/sections of rivers and on three lakes. No conflicts were reported from the Fisheries Society covering the River Gradašcˇica. Most conflicts were reported from the middle reaches of rivers, at widths of 10–50 m and altitudes of 100– 500 m. Most of these rivers are still natural and of low nutrient status.

Twenty-one fish species were recorded in conflict cases with Cormorants in the 19 Slovenian river case studies reported and a further two species were recorded in two lake cases. Slovenian studies on the diet of Cormorants have shown a wide variety of Figure 11.1 Determination of three potential Cormorant foraging distances around fish prey (see section 4.3), 88% three roosts in selected areas of Austrian rivers where fish sampling data are available of the wintering birds feeding on (dots indicate fish sampling sites).

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20 and 30 km around these roosts    (representing potential Cormorant %URZQWURXW*UD\OLQJ  foraging distances) were drawn   D  D 

in ArcGIS and all fish sampling K K G

QG 

,  sites and associated data were ,Q   taken from the extensive Austrian   fish data base (Figure 11.1).    Sampling sites (n = 32 for Brown  NP NP NP NP NPNP Trout and n = 23 for Grayling) in  'LVWDQFHWRURRVW 'LVWDQFHWRURRVW autumn were taken within each  Figure 11.2 Estimated mean fish density (individuals/ha) for Brown Trout and Grayling of the three possible foraging at three different foraging distances from Cormorant roosts, bars represent 95% CL. ranges around each individual Cormorant roost. Both abundance and biomass were determined for  Brown Trout and Grayling at each     %URZQWURXW  *UD\OLQJ fish sampling site, these species     D being of high fishery interest and  D  K  K  NJ the ecologically dominant ones NJ   in this region. For each sampling     site the requirements for Moran-   Zippin or DeLury estimations    NP NP NP NP NPNP were fulfilled. In other words,  'LVWDQFHWRURRVW 'LVWDQFHWRURRVW sites were fished repeatedly and the resulting depletion in catches Figure 11.3 Estimated mean biomass (kg/ha) for Brown Trout and Grayling at three was used (statistically) to estimate different foraging distances from Cormorant roosts, bars represent 95% CL. the original number (and hence density) of fish at the site. Brown Trout showed a continuous sites or different human pressures The mean value for numerical increase in both abundance and on fish stocks. As Cormorant roosts abundance and biomass (and 95% biomass with increasing distance are mainly situated in the lower confidence limits around the mean) from the Cormorant roosts but altitudes of pre-Alpine rivers, the were subsequently calculated this pattern was not apparent for observed ‘distance effect’ in fish separately with a bootstrap analysis Grayling despite higher values at abundance and biomass coincides method for each of the three sites farthest from roosts with a discontinuity in habitat foraging distances from each roost. between the areas where roosts Overlapping confidence limits The significant difference in fish are located and the more upstream indicated no significant difference abundance and biomass in relation areas where Cormorants forage. between sites. to distance from the Cormorant Furthermore, short-term abiotic roosts could be caused by the events like flooding or site-specific The estimated fish abundances and foraging strategy of Cormorants differences in recruitment rates biomasses at sampling sites located in that they could be preferentially could affect the local performance between 10 and 30 km from the using feeding areas closest to their of the fish populations. Thus, a roost sites differed significantly roosts in order to conserve energy. good knowledge of the sampling (Figure 11.2). The average However, this apparently intuitive sites and an adequate sampling abundance and biomass of both conclusion must be interpreted design are required before Brown Trout and Graying were with caution because other factors correlations like the ones described about three times higher within could produce similar results, for here (rather than direct observations the 20–30 km radius of roosts example, the differing ecological on the predators themselves) can compared to those within 10 km status (hydromorphological be used to explain the patterns of them (Figures 11.2 and 11.3). condition) between the sampling observed.

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Indeed, one further observation restricted to feeding on Salmonids from the available fish sampling in pre-Alpine streams for instance, data is in line with the alternative a highly mobile ‘generalist’ explanation outlined above that predator like the Cormorant could the differences in Trout and potentially impact on local prey Grayling density and biomass are populations, depleting stocks unrelated to increasing Cormorant before moving out of the area to predation with reduced distance other feeding grounds. from the roosts. When data for Chub (Squalius cephalus) are examined, using the same sampling 11.7 South Bohemia, Czech methods and foraging radii from Republic (category: medium the three roosts, no significant sized rivers, fishpond areas) differences in estimated fish density and biomass are found Important factors in the Czech in relation to distance from the Republic that are thought to influence roosts. This is revealing because the relationship and the conflict Chub is one of the more commonly between Cormorants and fisheries taken prey for Cormorants in this here are the trends in (i) Cormorant region (Suter 1991, Schratter & numbers (which are increasing) and Trauttmansdorff 1993, Govedicˇ (ii) the general economic situation Carp harvest in the Hranicny fish 2001), and so it might be expected (which is declining nationally). pond area, Czech Republic. that there would be a significantly Here, Cormorant problems are Photo courtesy of Petr Musil. reduced population of this closely associated with the pond species within the likely foraging farming industry, primarily for distances of Cormorants from Carp (Cyprinus carpio). There this were compared with those the roost sites. Thus, on current is no general problem with for another fish-eating predator available information, there is Cormorants on reservoirs where that occurs in the area. South very little (or no) evidence that there is little fish stocking and so Bohemia is renowned for its Otter Cormorants are depleting fish no significant economic loss to (Lutra lutra) populations that at the ‘population’ level around Cormorant predation. There are some are thought to be relatively large roosts in this region. Recorded Cormorant problems downstream and are covered by considerable changes in fish abundance and from reservoirs in secondary trout conservation legislation. The area density are more likely the result fisheries. Here, river sections (and thus includes two top predators in of other biotic and abiotic site- very occasionally reservoirs) are aquatic systems, one ‘globally’, specific factors than the result of stocked for angling. Although anglers considered scarce and the other Cormorant predation. Nevertheless, say there is a Cormorant problem considered abundant but both heavy localised predation pressure on rivers, the perception of damage being high-profile species from Cormorants could affect fish caused by these birds held by within local water systems. The abundance (of particular sizes different stakeholder groups appears ecological perspective explored and/or ages) in particular places to depend on local conditions, and a here involved calculating rough (although rigorous data are still nationwide overview of the situation estimates of the amount of fish lacking on this). Thus an important is currently lacking. eaten by both Cormorants and ecological perspective here is Otters. that some fisheries may well be Cormorants and Otters: very vulnerable to Cormorant a comparison Otters are a highly protected predation, not because Cormorants For a better ecological species throughout the country specialise on feeding at particular understanding of the fish and numbers have increased. locations on particular species, consumption by Cormorants in The species is widely distributed but the reverse. As they are not the Czech Republic, estimates of and has expanded in South

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Assuming that (sinensis) 11.8 Saxony, Germany Cormorants take around 400 g (category: complex of of fish each day, indicates that artificial lakes and reservoirs, roughly 940 tonnes of fish are eaten annually by Cormorants in small lowland rivers and fish the Czech Republic. Otters eat pond areas) approximately 1 kg of fish per day The area, a Biosphere Reserve, and 1.3 kg when they have offspring is a complex system comprising (during 4 months of the year). The medium-sized rivers, artificial lakes Czech Republic holds about 2,250 and many small ponds (Table 11.3). Otters and it can be calculated that this population consumes In this area, the average number of roughly 891 tonnes of fish each 1,000 ‘resident’ Cormorants rises year (Table 11.2). When comparing to about 4,000 birds in August these ‘global’ consumption rates and September, before declining (i.e. 940 t by Cormorants, 891 t by sharply thereafter. Few birds are Otters), the conclusion is that both present from March to June, and predators consume freshwater fish these birds are mainly on migration at an overall level that is certainly or non-breeders staying in the of the same order of magnitude. region over summer (Figure 11.4). The interesting thing here is that all Bohemia. Otters are an important discussion about economic losses Conflicts between Cormorants and widely esteemed part of at freshwater fisheries centres on and fisheries occur mainly in the mammalian fauna. Widely Cormorants whilst Otters (at least) the fishpond areas in this part of available data on fish consumption consume similar amounts of fish, Saxony. Financial compensation for from local experts and from the often in the same habitats, as do estimated fish losses to Cormorant available literature was used to Cormorants. predation is paid and fishing derive adequate fish consumption estimates for Otters. Table 11.1 Presence of Cormorants (bird days) in the Czech Republic for three major water system types during three different periods of the year. Roughly 8,000 Cormorants winter in Czech river areas Bird days Winter Summer Migration Total (from November till February), (x 1,000) about 1,500 migrate (in October Rivers 960 - 90 1,050 and March), whilst there are no Ponds 60 160 540 760 breeding birds. In pond areas about 500 birds wintering, about Reservoirs 120 - 420 540 9,000 migrate, and 1,000 birds Total 1,140 160 1,050 2,350 breed. In reservoirs roughly 1,500 birds winter, about 7,000 migrate, and no birds breed. Table 11.1 Table 11.2 Rough estimates of the total annual fish consumption by Otters shows the presence of Cormorants (Lutra lutra) in the Czech Republic. (expressed in ‘bird days’) based Number of Presence (in Daily Total on the actual numbers of birds Otters (2,250) months) consumption (kg) consumption counted and the length of time (tonnes) that they are resident on specific Solitary 8 1 540 types of water body during winter, With young 4 1.3 351 summer (breeding) and migration periods. Total 891

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companies can get permission to  remove nests and eggs by flushing   them out with high-pressure water  WV  DYHUDJH sprays. Cormorants also feed in a DQ  PD[

 RU nearby reservoir and so there are   UP no conflicts with surrounding fish   &R farmers at some ponds as the birds I 

 R have alternative foraging sites.  HU   In a similar situation to South PE   Bohemia, there is also a relatively QX   strong Otter population in the  MDQIHE PUW DSU PHLMXQ MXODXJ VHSRNW QRY GHF area (perhaps about 300–400  individuals), and they are also PRQWK considered an important element  Figure 11.4 Monthly changes in Cormorant numbers present in the Saxony of the regional fauna. There is also Biosphere Reserve study area. the possibility here of obtaining financial compensation if Otters are known to cause damage to fisheries. calculation suggests a range (based As well as Otters, other fish on maximum and minimum bird predators in the area include a Predation by Cormorants was numbers, variations in dietary variety of birds and mammals, estimated roughly in order to give a assessments, and amount of which are all inhabitants of the general, broad-brush context to the ‘available’ ice-free foraging habitat Biosphere Reserve. Some 150 biological picture in this case study in winter) of some 100–170 White-tailed Eagles (Haliaetus area. Starting with an assumed tonnes of fish consumed per year albicilla, 15 nests), 400 Otters, average fish consumption rate of by Cormorants. Of this, around and numerous Grebes, Herons, 400 g per (sinensis) Cormorant 50–130 tonnes is likely to be Carp. Egrets and Gulls all forage in per day, and multiplying this by the area. Thus a key ecological the number of Cormorant days Figure 11.5 shows the estimated perspective here could be explored per month, produced as estimate production of fish and associated by comparing rough estimates of of annual fish consumption. The predation by fish-eating birds the total fish consumption by all total amount of fish in the area including Cormorants in the region these species with that estimated was again very broadly estimated of the Biosphere Reserve. Carp are for the Cormorant (Figure 11.6). for three groups of water bodies, mainly found in the fishpond area, These calculations allow the amount (1) carp ponds, (2) reservoirs, and whilst other fish species are more of fish lost to Cormorants to be (3) ‘non-managed’ water bodies, abundant in other waters but do compared with that taken by other including recently formed lakes also occur in Carp ponds according members of the fish-eating predator in former coal mine areas. This to local experts. community in the region. They suggest that Cormorants might Table 11.3 Surface area of waterbodies according to water habitat consume roughly half of the overall type in the Saxony study area. estimated fish predation by wild in the area. Although crude, Water body type Surface (ha) these calculations suggest that it Special protected area (SPA reservoir) 700 is important to take these losses to other predators into account when Open cast mining (new reservoirs) 2,000 considering the Cormorant problem, Fish ponds (privately owned) 2,114 in order to put the latter into context. Others (small water bodies) 1,300 Another important ecological Total 6,114 perspective here is that landscape

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change their location according to local preferences or changes in food supply. Another ecological observation from the area is that the presence of large-scale, open water bodies in the form of impounded stretches of river, reservoirs and the new lakes in former coal mine areas, add significantly to the picture of extensive inland wetland habitat. The fishponds are thus surrounded by additional water bodies, which undoubtedly attract avian (and other) fish predators.

It is thus likely that any human- induced disturbance in the pond

Typical Carp pond during fish harvest, near Bautzen in Lower Saxony, Germany. Photo courtesy of Stef van Rijn. characteristics are very likely to affect predation levels in this area with a highly patchy distribution of water bodies. The ‘availability’ of these water bodies to Cormorants will be related to (1) the geographic location, (2) the position of roost sites, and (3) the accessibility of the waters to foraging birds (i.e through such factors as water transparency, level of disturbance, fish size and density, distance to nearest roost).

Figure 11.7 shows that Cormorant roosts in the area occur at regular distances from each other, well- spaced out across the entire area. The average distance between night roosts is 9–12 km, apparently the ecologically optimal distance for Cormorants to exploit the area.

Another important ecological Figure 11.5 Estimated abundance (tonnes) of Carp and other fish species in the perspective here is that the Saxony fishpond area and ‘other’ water bodies, together with the estimated amount entire fishpond system is thus of fish consumed annually by Cormorants and other predators. Predation levels are easily within reach from this set presented as minimum and maximum estimates. Year 1–2 Carp are specified as they of roosts and Cormorants can constitute the most common size taken by Cormorants.

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visit to the Hula Valley there was Annual estimated fish consumption (tonnes) discussion of the possibility that all the farms there will cease fish production within the next couple of years. As well as predation issues with Cormorants, wires and cables mounted above the ponds have been used to prevent White Pelicans (Pelecanus onocrotalus) from landing on fishponds.

Water in this region is too cold in winter (around 11°C) to grow Tilapia which are valued much more so than Carp. With Cormorant predation on top of this, these are Figure 11.6 Estimated amount of fish consumed annually by fish real concerns over the viability predators in the Biosphere Reserve Area, Saxony, Germany. of such farms. Farms here are radically different to those in the Bet Shean Valley further south area (in an attempt to reduce have recently been restored in the along the River. Here, the Cormorant numbers at ponds) can Hula Valley. Thus, an important water temperature is higher, which easily be overcome by the birds ecological perspective here is the facilitates the growing of a wider because of the large amount of general shortage of water systems. variety of fish. ‘refuge’ habitat available nearby. For economic reasons, some ponds The increased availability of in the Hula Valley area have been Cormorants roost in the Hula feeding and roosting sites caused converted to orchards in the last few Nature Reserve most of the day by restoring the landscape from years, and during INTERCAFE’s but leave to feed in the adjacent former mining activities is also very likely to have contributed to the increased levels of predation pressure on individual ponds.

11.9 Hula Valley and Bet Shean Valley, Israel (category: fishfarms) Cormorants from Eastern Europe (records of ringed birds from the Ukraine) winter in Israel but birds also pass through the country to areas further south. Thus one ecological perspective here is the migration and over-wintering pattern of the birds. Israel has Figure 11.7 Biosphere Reserve and adjacent territories in Saxony, Germany lost the majority of its freshwater (Biosphären Reservat Oberlausitzer Heide und Teichlandschaft), showing fish ponds, wetlands and many of them have natural water bodies and recently flooded lakes in former coal mine areas. Roost been diverted into arable land or location and maximum estimated roost size (number of birds) are indicated by black fish farms, although some patches circles. Some roosts are situated just outside the borders of the Reserve.

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The large and turbid waters of Lake Kinneret, Israel, attract large numbers of wintering Cormorants. Photo courtesy of Stef van Rijn. reservoir. However, they have important. Fish in their turn depend fish farms. Thus, influencing the caused few problems here in the on basic habitat characteristics like birds’ foraging site-choice is yet last few years because numbers are shelter, food and oxygen supply. another ecological element of local now much lower than previously. It These factors differ across water management. The Sea of Galilee is is interesting to note that this seems bodies and determine the position fished by commercial fishermen but to be a more common theme — a of predator and prey. Specific (perhaps also due to its huge size) Nature Reserve adjacent to a research was conducted to unravel Cormorants and fishermen do not commercial fishery. Management these factors and implement the appear to be in conflict here. of both areas is not considered system-based knowledge through in isolation but in an integrated local management. In Bet Shean the situation is manner; the predators need a safe economically much more powerful place to shelter but can be disturbed The reservoir Agmon can suffer than it is in the Hula Valley, and at vulnerable sites. severe oxygen depletion and, the methods to deter Cormorants under these conditions, fish move are considerably more intensive. Scientific knowledge about up to the surface and Cormorants Gas , fireworks and direct feeding conditions and the concentrate their feeding in the top shooting are applied on a large foraging behaviour and skills of layer of water. Moreover, the Sea of scale. Fish stocks are huge (over the predators plays an important Galilee (Lake Kinneret) is a natural 10,000 kg/ha) and this means that role in the way Cormorant feeding place for the birds. Part Cormorant predation (or visits problems are managed here. of the solution to the problem of from any predators) are seen as an Similarly underwater visibility is reducing the impact of Cormorants unacceptable stress factor, given the an important issue in the acuity of at farm ponds is supposedly to extremely high fish densities. The the Cormorant to detect, pursue and increase the use of this water body situation in Bet Shean was at the catch its prey (Strod et al. 2004) by wild birds, thus offering a extreme end of the range of possible so physiological issues are also good alternative to foraging at the anti-predator measures seen across

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Europe and was presumably Cormorant as this species can also sites in a natural environment in associated with the extraordinary be a nuisance to the fishfarmers at combination with maintaining the high investments and economic times of migration. As preservation ‘traditional’ fishfarm practices values of the fish farms there. of the White Pelican constitutes (Shmueli et al. 2000). Surplus a stronger conservation goal than food from fish farms was put in the The Israeli case of integrated does Cormorant conservation, Agmon reserve and was thus used management of water bodies for an integrated solution was first to concentrate the Pelicans in the different purposes was not confined developed for this former species. nature area. A similar strategy, this to Cormorants. For White Pelicans This was based on providing the time with agricultural crops, was too, the management solution flyway population with abundant also developed for Cranes (Grus bears parallels with that of the food and undisturbed stopover grus, Gutman et al. 2001).

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12 DISCUSSION

This chapter explores two aspects region (but often migrate out of that it is thus vitally important to of Cormorant-fisheries interactions it in winter). The birds of group define precisely the geographical in more detail: (1) the data on C are largely confined to non-EU area under consideration when numbers and distribution and (2) countries throughout the year. They talking about Cormorant numbers Cormorant ecology. We aim to put also move further south in winter ‘in Europe’, whatever area that the data into the perspective of and this part of the population is might be. It is also important to reliability, data completeness and far less studied, both in terms of recognise that, at this level of ecological context. number and in terms of migratory geographic scale, Cormorants are habits. distributed in significant numbers over a very wide area. Although 12.1 The number of In winter, the Atlantic-North Sea overlap occurs between the major Cormorants region (A) has about half of all regional groups, the majority of estimated birds, whereas in summer birds do not roam about freely in 12.1.1 What is ‘Europe’ and the largest proportion breeds the ‘super space’ of Europe, nor in the Baltic-Central European within any of the three regional which populations are we region (B). This is a result of the areas. Distinct (sub)-populations talking about? fact that some of the Baltic birds occur, often with discrete migration migrate west to winter in the area patterns. To date, knowledge Cormorants, like many other birds, included in the Atlantic North Sea about these migration patterns show large differences between region. It is important to emphasise has been described only partially. summer (breeding) and wintering areas. Compared to the breeding distribution, the wintering one covers a much larger geographical range and birds are far more widely dispersed. In summer, the majority of breeding colonies are found in coastal areas, whilst in winter inland lakes and rivers are also important habitats. Comparing the general patterns of distribution in summer and winter shows striking differences (Table 12.1) between ‘populations’ of Cormorants in three geographic regional areas (A, B, C, see also Figure 6.1). Thus, ‘Europe’ can be a fuzzy concept when considering Cormorant populations. In fact there are several populations existing at the same time and in different places across a very large land surface area. Only birds in regional groups Many Cormorants from eastern Europe winter in the Middle East as here at A and B correspond to the EU-27 Lake Kinneret, Israel. Photo courtesy of Stef van Rijn.

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Coordinated ring analyses could correspond to an estimated be used to expand our knowledge 558,000–615,000 birds in January with respect to the geographical 2003. This range depends on the segregation of regional groups and assumed number of non-breeders to refine our understanding how and the estimated total should be individual movement and migration compared with the actual number strategies have developed. Such of birds counted, which was almost knowledge and understanding is 427,000 sinensis Cormorants necessary in order to understand the in this region in January 2003. birds, especially when comparing Given the different methods and count data when analysing completely different geographic trends, or when the link is made areas used by the birds in summer between numerical distribution and winter (see Figs 6.2. and 6.3), and perceived damage. Merely both estimates compare reasonably mentioning the overall numbers of well. Because the winter count cormorants, suggesting that these includes ‘uncounted’ areas in would be one huge pool of birds Eastern Europe and/or some birds that could potentially show up at may have completely left the any one site, is very far from the region being counted (i.e. other actual situation described here for Middle Eastern countries, Sudan), the European continent. the estimate based on the summer count is higher. Another alternative Great White Pelicans (Pelecanus 12.1.2 How comparable are possibility is that the actual survival onocrotalus) and Cormorants fishing and/or the overall number of non- the population data? together in the Danube Delta, breeders is less than was assumed, Romania. Photo courtesy of Botond Kiss. The number of Cormorants thus leading to an overestimate of assessed independently both in the most recent count. winter and summer corresponds estimated wintering population reasonably well, especially for The proportional occurrence of there. In contrast, in summer, regional groups (A) and (B), that the Cormorants between summer the Baltic regional area (B) is is for western and central Europe and winter differs between the estimated to hold the largest together. Given the more recent different regional groups in proportion 44% of breeding birds. count of breeding Cormorants, Europe (Table 12.1). The Atlantic- the 755,000 sinensis estimated North Sea area (A) is relatively 12.1.3 How many for January 2007 (based on the more important in winter, being breeding count in 2006) would estimated to hold 51% of the Cormorants do we have in total?

Table 12.1 Comparison of counts of Cormorants in 47 countries in the Western To answer this question in a Palearctic, including North Africa and the Middle East, in winter 2003 (birds) and meaningful way it must be refined summer 2006 (occupied nests), separated into three geographic regional groups. to a specific geographic area. The regional division into three groups Regional Group January 2003 Summer 2006 suggested here (see Figure 6.1) is ‘metapopulation’ a first attempt at this. An analysis Number of birds (%) Number of nests (%) of the migratory movements (A) Atlantic-North Sea 346,524 (51) 121,763 (33) of ringed birds could be used (B) Baltic-Central Europe 214,413 (32) 162,691 (44) to elaborate, and to distinguish (C) Black Sea-East 114,898 (17) 87,882 (24) in a more sophisticated way, Mediterranean between different Cormorant Total 675,835 372,336 100% sub-populations. From the overall

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from counts of breeding pairs, an estimate for the production of young over the entire geographic range was needed. By applying sinensis data for the entire population (including the less productive carbo portion), will certainly lead to an overestimation of numbers. Similarly, the assumption of a cohort of 100,000 non-breeding birds is also not too conservative in this respect. Finally, the mortality rates of young-of- the-year birds may be higher than assumed here. The population data used are derived from the protected western parts of the species’ range, and mortality in the eastern parts is likely to be higher than this — but relevant data were not available to allow this assumption of equal mortality over the wide geographical range to be refined number of breeding pairs in maximum number of birds that spatially. There are thus several regional areas (A), (B) and (C) would have occured in July 2006, reasons why this overall population (carbo and sinensis combined), the just after most young have fledged, estimate, although based on best total number estimated is 372,300 as birds will have been dying available scientific information, breeding pairs. Applying the same continually from fledge in late should be considered with caution. conversion factor as derived for the summer throughout the autumn and However, as pointed out above, it sinensis population in areas (A) winter up to January. On the other is certainly not to be considered and (B) (i.e. 3.25), and ‘converting’ hand, this estimate is higher than an under-estimation of the actual from breeding pairs in summer to that just prior to the new breeding number. January numbers in the winter after, season, as mortality has continued it could be tentatively estimated over the entire winter period 12.1.4 Counting effort and that there were 1.2 million birds and during the spring migration. throughout the whole Western However, any interpretation of this numerical assessment during Palaearctic region in January 2007. figure must be treated with caution summer and winter It is important to note that this as not all these birds can be strictly geographical area is considerably classified as ‘European’, as this To date, two Pan-European larger than the EU-27 region. The ‘population’ is distributed over a Cormorant counts have been Western Palaearctic stretches from very large area, including parts conducted, one in summer the Iceland, Portugal and Morocco in of the Middle East and northern other in winter, and the spatial the west to the Caspian Sea, Turkey Africa. information provided by them gives and Iraq in the east, and from a reliable picture of distribution Greenland and the Barents Sea in Nevertheless, this estimated across large parts of Europe. As the north to Algeria, Egypt and January number derived from the birds are far more dispersed in Saudi Arabia in the south. breeding data can be seen as a winter than in summer, overall reasonable approximation of the trends in the overall population This January 2007 estimate is number of birds at that time of size are probably best censused lower than the post-fledge annual year. By calculating backwards by counts at breeding colonies.

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Nevertheless, winter counts are of counting breeding Cormorants, in a very large geographical useful to detect trends in regional see chapter 2 [especially section range. Again, it is important to areas and to provide important 2.2] of Carss et al. 2012 for consider the breeding counts additional information about full details) were not always in their geographical context. large-scale trends in regional straightforward. For example, The birds show strict migratory distribution. The amount of some countries were faced with patterns, which implies that only counting effort required in winter the difficulty in surveying coastal a proportion of the total number is far beyond that needed to count colonies, on cliffs, stacks or will ever migrate to any particular the colonies in summer. This is offshore islands and, in many region. This means that it is almost related to the larger geographical cases, not viewable from land and certainly invalid to consider the range to be covered in winter as so for some of these colonies, biological relevance and/or the well as the fact that there are at boat-based or aerial surveys were economic impact of Cormorants least five times more winter roosts conducted. After the end of the on fisheries in particular regions, than there are breeding colonies breeding season, the coordinators countries, or within the EU-27, in summer. Also, the severity of collated data from the counters purely on the total number of so- prevailing weather conditions (in most cases on a national scale) called ‘European’ Cormorants. across Europe during a mid- and then reported to the central January roost count should not be organising group who checked The census work of WI-CRG underestimated. Complete winter for mistakes and converted stimulated count initiatives on roost counts are very difficult to information into databases a national level in many places. achieve, especially in areas like the containing data from all countries. Furthermore a number of countries countries, Libya, Egypt have now reported the national and Sudan. In fact this holds for a The coverage of breeding counts results of the Cormorant colony much wider geographical range, was considered satisfactory, count in 2006 in reports, scientific as in , Turkey and although it took many months papers, official reports, popular Lebanon especially, current data to gather data from all relevant journals (including newspapers) are incomplete and do not show countries. By the end of the and/or on the internet (e.g. the numerical distribution at the work, the EU-27 region, Norway Eskildsen 2006, Staav 2007, most detailed geographical level. and Switzerland were very well Herrmann 2007, Kirikova et However, because the temperature covered. However, the WI-CRG al. 2007, Newson et al. 2007, gradient across Europe excludes a was unsuccessful in obtaining Shurulinkov et al. 2007, SYKE lot of potential winter habitat, the reliable information about the 2006, van Rijn & van Eerden situation described here will largely occurrence of breeding Cormorants 2007). A number of results from depict the real pattern of Cormorant in , the 2006 count of breeding colonies occurrence in Europe in winter. Albania, Macedonia and . have been published in scientific It was also difficult to obtain journals. A wrap-up from the Although breeding colonies are complete coverage of breeding counts has also been presented at situated over a smaller geographic colonies located in countries east a European parliamentary level in area than are winter roosts, it is of the EU-27 region, but also for the ‘Cormorants in the Western likely that some breeding attempts carbo birds on the remote Atlantic Palaearctic: Distribution and were missed, at least in some coasts. However, there was some numbers on a wider European countries. Despite best efforts success in 2008 in obtaining scale’ (WI-CRG, October 2008). to compile a complete list of information from countries like colonies for each country, either Ukraine, large parts of European It is interesting to compare the the existence of some colonies was Russia and Turkey. Population amount of effort that was needed to not reported or important details estimates for these countries can perform these counts. In summer were not available. Despite their still be improved but the survey the 2006 breeding count was done large and often conspicuous nests, was considered successful in by approximately 100 people, counts of Apparently Occupied that it showed for the first time whereas at least 2,500 individuals Nests (AON, the standard method the number of breeding pairs were involved in the 2003 winter

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count. From the point of view of the reproduction and dispersion and mortality rates and on the human-effort, a breeding census is of carbo birds needs further temporal (and spatial) trends in therefore easier to conduct than is a clarification for large parts of the these parameters must be followed- full-coverage winter count. range. For example, the degree to up by extensive modelling in which carbo birds intersperse in the order to predict future population 12.1.5 What future census continental winter range of sinensis developments. Modelling efforts is still largely unknown. so far have already pointed out work is needed? the plasticity of the European Another important point requiring Cormorant population with respect Based on the available data from clarification is the count of summer to counteracting the local effects two integrated Cormorant counts roosts and of non-breeders within of poor breeding performance. across Europe, a fairly clear picture colonies during the time of The recurring conclusion has of Cormorant status and distribution breeding counts. Total population been that only through enormous across the continent can be drawn. estimates are best based on management effort could However, as the populations are complete coverage during the same Cormorant numbers ever be subject to change due to weather year. The non-breeding summer brought back to the level of, say, conditions, shifting food supplies, gatherings consist of immature 1985. The carrying capacity of the management measures and other birds but also of adults that are foraging waters for Cormorants factors, repeated censuses are not breeding. Some of these birds in large parts of Europe is such necessary, both in winter and in are also present in the breeding that the population will ‘easily’ summer. From this (and earlier colonies and so information restore itself to the ecologically work), count data point towards about overall numbers needs to adjustable level, that is related to declining Cormorant numbers include these birds (which are not the availability of large quantities in the southernmost wintering covered through standard counts of of immature fish and smaller areas which may be due to milder of Apparently Occupied Nests). species which predominate in winters in central and Western Current (and future) data on overall many ecosystems at present Europe. Nevertheless, special effort population structure, reproductive (see 12.2). is required to have areas counted comprehensively in northern Africa, the Middle East and Turkey. On the other hand, the still expanding breeding population in the Baltic needs further study in relation to numbers and migratory pattern. The detailed distribution and migratory patterns of birds breeding in the eastern Baltics, Belarus, northern Ukraine, parts of the Russian Federation and Georgia are little, if at all, understood and require attention. For instance, the finding in Israel of birds ringed in Ukraine is actually no proof that other countries in that super-region (e.g. Belarus and Russia) are not also the ‘home’ countries to breeding birds during summer that also spend the winter in Israel. The ringing efforts in these countries is simply too low The Black Sea population of Cormorants has been relatively little studied so to draw such a conclusion. Finally, far, Danube Delta, Romania. Photo courtesy of Botond Kiss.

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12.2 Cormorant ecology

12.2.1 Distribution and environmental factors From the description and analysis of factors which determine Cormorant numbers and ultimate geographic distribution, climatic factors appear to be crucial. Wintering Cormorant distribution is shown to correlate well with an average January temperature of -5°C. This is the boundary temperature below which the average, larger standing waters freeze and also that at which slow-flowing larger rivers partly freeze, especially in shallow areas. Cormorants are distributed in an irregular manner in areas with mountainous landscapes. Here, regularly occupied roosts persist in the valleys of larger rivers from which Cormorants exploit the still unfrozen waters nearby. During periods of severe frost, birds are forced to move to ice-free regions but they also explore fast-flowing Zahori fish pond in the Czech Republic in winter. Most shallow and standing upstream areas. In these areas, waters in eastern Europe freeze in winter and Cormorants move further south the distribution of Cormorants and/or to running waters. Photo courtesy of Petr Musil. thus changes rapidly according to the weather conditions. In the North, the deeper coastal areas and Spain). Besides the actual maintaining body temperature also remain largely unfrozen freezing of waters, (which is the during foraging in cold water will at this temperature. Again, proximate factor affecting fish require more energy (ultimately comparable to large rivers, the availability if waters are frozen, being derived from food shallow sections do sometimes Cormorants can not feed there), intake) — such interrelated issues freeze and birds are forced to temperature also has behavioural could also ultimately contribute forage in deeper waters. At the and energetic effects. For instance, to the winter distribution of European level, this temperature it is likely that a species-specific Cormorants. threshold well describes the relationship exists between the general pattern of Cormorant temperature at which fish are still In summer, Cormorant breeding distribution. Interestingly, within active and at which they start colonies also appear to be the range of temperatures higher forming winter aggregations in distributed according to temperature. than -5°C, there is a gradient in deeper water. Similarly, falling A clear temperature-dependent start Cormorant distribution from the winter temperatures are likely to to the breeding season was found, colder to the warmer areas (e.g. reduce the swimming speed of to a large extent explaining the increasing density from northern fish (perhaps making them easier observed difference of more than and western Germany to France for Cormorants to capture) whilst five months in the start of breeding

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move out of the breeding area where them to move to other areas later in average maximum temperature the season. Interestingly, the birds exceeds 24°C and many move out could theoretically breed twice in a of breeding areas where it exceeds season if they migrated north. 22°C. The post-fledge staging sites around the North Sea and Baltic The conclusion from this Sea are situated in the core area ‘temperature window’ hypothesis of this temperature range (19°C to is that Cormorants are susceptible 22°C), both in relation to the start to climatic conditions. As milder of breeding (North Sea, March) and winters occur due to global post-fledge conditions (Baltic, July). warming, there is an increasing According to the analysis, this may possibility for this species to seem less true for the Black Sea and winter and breed at more northerly Azov Sea, as well as for the greater latitudes. As the total available part of the Mediterranean. However, water surface area is also likely due to the fact that ambient air to increase with climate change, temperatures were used in the this might well mean a further present analysis, areas close to large increase in Cormorant populations water bodies could in fact provide in Europe. a microclimate that is actually cooler than presumed (at least water temperatures are likely be 12.2.2 Food and feeding more buffered against temperature ecology extremes and wind effects near large water bodies provide extra cooling). The Cormorant is an opportunistic forager and, for the greater part There is still no explanation of the population across Europe, for why Cormorants in the depends on large-scale open water Mediterranean do not breed in bodies. Whether fresh, brackish or larger numbers than they do in salt water, suitability as a foraging across Europe. Interestingly, this January, as it is still not too hot in site is apparently dictated by the earlier start of breeding in western April. This is unexpected because presence of relatively easily-caught and southern Europe appears limited breeding in January, or even and abundant fish. For almost 180 in relation to the average maximum December, has been recorded in site-specific cases across Europe, temperature later in the breeding several cases in the Netherlands, the Water Systems Database season at the time when the young although the average start of developed during INTERCAFE fledge, as few colonies occur in breeding here is in March. Fish provided useful information the area where temperatures reach availability in January at these about feeding conditions and the more than 25°C at the time of Mediterranean sites could be a Cormorant’s response to it. The fledging. The colonies in this higher limiting factor and/or that the sampled area during this project summer temperature zone are in necessity of migrating considerable comprised about 30,000 km2 and the interior parts of Spain, Italy, distances north after the breeding was estimated to be used by a total along the middle and lower Danube season does not fit the annual cycle of around 350,000 Cormorants. The and the northern edge of the Black of movements. On the contrary, analysis of these data from widely Sea. That this summer temperature Cormorants with a late start of distributed sites confirmed the level is probably ecologically the breeding incur only a moderate broad-scale pattern that emerged highest the birds can cope with, is temperature increase after breeding. during the case studies where corroborated if considered alongside Those breeding in January regional conditions were examined data on post-fledge movements. generally face a sharp increase in in greater detail through exchange Almost all fledged birds quickly temperature which often forces of information with local experts

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fish species. This holds for Eel (Anguilla anguilla) in almost all waters, Pikeperch (Sander lucioperca) in large lakes, Grayling (Thymallus thymallus), Atlantic Salmon (Salmo salar), Brown Trout (S. trutta) and Rainbow Trout (Oncorhynchus mykiss) in running waters, all species for which the importance in the diet of the Cormorant is often over-emphasised to a variable degree in reports from these water systems. Compared to the published lists of fish species derived from pellet analysis, Cormorant diet is generally more diverse, reflecting the diversity of fish species in various water bodies, with a less prominent role for these relatively ‘rare’ species highlighted by a focus on Cormorant-fishery conflict cases/ sites. For instance, from extensive Cormorant feeding its young. Overall in Europe Cyprinid (‘Carp family’) fish studies of Cormorant pellets from species constitute the most common food items taken. birds foraging in running waters Photo courtesy of Florian Möllers. in Slovenia, between 25 and 30 fish species have been recorded as prey. The conclusion from these and stakeholder groups. However, This is perhaps not surprising, the and other more in-depth studies the Database comprises far more foundation of the Water Systems was that Cormorants rely on water systems than could be visited Database was invariably a specific relatively small, abundant (and thus and is thus of considerable generic location (or ‘case’) where there relatively easily caught) fish, rather value. was perceived to be some form than deliberately selecting the of conflict or interaction between economically important (and often It could be argued that the method Cormorants and fisheries interests. numerically less abundant) species of reviewing existing information It therefore follows that the prey of high commercial/recreational on different water systems could species highlighted most frequently interest. As such, this situation is be highly biased because of a in these cases are often those fully comparable to those extensive lack of certain information or an associated with both the habitat studies carried out in many large over-representation of particular types most likely to be used by rivers, lakes, estuaries and coastal water body types. To some extent fisheries interests and those species systems throughout Europe. this is the case. For example in that these fisheries catch or rear. Table 9.1, 69 cases out of 179 In general, Cyprinid fish species (38%) relate to fishponds and small Thus, generally, the data held constitute the most important prey reservoirs, sandpits and smaller within the Water Systems group of sinensis Cormorants in running waters. This is of course Database provides information on Europe. Of these, Roach (Rutilus proportionally much more than the particular fisheries habitats and rutilus) is undoubtedly the most water surface-related occurrence has a clear focus on the position commonly taken species (more than of these habitat types in the field. of commercially important 50% of overall biomass consumed

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on an annual basis). The Percids Sun Perch (Lepomis gibbosus, stocked fish, reared in captivity Perch (Perca fluviatilis), Ruffe an accidental release in ponds under artificial conditions are less (Gymnocephalus cernuus) together and artificial lakes), two species wary and probably show little, or with the Cyprinids Carp (Cyprinus of catfish (Wels Siluris glanis no, escape behaviour in response carpio) and Bream (Abramis from Europe and Black Bullhead to the presence of a predator. brama) roughly form another 30% Ictalurus melas from the USA), This makes these modified waters of the estimated overall food intake Grass Carp (Ctenopharyngodon additionally sensitive to predation. by Cormorants. The remaining 20% idella) and Silver Carp (Hypophth- Cormorants on the other hand, of the diet comprises more than 100 almichthys molitrix) which are are very well able to catch these fish species, proportions of which both from the Far East. The latter fish (as are other predators). For are site-specific and dependent on two are fish species accidentally the stocked fish themselves, the water systems and time of year. introduced alongside Carp. switch to foraging under natural Although for individual water There are also some non-native conditions and a limited adaptation systems such species may comprise populations of Arctic Char to naturally occurring diseases and an important food resource, for (Salvelinus alpinus) to mention parasites makes them additionally the Cormorant as a species they just a few examples of changes vulnerable and the question is how have little importance and the birds that have occurred due to the much the predation by Cormorants by no means depend on them. introduction of non-native fish adds to the other factors causing This conclusion that Cormorants species or subspecies. mortality amongst such stocked depend on only a few fish species fish. Apart from the difficulties has important implications with The Rainbow Trout is deliberately of assessing any damage to respect to the issue of the birds’ stocked and anglers do fish for fish stocks or populations by interference with man’s fishery it and eat it. Native fish species Cormorants in these systems, data interests, which will be discussed often have to be returned to the on predation of these introduced further in chapter 13. water but Rainbow Trout may be fish cannot simply be used as taken by anglers, although there surrogates for the situation in wild are places where this species is populations. Therefore it is very 12.2.3 Stocking manage- not wanted. There is evidence that difficult to deduce mortality rates ment, ecological research Rainbow Trout interact negatively in wild fish from studies using and monitoring of fish with Grayling when introduced released fish (e.g. tagged Salmon to the same waters (M Govedicˇ smolts [Jepsen et al. 2010] young Although many of the rivers pers. comm., for Brown Trout and sole Solea spp. and Eel in North and fish communities in many Grayling see Mäki-Petäys et al. Sea). The effect of stocking on sub-Alpine areas, such as those 2000). This further complicates the other fish species is also relevant in Slovenia, are deemed to be assessment of the role that predation in this respect but has been little ‘pristine’, a number of exotic, by Cormorants plays; interspecific studied. The habit of stocking non-native fish species are present. competition between fish predators is thus of great importance with This is due to the stocking of was often mentioned as an important respect to the composition of the non-native fish over many years factor determining the overall fish community. and is also common practice in development of the fish population. many cases where recreational Added to this comes the effect One very important aspect of this angling relies of regular stocking. of invasive species, whether they work requiring consideration here Stocking is also often a common be fish, or molluscs, is the lack of response to requests practice in lowland waters so as to on the fish fauna and this further for quantitative fish data from increase the standing stock of fish, complicates the assessment of any large areas of continental Europe again mainly for the purpose of predatory effects by Cormorants. (e.g. inland France and Spain, angling. Introduced species include but also coastal Denmark and Rainbow Trout (Oncorhynchus The vulnerability of stocked fish Italy) in relation to some of the mykiss, deliberately released to predation by Cormorants is important countries holding large and economically important), largely unknown. Most likely the numbers of Cormorants. These

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areas form an important winter or Perhaps the most striking thing of such enterprises is not usually summer habitat for Cormorants about INTERCAFE’s work in this publically available, particularly but, despite the best efforts of area was the commonly perceived in relation to the economics of the INTERCAFE researchers, lack of quantitative fish data for system/enterprise. very little information could be many water bodies. Although obtained either by reference to much emphasis has been placed There is potential here for a serious the published scientific literature on the gathering and validating debate over how best to measure or through direct enquiry to Cormorant data (with respect to Cormorant impact at fisheries national experts. Fisheries numbers, distribution, migration, (again see chapter 9 of Carss et al. institutes tend to focus mostly on food and population ecology), 2012). If fish biology were better the more rare, larger and most similar, analogous data are scarce understood in a quantitative manner often commercially important or completely absent for most fish comparable to that of ornithological species and consequently have species or communities. This is data, then it might be easier to less interest in a quantitative all the more striking because, in conclude something about the community approach that would many cases, the conflict between extent to which damage (or at least include commonly occurring Cormorants and Man is played out an ecological interaction) occurs. non-commercial species. Parallel (in even the ‘best’ cases), through Thus, if the next step in the process to this trend in inland waters, what is essentially circumstantial is to combine Cormorant and much research effort in marine evidence. fish data and devise sophisticated environments has been directed models to forecast trends in towards the deeper, offshore As discussed in detail in chapter 9 Cormorant status and distribution in waters. Again, this is probably of the INTERCAFE Field Manual relation to a changing environment, related to the ultimate commercial, (Carss et al. 2012), accurate for fishery data this would to a rather than scientific, interest in quantitative data on fish must be large extent mean the collection of these habitats/fish species. This available before any significant basic raw data for different water paucity of ‘fish community’ data effect of Cormorant predation (e.g. systems. Currently there appears may perhaps be addressed through impact or damage to a fishery) can to be an enormous gap to bridge the Water Framework Directive, be demonstrated. This is especially before it is possible to compare fish as monitoring and habitat quality true for the more natural, open data with bird data at ‘equal levels’, assessment are prerequisites for and larger-scale water systems. In particularly in relation to species the management schedules that smaller reservoirs, ponds and fish composition, standing stock and have to be set-up in Europe. farms, where fish populations are production in relation to trophic the result of repeated introductions, state of the system, food chain 12.2.4 What future in combination with high density relationships and studies on fish and limited possibilities for fish movement and migration. ecological studies are to seek cover and evade predation needed? or migrate to other systems, the It is obvious that this plea will situation is more complex. In these not be followed by any action if INTERCAFE has compiled a cases, Cormorants may cause there were no other drivers than considerable amount of new data considerable effects, either by just Cormorants. From a purely in relation to Cormorant ecology, direct removal of fish or indirectly biological perspective (but there are status and distribution. Thus a through increased mortality (e.g. others which may be equally, or even logical framework could be built physical damage to uneaten fish in more, valid (see chapter 9 of Carss by combining different sources the form of scars, stress, increased et al. 2012), in relation to Cormorant of information and this allowed a vulnerability to other predators ‘impact’ at fisheries, quantitative cohesive ecological view on the and/or diseases/parasites). ecological studies of fishes, interface between Cormorants and However, even in these cases it is including field estimates of natural Human interests. This view will not necessarily easy to judge or mortality for different species are be discussed in detail in the final quantify ‘damage’ because relevant urgently needed if the distinction chapter of this publication. information about the management between additive and compensatory

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mortality is to be made. This is data from fisheries sustained by periods of severe frost as most the basic question that is crucial stocked fish that were reared in birds move away further south but in relation to the whole issue of captivity (which tend to be those at the same time some birds shift Cormorant ‘damage’ or ‘impact’ where relevant quantitative data locations towards the remaining at fisheries from a biological are available) is of little use in this open (fast running) waters where perspective. In other words, is the respect. Only if we were to possess they can exploit fish which are effect of Cormorant predation partly fairly comparable data from above concentrated in these places. A or fully compensated for by extra and under water, could the claims similar, but still theoretical case growth and/or lower mortality in the of damage in more natural systems could be the predation at isolated group of remaining fish? In currently be evaluated in any form of robust, water bodies in areas where birds applied fish models, the mortality scientific way. only pass through. Again, local bird factor is assumed to be constant, at numbers visiting such a site could best cohort-dependent, but accurate However, as shown by the examples be higher than is sustainable for the data from the field are completely described extensively in this fish population there. At a larger lacking with regard to this. More study, the impact of Cormorants is scale than an individual water body, realistic (and, at least, dynamic) unlikely to have a direct effect on this mechanism may apply to the models are needed to judge the the composition and size of the fish proposed ‘watershed hypothesis’, effect of different predators (fish, stocks. There are a few exceptions describing the relatively high birds, mammals, not to say also and these are related to the fact that level of complaints about damage the individual species within Cormorants can fly from one water by Cormorants in the upstream these groups) in the same system. body to another and fish can not. As areas of an area grossly dividing However, these models require the numerical relationship between the Baltic-North Sea-Atlantic sophisticated assessment of the Cormorants and their fish food- Ocean on one hand and the Black relevant parameters. As discussed resource is probably set at the large Sea-Mediterranean on the other above, much of this information scale of a geographical region, local (see section 10.2). These areas on fishes appears to be lacking for concentrations of Cormorants may may be especially susceptible to many of the systems (sites) where occur in some instances at locations Cormorants that migrate through Cormorants are considered to be which are have no, or only a few, them to and from their breeding a problem for fisheries. Moreover, birds most of the time. This is the areas which tend to be in more using incomplete or inadequate case in pre-Alpine streams during lowland/coastal areas.

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13 SUMMARY AND SYNTHESIS

13.1 The Fishes-Cormorants- of fish extracted per hectare of Cormorants can therefore be Human Fisheries triptych surface water annually. In waters considered gross indicators of the poor in nutrients (oligotrophic trophic state of a water systems This chapter summarises the facts, and mesotrophic systems), peak and, given the relatively small figures and implications derived standing stock of fish ranges from amount of fish taken by them, are from the discussions in the previous between 40–100 kg per hectare. not considered the prime factor that chapters and attempts to synthesise In eutrophic systems this range is governs fish populations. In most these into a coherent view of between 200–400 kg per hectare. natural and semi-natural systems, the ecological aspects within Thus, based on these rather crude Cormorant numbers (and associated the Fishes-Cormorants-Human estimates, in most cases Cormorants predation levels, incorporating the Fisheries triptych. The aim here is take roughly not more than10% length of time the birds are present to summarise the ecological factors (and possibly up to a maximum of at a site) are dependent upon the and mechanisms that play a role in 20%) of the peak standing stock ‘available’ fish biomass and not the abundance and movements of of fish. As such they are not much vice versa. birds and fish, and to relate these different from other avian fish to the management practices of predators (see synthesis in van In accordance with this people in waters that are visited Eerden (1997) for Great Crested relationship, at a European scale by Cormorants. For the three Grebes (Podiceps cristatus), most Cormorants are found in players in this triptych, conclusive Goosanders ( merganser) eutrophic, large-scale and rather factors are discussed before the and Smew (Mergus albellus). shallow water systems. The bird relationships between them are population is thus likely to be sketched as a working model. At In water systems which have determined by the available habitat, a later stage we plan to use this been exploited for a long time either in summer or in winter. logical framework to quantify the by both Cormorants and human Estuaries, large lake and shallow relationships in order to forecast predators (i.e. fishermen), the coastal systems are among the future developments. greatest proportion of fish mass most frequently used habitats, there consists of young individuals, followed by large rivers in winter. 13.1.1 Cormorant either of the current year or At the moment it is not possible the previous one (the so-called to easily distinguish between any As measured over the large sample 0+ and 1+ age-classes). Fish clear summer or winter foraging of waters in INTERCAFE’s biomass generally correlates with bottle-neck, which would be database, the density of Cormorants Cormorant use of a foraging site, more important to set carrying expressed as average number per areas with higher fish abundance capacity and thus determine overall unit surface area is fairly constant. generally attracting more birds and/ numbers in the species. However, So, regardless of the size of surface or birds remain there for a longer the extreme geographical spread waters, Cormorants spend, on period. Most often this general in the Cormorant’s winter range average, about 10 bird-days per relationship is associated with the compared to that of the breeding hectare per year at a site but can trophic level of the water. In other range in summer suggests that, spend up to a maximum of 100 words, the amount of nutrients in ultimately, the availability of bird days per hectare per year. This the water determines the level of ice-free foraging grounds (and use by Cormorants corresponds to fish production and this in turn associated fish stocks) in the winter roughly 4.5 kg (but up to 45 kg) governs Cormorant numbers. period is likely to be limiting.

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Preferred Cormorant foraging obtaining higher prey yields than rivers, Dace, Nase and Barbel habitat consists of semi-turbid described above (often less than are commonly taken besides the (Secchi depth 60–90 cm), 10% of standing crop), even if the bottom-dwelling gobies. In all relatively shallow (2–7 m deep) Cormorants have adopted social habitats Cormorants also take prey water with a high abundance of hunting in these circumstances (van that are highly valued by Man. In small fish (10–20 cm), within Eerden & Voslamber 1995). standing freshwater systems these reasonable distance (<15 km) of are Pikeperch, Eel and Whitefish a fixed place — either a colony Cormorants are opportunistic (Coregonus) species, in coastal where birds breed or a night roost. foragers and do not select particular waters Herring (Clupea harengus), Cormorants are so called ‘central species of prey fish, their energy- Whitefish and Sole, and in riverine place foragers’ making foraging expensive foraging behaviour systems Grayling, Trout and Charr trips from a communal site. Roosts meaning that they generally almost species, and Atlantic Salmon. and colonies tend to be spread out always eat the most abundant prey regularly in the landscape in order species that they can find. On a Although the major proportion to optimise the balance between European scale, more than 100 of Cormorant diet consists of the energy expended in flying to fish species are regularly taken economically unimportant species, (and between) foraging sites and by Cormorants, with mid-water some birds do feed on the less the energy gained through foraging. living Cyprinids such as Roach common, commercially important The Cormorants’ ’harvest’ of fish and Bream the most important species. Whether this predation in natural waters is determined group across Europe. These are leads to any effect on the prey fish (besides by the availability of fish) followed by the Percids Perch is impossible to determine just by the foraging distance to and and Ruffe and, in coastal waters, from the percentage occurrence in from the ‘central place’ (i.e the Eelpout, Viviparous Blenny, Gobies the diet. However, it is important to individual’s current colony and/ and Sculpins as the commonest consider two important facts. First, or roost site) and the presence prey. In smaller, fast-flowing the Cormorant is not necessarily and location of other roosts or colonies. Cormorants spend a lot of energy during diving, and so their energetic return needs to exceed this and thus food intake rate can not drop below a certain threshold. This threshold is obviously higher if energy expenditure increases (e.g. flight distance and/or diving depth increases and/or ambient temperature decreases). The same is true for breeding adults rearing young compared to birds having no nestlings to care for. The important conclusion here is that habitat conditions and physiological state ultimately govern Cormorant numbers through energetic rules. These energetic constraints limit Cormorants with respect to the potential extraction of prey fish. In typical Cormorant habitat Productivity in Cormorant colonies varies according to the availability of food. the murky water conditions (by Most clutches contain 3–4 eggs (range 2–6) but the number of young that either suspended inorganic matter fledge varies greatly from 0.5–2.7 per nest on average (range 0–4). or algae) prevent the birds from Photo courtesy of Florian Möllers.

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selecting any particular species of water levels and high nutrient loads eutrophic (i.e. nutrient-enriched) fish while foraging in a particular reedbeds are known to retreat as shallow waters. water body. This implies that, on a result of the erosive mechanical a large geographical scale, rare power attacking the stems at the Due to predicted global climate and protected fish species are same point (e.g. Ostendorp et change, the climate window unlikely be threatened by this al. 1995). The man-made lakes that Cormorants operate within predator. Second, when relatively used for water storage, for energy will likely tend to move farther large numbers of Cormorants are supply or recreation, often have northwards. The current shifts in on migration (or making shorter artificial (hard stone or concrete) Cormorant distribution associated movements in search for ice-free or very steep shores without much with this will thus lead ultimately foraging sites) and visiting small vegetation which would serve as to more available space in summer running waters (e.g. in the pre- shelter. In all these cases, fish tend to breed and, perhaps more Alpine region), the fish there may to be more susceptible to predation important, to winter as well. The well be temporally vulnerable to by Cormorants although here, too, present expansion of breeding predation. The amount of available it is unlikely that their populations Cormorants in the is shelter will determine the fishes’ are negatively affected by predation certainly in accordance with this chance of escaping predation in the longer term. scenario. Whether this also holds and could limit any effect at the for southern areas in the Russian population level. Connectivity to The trend to increase the number Federation is not known. Besides other parts of the catchment area of reservoirs over earlier access to, and the availability is also important with respect the past decades has undoubtedly of, a larger breeding area there is to recovery from predation contributed to the wintering site also likely to be an effect of global losses. Generally, fish survival is possibilities of Cormorants. This is change in winter. Milder winters considered to be higher in more especially true for Spain, Portugal will eventually lead to more birds natural water systems but the effect and Italy, but also for Greece and beginning to winter in the same of stocking with naïve stock (both elsewhere in the Mediterranean region as they breed, as suggested particular breeds or individual where these water bodies are strongly by current increased fish), in combination with modified now important foraging waters numbers in the northernmost range habitats and water flows due to for Cormorants. Furthermore, the of the current ‘traditional’ wintering river management will usually lead resulting patches of drowned forest area. Parts of UK, The Netherlands to greater predation effects than in often serve as roosting areas for the and Belgium, northern Germany natural systems. birds in these waters. and deeper water areas in Denmark, Sweden and Poland will probably The role of artificial water bodies By contrast to the situation in thus see increasing Cormorant in relation to the predatory effects winter, when numbers are dispersed numbers in winter. This might also by Cormorants is similar. As fish over large areas, the area of be true for the northerly regions in here are often no longer able to available foraging waters in the the Balkans, Bulgaria and Romania. perform their annual movements, North Sea-Baltic region and the The future use of the Mediterranean (e.g. from rivers to the deeper parts NW parts of the Black Sea should, by Cormorants is also very of lakes, or from lakes to coastal at a European level, be considered interesting in this respect. North areas) they tend to concentrate at core areas for Cormorants. Both Africa (the traditional southern very specific places. This is often coastal, lake and larger river fringe of wintering sinensis birds) the case at weirs, sluices, locks, deltas and lagoon systems are is supposedly not used so much by near dams and other obstacles, present at a density that has no wintering birds anymore. Whether often in the deeper water sections. parallel elsewhere in Europe. It the overall increase in the Nordic The regulation of water levels is in these two ‘mega-regions’ populations of Cormorants will that accompanies the hydraulic that Cormorants breed (and part mean an increase in wintering restructuring of water bodies often of the population also winters) in numbers in this area again is means a degradation of densely large numbers, fully in accordance difficult to predict, although not vegetated natural shores. At fixed with their apparent preference for unlikely.

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13.1.2 Fishes Large numbers of Cormorants across Europe are known to be associated with eutrophic water bodies. After protective measures were taken in most European countries from the 1970s onwards, enhanced fish production, combined with less clear waters, have provided better feeding conditions for Cormorants. Eutrophication is considered a major driver behind the Cormorant’s recovery. The phenomenon of nutrient enrichment is still apparent in large parts of eastern and southern Europe, whereas in western and northern regions there is a reversed pattern of lower nutrients levels due to a strong reduction policy in the 1980s and 1990s. The Cormorants’ range expansion into more easterly and southerly Figure 13.1 Example of algal blooms in the Baltic Sea as depicted by satellite images has thus been facilitated by two taken during summer 2006. More blooms occur in southern and shallow water effects: those of a milder climate areas. Notice also the apparent bloom in the southern part of Lake Peipsi, and that and of greater fish abundance and the southernmost (and most polluted) part (Lake Pskov) has not been included in this availability due to eutrophication. picture (Source SYKE, Helsinki). As an example of the large-scale effect of eutrophication in the the Baltic Sea. The productivity amount of animal productivity. It is Baltic Sea, Figure 13.1 shows of the Baltic has increased at theoretically able to produce even the extent of algal blooms as least two-fold in the last 100 more, and the ‘unused’ primary visible by satellite, with peak years. This is ultimately apparent production may detrimentally affect values appearing in a wide belt in less-clear water, but has had the ecosystem. The timing and in the southern Baltic ranging drastic effects on other parts of species composition of seasonal from Öland all the way east to the ecosystem too. Although algal blooms is resulting in lower Latvia. The blooms in the shallow large cyanobacteria blooms are consumption levels of primary waters in western Estonia and the a natural phenomenon, their production in the food web (see pp. easternmost of the Finnish Gulf present intensity most certainly 147–54 of Wahlström et al, 1996, near St. Petersburg are obvious. In is not. Regardless of the reasons SYKE 2006). In combination with coastal areas these correspond to for increasing productivity in the higher water temperatures, the those regions where Cormorants Baltic Sea, it is impossible to assess increased organic matter content spend the summer months, how this additional production is in the water reduces oxygen levels either breeding or in post-fledge transferred through the food web. on the seabed, and this promotes aggregations. There are no proper estimates of blooms of toxic algae. As a the total biomass of top predators consequence, the water becomes Human influence is most likely (fish, birds and seals) over the more turbid (less clear) and benthic the main reason behind such past century, but the Baltic Sea is organisms receive less light and large-scale ecological changes in certainly able to sustain a large suffer from anoxia (that is periods

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when oxygen content in the water due to consumption by algae during nighttime is near zero), whilst the reduction of benthic filter feeders further increases the production of algal biomass. As a consequence, there is less seaweed and submersed macrophytes and fish populations become simplified. For example, pelagic plankton-feeding fish such as Herring and fish that prey by sight start to disappear from the system. This species shift causes more tolerant prey fish species like Gobies, Butterfish, Eelpout and Cyprinids to increase and, together with turbid water, offers very favourable foraging conditions for Cormorants on a very wide scale.

13.1.3 Human fisheries

Man as commercial fisherman Besides his effect through eutrophication, Man as a commercial fisherman plays Figure 13.2 long-term changes in catches and abundance of different key organisms an overriding role in many in the Baltic (after Österblom et al. 2006) and trophic relationships between cod, ecosystems. Through large-scale sprat and plankton as well as the alternative predators pike and perch (right). The over-fishing of predatory fish Cormorant’s appearance since the mid 1990s runs parallel to that of the reappearance cascading effects result at many of the Grey Seal. lower levels in the food chain. This is a pattern that has been of over-fishing, is highly attractive versus 4.7 years) and are generally observed in many marine, river to Cormorants. smaller than their ancestors (49 cm and lake ecosystems across the compared to 56 cm). The Baltic globe, ranging from China, , The next examples are again was not very rich in fish during the and also Europe (see taken from the Baltic Sea, further first part of the 20th century and, Scheffer et al. 2005). Ultimately demonstrating this area to be an compared to the present situation, this process leads to ever smaller increasingly important one for there were many seals (Phoca prey sizes, a phenomenon known Cormorants. By comparing Cod vitulina, P. hispida and Halichoerus as ‘fishing down the foodweb’ (Gadus morhua) from the grypus) and harbour porpoises (Pauly et al. 1998). As well as the period (5300–3900 BC) with (Phocoena phocoena), regarded dominance of smaller-sized fishes, Cod from contemporary times, as the natural top predators in high fishery pressure also results in researchers have discovered that the the system. Because of perceived a reduction in the reproductive age, species has evolved over a relatively competition with human fisheries, in other words fish stay smaller short period as a result of human these mammals were heavily and tend to reproduce at a younger overexploitation. According to a persecuted during the first half age as a result of the intensive recent scientific paper (Limburg of the 20th century (see Figures fishing. As described elsewhere, an et al. 2008), contemporary Cod 13.2 and 13.3). This and the effect abundance of small fish as a result attain adulthood earlier (3.7 years of eutrophication allowed higher

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productivity levels, which (after numbers of Cormorants seems Cod is the most valuable species II when fishing effort logical in this set of cascading for fisheries and the size of the was relatively low) resulted in large events. As a predator of both the stock has a large impact on stocks of both Herring and Cod, the near-benthic fish community and the economy for commercial cod now being the new top predator of the more pelagic schooling fish fishermen. Despite the advice in the system. species it may likewise have profited from ICES, that a substantially from the disappearance of Cod from decreased Cod fisheries could lead Catches of Herring increased the Baltic system. to improved long-term potential sharply to peak levels in the for catching more fish, politicians 1970s, followed by large catches This type of example is not have not yet had the courage of Cod during the 1980s. Both restricted to the Baltic. In many to take the necessary decisions species decreased as a result of fished ecosystems, that is to say (see Figure 13.4). Preliminary this heavy fishing pressure, and in nearly all large-scale waters, calculations indicate that a few then another pelagic fish, the there are indications that the large years of dramatically reduced sprat (Sprattus sprattus), began to predatory fish species have been fishing could lead to a rapid increase increase in the 1990s. This species over-fished, very often resulting of the Cod stock in this area (Hjerne is a food competitor of the Herring in conditions that are highly & Hansson 2001). From our results and, although of less economic favourable to Cormorants. and synthesis outlined above we importance than it, became heavily predict that the return of Cod would exploited too as a result of the Over-fishing during the 1980s thus mean that Cormorants are faced declining stocks of Herring and contributed to a decrease in the Cod with a less superfluous (small) fish Cod. Although not monitored stock, which has led to a number supply and that this might result in a specifically, the disappearance of the of effects on other components drastic decline in their population. Cod is likely to have had an effect of the Baltic Sea food web — it on the near-benthic fish community is becoming increasingly clear Man as fish farmer now released from predation by that Cod play an important part in Fish farms are artificially managed Cod. The appearance of large the dynamics of this ecosystem. water systems which tend to act

Very probable relationships When the Cod stocks decreases the stock of Sprat grows stronger and bigger and this leads to a decrease of zooplankton.

Probable relationships The decrease of Cod can also lead to a decrease of Perch and Pike because they have to compete with the stock of Sprat that has grown stronger and consumes a lot of food (zooplankton).

Interesting hypotheses When the Cod stocks decrease, the stock of Sprat grows stronger and bigger and this leads to a decrease in zooplankton. This could lead to an increase of which leads to muddy and hypoxic water.

Figure 13.3 Relationships between Cod and other trophic levels in the Baltic Sea. (From Österblom 2009). The abundance of small fish (here Sprat) in all routes is providing favourable food conditions for Cormorants.

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of over 10,000 kg per hectare of Carp occur in some fishponds in Israel. The more fish in the pond, the more susceptible the system is to foraging predators such as Cormorants. The actual predation of fish is not the only problem; also the mere presence of foraging birds and the associated disturbance can cause additional mortality to fish because of the stress it induces.

Man as sports fisherman Historically, angling was purely the exploitation of wild fish stocks, but  for decades anglers have intensively Figure 13.4 over-fishing of Cod in the Baltic in recent times. After the strong decline managed their stocks to enhance in catches the 1980s, ICES advice on catches (green bars) has been consistently lower their sport. As water quality than the politically achieved decision on allowable catches (blue bars), whilst actual has declined and hydrological catches have been higher still (red bars). ‘improvements’ to sections of river have become common practice, the demand for active management as ‘honey pots’ to Cormorants by over time. For example, though has become stronger. The stocking offering high densities of relatively less intensive than during GDR of fish from other water bodies, small fish (very often Carp) kept times, Carp production in Saxony the introduction of non-native in shallow water. Fish density is still intensive and there are species, the release of naïve is almost always higher in these local problems with water quality, ‘fingerlings’ (i.e. juvenile fish) to systems than it is in nearby natural including algae, the disappearance restore stocks are all commonly waters (up to a factor of 10 and of macrophytes, low oxygen applied techniques to increase even up to 100 times greater) and content and increased turbidity. catches and to make waters more water depth is usually less than Similar intensive production attractive for recreational angling. 1.5 m in most cases. Fish farms conditions occur in the larger pond Like fish farms, stocked angling can be used by Cormorants if a complexes in France, the Czech ponds and river sections become breeding colony is nearby but Republic and Poland. When Carp more vulnerable to predation because most fish farms tend to are grown for the consumption as densities of fish, relative to occur in regions without much market, fish farmers generally put adjacent habitats, increase. The use other open water, the number the one-year and two-year-old age of hand-reared fish stock further of breeding Cormorants in the classes to grow in larger ponds at increases the risk of considerable of fish farms tends higher densities. The 0+ (young- loss to predation. This is due to to be relatively low. More often, of-the-year) fish are generally kept the fact that fish reared in captivity Cormorants visit fish farms in late over winter in tanks or small ponds show little or no fear of predators. summer and autumn when the covered with nets. In less intensive As in fish farms, most Cormorant birds are on migration. In many situations like those in Brenne in predation at angling waters occurs places, Cormorants also frequently France, fish are grown over several during migration periods and also visit fish farm areas during the years. Here, the ponds usually in winter. During these periods, winter, especially if the fish farm have more aquatic vegetation birds very frequently switch area consists of many ponds and/ than do other systems and fish feeding location and look for or if larger lake or river systems densities are generally lower as alternative foraging sites and this are nearby. The way farm pond there is no artificial feeding. On is when these systems are most systems are used has developed the other hand, extreme densities commonly visited. Thus in pre-

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Alpine streams, Cormorants may would be treated as a kind of pest will also lead to higher use of local concentrate during periods of frost, species. Not withstanding the costs water bodies in the region of the as a consequence of the freezing of such an enterprise (which have North Sea and Baltic, if the current of their preferred lowland habitat. never been quantified), population pattern of milder winters continues. The effects of Cormorant predation modelling has shown that such a There is thus no reason to believe on fish stocks are generally found strategy would only have limited that there will be a shift towards to be lower in cases where (1) river effect. Given that the potential prey reduced Cormorant predation systems are connected (i.e. they are base for European Cormorants pressure on many of Europe’s more open systems allowing fish in natural waters remains ‘super fisheries in the near future at least. to move freely and to repopulate abundant’ (as is the case for the depleted areas), and (2) habitats majority of waters in Europe), Some stakeholder groups argue are relatively complex and offer the plasticity of the Cormorant strongly that Cormorants are the good cover/refuge for fish, often population is such that measures single most important cause of the deeper sections of rivers with to reduce it will very soon be the economic losses experienced natural shelter in the form of compensated for by increased by many fisheries, regardless of things like boulders and woody birth rates, higher survival and/or whether these be commercial debris or in ponds and small lakes immigration into the ‘population’ fisheries, fish ponds, or recreational with a strong natural growth of being managed. This section angling waters. However, as macrophytes and natural shore explores and synthesizes possible discussed elsewhere, the situation vegetation. solutions to the Cormorant conflict with respect to these different from an ecological perspective. fisheries activities is neither constant nor always sustainable 13.2 Epilogue: towards a Changing worlds but persistent from economic and/or social habits points’ perspectives (see Part Three solution of ‘the Cormorant European legislation and the local of Marzano & Carss, 2012). problem’ from an ecological protection of a species that has perspective? expanded widely in the eastern For example, the economic story part of its European breeding range of a decline in the prospects of the Concerted management activities has caused a significant increase Carp market became very evident to reduce Cormorant numbers in the number of Cormorants. during INTERCAFE’s work. overall have not yet been carried Landscape restoration activities, Customer demand for other fish out across Europe, but are as well as integrated protection species has redirected the market, continually demanded by some schemes such as those under and changing international trade fisheries sectors as the solution Natura 2000, have also greatly relationships have created a different to Europe’s Cormorant problem. improved the environment for perspective for the traditional Such coordinated management Cormorants. In the near future producers. From the ecological between countries and involving this situation will continue and perspective, Carp ponds can be seen the likely culling of many lead to larger populations of as ‘honey pots’ on the birds’ flyways thousands of Cormorants each Cormorants, related for example to and from the main foraging areas. year is certainly, on ecological to the poor environmental state Protection of these pond areas of grounds, considered inadequate of the Baltic. Along the coastal special interest is easier if wetlands to resolve the problem. This is areas of the Baltic States, in of sufficient surface area are because it does not recognise any Sweden, Poland and locally available to the birds as alternative of the causal relationships which in some states in Germany foraging sites when disturbance underly the present European (Mecklenburg-Vorpommern) for actions are undertaken. Cormorant situation. With any example, Cormorant numbers are large-scale culling or shooting likely to increase further. These Today, many commercial fisheries activities directed towards the higher numbers of birds will be face the prospect of over-fishing reduction of the total European increasingly often observed in the and, associated with this, ever Cormorant population, the birds Balkan countries in winter, but stronger regulation in the form of

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catch quotas. The new EU Member The conflict in the ecological stocks of Pikeperch in IJsselmeer) States are still in a position of perspective of the triptych or Sprat and Eelpout Zoarces transition from the original State- The ecological conditions that viviparus as result of diminishing directed system towards a more Cormorants face today appear to Cod stocks in the Baltic). free-market one, with all its many be very favourable for the species’ social and economic problems. good population status. The ‘Fishing down the food chain’ leads Given this socio-economic banning of pesticides, a Europe- to the abundance of smaller fish transition, often associated with wide amelioration of water quality species and a shift in size classes, a lot of tension for the individual and protective status has all had from larger species towards a stakeholders, the confrontation their effect. However, the changes preponderance of smaller species with a relatively recent arriving in the hydrographical conditions and/or individuals. Finally, natural predator as the Cormorant of many rivers and lakes that have the introduction of non-native accellerates the tension (Carss et al. been undertaken over the same species for use in angling waters 2003, Carss & Marzano 2009, see time frame have led to conditions has contributed to unfavourable also Marzano & Carss 2012). where fish populations have limited conditions for many native migratory space compared to earlier species. All these changes lead Like angling, bird watching is conditions. This has had negative to a situation in which the large an outdoor activity which is an consequences for the spawning fish predators (or, still earlier, increasingly popular form of of fish and has ultimately lead mammalian predators like small recreation. Especially in the more to simplified ecosystems where whales, dolphins, and otters) are densely populated parts in Europe fewer fish species are present. As being ‘replaced’ in food webs by wetlands are visited by increasing described above, these less natural avian predators, in this case the numbers of people and Cormorant conditions also offer higher chances Cormorant. The greater ability of colonies or roosts are among the of predation by Cormorants. The this species to move over large sites offering guided excursions eutrophic status that persists locally distances, coupled with higher (e.g. in The Netherlands, Denmark) for many water bodies enforces this reproduction rates, allows these or the opportunities of more effect and, combined with a heavy birds to feed and breed over wide informal visits visiting bird hides pressure from fisheries activities, geographic areas. High Cormorant (e.g. in The Netherlands, France, has lead to a further shift in species numbers are thus an ecological Belgium, Germany, Denmark, composition towards the increase sign of the super-abundance of Sweden, Poland). These activities of commercially non-important small fish prey, a situation which are also becoming an increasingly species (e.g. Ruffe Gymnocephalus under natural conditions prevails important part of local economies cernuus as a result of over-fished in estuaries, lagoons or shallow through the associated transport, accommodation and specialized equipment sectors. Interestingly, this trend is more apparent in densely populated areas than it is in rural ones in Europe where traditional land-use patterns like fish-farming still prevail.

As the European Cormorant population links all these very different social and economic worlds, it is clear that no single Commercial fisheries have a great impact on fish composition in many solution to the conflict is ever likely European waters (species and size distribution shifting towards smaller to be successful, given the fact individuals). Moreover, discards of fish form an attractive prey for many fish- that the perception of the problem eating birds including Cormorants, Lake Markermeer, The Netherlands. differs across Member States. Photo courtesy of Florian Möllers.

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coastal zones and large river ponds, Cormorants operate at a both ends of the geographical scale, sections, but is also the result of ‘global’ scale across Europe and management of basic resources disturbed aquatic ecosystems. beyond. Their geographical range is thus considered vital for any encompasses a vast diversity solution of the current Cormorant The suggestion from all this is that of human social, cultural and problems. Cormorants may be good indicators economic systems. The social and for the environmental state of a economic backgrounds associated For the short term at least, two water systems, rather than the with people’s perceptions of types of conflict cases remain, both ultimate cause of the ecological what is important and acceptable associated with smaller-scale water disturbance to it. Ecological or not in relation to Cormorant- bodies. The first and geographically monitoring of the species fisheries interests is dealt with most widely distributed group (especially numbers, food, status extensively in Marzano & of cases is that of fish farms and distribution) may thus provide Carss (2012). Here we confine (see also Seiche et al. 2012), the valuable information and indicate the discussion to an ecological other related to small upland and any changes in water quality and perspective on the conflict where mountain rivers. Larger numbers effects of fisheries management it is clear that for large-scale open of Cormorants, often migrating programmes. Managing basic water bodies the problems with or moving to and from their core resources in an ecologically Cormorants are mainly related habitat (focused on large-scale sustainable way would seem a far to the improper management of water bodies) can cause problems more viable option than to adopt wild fish populations by Man. with local fisheries. From this large-scale management of the Devising sustainable fisheries investigation, the area of most predators themselves. for the predatory fish species intense reporting of conflicts seems seems the most effective way to coincide more or less with that A regional approach for solving to shift these systems into more part of Europe where large-scale local problems: the European balanced situations. This needs waters are scarce. At a continental Watershed Hypothesis as coordinated action and will, of level this may be seen as the example course, not be simple. The result, ‘European Watershed’, dividing the This work has shown clearly however, will have important coastal Baltic/North Sea/Atlantic the complexity of the ecological consequences on the European river catchments from the Black relationships associated with population of Cormorants and for Sea/Mediterranean. Since historical Cormorants feeding on fish. the systems themselves. As most times, people have tried to manage As ecological conditions and Cormorants in Europe rely on their local fish supply by creating management in different parts these larger-scaled water bodies, fish ponds and using small streams of the species’ range vary consistently applying the principle as a local source of water. On considerably, there is little chance of ‘wise use’ will initially slow their way to their wintering areas, of a single pan-European solution down the population increase and Cormorants pass these watershed that can cope with all these subsequently turn it back to lower areas with a relatively limited differences. Cormorants react to levels. This will be the ultimate area of foraging waters and may differences in food abundance and, task if one is to control Cormorant eventually be present there in large because of their ability to fly large numbers. As a result of lower numbers. distances; they are perhaps better overall Cormorant numbers, fewer able than other predators to detect cases of conflict will also arise Can we use this ‘European areas where fish are abundant, on those river sections, lakes and Watershed Risk Hypothesis’ for either naturally or as a result of small streams which do not have the alleviation of local problems? Man’s actions (i.e. management unnaturally high concentrations of It may well be possible if detailed of wild stocks or commercial/ fish. Natural management, aimed knowledge of timing of bird recreational enterprises). Spanning towards variable habitat structure migration is linked to a temporal the complete range of marine and natural water level fluctuations recording of the development of to freshwater and from large- will allow fish to migrate, spawn weather patterns. Cold weather scale coastal waters to isolated and hide from predators. Clearly, at arriving from the north and tailwinds

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favouring are known needs. The work presented here has favouring the development of as important triggers for bird paved the way to such an approach, natural shores, allowing for migration (Alerstam 1981). As such, setting up the GIS framework naturally fluctuating water a GIS based warning system could and bringing together most of the levels wherever possible and be developed which may direct the biological data that are needed to promoting emergent and incidence of disturbance actions model Cormorant movements/ submerged vegetation used by to be taken against Cormorants. migration in relation to available fish to spawn, grow, and shelter Applying disturbance at a site before resources and such things as weather from predators. commonly used by the arriving birds and climate. ▪▪ Stimulating the communication during autumn and spring migration of information between is probably the most effective Recommendations in short different stakeholder groups, way to avoid settlement of larger From the ecological point of view, the exchange of common groups in a ‘new’ area. The same the main conclusions of this work practice to develop the probably holds for the pre-Alpine can be summarized and several sustainable use of complete lakes and streams at times of frost recommendations offered which are ecosystems which including when nearby still waters at lower considered crucial to the resolution Cormorants and other natural altitude freeze over. Based on GIS of European Cormorant-fisheries top-predators. information, the combination of problems: ▪▪ Developing an ‘early the water charts and the occurrence warning system’ of migratory of sensitive streams and fish-farm ▪▪ Reduction of the continuous Cormorants in risk-sensitive areas could be used to arrive at an over-fishing by man of stocks areas (the so-called EU integrated ‘early warning’ system. of large predatory fish species watershed area). Such an early warning system at sea and in large lakes, by ▪▪ Increasing the protection of system based on on-the-spot promoting the sustainable use of sensitive fish species and sites information has been shown to work fish resources. by netting, acoustic or other at a regional scale in Israel where it ▪▪ Reduction of extensive nutrient measures (see Russell et al. was successfully applied in case of loads that currently still affect 2012). managing conflicts in populations water systems, causing algal ▪▪ Adapting fish stock management of Crane Grus grus and White blooms and leading to simplified in the most vulnerable areas Pelican Pelecanus onocrotalus. This fish communities. by rearing larger-sized fish approach would combine detailed ▪▪ Removal of barriers in rivers and less prone to predation in geographical information and the lakes, thus restoring the aquatic recreational and commercial availability of resources, knowledge connections used by fish. fisheries. of bird migration habits and may ▪▪ Stimulating and restoring more ▪▪ On the spot disturbance or direct local managers to effectively natural conditions in smaller shooting of Cormorants at carry out protective measures. When still waters, avoiding intensive the most vulnerable sites carried out in such a sophisticated management with continuous when other measures fail, in way, the measures are likely to be stocking of non-autochthonous combination with the provision far more effective because they are fish species. of ‘buffer’ areas where the coordinated and timely reactions to ▪▪ Restoring habitat quality species is allowed to forage the birds’ movements and specific in aquatic systems by unmolested.

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REFERENCES USED FOR WATER SYSTEMS DATABASE

Bouchard, P, Chappaz, R, Cavalli, Dalsgaard, A J, Christensen, V, Gwiazda, R. 2006. Foraging L, and Brun, G. 1998. Influence Nicolajsen, H, Koed, A, Støttrup, J, strategies of fish-eating birds in of environmental variables on Grooss, J, Bregnballe, T, Sørensen, conditions of artificial reservoirs the growth of Leuciscus cephalus H-L, Christensen, J T, Nielsen, R. in southern Poland. Studia Naturae (Linnaeus, 1766) in the river 2008. Økosystemmodel for 51: 1–112 (in Polish with English Durance, South-east France. Annls Ringkøbing Fjord. Report 100, DTU. summary). Limnol. 34(2): 193–200. Danmarks Fiskeriundersøgelser, Haunschmid, R. 2009. Bzoma S. 1998. The contribution 2003: Notat vedrørende fiske- Untersuchung der Fischbestände of round goby (Neogobius bestanden i området nord for Fyn. in ausgewählten Salzburger melanostomus Pallas 1811) to Gewässern in Hinsicht auf den the food supply of cormorants Dikov and Živkov. 2004. Einfluss durch Graureiher und (Phalacrocorax carbo Linnaeus Abundance and biomass of fishes Kormoran. Endbericht 2008, 72p. 1758) feeding in the Puck Bay. in the Veleka River, Bulgaria. Folia Bulletin Sea Fisheries Institute 2 Zoologica 53(1): 81–86. Hoffman, E. 1968. En unders- (144): 39–47. øgelse af skrubbens (Plathichthys Đordevicˇ, V, Mikuska, J. 1986. flesus L.) frugtbarhed og gydning, Bzoma S, Goc, M, Brylski, T, Influence of the cormorant on the og den hermed forbundne Stempniewicz, L, and Iliszko, L. culture of fish on the fish farm PIK konditionscyklus. Specialerapport 2003. Seasonal changes and Belje; Ribarstvo Jugoslavije, 41: Danmarks Fiskeriundersøgelser. intra-colony differentation in the 74–76. exploitation of two feeding grounds Honsig-Erlenburg, W, and Friedl, T. by great Cormorants Phalacrocorax Engström, H. 2001. Effects of 1997. Einfluss des Kormorans carbo sinensis at Ka¸ty Rybackie Great Cormorant predation on auf die Fischbestände der mittleren (N. Poland). Vogelwelt 124, Suppl.: fish populations and fishery. PHD Gail (Kärnten). Österreichs 175–181. thesis, Uppsala University, Sweden. Fischerei 50, 113–117.

Campos, F, and Lekuona, Gassner, H, and Wanzenböck, J. Jungwirth, M, Muhar, S, J M. 1994. La población 1999. Hydroakustische Fisch- Zauner, G, Kleeberger, J, invernante de Cormorán Grande bestandserhebungen in vier Salz- and Kucher, T. 1996. Die (Phalacrocorax carbo) en el norte kammergutseen. Österreichs Steirische Enns-Fischfauna und de España y suroeste de Francia. Fischerei 52; 122–128. Gewässermorphologie. Universität Ardeola 41 (1): 13–18. für Bodenkultur, Abteilung Gmitrzuk, K. 2004. Influence of Hydrologie, Fischereiwirtschaft Costa, M J, Vasconcelos, R, Costa, cormorant Phalacrocorax carbo und Aquakultur, Wien 260pp. J L, and Cabral, H N. 2007. on water and forest ecosystems River flow influence on the fish of Wigierski National Park. Parki Kainz, E, and Gollmann, P. 2001. community of the Tagus estuary Narodowe i Rezerwaty Przyrody Beobachtungen über Fisch- (Portugal). Hydrobiologia 587, 23 (1): 129–146 (in Polish with bestandsänderungen in einer 113–123. English summary). Restwasserstrecke ÖF 54, 190–204.

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Limfjordsovervågningen Mathieu, L, and Gerdaux, D. 1998. Nienhuis, J. 1997. Food for Nordjyllands, Viborg og Etude comparee du regime choice of non-breeding Ringkjøbing Amter, 2002: alimentaire du Grand Cormoran cormorants in Matsalu bay Fiskeriundersøgelser med Phalacrocorax carbo sinsensis sur in spring: are cormorants and yngeltrawl på lavt vand i den les lacs Leman, d’Annecy et du smews competitors? Matsalu vestlige Limfjord, 2001. Bourget. Nos Oiseaux 45: 163–171. Looduskaitseala, Loodusvaatlusi 95/96: 33–42. Lorentsen, S-H, Grémillet, D, and Mellin, M. 1990. Preliminary Nymoen, G H. 2004. Annual results of the dissection of Opacˇak, A, Florijancˇic´ T, Horvat, variation in diet of breeding great Cormorants shot in the Mazurian D, Ozimec, S, and Bodakoš, D. cormorants: does it reflect varying Lakeland in spring 1987. Notatki 2004. Diet spectrum of great recruitment of gadoids? Waterbirds Ornitologiczne 31 (1–4): 53–59 (in cormorants at the Donji Miholjac 27, 161–169. Polish with English summary). carp fishponds in Eastern Croatia; Eur. J. Wild. Res. 50: 173–178. Marion, L, and Marion, P. 1984. Mellin, M, and Mirowska-Ibron, I. La nidification du Grand-cormoran 2002. Population trend of great Parz-Gollner, R, and Trautt- Phalacrocorax carbo au lac de Cormorant in the north-eastern mansdorff, J. 2003. Kormoran Grand-Lieu : premier cas d’une part of Poland with respect to — Monitoring Niederösterreich reproduction continentale réussie en fishpond areas. In: Der Kormoran 2001/2002 und 2002/03. Inst. f. France. L’Oiseau & Revue Française (Phalacrocorax carbo) im Wildbiol.u.Jagdwirtschaft, Uni.f. Ornithologie 54: 267–271. Spannugsfeld zwischen Naturschutz Bodenkultur. Auftrag der NÖ und Teichbewirtschaftung 1, Landesreg., 70p + Anhang. Marion, L. 1995. Where two Sachsisxche Landesstiftung Natur species meet: origin, habitat choice und Umwelt: 51–55. Przybysz, J. 1997. Kormoran. and niche segregation of Cormorant Wyd. Lubuskiego Klubu Phalacrocorax c. carbo and Ph. c. ´ Mikuska, J. 1983. Contribution to Przyrodników, Swiebodzin: 108 pp sinensis in the common wintering the knowledge of the feeding habits (in Polish with English summary). area (France), in relation with of the Cormorant in the Kopacˇevski breeding isolation in Europe. Ardea rit Zoological Reservation; Larus Ringkjøbing Amt. 1968. Ring- 83: 103–114. 33–35: 31–36. . købing Fjord. Fiskebestanden 1967. Marion, L. 1998. Comparison Myndighedssamarbejdet mellem between the diet of breeding Ringkjøbing Amt. 1998. Ring- Cormorants Phalacrorocax carbo staten og Limfjordsamterne om fiskeriet i Limfjorden, 2000: købing Fjord. Fiskebestanden sinensis, captures by fisheries and 1997. available fish species: the case of Fiskeundersøgelser i Limfjorden the largest inland colony in France, 1999. Ringkjøbing Amt. 2000a. Ring- at the Lake of Grand-Lieu. Suppl. købing Fjord. Fiskebestanden 1999. Ric. Biol. Selvaggina 26: 313–322. Neves, A, Cabral, H, Figueiredo, I, Sequeira, V, Moura, T, and Gordo, Marion, L. 1999. Le Lac de L S. 2008. Fish assemblage Ringkjøbing Amt. 2000b. Ring- Grand-Lieu. SNPN, Paris: 64p. dynamics in the Tagus and Sado købing Fjord. Fiskeæg og estuaries (Portugal). Cahiers de fiskelarver foråret 2000. Marion, L, Marion, P, Reeber, S, Biologie Marine, 49: 23–35. Carpentier, A, and Pont, Y. 2000. Skarprud, M. 2003. Summer Dynamique de population et impact Nielsen, E, and Bagge, O. 1985. food of great cormorant alimentaire de la colonie de Grands Preliminary investigations of Phalacrocorax carbo in Øra Nature cormorans du Lac de Grand-Lieu. 0-and 1-group plaice surveys in Reserve, Fredrikstad. MSc Thesis, Ministère Environnement, MNHN the Kattegat in the period 1950-84. the Agricultural University of et Univ. Rennes: 73p. DF&H-report No. 268. Norway, ÅS.

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Steiner, V. 1999. Fischökolo- Veber, T. 2001. Kormoranide ja fischökologischen Verhältnisse gische Beweissicherung ENNS, kalanduse vahelised interaktsioonid der Enns, Bereich Liezen bis Stauraumspülung KW Sölk Eesti rannikumeres. Magistritöö. Gstatterboden. Univ.f.Bodenkultur 1999. 1.Zwischenbericht - IST Tartu Ülikool. Wien, Abt. Hydrobiologie, ZUSTAND VOR DER SPÜLUNG- Fischereiwirschaft und Aquakultur. im Auftrag der Steweag/Graz, Wzia¸tek, B, Martyniak, A, Studie im Auftrag des Amt der Volker Steiner — Institut für Szyman´ska, U, Kozłowski, J, and Stmk Landesregierung, 58p. Fischforschung — 6020 Innsbruck. Dostatni, D. 2003. Composition of Great Cormorant Phalacrocorax Zauner, G. 2002. Überprüfung Tomiałójcˇ L, and Stawarczyk, T. carbo sinensis diet in the Dravien des Kormoraneinflusses 2003. The Avifauna of Poland. National Park, NW-Poland. auf die fischereilichen und Distribution, numbers and trends. Vogelwelt 124, Suppl.: 291–295. fischökologischen Verhältnisse der I. PTPP ‘Pro Natura’, Wrocław: Donau in der Wachau. University of 75–79 (in Polish with English Zauner, G. 1999. Untersuchung Natural Resources and Applied Life summary). des Einflusses durch Kormorane Sciences, Vienna. auf die fischereilichen und

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REFERENCES USED FOR OVERVIEW OF STATUS OF CORMORANT IN EUROPE

Boertmann, D, and Mosbech, A. Paquet, Jean-Yves et la centrale van Rijn, S, and Nienhuis, J. 2004. 1997. Breeding distribution and ornithologique aves 2002. Le Aalscholvers op slaapplaatsen in abundance of the great cormorant Développement de l’hivernage dus Nederland in Januari 2003 en 2004. Phalacrocorax carbo carbo in Grand Cormoran (Phalacrocorax Limosa 77: 1–4. Greenland. Polar Research 16 (2): carbo) en Wallonie et à Bruxelles 93–100. entre 1990 et 2003. Aves 39/3–4 Wahl, J, Keller, T, and Sudfeldt, C. (2002). 2004. Distribution and Crowe, O. 2005. Ireland’s numbers of the Great Cormorant Wetlands and their Waterbirds: Røv, N, and Paneva, T D. 2000. Phalacrocorax carbo in Germany Status and Distribution. Birdwatch Great Cormorant Phalacrocorax in January 2003 — results of the Ireland. carbo. S. 30-33 i: Anker-Nilssen, pan-German night roost census. T, Bakken, V, Strøm, H, Golovkin, Vogelwelt 125: 1–10 (2004). Marion, L. 2008. Recensement A N, Bianki, V V, and Tatarinkova, national des Grands Cormorans I P. (red.). The Status of Marine Worden, J, Hall, C, and Cranswick, nicheurs en France en 2006. Alauda Birds Breeding in the Barents P A. 2004. Cormorants 76: 135–146. Sea Region. Norsk Polarinstitutt Phalacrocorax carbo in Great Rapportserie Nr. 113. Norwegian Britain: results of the January 2003 Mavor, R A, Pickerell, G, Heubeck, Polar Institute, Tromsø. roost survey. The Wildfowl and M, and Thompson, K R. 2001. Wetlands Trust, Slimbridge. Seabird numbers and breeding Schifferli, L, Burkhardt, M, and success in Britain and Ireland, Kestenholz, M. 2005. Bestand- 2000. Joint Nature Conservation sentwicklung des Kormorans Committee. Phalacrocorax carbo in der Schweiz 1967-2003. Der Mitchell, P I, Newton, S F, Ornitholgische beobachter 102: Ratcliffe, N, and Dunn, T E. 2004. 81–96. Seabird Populations of Britain and Ireland. Poyser.

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REFERENCES USED FOR GIS AND OTHER WORK

Hijmans, R J, Cameron, S E, of Coastal Lagoon Fisheries and Volponi, S. 1997. Cormorants Parra, J L, Jones, P G, and Jarvis, Aquaculture in Italy. FAO Fisheries wintering in the Po Delta: estimates A. 2005. Very high resolution Technical Paper no. 293. of fish consumption and possible interpolated climate surfaces for impact on aquaculture production. global land areas. International Lilleleht, V. 2006. Kormorani Suppl. Ric. Biol., Selvaggina, Journal of Climatology 25: 1965– levik ja arvukus Eestis 2006. XXVI: 323–332. 1978. Jahinduse alamprogrammi projekti nr. 33 rakendusuuringu aruanne. Ardizzone, G, Cataudella, S, and Tartu 2006. Rossi, R. 1998. Management

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15 APPENDIX: WORK GROUP 1 MEMBERSHIP

The INTERCAFE Work Group 1 of INTERCAFE, the participants other Work Groups also made met and undertook work at each listed below attended some or presentations and contributions to of the stakeholder meetings and all of the Group’s meetings and Work Group 1 meeting, but are not during the between-meeting contributed greatly to them. named individually here. periods. Over the four-year span INTERCAFE participants from

Name Affiliation & country Mennobart van Eerden Institute for Inland Water Management and Waste Water Treatment (RIZA), Netherlands (WG1 Co-chair) Stef van Rijn Institute for Inland Water Management and Waste Water Treatment (RIZA), Netherlands (WG1 Co-chair) Stefano Volponi Instituto Nazionale Fauna Selvatica, Italy (WG1 Co-chair) Zeef Arad Institute of Technology — Technion, Israel Dariborka Barjaktarov Natural History Museum, , Serbia Janis Baumanis† Institute of Biology, Latvia Thomas Bregnballe National Environment Research Institute, Denmark Szymon Bzoma Sea Fisheries Institute, Gdynia, Poland Henri Engström University of Uppsala, Sweden Manfred Enstipp Centre for Ecological and Physiological Energetics, Strasbourg, France Marijan Govedic Centre for Cartography of Fauna and Flora, Ljubljana, Slovenia Federal Agency for Water Management, Institute for Water Ecology Fisheries and Lake Reinhard Haunschmid Research, Austria Mikael Kilpi ARONIA Environment, Åbo Akademi University & Sydväst Polytech, Finland Emmanuil Koutrakis Fisheries Research Institute, Greece Vilju Lillileht Estonian Agricultural University, Tartu, Estonia Svein-Håkon Lorentsen Norwegian Institute for Nature Research (NINA), Norway Loïc Marion University of Rennes, France Karlis Millers Institute of Biology, Latvia Ivailo Nikolov BALKANI Wildlife Society, Jean-Yves Paquet Central Ornithologique Aves, Belgium Josef Ridzon Society for the Protection of Birds in Slovakia, Bratislava, Slovakia Josef Trauttmansdorff Otto Koenig Institute, Stockerau, Austria Catarina Vinagre University of Lisbon, Portugal Ian Winfield NERC Centre for Ecology & Hydrology, Lancaster, UK

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COST — the acronym for European Cooperation in implementation and light management of the research Science and Technology — is the oldest and widest initiatives) are the main characteristics of COST. European intergovernmental network for cooperation in research. Established by the Ministerial Conference in As a precursor of advanced, multidisciplinary research November 1971, COST is presently used by the scientific COST has a very important role for the realisation communities of 35 European countries to cooperate in of the European Research Area (ERA) anticipating common research projects supported by national funds. and complementing the activities of the Framework Programmes, constituting a ‘bridge’ towards the The funds provided by COST — less than 1% of scientific communities of emerging countries, the total value of the projects — support the COST increasing the mobility of researchers across Europe cooperation networks (COST Actions) through which, and fostering the establishment of ‘Networks of with EUR 30 million per year, more than 30,000 Excellence’ in many key scientific domains such as: European scientists are involved in research having a Biomedicine and Molecular Biosciences; Food and total value which exceeds EUR 2 billion per year. This Agriculture; Forests, their Products and Services; is the financial worth of the European added value Materials, Physical and Nanosciences; Chemistry and which COST achieves. Molecular Sciences and Technologies; Earth System Science and Environmental Management; Information A ‘bottom up approach’ (the initiative of launching and Communication Technologies; Transport and a COST Action comes from the European scientists Urban Development; Individuals, Societies, Cultures themselves), ‘à la carte participation’ (only countries and Health. It covers basic and more applied research interested in the Action participate), ‘equality of and also addresses issues of pre-normative nature or of access’ (participation is open also to the scientific societal importance. communities of countries not belonging to the European Union) and ‘flexible structure’ (easy Web: http://www.cost.eu

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© COST Office, 2012 Legal notice by COST Office No permission to reproduce or utilise the contents of this book by Neither the COST Office nor any means is necessary, other than any person acting on its behalf in the case of images, diagrams or is responsible for the use which other material from other copyright might be made of the information holders. In such cases, permission contained in this publication. The of the copyright holders is required. COST Office is not responsible for This book may be cited as COST the external websites referred to in Action number — title of the this publication. publication.

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Short Title: COST Action 635 Final Report I

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ISBN 978-1-906698-07-2

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