The INTERCAFE Cormorant Management Toolbox
Methods for reducing Cormorant problems at European fisheries Photographs — Shutterstock
The INTERCAFE Cormorant Management Toolbox
Methods for reducing Cormorant problems at European fisheries Photographs — Shutterstock
Ian Russell, Bruno Broughton, Thomas Keller and Dave Carss the intercafe cormorant management toolbox
ACKNOWLEDGMENTS
This publication has been Miha Janc, Verena Keller, Manos During the drafting process, the produced by INTERCAFE’s Work Koutrakis, Loïc Marion, Petr Musil, Toolbox was reviewed by the Group 2, the ‘Conflict Resolution Simon Nemtzov, Erik Petersson, Work Group and was also made and Management’ group, which Henrik Lykke Sørensen, Tamir available to all INTERCAFE comprised 22 researchers from 17 Strod, Stefano Volponi and Ian participants for comment and countries across Europe and beyond Winfield. Helpful comments and correction. Numerous participants (for details of WG2 participants, corrections on various drafts from INTERCAFE’s other two please see Appendix). were provided by the above Work Groups made presentations and also by: Zeev Arad, Timo and contributions to the Conflict This publication was drafted by Asanti, Redik Eschbaum, Robert Resolution and Management group Ian Russell, Bruno Broughton and Gwiazda, Reinhard Haunschmid, meetings, and these meetings were Thomas Keller with substantial Scott Jones, Botond Kiss, Vilju also informed on occasions by editorial input and help from Dave Lilleleht, Oleg Nemenonok, Kareen discussions with invited experts Carss. Specific sections of text, Seiche and Josef Trauttmansdorff. and local stakeholders. Wherever figures and Case Studies were A number of people also kindly appropriate, information from these provided by: Michal Adamec, provided photographs for inclusion sources has also been incorporated Thomas Bregnballe, Henri and individual sources are into the Toolbox. Engström, Marijan Govedic, acknowledged under each picture.
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CONTENTS
1 PREFACE 5 4.4.5 Overview of habitat modification techniques 52 2 INTRODUCTION 7 4.5 Killing Cormorants — Lethal Measures 53 4.5.1 Reducing reproductive success 54 3 EUROPEAN CORMORANT MANAGEMENT 4.5.2 Shooting — at a site-specific or local TOOLBOX 8 level 57 3.1 Background And Some Words Of Caution 8 4.5.3 Shooting — coordinated culling for 3.2 What Is The Toolbox? 9 population control 59 3.3 What Does The Toolbox Contain? 9 4.5.4 Recent information on lethal actions 3.4 Legal Issues 9 against cormorants in Europe 61 3.5 Is A Particular Tool Suitable For Me? 9 4.5.5 Overview of lethal measures 61 3.6 How Do I Use The Toolbox? 10
4 CORMORANT MANAGEMENT TOOLS 12 5 FINANCIAL COMPENSATION 64 4.1 Scaring Cormorants Away From A Fishery 12 4.1.1 Auditory deterrents 12 6 CASE STUDIES 66 4.1.2 Visual deterrents 21 6.1 Case Study No. 1. Greece — Local use of 4.1.3 Chemical deterrents 30 visual/auditory deterrents to protect fishing 4.2 Protecting The Fish — Exclusion Techniques 31 sites on Lake Kerkini 66 4.2.1 Netting enclosures 31 6.2 Case Study No. 2. UK (England & Wales) 4.2.2 Using ‘wires’ 36 — Protecting a locally endangered species 4.2.3 Floating plastic balls 39 involving management of a cormorant 4.2.4 Facility design and construction 39 breeding colony 66 4.2.5 Overview of exclusion techniques 40 6.3 Case Study No. 3. Slovenia — An example 4.3 Reducing Fish Availability To Cormorants of collaborative shooting to protect a river — Fish Stock Management Techniques 40 fishery 67 4.3.1 Timing of stocking 41 6.4 Case Study No. 4. Germany — Wires over 4.3.2 Frequency and location of stocking 41 Carp ponds 69 4.3.3 Regulating fish density 41 6.5 Case Study No. 5. Greece — Netting 4.3.4 Size at stocking 42 enclosures to protect over-winter fish 4.3.5 Species vulnerability 43 holding facilities 69 4.3.6 ‘Buffer’ species 44 6.6 Case Study No. 6. Sweden — Fishery 4.3.7 Location of fish-holding facilities 44 management measures to improve fishery 4.3.8 Overview of fish stock management performance on two large lakes in the techniques 45 presence of cormorants 70 4.4 Reducing Fish Availability To Cormorants 6.7 Case Study No. 7. Israel — Coordinated — Habitat Modification Techniques 45 cormorant management on a relatively large 4.4.1 Elimination of resting or roosting scale in the Hula Valley 72 places 46 6.8 Case Study No 8. Germany, Bavaria — 4.4.2 Elimination of nests 47 relatively large-scale lethal techniques as 4.4.3 Improving habitat quality for fish 47 examples of cormorant population control 4.4.4 Artificial fish refuges 48 in practice 73
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6.9 Case Study No. 9. France — Large-scale shooting of wintering cormorants 74 6.10 Case Study No. 10. Czech Republic — Shooting to control population growth and expansion 75 6.11 Case Study No. 11. Switzerland — National cormorant management plan — scaring birds and preventing colonisation 76 6.12 Case Study No. 12. Denmark — National cormorant management plan — local actions and reduction of breeding output 78
7 SUMMARY OF MANAGEMENT MEASURES 81
8 FURTHER INFORMATION 85
APPENDIX: WORK GROUP 2 MEMBERSHIP 86
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1 PREFACE
This publication is supported by cormorant-fisheries interactions in countries in continental Europe COST. It is one of the outputs the context of the interdisciplinary (Georgia, Norway, Serbia) and the of the INTERCAFE COST management of human-wildlife Middle East (Israel). In addition Action (635). COST (European conflicts at local to international to these 28 countries, Ukraine and Cooperation in Science and levels across Europe. It also Croatia were also associated with Technology) is the longest-running aimed at delivering a coordinated the Action. INTERCAFE held intergovernmental network for information exchange system a series of eight meetings, each cooperation in research across and improved communication themed around a topic particularly Europe. between stakeholders. To this relevant to the host country: end, INTERCAFE attempted to INTERCAFE — ‘Conserving address: 1. Gdansk, Poland, April biodiversity: interdisciplinary 2005 — ‘Cormorant ecology, initiative to reduce pan-European i. the fundamental distrust between commercial fishing and cormorant-fishery conflicts’ — was the main stakeholder groups stakeholder interaction’ awarded funding for four years which was compounded by the 2. Saxony, Germany, September (2004–2008). COST Actions are disparate and uncoordinated 2005 — ‘Commercial carp charged with directing European nature of available sources of aquaculture’ science and do not pay for information; 3. Hula Valley, Israel, January researchers’ time. Instead, funding ii. the necessity of applying an 2006 — ‘Cormorant-fishery was available for INTERCAFE integrated interdisciplinary conflict management in the Hula to organise and run a series of research approach (biological, Valley, Israel’ international meetings, drawing social, legal) to cormorant- 4. Bohinj, Slovenia, October together researchers from a fishery conflicts (as these are 2006 — ‘Angling and EU number of disciplines (bird- as much a matter of human legislation’ related and broader ecology, interests as they are of biology 5. Hanko, Finland, April 2007 fisheries science and management, or ecology), thus recognising — ‘What to do when the sociology, social anthropology the need for different cormorant comes’ and international law) and other perspectives in the development 6. Po Delta, Italy, September 2007 experts (very often connected of collaborative strategies, and — ‘Extensive aquaculture with fisheries production, harvest iii. the lack of an integrated systems and relationships and management, or to regional/ understanding of the between stakeholder perspectives national policy and decision- interdisciplinary factors at the and different spatial and making). Under INTERCAFE’s heart of cormorant-fisheries institutional levels’ coordination, interested parties, conflicts that precludes the 7. South Bohemia, Czech Republic, from local stakeholders to provision of useful and practical April 2008 — ‘Management international policy-makers, were information and advice to all practices in a complex habitat thus offered a unique opportunity interested/affected parties. mosaic and at local, regional to address European cormorant- and national levels’ fisheries issues. The INTERCAFE network 8. Paris, France, September 2008 comprised almost seventy — ‘The management of The main objective of researchers from 24 EU Member cormorant-fisheries conflicts in INTERCAFE was to improve States (all except Luxemburg, France and the wider European European scientific knowledge of Malta and Spain) and other context’
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At each meeting, INTERCAFE overview of European cormorant- ▪▪ Essential social, cultural and participants worked in one of three fishery conflicts and associated legal perspectives on cormorant- Work Groups, covering the broad issues, which is as comprehensive fisheries conflicts. aims of the Action: as possible given the budgetary (ISBN 978-1-906698-11-9) and time constraints on all of ▪▪ Work Group One — Ecological INTERCAFE’s participants. Highlights from these publications Databases and Analyses are available in INTERCAFE: an ▪▪ Work Group Two — Conflict The INTERCAFE publications Integrated synthesis (ISBN 978-1- Resolution and Management are: 906698-06-5) and also from ▪▪ Work Group Three — Linking http://www.intercafeproject.net Science with Policy and Best ▪▪ Cormorants and the European Practice Environment: exploring Drawing on INTERCAFE’s cormorant status and distribution privileged opportunity to see and Most meetings included a field on a continental scale. hear about cormorant-fishery visit to allow participants to see (ISBN 978-1-906698-07-2) issues across Europe and beyond, cormorant-fishery conflicts at ▪▪ The INTERCAFE Field the INTERCAFE European first-hand. In addition, wherever Manual: research methods for Cormorant Management Toolbox possible the INTERCAFE cormorants, fishes, and the aims to explore the diverse range budget was also used to invite interactions between them. of mitigation techniques currently appropriate local, regional, (ISBN 978-1-906698-08-9) available. It is hoped that this national or international experts ▪▪ The INTERCAFE European exchange of information will to these meetings. Through these Cormorant Management help to reduce cormorant-fishery discussions and interactions, Toolbox: methods for reducing interactions where cormorant INTERCAFE participants tried to cormorant problems at European predation is a concern. The Toolbox understand the diverse cormorant- fisheries. is intended to provide fishery fishery conflicts in Europe and (ISBN 978-1-906698-09-6) managers and owners with the beyond. ▪▪ Cormorant-fisheries conflicts basis to experiment and devise at Carp ponds in Europe and specific mitigation techniques or This publication is one of a series Israel: an INTERCAFE programmes tailored to suit their of INTERCAFE outputs aimed overview. individual needs. at providing readers with an (ISBN 978-1-906698-10-2)
Photograph — Shutterstock
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2 INTRODUCTION
Large increases in Great Cormorant fisheries and aquaculture with fisheries will not resolve (Phalacrocorax carbo) populations sites as a consequence of themselves. have occurred across Europe over stocking, nutrient enrichment the past 30–40 years, and this has (eutrophication) processes and/ This Toolbox is intended to help resulted in widespread conflicts or changes in fish species/size guide those who seek to reduce with commercial and recreational composition; cormorant predation problems fishery interests in freshwater, ▪▪ a wider range of suitable by, for the first time, presenting estuarine and coastal habitats. habitats for cormorants to an authoritative, accurate and Indeed, the pan-European increase breed, roost and feed, including useable guide to the management in Great Cormorant numbers is flooded, man-made gravel techniques available and the most mirrored by equally dramatic pits and quarries; new water suitable techniques to employ rises in other parts of the world, supply reservoirs; regulated at different sites. Although the such as the increase in numbers rivers; nature reserves; newly- Toolbox focuses on management of the Double-crested Cormorant constructed stillwater fisheries. of cormorant conflicts related to (Phalacrocorax auritus) in North the Great Cormorant, many of the America. Although cormorant It is readily evident from this that techniques are equally applicable biology and ecology have been the cormorants will not disappear to other cormorant species, subject of considerable scientific ‘naturally’ at current levels of including the Pygmy Cormorant research, understanding the food supply and that conflicts (Phalacrocorax pygmeus). interactions between cormorants and fish and fisheries has remained problematic. This is inevitable ‘Under no circumstances should it be given the inherent difficulties in obtaining sound, quantitative assumed that because a particular information on fish stocks, particularly in large bodies of technique is described in this Toolbox, water. The consensus of scientific opinion on why cormorant numbers it can be used legally in a specific have risen so quickly centres on a country or region. You MUST check few key factors, namely: the legal position before proceeding ▪▪ more stringent controls, or prohibition, of indiscriminate to apply any technique at a particular shooting, as well as enhanced protection afforded to place or time. Your national or regional cormorants and cormorant authorities should be consulted; breeding sites; ▪▪ greater availability of suitable additional guidance is also available prey fish at many sites, especially in recreational from the European Commission’
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3 EUROPEAN CORMORANT MANAGEMENT TOOLBOX
3.1 Background And Some areas — for example, due to an individual site basis or as part of Words Of Caution weather patterns and climate. a coordinated cormorant cull. The notion that ‘one dead cormorant Across Europe there are These are all important issues is one less that will feed on fish’ considerable variations in when considering suitable deterrent is understandable, but the birds’ cormorant population sizes, measures, and they are likely to population dynamics and behaviour breeding and wintering play a key part in determining mean that actual situations tend to aggregations, and migration the efficacy of any particular be far more complex. Cormorants patterns. Hence, problems occur technique at a particular site. It is are attracted to, and will always at different times of the year also clear that there is no single attempt to exploit, the best feeding and concern both wintering and solution — deterrents may work sites, and these will often coincide breeding birds. Scientifically, at some sites or in some situations with those that are most valued by the population dynamics of the but not at others, and this makes recreational anglers, commercial birds are complex. Moreover, it very difficult to generalise. fishermen or fish farmers. Because there is a diverse range of fishery These potential constraints need of the mobility of cormorants, interests affected by cormorant to be recognised and taken into killing birds at such prime sites depredation across Europe in account when applying cormorant commonly creates opportunities freshwater, brackish and marine management tools. for new birds to replace those that habitats, affecting commercial have been killed, a process that can fisheries, fish farms (intensive It should also be remembered that occur within days at some sites and and extensive), recreational predation on fish by cormorants months at others, depending on the angling, and natural or semi- and other fish-eating birds, and time of culling and other factors. natural habitats. On occasions, predation by fish on other animals, Even where large, organised cormorants may also pose a is a normal part of the natural cormorant culls take place each potential threat to the status of interactions that occur between year, bird numbers often recover rare or endangered fish species. species in aquatic habitats. It is also quickly as replacements move in, true that the numbers of predators particularly at sites that are on The efficacy of control measures are typically closely linked to, established cormorant migration will therefore depend on many and governed by, the availability routes. Such cases highlight the fact factors, including whether birds of suitable prey species. In the that killing birds may not provide are sedentary or migrating (i.e. the absence of good access and ample the ready solution to cormorant levels of site fidelity — whether prey, predator numbers will fall. conflicts that is often imagined. local populations are ‘open’ This ‘density-dependent’ regulation or ‘closed’); the proximity of of cormorant numbers underpins It must be emphasised that alternative foraging sites; the the usefulness of many of the cormorant-fishery conflicts are numbers of birds and food resources methods described in this Toolbox. not simple. Studies have also in the area; the features of specific confirmed that the mere presence of sites, particularly the size or area of To some, the resolution of conflicts cormorants at a site may not indicate water; and inter-annual variations lies in the supposed effectiveness that there is a serious problem. in cormorant numbers in particular of shooting to kill cormorants on While the birds can seriously
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deplete stocks at some sites, their at different sites, and all of them be recognised and taken into impact elsewhere can be relatively have worked at some time in some account when applying any of the minor. The purpose of this document places. Emphasis is placed on the techniques described here. Under no is to provide some practical advice most effective tools, with detailed circumstances should it be assumed on the options available for those descriptions of these techniques. that because a particular technique is who may want to deter cormorants Where appropriate, photographs described in this Toolbox, it can be from visiting a site, or reduce the and Case Studies have also been used legally in a specific country or birds’ impact on resident fish stocks. included by way of illustration. region. You MUST check the legal The Toolbox covers: (a) a range position before proceeding to apply of cormorant deterrent techniques any technique at a particular place (auditory, visual and chemical), 3.4 Legal Issues or time. Your national or regional (b) options for excluding birds, authorities should be consulted and the modification of the habitat The Toolbox includes both lethal will be able to advise you further. or management of fish stocks in and non-lethal techniques and Additional guidance is also available order to minimise interaction with discusses the main advantages from the European Commission the birds, and (c) the use of lethal and constraints surrounding their in respect of applying derogations control measures. use. However, it is important to under Article 9 of the Birds Directive. remember that cormorants are Some further information on legal afforded protection under the and ethical issues is provided 3.2 What Is The Toolbox? Wild Birds Directive 79/409EEC, in INTERCAFE’s publication and in most countries additional ‘Essential Social, Economic and legal This Management Toolbox reviews cormorant protection legislation Perspectives on Cormorant-fisheries and assesses those techniques that applies. Conflicts’. have been employed for managing cormorant-fishery conflicts. Any In different countries and/or particular technique (or ‘tool’) may regions, further legislative controls 3.5 Is A Particular Tool be applicable at different stages of may also constrain what techniques Suitable For Me? the annual-cycle of the birds (e.g. are permissible for controlling breeding or over-wintering) and at a birds. Typically, these regulations For each main technique or group variety of scales — for example, to cover issues such as: of similar ones, the descriptive text protect a single pond, a particular, provided is followed by a general defined habitat or a commercial ▪▪ Techniques and the personnel evaluation in terms of a tool’s: fishery along a section of coast, or to permitted to use them deter birds from a larger, ‘sensitive’ ▪▪ Location ▪▪ Efficacy — including its area of water. ▪▪ Protected and special areas longevity ▪▪ Target and non-target species ▪▪ Practicability — how easy (or ▪▪ Timing otherwise) it is to apply the 3.3 What Does The Toolbox ▪▪ Breeding periods technique Contain? ▪▪ Nests and roosts ▪▪ Cost — some tools are not ▪▪ Proximity to fish or fishing gear expensive, while others may The Toolbox includes information ▪▪ Monitoring of results and incur considerable costs on techniques that have proved reporting ▪▪ Acceptability — for example, to be successful in managing there may be aspects of the cormorant conflicts in at least No attempt is made to detail method that disturb others or some contexts. It also describes the various regional, national or compromise nature conservation techniques that may have only international regulations in the limited, short-term benefit. Toolbox or to consider possible This evaluation is based on The aim has been to provide as ethical issues such as when and published information and comprehensive a list as possible of where lethal measures might discussions with stakeholders options that might be applicable be applied, but they need to and other experts involved in the
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INTERCAFE COST Action. It also builds on a similar evaluation ‘Protecting a fishery from cormorants that was included in the earlier is very often not easy, and sometimes it REDCAFE report (available from: http://www.intercafeproject.net/pdf/ may be impossible’ REDCAFEFINALREPORT.pdf).
The aim of the Toolbox is to area — for example at netting or international legislation on the provide as objective an overview stations, migration bottlenecks or use (or otherwise) of particular as possible of the effectiveness of aggregations of fish at spawning techniques. specific cormorant management sites. Furthermore, since deterrents techniques. However, it must be may often be most effective when Many of the techniques available remembered that techniques to used in combination, it is not the work by persuading cormorants to reduce cormorant predation at intention of this Toolbox to narrow leave one particular feeding site fisheries can be site-specific and down potential options for users and move elsewhere. The birds’ variable. by guiding them to specific tools. ‘willingness’ to move somewhere Rather, the aim is to provide users else will depend on both the with a number of options that might severity of the persuasion to 3.6 How Do I Use The be applicable for particular sectors leave a site, but also, and perhaps Toolbox? or situations. most importantly, on the relative attractiveness of alternative Cormorant-fishery conflicts affect Thus, this Toolbox is not merely feeding sites in the area. Thus, the different fishery sectors (including a list of recipes that, if followed, effective deployment of mitigation aquaculture, commercial fisheries will instantly solve any particular techniques at a specific location and recreational or ‘angling’ problem that cormorants are may depend on a good knowledge fisheries) across a broad spectrum causing at a fishery. Indeed, there of a much wider area. of natural and man-made aquatic appear to be no easy solutions to the habitats. However, a range of diverse problems that cormorants Given these undoubted factors will influence the efficiency are thought to cause. Protecting complexities, it is perhaps not of any particular technique at an a fishery from cormorants is very surprising that no magic solution individual site, and this makes often not easy, and sometimes it exists for reducing cormorant it impossible to provide specific may be impossible. predation at fisheries. The use recommendations for different of deterrents or other mitigation sectors or habitats. The effective use of mitigation techniques is thus an issue that techniques will also require individual fishery owners or One of the key factors affecting consideration of: (1) the time managers will need to address. It is whether a technique is successful that can be devoted to deploying hoped that the range of techniques or not will clearly be the size of them; (2) the size of the problem described in this Toolbox (Figure 1) the site that one wants to protect, (including the time of year, will help such people to experiment and this will inevitably constrain numbers of birds, and type and with different techniques and allow the use of certain tools. However, size of fishery); (3) the behaviour them to be creative in devising even at very large sites, localised of cormorants; (4) the associated mitigation programmes that can deterrents may have some role costs (outlay versus losses); better protect their stocks from to play in protecting sensitive and — often — (5) local, national cormorant predation.
[10] the intercafe cormorant management toolbox This illustrates the main fishery sectors and the habitat types affected by cormorants This illustrates the main fishery sectors and habitat types affected . Guide to navigating the Toolbox
Figure 1 Figure the techniques most likely to be useful in any particular context are where and guides users to the subsequent sections of Toolbox, indicates a tool that might be useful under certain conditions although it is largely untested in practice. described. The dotted arrow
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4 CORMORANT MANAGEMENT TOOLS
Limiting the interaction between 4.1 Scaring Cormorants Away combination. If these deterrents are cormorants and fish can be From A Fishery used in conjunction with highly- achieved in a number of ways, visible human presence, this will each falling into one of four broad The basic philosophy behind increase their overall efficacy but categories of action: techniques to scare birds away may reduce their cost-effectiveness. from a fishery is that cormorants As with many other techniques, 1. Scaring cormorants away from a are startled sufficiently to move to it seems best to operate these fishery. another foraging site by means of deterrents before or as soon as birds 2. Protecting the fish — by auditory, visual or even chemical arrive at a site — thus preventing preventing cormorants from deterrents. Clearly, the effectiveness them from getting used to the area reaching them. of these techniques relies on: (1) as a foraging site in the first place. 3. Altering fish availability to the deterrents being sufficiently Once birds have learned that a site cormorants — by making frightening to cormorants to make is good for foraging or breeding, it a fishery less attractive as a them move elsewhere; and (2) there will be much harder to deter them foraging site. being a ‘better’ alternative site for from coming to it. 4. Reducing overall cormorant them to move to. numbers — for example, by 4.1.1 Auditory deterrents killing cormorants locally to The main drawback of these reinforce scaring at specific techniques is that cormorants A number of commercially sites, killing them more eventually (often quite quickly) produced noise-generating bird intensively, or reducing their realise that they offer no real threat scarers are available — for example, reproductive efficiency. and the birds become ‘habituated’ through local agricultural suppliers. to the noises, sights or smells, These vary considerably in their In addition, under some ignoring them thereafter. However, price and complexity, from simple circumstances cormorant-fishery there is good evidence that birds humming tapes to relatively conflicts can be addressed through are scared consistently by human sophisticated, automatic devices the use of financial or other presence if they perceive that such as gas cannons. A general compensation measures. humans are associated with danger. consideration with all these devices Where this is not the case, the is noise nuisance, and any national The Toolbox aims to summarise birds can sometimes be approached and local controls on their use must information on each category of at close quarters and show no be taken into account. action with regard to the methods apparent fear of man. available, their efficacy, the 4.1.1.1 Gas cannons constraints on their deployment The key to the successful use of Gas cannons are deterrent devices or use, and the relative costs. auditory and/or visual deterrents that produce loud banging noises The aim is to provide a broad seems to be to make them as by igniting a mixture of gas (either overview of the effectiveness of unpredictable as possible by acetylene or propane) and air different management options for changing their location and under pressure. The frequency of different cormorant-fishery conflict frequency of use, and by using detonation can be regulated by situations. a number of techniques in adjusting the gas feed or with an
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Gas cannon. Photo courtesy of Thomas Keller. automatic timing device. Most produced by a cannon is similar to migrating fish such as Atlantic cannons produce a single bang at the noise of a shotgun and causes a Salmon (Salmo salar) smolts, or pre-set, timed or random intervals, startle reflex, thus prompting birds in the vicinity of obstructions or but some devices can produce in the vicinity to take flight. Their barriers in rivers that may cause double or triple bangs, and rotators efficacy is reportedly heightened fish to congregate and hence are available so that the noise can where birds have had prior increase their vulnerability to be aimed in different directions. experience of shooting to kill. predation. Some are regulated by computer to produce a random length of the Gas cannons are widely used The effectiveness of gas cannons volley and with random intervals throughout Europe at aquaculture depends on how they are used, the between volleys, or they may facilities and to protect inland size of the site to be ‘protected’, incorporate light detectors to allow fisheries, particularly at smaller and the availability of alternative the device to be turned off at night. sites. They have also been feeding areas for the birds close deployed at specific locations by. Local conditions, such as A gas cannon is relatively or for particular times at larger wind direction and strength, can expensive and prices vary, sites — for example, to protect also affect the intensity of noise. depending on whether it is fishing gear (e.g. fixed nets), or Cannons are more cost effective electronic or mechanically ignited; to restrict local damage for short, at smaller fishery sites, and the whether it is a single, double or highly sensitive periods. These cost of sufficient numbers to cover multi-bang device; and whether might include the draining and a large area may be prohibitive. features such as a rotator or harvesting of Common Carp Researchers have suggested that mechanical or electronic timer (Cyprinus carpio) ponds, during one cannon can protect 1.3–2.0 ha are fitted. The unexpected noise aggregations of breeding or at aquaculture facilities, if
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‘A cannon firing repeatedly without any variation in timing or direction quickly loses its potential to scare birds’ Vehicle-mounted gas cannon. Photo courtesy of Thomas Keller. reinforced with other techniques. The general consensus of opinion is away by it, especially if they have A survey of catfish(Ictalurus that gas cannons are most effective no experience of shooting to kill. spp.) farmers in the USA indicated when moved every few days, have A cannon firing repeatedly without varying levels of satisfaction with variable firing intervals and are any variation in timing or direction the use of gas cannons to deter deployed in combination with other quickly loses its potential to scare Double-crested Cormorants: scaring techniques. For example, birds. In such circumstances, around 10% of respondents felt placing a cannon in a hide used by cormorants have even been they were ‘highly effective’ and shooters, and frequently moving reported to use gas cannons as about half found them ‘somewhat it between hides, may prolong the perches. Although cannons can be effective’; others regarded them as scaring effects of both the shooting effective if the firing frequency and ‘ineffective’. and the cannon. Gas cannons direction are varied, these scarers employed at fish-rearing ponds in may be socially unacceptable near A simple field experiment carried Israel have also been mounted on residential areas due to public out in the Czech Republic recorded wheeled carriages or on vehicles to concern about noise nuisance, the reactions of cormorants to make them highly mobile, where especially if left to fire at night. the firing of a gas gun. A number their effectiveness is reinforced However, pointing cannons away of cormorant responses were by human presence and shooting. from houses and constructing recorded: (a) no reaction; (b) taking Products are also available that simple straw baffles around them fright; (c) diving; (d) soaring and combine visual and acoustic stimuli allows the devices to be placed at circling; and (e) flying out of the to scare birds — the ‘Rotating approximately half the distance pond. These were found to be Hunter’ consists of two propane of cannons without baffles, with correlated with the distance of the cannons and the metal silhouette of no increase in noise nuisance. As birds from the gas gun. Typically, a person that swivels with the force sounds tend to be heard at greater birds up to 300 m away displayed of each bang. distance at night, gas cannons near an active response (e.g. soaring and human settlements should be turned circling, flying out of the pond), The main reason for cannons off or programmed to stop at night, suggesting that this method would losing their effectiveness is unless Night Herons (Nycticorax be particularly effective on smaller habituation — birds get used to nycticorax) or other nocturnal birds fish ponds. the noise and are no longer scared are also a problem.
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Gas cannons may also have an crackers, screamer shells, whistling also require little manpower — undesirable effect on other wildlife and exploding projectiles, bird these are simply lengths of slow (e.g. birds and mammals) and bangers, flash/detonation cartridges burning fuse with bangers inserted humans (e.g. fishermen or fish farm and flares. These can be fired from at intervals to produce a series of workers), and they may also need modified pistols (with a range of loud explosions at approximately to be located in secure locations approximately 25 m) or shotguns 20-minute intervals. Placing them to guard against theft. One must (range of 45–90 m) and can produce inside clean, empty oils drums also be aware that the cannon noise noise levels of up to 160dB. As the can enhance the noise of the may be mistaken for gunshots, direction and intensity of firing can explosions, but particular care is and it would be prudent to inform be controlled to suit the bird species needed to ensure this is done safely. the police, wildlife rangers and, and location, an advantage of this Weather conditions can affect the in some countries where they may technique is that deterrence can be burning speed of the rope and there be deployed near national borders, targeted and disturbance of non- is also a danger of creating a fire the military about their presence. It target species minimised. Be aware hazard. As with all pyrotechnics, may also be wise to advertise the that both the cartridges and the gun great care must be taken with their use of such equipment widely to require a firearms certificate in some storage and transport. anglers, or others using a site, as countries, and legal restrictions on the loud report may be disturbing to their use may also apply. In some In Israel, some fishermen have those with a nervous disposition or countries, pyrotechnic operators been licensed to use professional certain medical conditions. need to be licensed or carry special fireworks and have also explored insurance. the use of remote-control devices Moreover, in other circumstances to set off pyrotechnics placed at the use of gas cannons may be various locations around fish farms. imprudent. For example, at fish Trials were completed with some over-wintering ponds stocked with success, but this approach was not very large densities of small fish, adopted for widespread use due to the noise of cannons can agitate the relatively high costs and some and stress the fish. At sites in technical problems. A large variety Italy, such stress has reportedly of powerful fireworks are available, caused fish to move, exposing them thereby helping to prevent bird to more environmentally harsh habituation, and many are much conditions and leading to mass less expensive than simple banger mortalities. shells. However, legal restrictions on their use apply in most 4.1.1.2 Pyrotechnics countries. Pyrotechnic devices are widely used as a cormorant deterrent at In a survey of Mississippi catfish aquaculture facilities and to protect farmers, 21 of 281 respondents inland fisheries, particularly at (around 7%) regularly used smaller sites. They produce loud Pyrotechnic rocket. pyrotechnics. Of these, 24% bangs or whistles and emit flashes Photo courtesy of Paul Butt. considered them to be ‘very of light and colour, and they effective’, 57% ‘somewhat can provide a cheaper and more effective’ and 19% ‘not effective’. flexible alternative to gas cannons, Alternative pyrotechnics include Other researchers have reported depending on the level of use bird-scaring rockets — similar variable effectiveness in the use and whether their use introduces to recreational fireworks — and of pyrotechnics against different additional manpower costs. rope-firecrackers. These devices are species of fish-eating birds. This relatively inexpensive (for short- may be partially dependent on the There are a wide variety of noise- term use) and easy to use. The availability of alternative feeding producing cartridges, including shell rope-firecrackers (‘banger ropes’) and loafing areas for birds.
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As with gas cannons, pyrotechnics roosts in the Northern Po Delta and problems of public safety. are not considered effective in Italy, with varying results. They should also not be used in on large bodies of water and They proved useful at smaller situations where there could be habituation can occur rapidly roosts, particularly during the a fire hazard, such as near dry if they are used too frequently. initial establishment period. vegetation. Like gas cannons, Moreover, if they are used in large At a large roost (2,500–3,000 the noises can also have negative numbers they are also unlikely to birds) established 10 years impacts on other wildlife and be cost-effective. Habituation can previously, a large number of humans. be delayed by using pyrotechnics pyrotechnics were deployed on selectively — i.e. infrequently several after-dark occasions, 4.1.1.3 Shooting to scare and at close range, and by varying with reinforcement using a laser Shooting to scare is one of the the type of shell used (whistles, rifle. However, there appeared most widely used techniques bangs, flashes). However, they to be no clear or lasting effects for deterring cormorants at sites can be very effective at smaller in this instance; the financial across Europe and elsewhere. It sites, particularly in combination costs were high and the logistics is one of the few techniques that with mobile, visual scarers, other complicated, and staff motivation is employed at all types of water deterrents, or by occasionally proved difficult during inclement body, from small to large and killing individual cormorants. weather conditions. from inland to coastal, as well as at aquaculture facilities. There Pyrotechnics are often used in Nevertheless, pyrotechnics can are fewer legal restrictions on Israel, in combination with other be an extremely effective and the use of this technique than on techniques, in effective deterrence relatively low-cost, non-lethal shooting to kill (although non- programmes and for effective method of bird scaring. They toxic ammunition must be used dispersal of night roosts. It should are easy to operate, the risks near water bodies in many places), be noted that their effectiveness of habituation are reportedly and in some countries a shooting may be partly due to the presence negligible if their use is licence and appropriate insurance of an active human operative ‘randomised’ as much as possible may be a legal pre-requisite even and, with the exception of rope- (i.e. applied on an ad hoc, as-needs for shooting blank cartridges. firecrackers, pyrotechnics therefore basis at different locations) and represent a fairly labour-intensive they pose fewer safety problems Shooting to scare can be used to method of bird scaring. than shooting. However, their deter birds or reinforce the scaring use should be limited to sites effect of other deterrents, such Pyrotechnics have been used away from residential areas to as human presence, gas guns and to scare cormorants at several avoid causing a noise nuisance pyrotechnics. It is more widely
Verey Pistol. Photo courtesy of Paul Butt. Blanks. Photo courtesy of Paul Butt.
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‘Shooting to scare is one of the most widely used techniques for deterring cormorants at sites across Europe and elsewhere’
used than the use of pyrotechnics possession and operation, the use of treatment phase. An average because live ammunition is often bird-scaring cartridges is probably bird reduction of over 50% was cheaper and more readily available. somewhat limited. reported. However, bird numbers The most commonly deployed recovered to pre-treatment levels weapon is a 12-bore shotgun, Shooting to scare can be an over a period of two to six weeks. although relevant certificates for effective deterrent, and it is To be effective in the longer term, such use may be required. The sometimes the only option available this means that such scaring would safest way to use a shotgun for this on a river or still water to which need to be repeated at regular purpose is to fire blanks, which are the public have access. It has intervals for as long as cormorants available from local gun dealers. been demonstrated in a recent remained in the area. When done This also avoids any possibility study in the UK that shooting to properly (e.g. as birds first arrive), of actions being misconstrued, of scare can reduce the number of and in conjunction with other birds being injured, and of adding birds present at fisheries for the deterrents, this can be highly lead to the ecosystem. duration of the shooting period effective over a long period of time. and for a ‘post-treatment’ period. Live ammunition can also be used, A large-scale experiment was 4.1.1.4 Bio-acoustics, acoustics, but care needs to be taken not to undertaken involving thirteen, ultrasonics and high intensity kill or wound birds, unless the six-week field trials carried out sound appropriate authorities approve over two years at a range of Bio-acoustic deterrents are sonic this. The practice of ‘peppering’ fishery types (including river and devices that transmit sounds with a cormorants with small lead shot stillwater fisheries, stocked and biological meaning — for example, pellets in order to deter them is unstocked sites, and fisheries recorded bird alarm and distress commonly considered inhumane with and without cormorant night calls. Typically, alarm calls are and illegal in most places. A roosts). The experimental design used when birds perceive danger, starting pistol can be used as an involved three treatments: control while distress calls are used when effective alternative to the use of (no shooting), lethal shooting and birds are captured, restrained or a shotgun, although care should non-lethal shooting (at the same injured. Both types of calls are be taken so that others do not intensity). Each six week trial was usually species-specific and can misinterpret this course of action. divided into three two-week phases: cause members of the same species pre-treatment, treatment (when to take flight, but they may also It is also possible to purchase a shooting with blanks was carried elicit a response in other species variety of special bird-scaring out) and post-treatment. Numbers that are taxonomically related or cartridges. However, these of cormorants were then compared which closely associate with the are specially designed to be before and after commencement of call-producing species. fired through a signal (Verey) shooting and between control and pistol sleeved to 12 gauge and shooting sites. Recorded alarm calls are widely not through a normal shotgun. used as bird deterrents, and such Appropriate firearms certificates The results indicated that shooting biologically meaningful sounds may also be required for these. (to kill or to scare) significantly should be more repellent and Furthermore, because of the noise reduced the number of cormorants resistant to habituation than other they make and the restrictions on for both the treatment and post- sounds, although responses vary
www.intercafeproject.net [17] the intercafe cormorant management toolbox
between species (e.g. some species An underwater acoustic system of gull [Larus spp.] are initially (‘Cormoshop’®) has recently attracted to the noise, apparently to been developed and produced investigate). There are reports of the commercially in France, based successful use of broadcast distress on the calls of the Killer Whale calls to deter some species of heron (Orcinus orca). Underwater (Ardea spp.) and Night Heron. loudspeakers, supported by floats However, in trials in Italy and situated 40 cm under the water Israel the broadcast of Night Heron surface, diffuse sound waves into distress calls at night and early in the water to frighten cormorants the morning caused unacceptable when they are diving. Various disturbance to people living nearby. frequencies have been tested and those at 90 kHz — the frequency of Researchers have reported that sounds from a Killer Whale — were locating sources of cormorant found to be most effective. The distress calls is problematic. manufacturers have continued to It was discovered that some revise the frequency settings and commercially-sourced distress calls power output to further improve the trialled in Italy were actually the effectiveness of the device. cries made by nestling cormorants when calling their parents. Further, Initially, the ‘Cormoshop’® it has been noted that the birds system was tested at commercial rarely seem to make distress calls fish ponds in France and feedback anyway. Despite repeated attempts from the pond owners was largely by one researcher to induce and positive. Experience indicated record such sounds from injured that diving cormorants took and captured adult cormorants, flight immediately and stayed and while ringing nestlings, the away from the protected ponds. birds always remained silent. However, the device appeared Nonetheless, trials have been to work only on ponds where that birds habituate to the device carried out in some countries with the fish density was relatively at extensive aquaculture facilities, cormorant distress calls, but the low (<300 kg/ha). At higher fish and it has reportedly proved too results have suggested that the densities the system appeared to be expensive for use at such locations. technique is of short-term use only less effective, possibly as a result The device has been used with and ineffective in the longer term of the cormorant’s dive time to more success at fish ponds used for due to habituation. Similar reports catch a fish being shorter because recreational angling, possibly as a from North America indicate that of greater food availability. The result of the presence of the device distress calls were generally found system reportedly has no adverse being reinforced by regular human to be ineffective against Double- effect on fish behaviour and can disturbance. crested Cormorants, at least over be reliably used under all climatic long periods of time. conditions. However, it requires a Sonic bird scaring systems that reliable electric power source and produce a variety of electronically- The possibility of broadcasting thus may not be applicable at more produced sounds, sometimes cormorant distress calls underwater remote sites. associated with randomly- to enhance their effect (sound activated lights, are also available propagates more effectively Units have mainly been used in commercially. The range of loud underwater) has been considered, France and Belgium, although and sudden noises they produce but it does not appear to have been they have also been deployed at can frighten birds but, as they tested as yet or made commercially sites in Italy and Germany. Initial have no biological meaning, the available. feedback from Belgium suggests risk of habituation is greater. With
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involved. Some reports suggest such devices can deter cormorants, although a proportion of the birds present were reported to dive rather than fly away.
In the Po Delta in Italy and in Sardinia, extensive trials have been conducted with sonic bird- scaring devices to scare cormorants away from their night roosts and to keep birds away from particular areas within extensive aquaculture lagoon systems where high densities of fish are held over winter. Two commercially-available devices were tested. The trials indicated that electronic sounds could be useful, at least in the short term, to deter groups of birds, but appeared to be ineffective against single birds, particularly if these birds were well used to the area. Habituation was seen as a problem and strong winds dispersing the sound away from the desired direction was also considered to have affected the efficacy of the devices.
Evidence indicates that most species of birds do not hear in the ultrasonic range (>20 kHz) so there is no biological basis for using ultrasonic devices and no evidence that such devices deter birds. Ultrasound loses intensity far more quickly with distance than regular sound, so it is usually ineffective outdoors.
High intensity sounds, such as air horns and air-raid sirens, can distress birds and cause them to Sonic bird scaring devices. Photos courtesy of Josef Trauttmansdorff and Paul Butt. leave a site. However, they have a relatively short range and birds static systems, frequent changes mounted) systems that can be used appear to habituate quickly to their in location and adjustment of the in response to bird problems are use. Trials at aquaculture facilities sounds produced can reduce this more effective, though they are also in Israel and Italy with vehicle risk, and mobile (e.g. vehicle- more expensive due to the labour horns and sirens have reportedly
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proved largely ineffective or devices have a limited range, and from the viewpoint of practicality effective only for short periods. this can be influenced by wind for many sites. Legal constraints These devices can also cause strength and direction, ambient on the use of some of these hearing damage to humans and temperature, and surrounding techniques may apply and licences are generally not recommended features such as buildings. Thus, or permits may well be required for general use. However, sirens they are most effective at smaller for their operation. Local guidance mounted on vehicles can provide sites, or at particular locations at and necessary approvals should an effective combination of human larger sites (e.g. netting stations thus be sought prior to using presence with an audible deterrent, or known predation ‘hot spots’) to these devices. The deployment and they have been used with some address specific, local problems. of audible deterrents should also success in Israel to scare birds at All audible deterrent techniques are take account of appropriate safety fish farms. subject to habituation (birds learn issues (e.g. use near members of that they pose no danger and ignore the public or in the vicinity of Sound transmission from all sonic them), and hence they are more sensitive sites). devices is influenced by ambient likely to be of short-term benefit, temperature, wind direction and generally for weeks or shorter In addition, there will be a reflections from surrounding periods. However, efficacy can be need to guard against the use of features such as buildings, and extended considerably by moving pyrotechnics in situations where this should be taken into account devices regularly or mounting there could be a fire hazard, such when setting up such devices. As them on a vehicle for maximum as near dry vegetation. It might with most methods of bird control, mobility, where they are reinforced also be necessary to consider the using such devices as part of an by human presence, using variable security of the device to minimise integrated approach with a variety firing intervals and by employing the risk of possible theft or of techniques is likely to be more them as part of an integrated vandalism (e.g. by deploying the effective and will help reduce the control strategy alongside other device on an island). risk of habituation. measures. Many audible deterrents require 4.1.1.5 Other sound-producing In general, techniques such as some form of power source, and techniques pyrotechnics and shooting to scare this may render them more difficult Other sound-producing techniques appear to be more effective and and expensive to deploy, and can also be used to deter longer lasting against cormorants perhaps impractical, unless there is cormorants. For example, tapes that than static devices, probably due a supply of electricity or suitable produce a humming or clacking to the reinforcing effect of human batteries that can be re-charged. It sound when they move in the presence and, where this is used, is also important that such devices wind can also be used, and the shooting to kill, as well as the will operate reliably and effectively combination of sound and a visual more flexible and targeted means in what may be extremely variable deterrent can be effective (see in which they are deployed. Such environmental conditions. Section 4.1.2 on visual deterrents). measures also appear to be more effective if birds are exposed to Costs true danger (e.g. due to shooting The price of auditory deterrents 4.1.1.6 Overview of auditory or if hunting is permitted) in the varies considerably and depends on deterrents surrounding area. the complexity of the device itself Efficacy (e.g. from simple humming tapes to Auditory deterrents can be Practicality relatively sophisticated automatic effective against cormorants. The Auditory deterrent devices are devices) and the operating costs. effectiveness varies with the device used widely for a range of bird Static devices such as automatic chosen, the method of use, the scaring purposes. They are gas cannons, bio-acoustic size of the site and the availability readily available, relatively easy deterrents and sonic devices are of alternative foraging sites to to deploy and simple to operate. relatively expensive, and the which the birds can relocate. Such Such deterrents thus rate highly costs involved in trying to apply
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these over a large area are likely bang may be disturbing to those specific areas either deliberately, to be prohibitive. However, once with a nervous disposition or by direct harassment, or indirectly purchased, such devices can be certain medical conditions. through, for example, leisure used over many years and running activities or routine day-to-day costs are relatively low. 4.1.2 Visual deterrents activities. However, frequent or extended periods of human The costs of pyrotechnics or There are a number of relatively presence may be needed for this shooting to scare are relatively simple and inexpensive visual to be effective. Thus, options to low in terms of the materials, in deterrents, mainly used for scaring encourage or extend incidental the short term at least. However, birds from farmland, which can human presence at ‘problem’ sites manpower costs have to be taken be successfully adapted to deter might be considered. into account, particularly if fish-eating birds at fisheries and dedicated staff are used for bird aquaculture facilities. Human presence is also a feature scaring duties, and recurrent costs of many bird deterrent methods, can be high if such deterrents are 4.1.2.1 Human Disturbance and it should be appreciated used repeatedly. Staff costs can be Human activity has been shown to that it is difficult to separate reduced where volunteers or local be consistently effective for scaring the effects of another deterrent stakeholder groups are involved in cormorants away from fisheries (e.g. pyrotechnics) from the bird scaring programmes. and aquaculture facilities, and it effects of human presence. is not constrained on grounds of Cormorants can habituate to Acceptability acceptability to other people as human presence, particularly if The use of auditory deterrents for some other techniques often are. this carries no perceived threat, deterring birds is widely recognised Human disturbance is one of the so the simultaneous use of other and accepted. However, general most widely used techniques for deterrents is advisable. considerations with the use of all deterring cormorants, particularly auditory deterrents relate to their at aquaculture facilities and at The timing of human activity is potential noise nuisance and their fisheries on smaller rivers and important. Cormorants normally indiscriminate impact on non-target stillwaters, and it can be conducted leave their roost before sunrise species. Auditory scarers may be on foot, using vehicles or by and feed most actively just after socially unacceptable in residential boat. Birds can be disturbed from dawn, so human presence needs areas, and they may also have an undesirable effect on other wildlife and humans in the area (e.g. fishermen or fish farm workers). To an extent, the level of possible disturbance can be regulated by the way these devices are used — for example, by pointing them away from houses or constructing simple straw baffles around them. It may also be wise to advertise the use of such equipment widely to anglers, or others using a site, as the loud
‘Timing of human activity Whilst some types of human disturbance will be innapropriate at fisheries, this is a consistently effective method of deterring Cormorants. is important’ Photo courtesy of Paul Butt.
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to be targeted at this time. This motionless devices either provide will be easier where personnel only short-term protection or are live on, or very close to, the site ineffective, as the threat from to be protected, but it may still them is perceived, rather than prove to be costly or impractical. real. Some birds reportedly even Nevertheless, human presence begin to associate the presence over a reasonable period has the of scarecrows with favourable advantage that it will enable an foraging conditions. In a survey accurate count to be made of the of fish hatchery managers in the numbers of birds affecting a site United States, only one of the and, thus, better assessment of the 14 hatchery managers (7%) who extent of any problem. However, it commented on the effectiveness of might be noted that a study in Israel various control techniques said that showed that cormorants shifted scarecrows had a high success rate their main feeding time from early against fish-eating birds; six (43%) morning — when worker presence said they had no effect. was high — to early afternoon, Scarecrow with replica gun and when the workers went to lunch. In a survey of 13 freshwater fish dressed in yellow coat. farms in the Modena district of Photo courtesy of Simon Nemtzov. Although the use of a dedicated Italy, where damage from 11 fish- human scarer is likely to be more eating bird species was reported, expensive than other visual and the owners or managers of four undertaken by people dressed in acoustic methods, these costs can farms reported that human-shaped similar yellow, hooded coats. be offset by a greater reduction in and/or moving scarecrows had losses. Costs can be particularly no effect, three reported success Revolving scarecrows are brightly high if specific working time is for a matter of days and only two coloured devices that spin slowly as dedicated to this activity and other indicated benefits lasting weeks or the wind blows. Some are human- costs are taken into consideration months. shaped, while others consist of a (e.g. fuel costs for vehicles), revolving square, sometimes painted but they can be relatively low To maximise the effectiveness of with large predator eyes (also where human presence involves scarecrows, it is recommended that known as ‘hawkeye’ deterrents). volunteers (e.g. unpaid anglers or they are made to appear life-like, Both designs can be enhanced by hunters). Casual scaring associated possess biological significance, the addition of a mirror that flashes with routine day-to-day activities be highly visible and have their as the device revolves. As these can also be effective and of low location changed frequently to delay devices are wind operated, there cost. However, as with all scaring habituation. Fitting scarecrows is minimal maintenance and these techniques, the success of human with loose clothing or bright devices are relatively inexpensive. scaring is dependent on alternative streamers that move and create feeding areas being available. noise in the wind can also enhance There are many types of automated their effectiveness. Alternatively, scarecrows available for fishery 4.1.2.2 Scarecrows scarecrows might mimic clothes use, most of which have been Scarecrows are a traditional, worn by active human scarers. For adapted from scarers used in widely used method for scaring example, dressing both scarecrows agriculture. The more sophisticated avian pests. These are sometimes and the farmers in bright yellow devices are powered by 12-volt designed to mimic the appearance raincoats with hoods and having the car batteries, and they display and of a predator (e.g. a bird of prey), scarecrows ‘hold’ a black pipe (as a collapse on a controlled-time basis but they are most commonly replica gun) enhanced the efficacy of or with motion detectors. These human-shaped effigies, usually scarecrows at an Israeli aquaculture scarecrows can also be fitted with constructed from inexpensive facility. This scaring was reinforced various extras such as hooters, materials. In general, however, by periodic shooting in the area, sirens and lights.
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Revolving bird scarer — ‘predator eyes’. Photo courtesy of Paul Butt.
The most effective techniques appear to be those that simulate shooting through the use of effigies that suddenly appear from cover. One example is a model of a man with a gun that is attached to a gas cannon in such a way that the effigy appears a few seconds before the cannon is fired. This can also be used for purely visual scaring when simultaneous use of the cannon is inappropriate.
Large (around 5 m high), brightly- Inflatable ‘Scarey Man’ deterrent coloured inflatable ‘men’ have also (top), and inflatable ‘man’ (right). recently been produced, primarily Photos courtesy of Paul Butt and for advertising purposes. This type http://www.immagoinflatables.co.uk/ of device is powered by an air skyguys.html. pump in the base, and it flaps and sways, both in a breeze and due to the continual flow of air through the One drawback is that automated device. The long arms also wave scarecrows can be quite expensive and flap about. The devices are thus to purchase and maintain, and unless highly visible over relatively long the site is secure (e.g. an inaccessible distances, and in the UK they have island) they can be stolen or reportedly been successfully used vandalised. Trials with these against cormorants. A potential devices have had some success in disadvantage, however, is that the reducing the presence of cormorants scarecrows have been reported as inflatable ‘men’ require sources (and herons), but it is commonly ‘ineffectual’ against cormorants of electrical power with which to reported that birds habituate to the at some sites. Regularly changing operate the air pumps. devices quite quickly, and animated the position of such devices is
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recommended to maximise what producing or visual deterrents, effectiveness they may have. or, to improve effectiveness, by ‘Model birds of periodic human activity, especially prey are reported Both static and animated if they are dressed like the scarecrows are commonly used at scarecrows. to be effective aquaculture facilities and fishery sites, particularly smaller ones. The 4.1.2.3 Predator models at scaring major drawback with scarecrows, Model raptors deter birds by cormorants at however lifelike they may be, is that mimicking real birds of prey they do not present a threat that is and creating fear and avoidance some sites’ sufficiently alarming to birds under behaviour in the target species. most circumstances. Consequently, Many potential prey species react over a period of time, birds learn to predator models. However, the predator across Europe, the White- that effigies do not represent an strength of the response varies tailed Eagle (Haliaeetus albicilla), actual threat and begin to ignore between species, and model raptors is absent from many areas where them. To increase the threat and fail to incorporate behavioural cormorants are present. therefore lengthen the time before cues, which may be critical to the habituation, it is recommended induction of fear and avoidance in The flying of live, trained birds of that all these devices are moved the target species. Model birds of prey across bodies of water by a regularly, rather than left in one prey are reported to be effective at falconer might also be used. This place. Moreover, devices should scaring cormorants at some sites. has been tried in Israel. However, not be left in place once cormorants However, there is evidence that although its efficacy was relatively migrate from an area because, the avoidance response to large high, the farmers stopped using the when the birds return, the period of avian predators is, in part, a learned birds due to the very high cost. habituation can be particularly short. behaviour. This may diminish the potential for the wider application While most raptor models are The effectiveness of scarecrows can of this technique against inexpensive and easy to deploy, be reinforced with other sound- cormorants, since its main avian cormorants can rapidly learn that the model poses no threat, become used to its presence and no longer react. The deployment of a Peregrine Falcon model adjacent to cormorant feeding areas in the southern Po Delta, Italy, appeared to be largely ineffective and tends to support this view. Thus, the effectiveness of such models is increased if they can be made to look lifelike, are animated and moved frequently.
Another form of predator model that has been used is that of tethered floats made to resemble the head of a crocodile or alligator. These floats are distributed around the pond and purportedly can deter water-birds from landing on the pond. It is not known whether these Mobile scarecrow dressed identically to local workers and also incorporating have been used successfully against an auditory deterrent device. Photo courtesy of Paul Butt. cormorants.
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4.1.2.4 Displaying corpses The deployment of replicas or actual dead individuals in a manner which signals danger to members of the same species can be used as a visual deterrent for many bird species, especially crows (‘corvids’). Reportedly, corpses have to be in good condition to remain effective and, as with other static deterrents, they should be moved frequently to reduce habituation. Efficacy depends on the availability of alternative foraging sites and is enhanced Raptor kite. Photo courtesy of Paul Butt. when it is reinforced with additional deterrent techniques. While this technique is reportedly three-dimensional appearance may place, such balloons have been used highly effective for corvids and further enhance the effect, and large as opportune targets and their use there is some evidence it has been eyespots are considered better than to help deter cormorants has had to effective against egrets (Egretta small ones. Although easy to set up be abandoned. spp.), it is not clear whether or not and move around, balloons can be it deters cormorants. easily damaged in high winds and 4.1.2.6 Kites can deteriorate in sunlight, leading Kites and kite-hawks are The desirability of displaying corpses to a loss of helium and thus height. commercially available, airborne in areas accessed by the general Balloons also need to be checked devices that are meant to act as public may also need to be taken regularly to ensure they cannot break mobile model predators which into consideration in case the corpses free from their moorings and present ‘target’ birds perceive as a threat. raise public concern and complaints. a hazard to aircraft. Their use near Kites commonly bear an image of There are also other considerations aerodromes may be restricted by air a soaring raptor and are tethered if real corpses are used, notably navigation regulations. A cheaper to the ground. Some varieties because of possible pollution arising alternative is to fill the balloons with are secured to a length of line from decomposition, particularly in pressurised air and to hang them (commonly about 80 m), but these fish farm areas, and health and safety from T-shaped poles. only operate in a wind and, once fears about the possible spread of grounded, have to be re-launched avian ‘flu. Balloons, and other visual scaring manually. Alternative models are devices, have been used against tethered to a flexible 13 m pole 4.1.2.5 Balloons cormorants to increase the deterrent and re-launch automatically when Helium-filled balloons are used effect of other physical exclusion the wind starts blowing. The as an inexpensive method of bird devices such as wires and floating ‘Helikite™’ is a cross between a deterrence in agriculture. Their ropes (see 4.2). large helium balloon and a kite, effectiveness can be enhanced by which ‘flies’ above a pole. This has the inclusion of eyespots, consisting Studies indicate that the the advantage that it does not need of a circular pattern that resembles effectiveness of balloons at scaring wind to stay in the air. the general appearance of vertebrate birds varies between species, the eyes. Two circular eyespots arranged eyespot design and with the mode Like balloons, kites and kite-hawks horizontally, each containing of presentation. However, effects can be damaged by strong winds concentric rings of bright colour, are commonly only short-term and and may be difficult to keep up in appear to be the most alarming and birds quickly habituate to them. In the air when wind speeds exceed effective designs. Those that have a some places where hunting takes 8 km/hr. Since they pose no real
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threat to birds, do not behave like raptors, and remain visible for long ‘Lights may be relatively ineffective periods, birds quickly habituate during daylight hours but they may be to these devices. Hence, they are effective only over a small area and particularly useful at night roosts’ for a short period of time. As with balloons, their use near aerodromes may be controlled by air navigation regulations. birds and can produce an avoidance or no success as a depredation response. Lights may be relatively control technique. However, it 4.1.2.7 Radio-controlled model ineffective during daylight hours is known that reflectors can be aircraft but they may be particularly useful effective at deterring cormorants Radio-controlled aircraft have been for deterring night-feeding birds at some sites, particularly in sunny used to scare bird pests since the such as herons, or at night roosts. locations. For example, in Israel, early 1980s. Although mainly used They are easy to deploy and require hand-held mirrors are reported to over airfields, this technique has also very little maintenance, but birds be very effective. As with many been applied at other sites, including will quickly become habituated other deterrent techniques, they are deterring cormorants and herons at and so lights are best used in best combined with other methods fisheries and aquaculture facilities. combination with other deterrent of scaring. For instance, on a For cormorants, experience has methods. They should not be large lake in Greece, mirrors and shown that model aircraft should be deployed where they might cause audible deterrents have been used used to scare birds while they are a visual nuisance to neighbouring successfully to deter cormorants still in the air, as birds already on the properties or near airfields. from sites close to the shore (see water are only encouraged to dive. Case Study No. 1). At larger, land-based fish farms it 4.1.2.9 Mirrors/reflectors has been estimated that one model Mirrors and reflectors work on the 4.1.2.10 Reflective tape aircraft is required for approximately principle that sudden bright flashes Tapes can best be regarded as a every 100 ha. Using a falcon-shape of light produce a startle response combined visual and exclusion aircraft, or a conventionally shaped and so drive birds from an area. deterrent (see Section 4.2.2). A aircraft painted with a raptor design, For example, CD discs are highly wide variety of twines and tapes can enhance the efficacy of this reflective and can be hung on are readily available, including technique. While quite effective, the wires or other objects where they varieties such as Mylar® Tape, use of model aircraft is relatively will move with the wind to deter which has a metal coating on one expensive, labour-intensive, not birds. Rotating, reflective pyramids side that reflects sunlight and also suitable in bad weather and requires have also been developed that produces a humming or crackling skilled operators — training to are powered by a 12-volt battery noise when moved by the wind. become fully competent can take up and deflect light into the air at the Tapes are relatively cheap and to two months angle of the birds’ approach. These easy to deploy, but they can break automatically switch off in the easily in bad weather conditions, In Finland, an attempt to scare dark and will run for several weeks necessitating extra labour for cormorants was made using a between battery changes. Although repairs and, potentially, causing small, wind-driven helicopter rotor inexpensive and easy to put up an unsightly litter nuisance. mounted on a tripod. Although the and relocate, the effectiveness of Good maintenance of the tapes efficacy of the device was not fully mirrors and reflectors as a bird is essential in order to stop gaps monitored, it is thought to have scaring technique is variable. resulting from broken tapes been partially successful. being exploited as entry points In a survey of 336 fish hatchery by birds. Strips of reflective tape 4.1.2.8 Lights managers in eastern USA, eight are often hung from wires that are Flashing, rotating, strobe and reported using tin reflectors of stretched across fish ponds (see searchlights are a novel stimulus to which seven said they had limited Section 4.2.2) to make the wires
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more visible and to increase their directed over distance on specific sure of the precise target and what effectiveness as deterrents. problem birds. Birds are startled the end of the beam will hit. Some by the strong contrast between the lasers can be dangerous at short or Reflective tapes are in regular use ambient light and the laser beam, even large distances, and proper at aquaculture facilities in a number by the bright spot moving toward training and adherence to local of countries (e.g. Germany, Italy them on the ground or in the tree laws is essential. Lasers can blind and UK), and close configuration of and by the actual beam when it people or animals, permanently these tapes can provide successful reflects dust particles and appears or temporarily, and this can also protection, particularly if an as a large ‘stick’ moving toward lead to unexpected accidents (e.g. alternative feeding area is available them. The laser light need not be car crashes) if devices are used nearby. However, since the tapes shone into the bird’s eyes to startle inappropriately. are short-lived, the technique is them, and indeed it is inadvisable to probably best suited to protecting do so. During low light conditions Trials with low power (5 mW) red small areas of high value stock in this technique can be applied very laser (650 nm) guns, such as the the short term. selectively, but at night the light Desman rifle®, in France, Italy beam is visible over a large distance and the UK have demonstrated A cheap source of reflective tape and hence can cause non-selective that cormorants are sensitive is the magnetic tape in old video disturbance. These devices are to this laser light and that these cassettes, since this is highly ineffective in daylight and in misty devices can be effectively used reflective and easily available. or foggy conditions. at cormorant roosting sites. In However, it is inadvisable to use tape from video cassettes with a play length of longer than two hours, as these are made of thinner ‘Birds are startled by the strong (and more breakable) tape. contrast between the ambient light
4.1.2.11 Flags, rags and streamers and the laser beam’ Flags, rags and streamers, including reflective silver or Mylar® streamers, can be readily deployed The possession and use of lasers one trial in the UK, conducted at fishery and aquaculture sites may be prohibited or restricted during cloudy weather, most of the and — potentially — also at roost by legislation or be subject to a cormorants at a night roost were sites. These are cheap and easy licensing regime, depending on the scared away within 20 minutes, to deploy and can prove effective power of the laser being deployed. and treatment over consecutive deterrents, in the short term at There are growing safety concerns evenings caused the temporary least. Their success depends on regarding the availability and desertion of the roost. alternative feeding, roosting or use of lasers and calls for tighter loafing sites being available nearby. regulation in some countries. Thus, In similar trials in roosts in the the legal aspects of using this northern Po Delta, Italy, birds left 4.1.2.12 Lasers technique should be checked with the roost almost immediately. In As the demand for non-lethal, the local authorities before any Italy, lasers have been successfully environmentally safe methods of laser devices are considered for used against birds in both tree bird scaring has increased, there deployment: laser devices should roosts and bankside areas, has been increasing interest in only be used within the limits of sometimes hundreds of metres the use of lasers to scare birds. appropriate laser safety regulations. from the bank- or boat-based Lasers, particularly ones that work operator. The gun ‘scope’ on laser under low light conditions, are From a safety point of view, guns proved useful to accurately an attractive alternative to other shooting a laser light must be target the laser light, and the use bird scaring devices since they regarded the same as shooting a of a light amplifier also helped to are silent and can be accurately bullet — the operator MUST be enhance the efficacy of the device
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in the dark. It was reported that expensive as the red laser guns had four arms that sprayed a mist lasers were particularly effective (above). However, low-cost, hand- of water over the ponds, reducing at preventing the establishment of held green laser pointers are also visibility and preventing birds from new roosts, especially when used in available with a wide variety of seeing the fish. The spray also conjunction with shooting to scare power levels, and these have been provided shade by diffusing direct techniques. used successfully for bird scaring sunlight, and oxygenated the water. at night roosts in Israel and Italy. The latter technique was not tested Similar findings have been Low power lasers of less then against wading or diving birds, demonstrated at other cormorant 5 mW have fewer legal restrictions, but both methods may be useful night roosts, although in some though these can potentially to deter cormorants, particularly trials the laser gun has been less still cause eye injuries, and can at smaller ponds on fish rearing effective, with some birds failing be effective at ranges of up to a sites. The potential for their use in to leave the roost site (e.g. if the few hundred metres. Green laser protecting larger, irregular water bird is facing away from the light pointers of 20–30 mW are effective bodies may be limited because source), thereby discouraging over larger distances (1–2 km), but of the cost and the practical other birds from leaving, too. usually carry more stringent legal installation difficulties. This reinforces the desirability of restrictions and safety standards deploying a mixture of cormorant than the 5 mW lasers, reflecting the 4.1.2.14 Dyes, colourants and scaring devices and techniques. greater risk that they pose. Green turbidity laser pointers of 50, 100 or even There has been little research into Laser guns are available 200 mW are also available, but the use of dyes or colourants to commercially for avian these are increasingly dangerous deter fish-eating birds, but it is deterrence (e.g. Desman rifle®, and apparently no more effective known that cormorants are visual Avian Dissuader), and some in scaring birds than the less feeders, in part at least, and that manufacturers also provide training powerful ones. It is anticipated that birds can abandon feeding sites in in their use. Other, automatic further controls are likely to be response to changing water quality laser devices have been developed placed on the availability and use conditions such as turbidity (i.e. for deterring birds, particularly of lasers and thus particular care reduced water clarity). Studies have near airfields to reduce the risk is needed to ensure compliance also indicated that the foraging of ‘bird strike’. However, these with local regulations, as well as efficiency of egrets was reduced devices are relatively expensive. to ensure safe usage where this is by increasing the turbidity in trial Due to concerns about the safety appropriate. ponds (obtained by dilution of of such devices for humans, one natural sediment). Thus, some commercially available laser gun 4.1.2.13 High-Pressure Water Jets researchers have suggested that was tested for safety at the UK High-pressure water jet systems such measures might represent a Government’s Defence Evaluation have been successfully tested on cost-effective method for protecting and Research Agency (DERA). Carp ponds in Germany. Aside stocks at fish farms or in ponds This was found to be safe if it from deterring predators and and small lakes, since these could was not pointed at an unprotected making the fish less accessible, be relatively easy to apply in such human eye within a distance of a positive side-effect of this small, confined water bodies. 155 m, although the safe distance technique is that the ponds are also In practice, such an approach was considerably reduced if viewed aerated, an important benefit during may conflict with fish husbandry with binoculars. summer when the dissolved oxygen practices in fish farms (and perhaps in Carp ponds can fall to very low feeding of the fish). Green lasers (530 nm) are also levels. available and tend to be brighter Equally, the practice of deliberately than red lasers of the same power A similar device has also been used increasing turbidity at a site may be level. Green lasers are being in Sweden for protecting circular questionable from an acceptability sold commercially as laser guns fish ponds from gulls and terns viewpoint on biodiversity/ for bird scaring, but these are as (Sterna spp.). This rotating device aesthetic grounds, although the
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presence of benthic (i.e. bottom visibility and how real a threat they required. Simple static scarecrows feeding) species such as Carp at are perceived to present: visual and flags are usually constructed fisheries often has this side-effect, scarers are most effective if they from inexpensive materials, while particularly at small stillwater sites are life-like, move and possess automated devices are relatively where stocking rates are high. biological significance, or if they more expensive, depending on their The potential for using dyes or are associated directly with a real level of sophistication, and devices artificially manipulating turbidity threat. such as some lasers can be costly. as a cost-effective method of Commercial bird-scaring laser guns cormorant control has yet to be Disturbance by humans is regarded can be very expensive, but cheaper, proven. as the most effective visual hand-held laser pointers can be just deterrent, but cormorants can learn as effective. Laser licensing and 4.1.2.15 Dogs to feed during even short periods training costs must also be taken Trained dogs, such as border when humans are absent (e.g. into account. collies, can be used to scare birds meal breaks), especially where away from a site. The efficacy of feeding success can be assured For many visual scarers, manpower such an approach for deterring (e.g. at heavily-stocked fish ponds). costs are low, being mainly cormorants is not known. Studies suggest that human effigies confined to initial deployment, and raptor models may be more periodic checking and, perhaps, 4.1.2.16 Overview of visual consistently effective and longer movement around a site. However, deterrents lasting as bird deterrents than kites, the cost of using dedicated staff for balloons and flags. ‘human disturbance’, or to operate Efficacy a laser gun, may be considerable, As with auditory deterrents, the Practicality particularly if required on a regular effectiveness of visual deterrents Visual deterrent devices are used basis. Manpower costs might be varies with the device chosen, widely for a range of bird scaring reduced where incidental human the method and timing of use, the purposes and most are readily presence at a site can be arranged size of the site and the availability available, easy to deploy and or where volunteers or local of alternative foraging sites for simple to use. Such deterrents thus stakeholder groups participate (see the birds. Typically, fixed visual rate highly from the viewpoint Case Study No. 4 — Slovenia). deterrents are only thought to have of practicality for many sites. an effective range of up to about Regulations may cover the use Acceptability 200 m. As such, these techniques of some visual deterrent devices The use of visual deterrents for will be of limited, if any, use on (e.g. lasers, model aircraft, scaring birds is widely recognised river systems, coastal areas or flashing lights) and/or restrict and, since their impact is usually larger stillwater sites, with the their operation in sensitive areas very localised and non-lethal, they possible exception of localised such as airfields. Local guidance have a high level of acceptability predation ‘hot spots’, or in the and necessary approvals should and are generally not a matter of vicinity of fishing gear. always be sought prior to using public concern. However, such such devices. For more expensive devices are not selective and so All visual deterrents, particularly visual deterrents (e.g. automated may impact on other wildlife, and static ones, are subject to inflatable scarecrows), security this should be taken into account. habituation by cormorants, and should be considered carefully to Some visual deterrents may not hence they are generally of short- safeguard the devices against theft be acceptable in certain locations term benefit (typically days to or vandalism. (e.g. flashing lights or perhaps weeks) as the birds eventually bird corpses near residential areas, get used to them, unless they Costs model aircraft and kites near are moved regularly and used in The costs of visual deterrents airfields, or lasers near roads). conjunction with other deterrents. vary widely, depending on the Particular care is also necessary The effectiveness of visual complexity of the device itself and with all uses of lasers even where it deterrents also depends on their the level of human participation is legal to use them.
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4.1.3 Chemical deterrents these reasons they are difficult Individual birds learned to avoid to apply effectively outdoors, Brown Trout (Salmo trutta), the Chemical taste repellents are especially in large areas such as fish treated species, but continued to eat quite widely used for reducing the growing areas. In addition, most are other species of fish, and this effect impact of pest birds in agriculture relatively expensive. Furthermore, lasted for seven months - the entire and forestry, as well as a means of methyl anthranilate can be toxic duration of the trial — without deterring birds from perching on to aquatic fauna and may not be reinforcement. buildings. Such techniques have sprayed near water bodies unless it not been widely tested against is in a special formulation designed Clearly, applying such a technique fish-eating birds, but they may for this purpose. in the wild presents significant have some potential. Chemical difficulties and would not be repellents fall into two broad Despite these drawbacks, chemical appropriate at sites on cormorant categories: primary repellents and repellents have been used effectively migration routes, due to the secondary repellents. Primary to deter birds, including cormorants, extensive turnover of the birds. repellents are avoided upon first from large areas, such as airports. However, it might have potential at exposure because they smell or The repellents are typically applied some sites where birds demonstrate taste offensive or cause irritation. using a fogger machine; in some local feeding-site fidelity and Secondary repellents are not places the foggers have been where there is a need to protect immediately offensive, but they attached to motion detectors so a particular species of fish. cause illness or an unpleasant that they only spray chemical when Considerable further work would experience following ingestion. The flocks of birds approach, to avoid be required to develop an effective bird links this negative experience habituation and to reduce costs. method for delivering the chemical to the taste of the treated food and The potential of applying repellents to the target birds. will avoid this food in future. Due as a very thin surface film, in to their toxicity, and concerns about order to deter birds from entering Because of the complexity and adverse effects on the environment, particular water bodies, has also drawbacks of using chemical the use of chemical repellents is been investigated. Research in this repellents for deterring birds usually tightly regulated. area is believed to be ongoing. outdoors, and the associated controls on their use, it is A number of chemicals (such as Most bird deterrent chemicals do important that all aspects, potential methyl anthranilate, dimethyl not impact mammals, and mammal repercussions and regulations anthranilate, cinnamide, deterrents such as hot-sauce are considered carefully before anthraquinone, adirachtin, (capsaicin) are ineffective against commencing any programme to use 4-aminopyridine, methiocarb, birds due to differences in their them against cormorants. and caffeine) have been proven nervous systems. Nevertheless, 4.1.3.1 Overview of chemical as effective deterrents against many people dislike the smell deterrents different bird species. Some of of some of these chemicals, these substances are registered as especially the sickly-sweet, grape- Efficacy bird repellents in the USA, but they like smell of methyl anthranilate, The efficacy of chemical are not authorised for use in many so it should not be sprayed near deterrents will be highly variable other countries and few chemicals settlements. depending on which chemical are believed to be registered for is used on which species and use in Europe. In addition, not Trials have also demonstrated on the mode of delivery. While all of them have been tested on that conditioned taste aversion proven to be effective for captive cormorants. (a subconscious association cormorants fed on dead fish, safe between taste and a feeling of and effective chemical repellents Chemical repellents are generally illness experienced after ingesting have not been developed to a level most effective on surfaces or treated food) can be successfully where they can be recommended indoors, and animals usually induced in captive cormorants fed for use in fishery or aquaculture habituate to smells quickly. For on dead fish dosed with carbachol. applications at the current time.
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Practicality fixed permanently. At other sites, be possible to make it difficult, Chemical deterrents are most such as off-shore fish farm cages, or impossible, for cormorants effective on surfaces and in anti-predator netting can be hung to land on, or take off from, the enclosures, and they are more in curtains underwater to prevent water’s surface. Although certain difficult to apply outdoors. The diving birds reaching fish stock spacings of these wires appear practicalities of administering in the mesh ‘bag’ of the cage. In to be more effective than others, repellents to cormorants and/or larger water bodies, complete there is considerable scope for water bodies require considerable exclusion is far more difficult experimentation at fishery sites. further work before the technique and may well be impractical. At could be recommended for wider such sites it may be possible to 4.2.1 Netting enclosures use. take advantage of the fact that cormorants generally require Complete enclosure of a site with Costs quite long distances for take-off netting is undoubtedly the most Most chemical deterrents are and landing. By positioning wires effective option for preventing expensive, although fogging or ropes across waters it may predation by fish-eating birds, machines can reduce the amount of chemical needed. However, in large areas the costs can be prohibitive.
Acceptability Chemical deterrents that do not harm (but only deter) wildlife are generally very acceptable as a non-lethal method to stakeholders. However, the use of potentially harmful chemicals in the environment does raise acceptability issues and requires mechanisms to ensure that substances could be administered to cormorants without a risk of lethal poisoning, or threatening other bird and other, non-target wildlife species. Thus, any possible human health or environmental implications would have to be taken into account to ensure any such techniques did not have adverse effects.
4.2 Protecting The Fish — Exclusion Techniques These tools involve excluding the birds from the fish. Not surprisingly, the techniques work best when fish are concentrated in relatively small areas. Thus, they are ideal for land-based ponds or raceway fish farms Netting enclosures at fish farms. where netting enclosures can be Photos courtesy of Bruno Broughton and Thomas Keller.
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including cormorants. Properly designed, such netting enclosures can provide people with uninhibited access to enclosed waters, allowing fishery management or aquaculture tasks to be undertaken. Relatively inexpensive, lightweight netting is now available and, secured to frames or supported by overhead wires, this has enabled the enclosure of water bodies extending to several hectares and the protection of long lengths of linear waterways (extending to several km) at some fish farm sites, for example in Italy. Such enclosures are widely used to protect fish farm sites in many countries, although costs can still be substantial. There are commercial companies that sell and install complete enclosure systems for such sites.
Full enclosures also provide secondary benefits in helping to reduce or prevent predation from non-avian predators such as American Mink (Mustela vison) or European Otter (Lutra lutra). However, experience has shown that small carnivores can gnaw through netting or slide under it if it is not held down securely. Thus, more robust wire netting might be required close to ground level where losses to such predators are a Large-scale netting enclosures in the Commachio lagoons, Italy. particular problem. Photos courtesy of Stefano Volponi.
A study in Israel investigated the problem of birds becoming birds entered but couldn’t find a well maintained and any holes and entangled and dying in netting way out. These birds lived in the tears repaired. enclosures over fish ponds. The ponds and actually consumed more results showed that birds are more fish than birds at unprotected ponds. There are a number of general likely to become entangled and die The conclusions of this study were considerations regarding the in thin, colourless or light-coloured used to establish a set of guidelines effective deployment and use of netting with large mesh size; in Israel for fish pond netting that netting enclosures: monofilament fishing nets were included the provisions that the especially dangerous. In addition, netting must be of a small mesh ▪▪ Netting should be sufficiently poorly maintained netting, with size (5–7 cm), made of thick, dark robust to withstand wind and many holes and tears, could turn an material and not of monofilament snow/ice accumulation and entire fish pond into a trap where fishing net. The netting must also be to withstand degradation by
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Where nets are strung close to the water but prevent them to the water surface, this from getting out, thus potentially additional weight could allow increasing fish losses. birds direct contact with the fish. However, nets should not The use of full netting enclosures be strung too tightly: research may be largely restricted to in Israel has demonstrated that aquaculture facilities and netting that is too taut tends to stock ponds, and is likely to be incompatible with angling waters. entangle more birds (probably However, it might be realistic to as a consequence of its reduced use the technique at some smaller visibility compared with a recreational fishery sites as a slightly sagging net that moves a temporary measure, perhaps in bit in the wind). winter when bird numbers tend ▪▪ Netting should be of a fairly to be highest and when angler Birds trapped in netting. small mesh size (5 to 7 cm mesh visits are often substantially Photos courtesy of Thomas Keller and width), to provide complete reduced, assuming that the nets Stefano Volponi. exclusion of all birds, although could be installed and removed larger mesh sizes (15 to 50 cm) relatively quickly. For example, can be sufficient for larger birds weathering (e.g. exposure to two parallel wires fixed around the such as cormorants. Dark- sunlight). More expensive, circumference of a pond, one above robust netting may be more coloured material is preferred head height and the other close cost effective than cheaper nets to ensure maximum visibility to to the ground, would allow sheet when the frequency and cost birds. Very thin monofilament netting to be strung over the pond of repair and/or replacement is fish nets must be avoided to and secured with simple nylon ‘S’ considered, and these will also prevent possible entanglement hooks (i.e. stretched over the upper be more visible to birds. of birds. wire and secured to the lower wire). ▪▪ Netting should be strung ▪▪ Netting should be checked reasonably tightly to prevent regularly and maintained as Partial netting enclosures have the weight of any birds standing necessary. Poorly maintained also been used with some success. on it from causing it to sag. nets may allow predators access A survey of hatchery managers in
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In Israel, floating cages of approximately 10 m diameter have also been located in fish farm ponds over the spot where fish congregate near automatic, pellet feeders. This prevents birds from attacking these large concentrations of fish near the surface.
Underwater netting Submerged netting enclosures can also be used to protect fish held in floating fish cages from diving predators, particularly cormorants. On the Scottish west Vertical netting across recreational fishery, UK. coast, underwater anti-predator Photo courtesy of John Black. nets are commonly placed around fish farm cages to protect fish stocks from seals and fish-eating birds, including cormorants. There is no evidence that cormorants tear holes in the netting, nor that they take fish directly from farm cages. To do this, such holes would need to be large enough to enable stock to escape. However, cormorants can cause damage to fish by poking their beaks through the nets. They have large, powerful beaks with a formidable hook and are capable of wounding or killing fish.
In order to prevent cormorants Floating anti-predator net over fish farm pond, Israel. reaching the fish held in cages, Photo courtesy of Simon Nemtzov. underwater nets (commonly of 10 cm square mesh) are suspended the USA found that netting placed protected part of the pond, but they below the cages, outside the net bag over fishery ponds (top screens used the whole water body for holding the fish. These nets protect only) was one of the most effective feeding at night. A similar approach all four sides and the bottom. At methods of deterring fish predators. has been used in Italy, where sheets some sites, weighted curtains of In Germany, small mesh covers of netting have also been hung net are suspended from the cage (mesh sizes <20 cm) were placed vertically, close to the water surface superstructure but these do not over just part of a large pond, and across channels at extensive protect the bottom of the cage. Loose covering about 10% of the water fish farm sites to interfere with the netting is more likely to ensnare birds surface. These served as a refuge ability of cormorants to take off and and fish, so netting needs to be taut. It area that fish could enter during the land. Reportedly, these have proved should also be checked regularly and day when cormorants were feeding. effective, although there is a risk maintained, and it will therefore need Here, the fish (Carp) were provided that other bird species can become to be fixed so that it can be raised with supplementary food in the entangled in the netting. easily to the surface. A separate sheet
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Diagram of fish cage of several metres — the nets can showing (a) walkway, be relatively easily pushed together (b) top hand-rail, (c) by water movement, potentially feeder pole and (d) top allowing birds or other predators to netting. Underwater access the fish. anti-predator netting can be seen below the Trials have also been conducted in water surface offering Denmark to evaluate the potential protection to the fine- of using ‘barrel’ nets inside coastal meshed net which pound nets (a commonly-used holds the fish stock. fishing technique). The barrel Figure courtesy of nets were located in the central Dave Carss. fish capture area of the pound net known as ‘the pot’. They were mounted vertically from the bottom to 0.5 m above the water surface in the pot and a variety of configurations were tested. The barrel nets were intended to hinder cormorant swimming and foraging behaviour and make it unprofitable of netting stretched over the top of effective at protecting fish than are for cormorants to forage in the the fish cage will also be required nets fouled with seaweed. However, pound nets; they did not prevent to keep predators from entering the underwater anti-predator nets are birds from entering the pound nets cage itself. not totally effective, even when themselves. The presence of the installed and maintained correctly. barrel nets was shown to increase There is evidence that such This is because common cage cormorant foraging costs (e.g. underwater anti-predator netting design usually only allows for a number of dives per fish caught), reduces the numbers of fish injured maximum of 1 m between the cage to reduce the amount of time birds or killed by cormorants in cages, net and the anti-predator net. Thus, spent inside the net, and also to and also that clean nets are less underwater — possibly at a depth reduce the number of cormorant visits to the net. However, while the barrel nets were designed to allow unhindered access for
‘Cormorants can cause damage to fish by poking their beaks through the nets. They are capable of wounding or Salmon smolt killed by cormorant beak through fish cage netting. Photo courtesy of Dave Carss. killing fish’
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fish, fishermen have indicated cormorants has not necessarily they are at obstructing birds from that their presence has a negative worked for other bird species. landing and taking off. Thus, wires impact on catches. In light of this, should ideally be spaced as closely and the cost of installation, the A number of factors have been as possible within the constraints technique has not been widely shown to affect the efficacy of of cost and practicality. Some trials adopted. Other similar underwater wiring systems. Studies in the have indicated that parallel wires netting deterrents are reported to Netherlands and the USA indicated set 20 m apart can be effective have been used to try to exclude that wiring exclusion devices are in reducing cormorant predation, cormorants from fishing gear in more effective at deterring large but other studies have found this Finland. flocks of cormorants but that single ineffective, with birds learning to birds learned to feed at the ponds move easily between wires with 4.2.2 Using ‘wires’ ‘protected’ by wires. Further, the such spacing. Most trials have been effectiveness of wires has been conducted with wires spaced more The word ‘wires’ is used here shown to depend upon alternative closely than this. For example, see as a generic term that could also foraging sites being available. For Case Study No. 5. include cords, ropes or tapes. example, in a trial at gravel pits in Wiring systems provide a cheaper the UK, cormorants avoided a pond In addition, experimental trials alternative to complete enclosure protected by wires (2 m spacing) conducted at commercial fish with netting. but regularly used an adjacent pond ponds in Hong Kong in the of the same size and similar fish winter of 2001–02 investigated Fish-eating birds searching for stock composition where protection the effectiveness of wires spaced feeding opportunities can be was absent. However, when the at 5 m and 10 m intervals, and deterred from utilising waters second pool was also wired, suspended 5 m above the water protected by wires as these affect cormorants resumed fishing on the surface. Eighteen ponds were the birds’ ability to land, feed and original pond, despite the presence used in the trial, from an extensive take off. For example, cormorants of wires there. area of ponds, with the trial ponds require 8–12 m of open water allocated into six groups of three, in their take-off run. There are As with most deterrents, birds can with each group containing a various ways in which wires can become habituated to the presence pond with 5 m wiring, one with be deployed in order to deter of wires and may learn to evade 10 m wiring and a control pond fish-eating birds from foraging at them, perhaps even specialising at (no wires). Ponds were allocated a site. Commonly, wires are held feeding on wired ponds. There is to groups so that the three ponds taut above the water surface fixed evidence that some birds can avoid within each group were broadly securely to posts set into the banks, wires by walking into the water and similar with respect to the extent but ropes can also be floated on the under the wires from the adjoining of cormorant utilisation and their water surface, and a wide range of bank, while others have been location within the site. spacing and deployment patterns observed hovering above the water can be used to facilitate other uses before dropping into it between The results demonstrated that of the water bodies. Options are wires. Cormorants have also been installing wires significantly discussed in greater detail below. shown to use starting positions that reduced the number of cormorant- allow completion of their take-off visits to the experimental ponds. Trials conducted in a number of runs between wires. Birds that learn However, cormorant visits to countries have clearly demonstrated to land, feed and take off on wired all the trial ponds, including that the deployment of wires can ponds may attract others to the the control ponds, were lower substantially reduce cormorant site, so it may be necessary to use a following the installation of the impacts on fish (see Case Study combination of deterrent measures wiring. Essentially, the numbers No. 5). However, results have been to counteract this. of cormorants utilising the very variable, and in some trials overall study area decreased, there has been no apparent benefit. It has been shown that the closer most probably since the birds had Furthermore, what has worked for wires are spaced, the more effective abundant alternative feeding sites
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nearby, away from the study area. cormorant can complete its take-off require no permanent fixing points. A median reduction in cormorant run underneath the wires. Dependent This could thus be another measure visits of 99.5% and 98.5% was on the span of water to be covered, that would be suitable for use at recorded in the ponds with wires wires may have to be supported by stock ponds, although there is also spaced at 5 m and 10 m intervals poles located in or around the pond scope to consider their use on small respectively, while there was to maintain the required elevation. recreational fisheries, perhaps on also a smaller median reduction However, other practicalities may a temporary basis (e.g. at times of in cormorant visits at the control require alternative deployment peak predation or when there are ponds of 48.4%. The decrease in arrangements. For example, it may few angler visits). cormorant visits was significantly be necessary to deploy wires at greater in the wired ponds (both greater heights in order to facilitate Wires should be made as visible 5 m and 10 m) compared to access to the water (e.g. to carry out as possible to incoming birds, both the controls, but there was no fishery management or fish farming to act as a deterrent and to prevent significant difference in the number activities). Alternatively wires might the deaths of cormorants or other of cormorant visits between the 5 m be more conveniently strung close birds through collision. Steel wires and 10 m wiring. to the water surface supported by may offer the most permanent and floats. durable option. However, coloured Other trials with wires set at 10 m nylon cord is also commonly used spacing have produced more variable Floating ropes provide another for overhead ‘wires’ because this is results and, in general, more success ‘wiring’ option for deterring relatively cheap, durable and easy has been achieved with wires spaced cormorants from water bodies. to deploy. For example, coloured 4–8 m apart. Spacing of 7.5 m or less Trials on catfish ponds in the plastic tape (4 mm width and spaced is generally recommended, although USA using parallel lines of thick at 20 m intervals) was successfully spacing may need to be balanced (9.5 mm diameter) yellow rope, used to deter cormorants from a with any potential impacts on fish spaced at 15–17 m intervals with 3.5 ha gravel pit located in a core husbandry practices. foam floats attached, reduced cormorant breeding area close to the the numbers of Double-crested River Danube upstream of Vienna. The height of the wires above a Cormorants using the ponds by The tape took around two hours pond is also believed to affect their 95% for the 3–5 weeks that the to deploy and ducks continued to efficacy. Reports indicate that wires ropes were in place. However, utilise the site. suspended 30–40 cm above the towards the end of the trial, some water surface are most effective, as cormorants appeared to have Parachute cord is another practical at this height the wires interfere with learned how to negotiate the ropes. alternative, especially as its a cormorant’s take-off run. If set Such floating rope deterrents have elasticity enables it to be drawn lower the cormorant is able to ‘jump’ the advantage that they can be taut over a pond. Bird deterrent over the wires; if set higher, the deployed and removed quickly and tapes are also available for
Wiring configurations at fish ponds, Germany. Photos courtesy of Thomas Keller.
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purchase and are highly visible, although these degrade over time and may be more suitable as short-term measures. Attaching coloured ‘flags’, reflective tape or CD discs at appropriate intervals can readily enhance the visibility of wires. Once installed, wiring systems require little upkeep, other than maintaining proper tension and replacing occasional broken wires. For this reason, it is better to use multiple single cords to span a pool, as these can be easily replaced, rather than a continuous cord looped from bank to bank, where a single break might cause the whole network to collapse.
Various wire configurations have been used in trials, but no optimum design has been identified. It appears that spacing of the wires is probably more critical than the arrangement used. Configuration options have included parallel lines, regular rectangular grid patterns (the latter techniques are most Parallel cords protecting a fish-rearing pond, UK. commonly used) and irregular Photo courtesy of Bruno Broughton. zig-zag patterns. An alternative ‘circus-tent’ construction has also proved effective in the Netherlands, predation, but allowed ducks to fly In Slovenia, agricultural string where wires were strung from the onto the pond successfully. (used in hop growing) has been top of a 10 m post in the middle of stretched in a zig-zag pattern over a pond to the bank, like the spokes Overhead wires have been employed pools in small streams — known of a wheel, with wire spacing at with some success to deter to be predation ‘hot spots’ — the pond edges of 14–15 m. This cormorants in a number of countries. where it proved both cheap and had advantages over a grid system They have mainly been used at successful at protecting fish in by reducing obstacles to boat fish-farming sites containing small these environments. However, the operation. This arrangement caused ponds of uniform shape, rather than technique required considerable less hindrance to cormorant take- on recreational fisheries where the maintenance to remove vegetation off runs, but it appeared to be more size of the water bodies and their debris falling from bankside trees. effective than a grid arrangement at more complex shapes can present deterring birds from landing. insurmountable difficulties. However, In Austria, several upland river overhead wires have been deployed sections were protected with At one fish-rearing site in the in conjunction with brightly coloured 3–4 mm diameter wires in order UK, parallel parachute cords warning wires and tapes to protect to prevent cormorants reaching stretched tautly across a pond at small rivers and other linear water their prey, principally Grayling approximately 30 cm intervals bodies in some countries, including (Thymallus thymallus). The wired completely prevented cormorant Austria and Italy. sections extended up to some
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hundred metres of river length, some damage to the wires — for the wires being attached between example, as a consequence of the trunks of trees or bushes on flooding and vandalism — the both banks. The distance between density of some fish species was the wires — generally less than higher in the covered sections. 10 m — and the water surface was chosen carefully to enable sporting Similar techniques have been used activities like canoeing or rafting successfully to protect wild trout to continue. To avoid injuries to and Grayling on the upper River cormorants and other birds that Tevere in Italy. However, they were sometimes do not recognise wires, considered to be visually intrusive conspicuous warning tapes were by some walkers and tourists, and also attached to the wires. local wild boar hunters thought that the wires caused the animals to The wires were kept in place abandon their usual tracks, making between October and March/April, them harder to kill. the period when cormorants are present. Anglers inspected some of 4.2.3 Floating plastic balls the wired river sections on a daily basis and reported that they had not Covering a pond with floating seen any cormorants entering these plastic balls has been used as a either by flying in or by diving and very effective method of keeping swimming into the sections from birds from landing on small bodies adjacent areas. Other bird and fish of water. This method has been ecology monitoring is ongoing in the especially useful for keeping wired and adjacent, unwired sections. waterbirds away from effluent Interim results show that despite ponds or bodies holding toxic water where the birds may be harmed. Due to the relatively high cost of this method, it may not be suitable for fish breeding ponds unless the ponds are small or the fish are especially valuable (such as brood stock or ornamental fish).
4.2.4 Facility design and construction When establishing new aquaculture facilities or stock ponds, careful design of the site can greatly help the incorporation of measures for deterring predators from the outset. For example, fish farms for salmonid production in Denmark were designed in a way that allowed wires to be easily incorporated. Nets and wires can be used on Wires with warning tapes across a river, Austria. square or rectangular ponds far Photo courtesy of Reinhard Haunschmid. more easily than on round or oval
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ponds, or those of irregular outline. to protecting small areas of water less durable, cheaper, temporary Where anti-predator nets are to be and particularly valuable fish structures might also be considered used over man-made ponds, the stocks, such as those found at at some sites, such as stock ponds water bodies could be designed with fish farm sites. Permanent wiring and, perhaps, small fishery waters. dimensions that enable standard- systems are probably more widely sized nets to be deployed over them. applicable and can be used for Acceptability Ideally, new aquaculture facilities protecting larger fish farms and The use of exclusion techniques is should not be constructed in known stock ponds, but they are probably widely recognised, highly effective cormorant flyways. also more cost-effective at relatively and has a high level of acceptability small sites. Both nets and wires will in most instances. Such measures 4.2.5 Overview of exclusion be inappropriate at most fishery are mainly used locally at fish farm sites where the size of these water businesses to protect relatively techniques bodies will be a major constraint. small sites containing valuable Efficacy stock. Generally, they are unlikely Nets and wires are readily available In addition, aesthetic considerations to attract criticism or comment and can provide reliable, long-term, and the problem of entangling from the general public. However, cost-effective options for removing fishing lines will also be problems, aesthetic concerns might arise or reducing cormorant predation although some types of angling where exclusion devices are used at a site; their effectiveness might still be possible in the open at natural sites and reduce the depends on proper installation ‘lanes’ between wires if these perceived amenity value. The and maintenance. Indeed, netting were of sufficient width. However, use of netting will clearly not be enclosures that completely enclose wiring systems can be deployed on appropriate at sites of designated a site provide the only reliable a temporary basis and so might still nature conservation status, means of excluding all birds (and offer the potential for short-term, particularly where this is in respect other predators) from a site. In seasonal protection at such sites. of other bird species. It should be contrast, ‘wires’ typically deter borne in mind that the deployment birds from using sites, but they Costs of such structures will also affect are unlikely to exclude them The cost of installing a full the ability of waterfowl and other altogether. Nonetheless, wires can netting enclosure at a site will wildlife to access protected sites. still be very effective at reducing be high and this will need to be Further, nets and wires can result fish losses. The efficacy of such balanced against the level of in birds getting entangled and structures varies according to protection required and the value damaged — especially where such the system chosen (particularly of the stock being protected. In structures are poorly maintained or the spacing of the wires) and can contrast, wire deterrents can be deployed in a manner that increases be particularly effective where deployed relatively cheaply and the risk of accidental capture (e.g. cormorants have access to other need little labour to maintain, low visibility, fine mesh). feeding areas in reasonably close but like netting they need to be proximity. Efficacy may also checked regularly for damage decrease over time as birds learn to that will otherwise be exploited 4.3 Reducing Fish Availability avoid the wires. It may therefore be by birds. For both techniques, the To Cormorants — Fish Stock necessary to use other deterrents in potential durability and long-term Management Techniques conjunction with wiring. efficacy of the measures need to be weighed against the losses of fish The idea behind this selection Practicality to cormorants, the inconvenience to of tools relies on the fact that The applicability of enclosure those requiring access to the water, cormorants, like all predators, need techniques will inevitably such as anglers or farm managers, to make a number of choices when be constrained by practical and the costs of alternative selecting where to feed. Although considerations and costs. In deterrent measures that may require whether cormorants are actively practice, netting exclusion substantial ongoing expenditure. It ‘choosing’ where to forage is open structures are likely to be restricted should also be borne in mind that to debate, a number of issues must
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be balanced if birds are to obtain the introduction of fish so as Furthermore, prior to stocking their daily food requirements. to minimise the likelihood of all fish will have undergone These will include the body state encounter between birds and fish. some stress in handling and/or of the bird (whether it is losing or For example, this might involve transport. Once released into a new gaining weight), environmental delaying stocking to reduce the environment, often where they are conditions (more food/energy availability of fish during the no longer fed artificially, stocked is required during colder/wetter period of peak cormorant numbers, fish thus need to learn quickly how periods), the state of the annual or draining and removing fish to survive, perhaps foraging on cycle (migration periods, breeding from more vulnerable fish farm new prey species, learning to use season, over-wintering) and ponds prior to the arrival of cover and to avoid a range of new the distances between roosts or cormorants. Delaying stocking predators. colonies and feeding sites. Foraging can be appropriate in the case of site choice is also dependent on recreational put-and-take trout Where fish are stocked regularly, the ‘availability’ of suitable areas fisheries, particularly where it is advisable to ‘trickle’ stock and both the number of potential they mainly operate from spring fish at regular intervals rather than feeding sites and their ‘quality’. through to autumn and where release larger batches of fish less In simple terms, ‘high-quality’ cormorant numbers are highest frequently. Furthermore, stocking foraging sites will be those that in winter. In such instances, it fish at a number of locations around offer risk-free, undisturbed access would be advisable to stock fish the fishery margins, for example and feeding, with good supplies of as late as possible prior to the from a boat, or deploying scaring relatively easy-to-catch fish. start of the fishing season and to devices at stocking sites, may help ‘run down’ the numbers of fish to avoid predators aggregating at While many of the techniques at the end of the season to avoid specific release points. It should described already in this Toolbox leaving high densities of fish to be recognised that increasing have involved the deterrence or over-winter. However, the viability the frequency of stocking and exclusion of cormorants, there of this approach will be limited the number of release sites will are also a number of ways in where fisheries remain open, or entail additional transportation which cormorant-fishery conflicts where cormorants are present in and handling costs, and so these might be influenced through the substantial numbers throughout the management options may be more management of the fish stocks year. appropriate at larger fisheries themselves. Such techniques (where economies of scale may attempt to alter the ‘quality’ of the 4.3.2 Frequency and apply) or for those that have their foraging opportunities available location of stocking own rearing or on-site fish holding to cormorants by trying to make facilities, such as tanks or floating fish less easy for the birds to catch. The frequency and location of cages. The underlying principle is that stocking can also be managed if fish are difficult to catch, then to reduce the chance of large 4.3.3 Regulating fish density the birds may choose to feed on aggregations of recently released, other waters where the fishing is naïve fish attracting predators. At aquaculture sites there may also easier. For example, where fishery Newly-stocked fish can be at a be opportunities for regulating managers have control over fish significant predation disadvantage fish densities during sensitive stocking regimes, there are several because anti-predator behaviour periods. For example, pond options that might reduce fish are learned during a fish’s lifetime owners in Germany can reduce losses and make sites less attractive as well as through instinct. Fish the fish density in some Carp to foraging cormorants. from a hatchery or fish farm are ponds at times of increased threat likely to have poor anti-predator from cormorants. However, such 4.3.1 Timing of stocking behaviour. They may have lived in stock density manipulation is not artificial environments with little or feasible at most fishery sites, and One simple means of reducing no cover and they might have little anglers at recreational fisheries cormorant predation is to time experience of avoiding predators. would probably not accept lower
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fish densities during the main cormorant feeding period.
While of limited applicability, this simple technique can be an effective short-term measure in aquaculture and at some recreational fishery sites that are routinely stocked, and associated costs can be relatively low.
4.3.4 Size at stocking A further option for reducing losses to predators in some situations is to stock with larger fish. This is Cormorant damage to rainbow trout. because above a certain size, fish Photo of unknown origin (UK). become less vulnerable to capture and, ultimately, too large to be swallowed by cormorants. The size kg), the increased rearing costs are at which fish become significantly reported to have been covered by less vulnerable will vary for the better catch return rates and different species of fish depending reduced levels of scarring damage on factors such as their body caused by cormorants. The size Specimen-sized Carp. shape. The potential for stocking of the cormorant winter roost and Photos courtesy of Bruno Broughton. larger fish will be more applicable breeding populations near Grafham to fisheries that are dependant on has fallen since these measures were regular introductions of fish, such introduced, quite probably reflecting among the smaller (25–35 cm) trout as put-and-take trout fisheries, than changes in local prey availability stocked (although return rates of this to ‘natural’ fisheries. at these fisheries. The stocking of size group were poor due to higher larger trout is now routine at put- losses), but much higher among fish This method has proved fairly and-take trout fisheries in the UK. of 35–45 cm in length. Above this successful at trout fisheries in the size, the incidence of cormorant UK where, after stocking with The extent to which fish are marks on the fish was low. relatively large trout, cormorants damaged by cormorant capture (and consumed fewer stocked fish and subsequent escape) also appears However, this approach has limited either had to switch their diet to to be influenced by fish size. It use for many freshwater fisheries, resident ‘coarse’ fish (i.e. non- seems reasonable to assume that especially those on rivers. Natural, salmonid) populations or move to the chances of a fish escaping from sustainable fisheries cannot be other sites. Both Rutland Water a cormorant, once grasped in the established if stock regimes are and Grafham Water, two of the bill of the bird, will be relatively constantly being manipulated, best known, large trout stillwater slight for smaller fish, but will and fisheries biologists in many reservoirs in England, have increase progressively as the fish countries do not favour the stocking followed such a successful fish gets larger up to the point where of unusually large fish to enhance stock management programme the fish becomes too large for the natural fish populations. However, in recent years. Although the cormorant to catch. Investigations not all anglers may share this view. minimum size of the fish stocked at a stillwater trout fishery in the Fish of a size that are too big for has been increased from about 1lb UK support this. The incidence of cormorants to eat do not occur to 1.4lb (0.45–0.64 kg), with a high fish bearing wounds consistent with naturally in many species and are not proportion of fish above 2lb (0.91 ‘handling’ by cormorants was low available commercially in others.
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year old (>700 g) Carp through Saxony fish farm Carp showing supplementary feeding, a technique cormorant damage. tested successfully in Saxony Photo courtesy of INTERCAFE. (eastern Germany). The aim here is to encourage the Carp to grow more quickly, so that in their second summer (when they would otherwise be of optimal size for cormorants under ‘normal’ growth conditions) the fish are generally too big to be consumed by the birds.
Similarly, at cyprinid farms and recreational fisheries in the UK, the aim is to grow Carp up to or over 1 kg in weight during or towards the end of their second summer. At this and greater weights, anti-cormorant measures can be The possible exception is stocking Carp fishing in the UK in recent withdrawn in the knowledge that recreational fisheries with Carp of years has been partly influenced they will no longer be required to 2lb (0.91 kg) and larger, but this by the vulnerability of smaller, protect the fish. is not applicable to river fisheries native freshwater fish species to (in the UK at least) and is regarded cormorant predation. 4.3.5 Species vulnerability by many people as inappropriate for many stillwater fisheries, A variation on this approach is Prey vulnerability is known to on environmental grounds. It also used in aquaculture, with vary for different fish species as is widely recognised, however, the rapid production of larger, a consequence of factors such as that the marked development of one-year old (>100 g) and two- fish size, body shape, behaviour
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and the type of habitat they prefer. Thus, for example, species with larger potential size (e.g. Carp and Trout), deeper bodied fish (e.g. Common Bream, Abramis brama) and those that make extensive use of habitat features, where available (e.g. Tench, Tinca tinca) are likely to be less vulnerable to cormorants. It also appears that Brown Trout are relatively more vulnerable to cormorant predation than the non-indigenous Rainbow Trout (Oncorhynchus mykiss). While wider biodiversity issues also need to be borne in mind, such differences may have some application for fishery managers when considering the cost- effectiveness of different stocking Alternative prey species — small Roach (Rutilus rutilus) and Perch (Perca policies. fluviatilis). Photo courtesy of Bruno Broughton.
4.3.6 ‘Buffer’ species and continue to forage there after sizes, rather than managing the The idea of managing fish stocks any spare buffer fish have been waters only for fish species of to enhance or introduce alternative, consumed. direct use to man. less valuable prey species, either in the ‘target’ fishery or in nearby Investigations in Australia indicated 4.3.7 Location of fish- bodies of water, has been proposed that fish losses to cormorants were holding facilities as a way of reducing cormorant lower in farm dams (used mainly impact on more valuable species. for irrigation) where these also Locating the most susceptible This is unlikely to be appropriate for contained resident populations fish species or size classes close rivers and costs may be prohibitive. of crustaceans (crayfish). It was to centres of human activity or However, the presence of Cyprinid therefore suggested that stocking near buildings is a simple option (Carp family) fish at a stillwater farm dams with crayfish could be for reducing cormorant impact at trout fishery, for example, does used as a method to buffer cormorant fish farm sites. For example, fish reduce the losses of trout. It is not impact and reduce fish losses. wintering basins and fishing gear clear whether or not higher overall in Italian extensive aquaculture fish densities, due to stocking buffer The natural availability of different facilities are often located close to prey alongside commercial species, fish species in a community can buildings and areas most regularly may serve as an increased attraction also have this buffering effect: used by humans. However, to predators. If so, the stocking if a proportion of the birds’ diet cormorants were not deterred of buffer prey at alternative sites comprises fish species of little from foraging here unless active away from important fisheries may recreational or economic value, deterrents (e.g. blank shots, be a preferred option, although this will reduce the impacts on shooting, human patrolling) were an increase in the total density of more desirable or valuable species. used as well, and the birds can prey in an area might also attract On natural or semi-natural water also learn to feed intensively for more predators to the area as a bodies, this consideration underpins short periods when humans are whole, with the added danger that the desirability of maintaining absent — during lunch breaks, for fish might habituate to an area a wide range of fish species and example.
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Moving fish to less vulnerable periods of days or perhaps months of managing fish movements and sites may also be an option at at others. rearing locations at aquaculture some recreational fishery sites that facilities can be low, particularly feature a range of adjacent water Practicality where these can be incorporated bodies and where different species Fish stock management techniques into standard operating procedures. are kept in each. may be less widely applicable than other deterrents, and practicality Acceptability 4.3.8 Overview of fish stock is expected to range widely as The use of fish stock management management techniques a result of considerable site- techniques is likely to be a possible specific differences. However, solution only in certain sectors Efficacy where regular stocking or fish and will often be less widely Where fish movements and movements take place anyway, applicable than other cormorant stocking are carried out as routine this can provide practical options management techniques. Where fishery management practices, for reducing cormorant impacts at applicable, it will have a high or within aquaculture operations, a range of fishery sites, including degree of acceptability in most regulating these (e.g. timing and rivers, stillwaters and aquaculture instances. Anglers, for example, frequency of release, location or facilities. Such measures might generally welcome the availability size of fish at release) can provide be incorporated into standard of larger fish and it is unlikely to simple and effective measures for operating procedures where this is attract criticism or comment from reducing cormorant predation. Such appropriate. In large water bodies the general public. However, it is techniques are typically of short- and river catchments, fish stock recognised that such an approach term duration (weeks to months) and manipulation may prove difficult has limited use for many natural, effectiveness will vary, depending or practically impossible to carry sustainable freshwater fisheries on the flexibility in the timing out. where the stocking of atypically of fisheries and/or aquaculture large fish to increase natural practices relative to periods of peak It should be recognised that fish fish populations is generally cormorant occupancy. movements and releases into water not favoured on ecological and bodies may be covered by regional biodiversity grounds. The use of alternative ‘buffer’ and/or national regulations, and fish species is unlikely to be local guidance and any necessary widely applicable (and artificially approvals should be sought in 4.4 Reducing Fish Availability elevated fish stocks may attract advance. To Cormorants — Habitat more predators), but it may still be Modification Techniques effective in certain instances — for Costs example, where surplus fish are The costs of implementing fish The philosophy behind this set readily available during periods stock management techniques are of tools is an extension of that of peak cormorant abundance and likely to vary widely, dependent on described previously in relation to can be stocked at waters away the individual site, the flexibility fish stock management. These tools from sites sensitive to predation, available and the group of aim to make sites less attractive to or to relieve the pressure on key stakeholders concerned. However, cormorants for either roosting or target species. Such measures may in many instances costs can be low. nesting, or as feeding sites. Such be best employed alongside other Even where larger fish are stocked, tools will never stop cormorants deterrents in order to maximise the higher rearing costs can be from roosting, breeding or feeding their benefits. The effectiveness offset by better survival, higher altogether. However, at a site- of relocating the holding facilities returns to anglers and greater specific level they may reduce or for particularly sensitive fish is angler satisfaction. This has been eliminate cormorant presence in reported to be strongly dependent shown to provide a cost-effective an area, prevent birds colonising, on the local situation. It has been option in some fishery situations, or may help to make foraging reported to be ineffective in some particularly for recreational trout sites less attractive to birds, situations, but effective over angling in lakes. Similarly the cost thus encouraging them to move
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elsewhere. A possible danger is that ▪▪ The effects of vegetation at use of deterrents at existing roosts this may result in greater dispersal the edge of water bodies on and the provision of alternative of the cormorants in a region, shade, temperature, and other roost sites, complete with nesting leading to the establishment of new, aspects of microclimate and materials/artificial nests elsewhere. smaller roost sites. microhabitat. This has been used to reduce the ▪▪ The impact of removal on tree impact of cormorants on important If there are no other safe roosting populations locally and on other migratory salmonid species. sites for some distance, cutting species that use the tree(s). down a few trees on the banks of a Disturbing night roosts can be pond may be enough to make a site Thus, the removal of the only tree effective at deterring birds from a unattractive for birds. Preventing alongside a fishery or fish pond site. To prevent birds from using a the establishment of a cormorant may prove effective for cormorant night roost the cormorants should roost site may stop cormorants control, but could alter desirable be disturbed repeatedly at the being attracted to an area by the shade, microhabitat and microclimate site at night using pyrotechnics presence of other birds or may characteristics. This technique will or visual deterrents (described prevent subsequent attempts at generally not be appropriate for previously in this Toolbox). This breeding — roosts are often the rivers or larger sites where there should be repeated at least three precursors of colonies. As with most, are numerous alternative roost sites times during the course of the if not all, of the techniques described available for the birds, as the removal night for a number of consecutive here, their use will be most effective of these resting places may prove nights. By repeatedly arousing the if applied with a good knowledge impossible. However, the method can cormorants and forcing them to of the region and the behaviour, be targeted at a particular area, rather fly around in the dark, the birds movements and daily foraging than at a single fish pond or fishery, learn that the site is an unsafe place patterns of cormorants in the area. particularly where feeding and to spend the night and will find There are thus a number of options roosting sites may be some distance alternative sites. for reducing cormorant-fishery apart. conflicts by altering the habitat both This method is also highly above the water and below it. The practicality and cost of removing effective at preventing birds from or modifying roosts also depends establishing new nesting sites, as 4.4.1 Elimination of resting on the type of structures being used they will initially roost in a site or roosting places as the roost site. For example, it before building nests there. By may be possible to remove isolated demonstrating to birds that a site is It may be possible to cut down trees trees or cover them with wires or unsafe they are less likely to begin or modify the resting and roosting netting, but commercially available nesting there. Once the nests have sites used by cormorants to make a anti-perch devices would need to be been built and the eggs are laid, it is nearby or adjacent foraging site less used for roosts on pylons or lamp very difficult to ‘persuade’ birds to attractive. However, the long-term posts. Other techniques such as leave using this method. In Israel, effectiveness and true cost of this pyrotechnics, bio-acoustics and laser for example, a Pygmy Cormorant approach is likely to vary with the light can also be used, either on their nesting site was successfully moved function of the site, for example: own or in conjunction with physical from an important fish farming area methods, to make roosts unattractive. to a natural lake through repeated ▪▪ Whether cormorants are using On the Columbia River in the USA, disturbance of night roosts prior to the site for breeding, potential researchers have had some success in the nesting season. No birds were breeding, night roosting or day relocating Double-crested Cormorant harmed and it was not necessary to loafing. roost sites through the combined destroy any nests. ▪▪ Any adverse environmental or amenity impacts of tree removal. ‘Disturbing night roosts can be effective ▪▪ The availability of alternative local roosting and foraging sites. at deterring birds from a site’
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the establishment of new colonies and to contain cormorant-fishery conflicts within certain areas. Descriptions of other methods for reducing reproductive success are provided in Section 4.5.1.
Other techniques can also be used to disturb birds and prevent nesting taking place. These include the use of audible deterrents, human disturbance and other visual deterrents (e.g. laser light, water jets and model helicopters and aircraft). Regular disturbance of adult birds at breeding sites can also allow predatory birds and carnivores to attack the nests and enhance the deterrent effect. In general, the use of other scaring methods together with nest disturbance and destruction is considered more likely to cause potential breeding birds to abandon an area. However, the possible disturbance of other non-target species must be taken into account when considering this Cormorant roost in Israel. Photo courtesy of Bruno Broughton. technique, especially as cormorants often share their colonies with The destruction or disturbance of However, disturbance at colonies a number of other bird species. cormorant night roosts is used to must be undertaken carefully in Further, if a site is part of the deter cormorants in a number of order to avoid the risk of spreading Natura 2000 network, deliberate countries around Europe. However, birds to new sites where they are disturbance would first require an it should be remembered that, in not wanted. Nest destruction has impact assessment under the EU some countries, nests (when in use been used at a site in America Habitats Directive. or being built) may be protected to reduce the impact of Double- under national legislation and it crested Cormorants on local fish 4.4.3 Improving habitat may be an offence to damage or stocks and on the nesting habitats quality for fish destroy these without a licence. of other colonial waterbirds. Weekly visits to the colony were Underwater habitat plays a key 4.4.2 Elimination of nests carried out, nests on the ground part in the interaction between fish were removed by hand and those predators and their prey. Weed cover Nest destruction is subject to in trees dislodged with a telescopic and other submerged structures formal controls in most countries pole; nesting material was scattered are widely used by prey fish to and requires a licence. The to discourage attempts to re- reduce the risk of predation from technique is time-consuming, build the nests. This programme Pike (Esox lucius) and other fish though relatively inexpensive if prevented further cormorant predators. Research has shown labour costs are ignored, and it breeding in the area. In Denmark, that the survival of prey species can be very effective at controlling the removal or destruction of nests can increase, and the growth of bird numbers in a specific area. is also used successfully to prevent predators such as Pike decrease, as
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vegetation density becomes greater. smaller rivers and stillwaters. to help attract and hold fish. The extent to which similar factors Typically, these are implemented as Structure might be provided in might regulate interactions between general management measures to a number of ways, for example: cormorants and fish is less well improve fish habitat and hence fish brushwood bundles, branches, established, but there is every reason populations and are not undertaken old Christmas trees, frayed rope to believe that they will apply to all primarily to reduce cormorant to mimic artificial weed, etc. fish-eating predators be they fish or predation. However, reduced ▪▪ Overhead cover — it is also well birds. Indeed, prey accessibility as predation risk is quite likely to known that shading/overhead well as prey density has been shown be an additional benefit of such cover attracts fish. Additionally, to influence the foraging success of improvements. shading also provides fish fish-eating birds and, consequently, with an enhanced ability to the selection or abandonment of 4.4.4 Artificial Fish Refuges detect oncoming predators. For individual feeding sites. Thus, example, a shaded observer can habitat features are expected to play In some parts of Europe see a sunlit target at more than a major role in the anti-predator cormorant numbers are highest 2.5 times the distance that a behaviour of many freshwater fish during the winter period when the sunlit observer can see a shaded species and in determining their natural cover available to fish is target. vulnerability to predators. at its lowest because aquatic weed ▪▪ Cormorant exclusion — has died back. Fish swimming Cormorants must be excluded Good habitat is vital for successful, speeds, which are governed in from the refuge areas if these all-round fisheries management and part by water temperature, are structures are to be effective. for healthy, sustainable fish stocks also at their slowest during this Refuges therefore need to be in both rivers and stillwaters. A period, and cormorants can swim surrounded with a protective successful fisheries management faster than most of their prey mesh to make them cormorant- strategy might, therefore, be to species at this time of year. Using proof. Research has indicated provide sufficient cover for fish, artificial refuges to modify the that use of a mesh of about recognising that the most cost- habitat and provide additional 10 cm (e.g. typical stock effective way of minimising the cover for fish could therefore be fencing) will effectively exclude impact of predators on any fish used to reduce their vulnerability cormorants, while optimising population is likely to be by making to cormorants at a period of the access for fish. sure that the environment provides year when they might otherwise fish with the best opportunities to use be particularly at risk to Trials using simple cage refuges their natural defence instincts, as well predation. To be effective, such have demonstrated that fish will as meeting feeding and spawning refuges need to both attract fish very rapidly locate and utilise these requirements. In seeking to provide and provide them with protection in the absence of other available adequate cover for fish in fisheries, from predators. cover. Fish prefer these structures there may be potential for enhancing to open water, particularly during natural habitat features through, for Investigations have shown that daylight hours (when cormorant example, the creation of marginal there are a number of key design foraging occurs). Investigations at reed fringes, permanent overhead features to help ensure fish use inland fisheries have also confirmed and in-stream cover and off-channel artificial refuges and confer some that large numbers of fish can areas (e.g. shallow pools, backwaters benefit. These are: locate and use refuges, although and ditches). Alternatively, the use of this appears to be moderated by the artificial refuge structures might be ▪▪ Structure — many species of extent of existing available habitat considered (see Section 4.4.4). fish are attracted to natural (e.g. marginal reed beds) at any habitat features, such as weed particular site. It is known that actions taken to beds and underwater tree roots. improve habitat quality for fish The inclusion of some form of Research in the UK has provided are common and widespread structure within a refuge is thus clear evidence that refuges can, across Europe, particularly in seen as an essential requirement in some cases, protect fish and
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Simple cage refuge used in experimental trials in the UK. Photo courtesy of Ian Russell. reduce the foraging efficiency of refuges were made from a number higher and the foraging efficiency cormorants. A series of comparative of individual cage units, each of the birds (prey capture rate trials were carried out in two measuring 2 m x 2 m x 1.2 m high, and the proportion of successful identical, small (0.12 ha), shallow and incorporated overhead shading foraging bouts) significantly lower. (1.35 m) rectangular ponds located (commercial shade netting), internal In effect, the birds were working in a disused water treatment structure (small conifer trees) and an harder for fewer captured prey. works. The ponds were adjacent overlay of light-gauge stock fencing There were 77% fewer cormorant to one another and were drainable, around all four sides and the top visits to the refuge pond than such that fish stocks could be (see picture). Twelve refuge cage the control pond, on average. unambiguously sampled at the end units were deployed in each trial, There was also a 67% fall in the of each trial. At the start of each grouped in two discrete blocks of mean mass of fish consumed per trial, the ponds were filled and six. In total, the refuges represented cormorant visit and 79% less fish stocked with Roach and smaller about 3.5% of the water volume in mass lost in the refuge pond. The numbers of Perch and Carp, with the refuge pond. The upper surface trials clearly demonstrated that, an overall stocking density between of the refuge was approximately where alternative foraging sites 259 and 459 kg/ha, consistent 15 cm below the water surface. are available, the presence of with those at many recreational refuges can dramatically reduce stillwater fisheries in the UK. One The results indicated that the quantity of fish eaten by of the ponds contained refuges and cormorant dive duration in the cormorants at a site and make a site the other had none (control). The refuge pond was significantly less attractive to foraging birds.
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While these large benefits were The extent of existing natural cover achieved with a refuge volume of at a site should also be considered 3.5% relative to the volume of the in assessing whether refuges might pond (no other cover was available), be beneficial. Refuges may be more recent trials have shown that of particular value in relatively smaller refuge volumes, down to featureless sites that have little or between 0.5% and 1% of the pond no existing cover for fish. Refuge volume, also have very marked placement is likely to be less critical positive effects. Indeed, while in such sites, since investigations evidence derived from a range of indicate that fish will quickly find trials using different sizes of refuge and use the new structures. In such suggests that there is a positive instances, trials have indicated that relationship between refuge size deploying refuges together in one and protection of fish — i.e. the or more bigger groups is likely to larger the refuge size the better provide better protection for fish the protection provided — this is than using a large number of very not a simple additive relationship. small, widely dispersed refuges. Thus, the largest net benefit, in However, where some existing the absence of other cover, results cover is available, enhancing from the provision of even a small these natural features may be quantity of refuge. better than positioning refuges elsewhere. Thus, placing refuges The potential benefits of using adjacent to, and integral with, refuges are likely to vary with the emergent vegetation may well be fish species present and from site more beneficial than providing Refuges made from coils of stock to site. Initial evaluation suggests alternative refuge areas in open fencing, UK. that refuges might be most suitable water, well away from any existing Photos courtesy of Mark Ives and for smaller shoaling species such cover. Alternatively, protecting Martin Read. as Roach, Perch, Rudd (Scardinius existing natural refuge areas, such erythrophthalmus), and small as marginal emergent vegetation, Bream and Carp, but a range of through the use of fenced and Another popular option has been the other species may benefit. Refuges covered enclosures, or adding use of floating refuges, sometimes may not be a suitable option in additional natural features (e.g. tree referred to as ‘eco-islands’, since some recreational fisheries where branches), can represent effective these can be planted with various it is necessary to have large ‘snag- alternative strategies. emergent plants (rooted in coir free’ areas for playing larger matting). Once established, the fish, such as in specialist Carp Fishery managers have deployed fish roots from the emergent plants fisheries. The size of a fishery and, refuges at a number of inland sites extend well down into the water possibly, the water transparency in the UK and a number of designs providing cover for fish, and the will also be important in deciding have been tried. The most widely vegetation also provides a habitat whether fish refuges are likely used option to date has been that of for other wildlife. Mesh enclosures to be a practical option. Refuges small ‘reefs,’ constructed by joining should be suspended beneath the are likely to be most effective in together coils of stock fence. The island to exclude cormorants and smaller stillwater fisheries (<5 ha), coils of wire in such designs provide provide a secure refuge area for and costs and practicalities may both the cormorant-proofing and fish. This type of refuge has the preclude extending the technique some structure, although this can be advantages of being more ‘natural’ to large water bodies, although in further enhanced through the addition and aesthetically pleasing and is the absence of any cover even small of brushwood or other materials; now commercially available in the refuge areas should provide some shade netting should also be included UK. However, these designs are benefit for fish stocks. to provide overhead cover. more expensive than some others.
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There will, of course, be a number important to ensure that the refuge of constraints and practical structures themselves do not pose limitations to using artificial refuges, a risk of entanglement for fish and and they may be impractical in large other wildlife. commercial fish-growing ponds with very high densities of fish. However, correctly designed These structures may cause fish to to prevent birds entering them, aggregate unnaturally, a particular refuges should provide the fish with problem where competitive ‘match’ some protection and help reduce angling is practised. There is also expensive stock loss. Refuges the risk that, without appropriate could be used on a seasonal identification, fishing tackle may basis, being deployed only for the become snagged, with the resulting winter period, when fish are most loss of gear becoming a hazard vulnerable and there are usually for other wildlife. It will also be fewer anglers fishing. Further details are available at: http://www. naturalengland.org.uk/conservation/ wildlife-management-licensing/ leaflets.htm#piscivorous.
Initial feedback from anglers in the UK and in other European countries has been largely positive, with perceived improvements in catches and fish abundance as a result of using refuges. Many anglers also reported that catches around fish refuges were good and that refuge structures were therefore often targeted as favoured angling ‘marks’. However, to avoid problems with snagging gear and potential conflict with anglers it is recommended that the position of
Floating ‘eco-island’ refuges, UK. Photos courtesy of Mark Ives.
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any refuges is clearly marked with Targeted management of the natural not represent a hazard to other small floats, and that they are sited environment, or the use of natural wildlife. There is also potential to minimise impact on angling or artificial structures, can also be to utilise refuges on a seasonal stations. It is also important that used to provide additional cover basis, deploying them only for refuges are constructed carefully, for fish and reduce cormorant the winter period when fish are using appropriate materials, to impact. Trials with artificial fish most vulnerable (and fishing effort ensure that they do not pose any refuges have demonstrated that, typically at its lowest). risk to fish or other wildlife. where alternative foraging sites are available, the presence of Costs While initial trials with refuges refuges can dramatically reduce the The costs of habitat management have mainly taken place in the UK, quantity of fish eaten by cormorants techniques will vary considerably the technique is now also being at a site and reduce the numbers of depending on their scale. For trialled at stillwater fishery sites cormorants visiting that site. example, the cost of removing a in a number of other European single roost tree at a site would countries and in aquaculture The size of a water body, the extent be low, while more extensive facilities in Germany, Italy and of existing natural cover at a site roost management measures over Spain. Preliminary results are and the fish species present are a larger area, or at a number of encouraging. all likely to affect the efficacy of sites as part of a broader scale artificial fish refuges. These may plan, would be relatively high. 4.4.5 Overview of habitat be of particular value in relatively Costs may also be affected by featureless sites that have little or any overarching objectives. Thus, modification techniques no existing cover for fish and that incidental benefits (at minimal Efficacy contain smaller shoaling species. costs) might be expected from Modifying the habitat, both general habitat improvement above and below the water, can Practicality works, with higher costs likely offer reliable, long-term (months The applicability of habitat for actions targeted specifically at to years) options for reducing modification techniques will cormorant-fishery interactions. Fish cormorant predation. The removal inevitably be constrained by refuges also vary markedly in price of resting/roosting places has practical considerations. The depending on the numbers used, been employed at sites around removal of cormorant resting or their design, the materials used and Europe to deter cormorants from roosting sites is probably only the manpower costs. Costs can be feeding in particular sites. The practical at smaller sites, or in substantially reduced where labour technique has been reported to localised areas, where birds can be provided on a voluntary be effective at some sites, with have limited alternative roosting basis — by stakeholder groups, the proviso that much depends options; the use of additional for example. However, for all on the characteristics of the site, deterrent measures may help with habitat management techniques, the particularly its size and the number making such sites less attractive. cost-effectiveness should take into and proximity of alternative Similarly, the size of a fishery account the potential durability and roost and foraging sites, as well will be important in deciding long-term efficacy of the measures, as the ecological and other costs whether or not fish refuges will as well as the scale of the losses associated with roost removal. be a practical option. Refuges to predators. It should be viewed are likely to be most effective against the potential recurrent While not specifically targeted in smaller stillwater fisheries, costs of using alternative deterrent at managing cormorant-fishery and costs and practicalities may measures. conflicts, the effective management preclude extending the technique of water bodies to optimise to larger stillwaters and rivers. The Acceptability environmental conditions for fish deployment of refuges must take Habitat modification techniques are will go a long way to ensuring that account of the needs of recreational generally considered to have a high fish populations are maintained fishermen and any other water level of acceptability. Widespread at healthy and sustainable levels. users and ensure that they do removal of roost trees might attract
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criticism from the general public all naturally occurring wild birds, numbers over a wider area or at and raise aesthetic concerns, but unless this is carried out under the the population level. such actions on a broad scale are provisions of Article 7 or 9. Article unlikely to be realistic or cost- 7 allows the hunting of certain Increasing numbers of cormorants effective anyway. General habitat species listed on Annex II of the need to be shot under these three improvement initiatives are usually Directive; this does not include scenarios. highly acceptable and broadly the cormorant. However, Article 9 welcomed. In relation to artificial provides that Member States may Cormorants can also be killed at fish refuges, feedback from anglers derogate from the protection of the other stages in their annual cycle has been largely positive, with Directive for a number of purposes, and perhaps the easiest is to take perceived improvements in fish including preventing serious damage advantage of cormorants’ colony abundance at sites containing to crops, livestock, forests, fisheries formation and to destroy nests or refuges. Many anglers have also and water, or the protection of flora eggs at breeding sites. In theory at reported good catches around fish and fauna, provided that there is no least, such nest or egg destruction refuges, with the structures often other satisfactory solution. Current will reduce the breeding output of being targeted as favoured angling information on lethal measures the birds (see below) — so that, ‘marks’. To avoid potential problems taken across Europe is summarised ultimately there should be fewer with the snagging of fishing gear it in another INTERCAFE report fledged birds at the end of the is recommended that the position of (see ‘Cormorants and the European breeding season, fewer older birds any refuges is clearly marked with Environment: exploring cormorant to visit fisheries in winter, and, small floats, and that they are sited status and distribution on a subsequently, fewer adult birds to carefully. It is also important that continental scale’1). The numbers breed. However, like most animals, refuges are constructed correctly of birds killed or taken under such cormorants are both flexible in so that they do not pose a hazard to derogations have to be reported to their breeding behaviour and their birds, fish or other wildlife. the Commission annually. populations are quite resilient to mortality — particularly if However, there are problems with experienced early in the life-cycle. 4.5 Killing Cormorants- killing birds in practice because dead For example, it is possible for Lethal Measures birds are very often quickly replaced cormorants to re-build their nests by others. This is particularly true at (sometimes at new sites) and to It is not surprising that the notion of sites on cormorant migration routes re-lay clutches of eggs. A reduction killing cormorants is very attractive especially in autumn and winter. It in breeding birds in an area also to many stakeholders. After all, a may also be the case at other times often leads to an increase in the dead cormorant represents one less of year if cormorants are moving numbers of young birds per nest bird to eat fish. Killing cormorants freely between locations. Shooting that are fledged successfully. This also gives the satisfaction of an cormorants is usually done for one is thought to be a consequence of ‘instant solution’. However, it must of three reasons: the reduced competition among be remembered that cormorants, like cormorants for food and the greater most wild birds, are subject to legal 1. As an aid to scaring, in order to availability of fish with which protection throughout much of their reinforce other deterrents (often adults can feed their offspring. range. In Europe, cormorants are auditory or visual ones). Similarly, reducing the breeding protected under the Birds Directive. 2. To (temporarily) reduce the output of one, or a few, colonies Article 1 of the Directive provides number of individual birds may relax feeding pressure on that all birds naturally occurring in feeding at a particular site. some sites, allowing other birds to the wild and their habitat should 3. As a larger ‘cull’ with the capitalise and improve their own be protected; this extends to their intention of reducing cormorant breeding output. eggs and nests as well as all stages of their life cycle. Article 5 of the Such ‘density-dependent’ Directive requires Member States relationships are common in nature, 1 van Eerden et al., (2012) COST Action 635 to prohibit the deliberate killing of Final report I. making it particularly difficult
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to reduce numbers over large aquaculture facilities. Examples by density-dependent factors. areas or at the ‘population’ level. of such coordinated approaches Active measures would be required Indeed, it is likely that the greater are provided in the Case Studies outside this area in order to restrict the (downwards) ‘pressure’ that is section at the end of this Toolbox. expansion and, of course, this applied to reduce bird numbers, would not be easy, particularly at a the stronger will be the (upwards) This sort of coordinated approach, larger scale. Nonetheless, such an compensatory mechanisms that if applied consistently, also approach may have applications in will operate to re-build population provides a way of avoiding, at least certain situations. sizes. For cormorants, such density- in part, the problem of constantly dependent factors operate both fighting density-dependent, There have also been continued within and outside the breeding compensatory mechanisms. If birds calls from some stakeholder groups season. can be restricted to a particular for longer-term, internationally area and their expansion to other coordinated cormorant control Typically, lethal measures are surrounding (‘no go’) areas is at the pan-European level, with applied at a relatively local, often controlled, the population within the aim of reducing the overall site-specific level, where effects are the restricted (‘permitted’) area population size of cormorants likely to be relatively short term would become regulated by the across Europe. The possibility of in nature. The aim is to reduce the available resources (e.g. food and control at this level has been the numbers of cormorants visiting breeding sites). In such a scenario, subject of previous investigation specific sites or areas. numbers would be expected to using population models, with oscillate about some equilibrium or efforts to determine the levels However, the use of lethal carrying capacity level, regulated of control necessary to reduce measures (in combination with other non-lethal deterrents) can also be coordinated over a wider area — for example, to protect a ‘Egg destruction is used in several network of particular habitat types, countries to reduce local populations or to deter birds from using areas containing valuable, extensive of Cormorants’
the overall population size and to predict the ultimate size and distribution of the population. The widespread nature of cormorant breeding populations, with birds mixing and dispersing across Europe in winter, makes this a particularly challenging task. Nonetheless, efforts have been made here to summarise the main outcomes of this work and the factors likely to influence or constrain such a widespread management approach.
4.5.1 Reducing Reproductive Success
Cormorants shot on an Israeli fish farm. The technique of egg destruction is Photo courtesy of Ian Russell. used in several countries to reduce
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local populations of cormorants destruction methods. For example, dispersion of cormorants from (see Section 4.4.2). As with other egg removal can encourage re- nesting colonies where oiling takes lethal methods, this may be subject laying unless eggs are replaced by place, but this can be prevented if a to formal controls and require a hard-boiled or wooden replicas, small number of chicks are present licence. This technique is generally some pricked eggs may still hatch, in the colony. To be effective, only useful for ground-nesting and birds may abandon treated oiling needs to be repeated cormorants as it is more difficult clutches to re-lay eggs elsewhere. approximately every two weeks and costly to reach nests in trees. The efficacy of egg destruction to ensure almost all the eggs are Eggs can be destroyed by several is also believed to vary among oiled. Studies have shown that in methods: egg removal, egg pricking species. order to be successful in the long or egg oiling, although oiling run, at least 74% of the eggs need is the method most commonly The oiling of eggs is widely used to be oiled, and one cannot expect used and generally regarded as a on Double-crested Cormorants in to see reduction of the population cheaper, more effective and more the USA and Canada to reduce for at least two years, since humane method of egg control. This cormorant hatching success and cormorants do not reach sexual technique involves coating the egg to prevent colony establishment. maturity until two years old. shells with oil such as liquid paraffin It has the advantage over egg- or vegetable oil, which stops air removal or destruction in that the Oiling has been used in a number from passing through the shell to the adults will not lay a new clutch of colonies around the eastern basin embryo, thereby preventing it from and will continue to sit on the of Lake Ontario in recent years. developing properly. oiled eggs until it is too late in the This has been carried out using a season to breed effectively. Studies backpack sprayer on five occasions A number of factors can influence in North America have shown during the incubation period, at two the efficacy of different egg that there may be an increase in to three week intervals, to ensure
Egg oiling, Denmark. Photos courtesy of Henrik Lykke Sørensen.
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that each readily accessible nest Contrary to expectations, breeding However, re-nesting could not was treated at least twice over the numbers increased in 2006 (Figure explain the increase in 2008. Records period. A simple model has been 2), probably due to immigration of ringed birds among breeders developed to estimate cormorant from the nearest neighbouring showed that the increase in 2008 was feeding days and fish consumption in colony where nest numbers partly or entirely due to immigration. treated colonies relative to other local declined by 350 nests in 2006. The sudden immigration was untreated colonies. Thus, egg oiling However, as predicted, breeding probably related to a marked increase at one island colony in 1999 was numbers declined in 2007 and in the local abundance of Flounder estimated to have reduced the number 2008. The marked decline in 2008 (Platichthys flesus) which provided of cormorant chicks produced by might be a result of a combined prey of the right size for cormorants. 8,300, while fish consumption over effect of lack of recruits due to the The ringed immigrants were a the breeding and rearing period was egg oiling and poor food conditions combination of young birds that estimated to have been reduced by in that year leading to non-breeding presumably bred for the first time around 28% (~350 t). among some potential breeders. and older experienced birds that had nested in other colonies. Most of Because of seasonal variation Example 2 — Egg oiling followed the ringed immigrants came from in the diet of cormorants in the by a decline then an increase colonies located within 170 km from area, this oiling work is thought In the colonies in Ringkøbing Fjord Ringkøbing Fjord, but there were to provide the greatest protection in West Jutland, 80–93% of all nests also cormorants raised 300–700 km for those fish species that feature were exposed to egg oiling from 2003 away. most prominently in the diet during to 2008. As anticipated, nest numbers the chick-feeding and post-chick began to decline in 2005–2006, but The process of egg oiling (or other feeding periods (assessed from contrary to expectations, breeding egg destruction methods) is time- pellet analysis). This includes the numbers increased markedly in 2007 consuming and labour-intensive, commercially important Smallmouth and 2008 (Figure 3). Some of the since as many nests as possible Bass (Micropterus dolomieu). increase in 2007 was explained by may have to be located and treated, re-nesting of the same birds in a new and this can be hindered by In Europe, the technique is in colony established late in the season. problems of access (particularly common use on Great Cormorants mainly in Denmark where it has been used mainly in the large, 1500 Eggs were oiled ground-nesting colonies in western No oiling of eggs and northern Jutland to reduce the number of cormorants foraging 1200 in the fjords in West Jutland. The following examples illustrate that the effects on cormorant numbers 900 in subsequent years can vary depending on local conditions and conditions elsewhere. 600 Numbers of nests Example 1 — Egg oiling followed by an expected decline 300 In the Rønland Sandø colony in northwest Denmark, 80–93% of all nests were exposed to egg oiling 0 from 2003 to 2008. It was expected 1993 1995 1997 1999 2001 2003 2005 2007 that breeding numbers would Figure 2 Cormorant nest numbers in the Rønland Sandø colony in northwest begin to decline at a rate of about Denmark 1993–2008. The lighter shading in the columns indicates nests exposed to 10% per year from 2006 onwards. egg oiling.
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Eggs were oiled ammunition). Thus, anyone wishing to shoot cormorants should be aware 3000 No oiling of eggs of, and comply with, any regulations and controls that apply in their 2500 country/area.
It has been demonstrated that both
s 2000 shooting to scare and shooting nest to kill a small number of birds as of s 1500 an aid to scaring can reduce the er
mb number of birds at a site for the
Nu duration of the shooting period and 1000 for a ‘post-treatment’ period. In the UK, a large-scale experiment 500 was undertaken involving thirteen six-week field trials carried out over two years at a range of fishery 0 types (including river and stillwater 1993 1995 1997 1999 2001 2003 2005 2007 fisheries, stocked and unstocked Figure 3 Cormorant nest numbers in Ringkøbing Fjord in West Denmark sites, and fisheries with and without 1993–2008. The lighter shading in the columns indicates nests exposed to egg oiling. cormorant night roosts). The experimental design involved three treatments: control (no shooting), for tree-nesting cormorants). For 4.5.2 Shooting — at a site- lethal shooting and non-lethal total success, spraying may also specific or local level shooting (at the same intensity). need to be undertaken several times Each six week trial was divided during incubation and this increases Shooting is one of the most into three two-week phases: pre- costs. The timing of destruction is commonly used techniques for treatment, treatment (when shooting also important in order to minimise reducing cormorant numbers at was carried out) and post-treatment. the risk of birds re-laying. It various sites, and killing cormorants Numbers of cormorants were should also be recognised that any by shooting is permitted in most, then compared before and after reduction in a population caused but not all, European countries in commencement of shooting and by the loss of young birds can be appropriate circumstances. Indeed, between control and shooting sites. offset by immigration of new birds in a small number of countries from nearby non-treated areas, cormorants are on the list of The results indicated that shooting (to particularly if the technique is ‘huntable’ birds. For instance, in kill or to scare) significantly reduced employed as a short-term measure. Norway there is a tradition of hunting the number of cormorants for both the birds for food. The majority of the treatment and post-treatment Intense harassment of adult birds that are killed in Europe are phase. An average bird reduction of cormorants at nesting colonies has shot at feeding sites outside the over 50% was reported. However, been used to reduce reproductive breeding season, or in the vicinity of bird numbers recovered to pre- success by allowing predatory birds fishing gear, but in some countries treatment levels over a period of two and carnivores access to the nests. breeding birds are also shot. Country, to six weeks. Thus, to be effective If the harassment is intense enough, regional or site-specific limits may in the longer term, such shooting the adults have even abandoned the be placed on the numbers of birds would need to be repeated at regular nests all together. The most effective that can be shot and shooting may intervals. Localised shooting has harassment is human presence but be confined to specific regions or also been shown to be effective on scaring techniques (as described waters, or may be restricted in other the Sava Bohinjka River, Slovenia, previously) can also be effective, ways (e.g. only near fish farms or where wintering birds (around 200) especially if employed at night. fishing gear, or using only non-toxic were removed from an area after
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two winters of relatively intensive Fjord was uncoordinated and respond differently. For cormorants, shooting (see Case Study No. 4). dispersed over most of the feeding shooting is more effective at smaller area. Furthermore, all forms of sites than at large ones. The number An investigation to assess whether human activities were prohibited of shooting parties/events and the shooting in the autumn/winter within 1,000 m of the islet used by number of consecutive days over (the hunting season) would be cormorants as their main day and which shooting occurs have also an effective means of reducing night roost. been shown to affect the magnitude cormorant numbers at large water of reduction in bird numbers. It is bodies, and perhaps advance the It was concluded that it may be generally accepted that shooting is autumn migration of the birds, was possible to use shooting as a tool to best used in conjunction with, and to recently carried out in Denmark. make cormorants leave larger water reinforce, other non-lethal deterrent A three-year experiment was bodies earlier in autumn (at least in measures. However, in order to conducted in two fjords in West northern Europe). However, success be effective over a wider area, Jutland, with more than 190 may require coordinated shooting shooting, and the use of any other hunters in each fjord issued with a near to day and night roosts. associated deterrents, also needs licence to shoot cormorants from to be coordinated effectively - for 1 September to 31 January (the It is generally accepted that killing example, see Case Study 7 — Hula hunting season). However, in each cormorants enhances the scaring Valley. season only 22–59 hunters actually effect of shooting. However, shot at least one cormorant. A total scientific evidence to substantiate The weapons and ammunition of 1,131 cormorants were shot in this view is not clear, and both used for killing cormorants may the two fjords over the three hunting shooting to kill and shooting to scare also be stipulated under national seasons. These birds were estimated have been shown to be effective at or regional regulations, and to constitute 3–7% of the cormorants reducing bird numbers at specific individuals will probably also that occurred in the fjords during the sites. The effectiveness of shooting require firearms certificates or September to January period. depends on a number of factors: the licences to cover their use (as well target species, the site characteristics as the permission of land owners). In Nissum Fjord, cormorant and the shooting regime. Individual The most commonly used weapon numbers declined immediately after birds of the same species may also is a 12-bore shotgun. The loud the onset of one of the three hunting seasons to around 25% of the numbers present in the weeks prior 1500 to 1 September (Figure 4). Numbers did not increase again later in 1200 autumn, probably because shooting ts
continued during September and os because the number of new naïve ro 900 day birds arriving after mid-September at was modest. The clear impact s 600 on autumn staging numbers was ber m
probably the result of intensive Nu shooting over a few days near to 300 the main night roost and close to some of the day roosts. In the other 0
fjord, Ringkøbing Fjord, no marked t t t t g g g g g p p p Oc Oc Oc Oc
decline in cormorant numbers -Se -Au -Au -Au -Au -Au 5 3- 1 8 12 -S ep 19 -Se 26 -Se 10- 17- 24- 22 occurred after the onset of shooting 15 29 and up to 2,000 cormorants were Figure 4 Numbers of cormorants present on day roosts in Nissum Fjord present on the day roosts until mid- in West Jutland in 2003. Shooting of cormorants took place from 1 September October. Shooting in Ringkøbing (indicated by arrow).
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report made by such weapons, overall numbers. This may reflect This model also suggested that and the need for the shooter to be the fact that the numbers killed increasing the number of culled in reasonably close proximity to by shooting did not exceed the cormorants was risky, since the birds, maximise the scaring recruitment rate from immigration once the compensatory power effect. Targeting individual birds and breeding. Thus, shot birds were of the population is overcome, it within a group of cormorants, so quickly replaced by individuals will inevitably decline towards that surviving birds are conditioned from elsewhere. Alternatively, extinction if the cull is unchecked. to avoid the site in future, will shooting might have mainly killed One general inference of the also enhance this. However, rifles ‘surplus’ birds that would otherwise model was that culls would may also be permissible in some have died of natural causes such as need to be planned so that they situations. These have longer starvation or disease. Commonly, became the most powerful, range than shotguns and may be population control has proved most density-dependent mechanism particularly useful for removing cost-effective and long-lasting affecting the target population. It lone birds or specific, persistent where the bird species causing was felt that this would require individuals; they will also generally problems have been relatively a well-parameterised population cause less disturbance to other small, localised populations. model and would also need to water birds. Examples of the use of relatively be accompanied by monitoring large scale cormorant population programmes and appropriate The use of rifles is likely to have control measures in France, the feedback mechanisms. limited, if any, effect in conditioning Czech Republic and Bavaria other birds, so there may well be (Germany) are provided in the Case One drawback of this early model little potential scaring effect of killing Studies section (Section 6). was that it did not take into account birds with rifles. Safety will be a key geographical variation in culling consideration with regard to any use There have been a number of intensity. Managers, however, will of firearms, but it will be a particular efforts to model cormorant often be most interested in the local concern where rifles might be used. population growth in Europe in effect of culls, which will depend on Bullets can travel for distances of a management context and to both local culling intensity and the over 2 km and may ricochet off investigate the interplay between extent to which the local population water, rocky outcrops, gravel banks large-scale cormorant culling and is isolated from other cormorant and other surfaces. Thus, rifles will aspects of the species population populations. This will depend on not always be suitable for use on or dynamics. A simple model how ‘attached’ cormorants are near water bodies, particularly where scenario, based on the 1998–9 to particular areas and on how there is public access. continental cormorant populations much movement there is between (then estimated at around 100,000 locations, particularly in winter. breeding pairs), suggested that Thus, local culls will have a greater 4.5.3 Shooting — the then current level of culling effect on ‘closed’ populations, with coordinated culling for (around 17,000 birds per year) little, if any, interchange of birds, population control would have limited effect. It was than it will on ‘open’ populations predicted that this degree of culling where there is a lot of bird The use of lethal techniques for would result in a stable suppression movement. Taken to extremes, for population control at a broad of population size of less than 10% a place where birds are absolutely scale is constrained by a range below the equilibrium population site-faithful (i.e. they go there and of factors, including the level expected in the absence of culling. only there), a cormorant population of mortality achieved relative to The models suggested annual culls could be controlled without immigration and breeding rates, of over 30,000 birds across Europe any measures being necessary migratory patterns and the relative would still have only a limited elsewhere. However, if birds levels of controls in different effect, whereas shooting 50,000 distribute themselves randomly areas. For a number of bird pest birds would result in long-term across the continent, the effects species, shooting has proved population declines in Northern of culling at particular sites will largely unsuccessful at reducing Europe. only be manifest at the scale of the
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overall wintering range and not at Action Plans — see: http://www. This provides an example of how specific sites per se. frap-project.ufz.de/). A generic modelling can be used to identify matrix model was developed and threshold values for certain key A later model was developed that specific modelling was carried out parameters related to population included some geographical sub- for cormorants and other species. viability, above which regulation division of the winter range (France The modelling of cormorant management can be continued, but vs. the rest of Europe), as culling populations was based on published below which it has to be stopped intensity has been higher in France and unpublished information about in order to avoid jeopardizing the in recent years than elsewhere in the demography of cormorants viability of the managed population. Europe (see Case Studies). The breeding in Denmark. model confirmed that the effects The modelling also demonstrated of culling are highly dependent To make this generic matrix that constant population on the extent of immigration into model potentially usable for management with fixed rules, an area, and it suggested that practitioners (especially managers quotas or rates was either too culls at the present level in France and decision-makers), a special ineffective in terms of population could only be sustained as long as tool was developed: the so- reduction or too risky for substantial immigration occurs. It called FRAP-Calculator. This population viability. Hence, an was suggested that even a relatively software uses the demographic adaptive management approach minor increase in the present cull attributes of the species as input was suggested, which with could lead to a crash in the French and allows appropriate population increased levels of monitoring cormorant population. However, management scenarios to be would allow management rules to the effects of the annual culls tested. This model describes the be adopted taking the current state outside France were predicted to be development of the population over of the population into account. This very small (about 3% on average), time and provides outputs which was judged to be both effective and although they could be higher than include: the number of individuals safe, since it provided feedback this locally. in different age classes, the number mechanisms and the opportunity of breeding and non-breeding birds, to stop control measures before the Such modelling work has indicated as well as the risk of extinction of population was critically reduced. that cormorant population control the population after 100 years. through culling is feasible, in Modelling and an adaptive principle. In practice, there are many The model allows different management approach have biological reasons why attempts to types of population management previously been used in England to reduce the continental cormorant to be assessed and compared, determine a prudent upper limit of population would be extremely such as culling of adults, eggs cormorant numbers allowed to be difficult. However, there is also a or manipulating the breeding shot each year. A policy change, in widespread view that population- capacity (e.g. by keeping birds 2004, allowed the number of birds reduction culling may not be the from exploiting certain areas). For shot under licence to be increased most efficient, practical, economical example, the modelled effect of from around 500 per annum up to or ethical way of limiting cormorant various intensities of egg oiling a maximum of 2,000 per annum, damage to fisheries, and other on the development of pre- although with the potential to interests, across Europe. breeding numbers of cormorants increase this to 3,000 per annum in in the cormorant population in the first two years. The policy was The use of population modelling as Ringkøbing Fjord, Denmark supported by a stochastic Monte a tool to predict the consequences predicts that this population will Carlo annual population model, of culling has also been tested go extinct within 100 years if all which was produced to examine the during a recent EU-funded the eggs in more than 85% of the effect of changes to the numbers of project on fish-eating mammals nests are oiled annually. It also birds shot each year. and birds in conflict with indicates that there is a critical level humans (FRAP — Framework of 75% of nests, above which the An index of the annual cormorant for biodiversity Reconciliation population collapses sooner or later. population size in England (the
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annual WeBS-wetland bird 4.5.4 Recent information reasonable basis for comparison survey — count) was converted on lethal actions against with the REDCAFE data (compiled to a population estimate based in a similar way) and a means for on the latest available data and cormorants in Europe indicating possible trends. was used to determine annual In 2003, information summarising population growth rates, and the the extent of lethal measures applied The information in Table 1 is presence and strength of density against cormorants was compiled summarised merely to offer the dependence. The model was used for each of the 25 countries involved reader some sense of the scale of to produce short-term population in the EU-funded REDCAFE lethal activities undertaken against projections based on different Framework 5 Concerted Action2. cormorants across Europe under levels of shooting. For example, During the INTERCAFE Action, current legislation. The data are it was estimated that the 1,300 this information was updated and comprehensively described and birds shot under licence in 2004/05 data for 30 countries are summarised discussed in the INTERCAFE represented about 4.5% of the in Table 1. It should be noted that publication ‘Cormorants and the English population, and that if this the compiled information has been European Environment: exploring level of shooting continued the derived from both published sources cormorant status and distribution population would be expected to and informed estimates from the on a continental scale’. decline by 3% by 2007, compared various experts involved in the to the long-term average, and Action. These estimates should 4.5.5 Overview of lethal increase the risk of decline by 4%. not be regarded as an authoritative, measures official, or even a particularly Enhanced monitoring and accurate estimate. However, it is Efficacy Adaptive Resource Management felt that INTERCAFE’s most Egg destruction methods are time- (ARM) are now applied to allow recent data (mainly relating to consuming and labour-intensive, continuous evaluation of the information for the year 2006 or and they can be hindered by effects of culling on development the winter 2006/07) do provide a problems of access and may need of the population. Thus, the model to be repeated several times during parameters and model are updated, the course of incubation to be and this allows the number of effective. The loss of young birds 2 birds licensed to be shot each year Carss, D N. (ed.) (2003): Reducing the can be offset by immigration of to be reviewed and, as necessary, conflict between cormorants and fisheries on a pan-European scale: REDCAFE. Final Report new birds from nearby, non-treated adjusted should the population to European Union DG Fish, August 2003, areas, particularly if the technique is respond in a manner other than pp169. Available to download as REDCAFE Final Report at http://www.intercafeproject. employed as a short-term measure. that expected. net
Table 1 Summary of lethal measures against cormorants in Europe, comparing 2001/02 with 2006/07 (* denotes estimates are minimum values).
Lethal Measure REDCAFE INTERCAFE Main countries where 2001/02 2006/07 measures used
Breeding colonies destroyed/ 50 63* Sweden, Denmark disturbed
Nests destroyed/eggs oiled 7,094–8,094* 9,845–10,845 Denmark, Sweden
Nestlings killed 600–700* 0 Germany
Adults killed (non-breeding 51,953–54,003* 86,520–89,680* France, Germany, Norway season)
Breeding adults killed 3,598* 4,175–4,180* Sweden, Italy
Night roosts destroyed 248* 510* France, others
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However, research has demonstrated movements of birds have been Thus, although generally fewer that intensive egg destruction can underestimated by such models birds should mean fewer fisheries reduce the size of breeding colonies which are based mainly on ringing with problems, the problems are in an area in the long-term. data from adult birds. Young birds likely to persist at many sites, are probably more erratic and less particularly the ‘best’ ones (e.g. fish Shooting cormorants to reinforce predictable in their movements. farms), unless a major reduction in other, non-lethal harassment and cormorant numbers is achieved. to reduce bird numbers at local The efficacy of large-scale sites is widely used across Europe. population control will be Practicality Its effectiveness is generally constrained by many factors. For The practicality of egg oiling (or short-term, ranging from days at example, the large territory occupied other egg destruction methods) larger sites to weeks or months at by the birds, with widespread depends to a large extent on the aquaculture facilities and smaller breeding populations and birds accessibility of cormorant colonies fishery sites. Typically, shooting is further mixing and dispersing in and individual nests. Clearly, the only effective over a longer period the winter, means that there will technique is much more practical where the measures are targeted at be no simple relationship between for localised ground-nesting stable bird populations with little management actions in breeding colonies than for tree or cliff- exchange (‘turnover’) of birds. areas (e.g. in one country) and nesting cormorants. For lethal the consequences of these actions shooting, practicability ranges from The success of shooting depends for wintering areas, or vice versa. low to very high depending on to a large extent on the nature of Further, since numbers and factors such as the size of the water the local cormorant population. distribution patterns of the birds body to be protected, manpower However, efficacy also depends are partly determined by density- availability and the nature of the on factors such as the physical dependent factors operating both local cormorant population (e.g. characteristics of the site, the within and outside the breeding relatively sedentary or highly shooting strategy and the availability season, the population as a whole has migratory). Shooting may also be of alternative sites to which the birds considerable potential to compensate constrained in some areas due to can move. Shooting may thus just for reductions in numbers. the proximity of human habitation, move birds to alternative feeding designated nature conservation sites sites in a locality and alter their If successful, any reduction and or in areas of public access due to distribution, rather than reduce their stabilisation of the cormorant safety concerns. overall numbers in an area. Shooting population at a lower level as a is thought to be most effective where result of culling would reduce the Where lethal measures are to be it is used in combination with other overall impact of the birds on fish employed on a larger scale — for deterrent measures. stocks and fisheries. At its simplest, example, to protect particular if there were fewer cormorants areas — an additional significant Field studies at sites in Europe (e.g. across Europe they would eat practical consideration will be Germany, Austria and France), fewer fish. However, it is highly the need to coordinate actions where shooting has been carried out unlikely that this would result in effectively. This may require the on cormorants migrating between an even decline in the pressure on establishment of collaborative breeding and winter feeding areas, perhaps all but the poorest fisheries, stakeholder groups and effective, have indicated that shooting was as birds are likely to continue to real-time communication networks not generally effective in reducing favour high quality habitats that to ensure that efforts are targeted to cormorant numbers, with shot offer the best foraging potential. best effect at appropriate times and birds being rapidly replaced by Where cormorant populations are places — see Case Study 7, Hula birds from elsewhere, especially constrained by available resources, Valley. Thus, knowledge of the at attractive feeding sites. This studies have demonstrated that a local behaviour, movements, and is in contradiction to theoretical reduction in bird numbers results favoured locations (for foraging, simulation models and probably in the abandonment of marginal, roosting, loafing and feeding) of the reflects the fact that rapid sub optimal, foraging areas first. cormorants will also be needed.
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Costs regarded as taking positive action noise of lethal shooting can have The application of all lethal towards solving a bird problem (‘one negative impacts on other wildlife techniques requires repetitive use dead cormorant is one less that will and people. The acceptability of of manpower, so costs depend to feed on fish’), and provides some lethal measures may also be affected a large extent on whether or not immediate sense of satisfaction for by the presence of bird carcases and wages are paid to those involved the shooter. The use of lethal control concerns about pollution arising in any control programmes; costs measures to address localised from the release of lead to the can be substantially reduced or short-term conflict issues is environment from shotgun pellets. where manpower is available on commonly seen as a necessary and However, cormorant carcases can a voluntary basis, or where it may acceptable management option, be usefully used for post mortem be possible to implement controls with general support from many analysis (e.g. to provide information in conjunction with other activities stakeholder groups. on diet at different sites), and the (e.g. hunting, or as part of normal use of lead in shotgun cartridges for fish husbandry activities). Where However, large-scale population waterfowl hunting has recently been dedicated wages are paid, costs will control at a national or pan-European banned in the EU. be relatively high, and the costs of scale is much more contentious, weapons and ammunition can also and while this is advocated by It is also worth noting that if be substantial. Beyond this, the some stakeholders it is contested licensed hunters are used to shoot costs will mainly be dependent on by others. There are particular cormorants, conflicts of interest the scale of the programme, ranging concerns that should unregulated can occur. For example, during from relatively modest costs where control be permitted, this could lead the initial part of the shooting such techniques are employed to sustained decline and possibly season, when cormorant numbers locally and in the short term, to very local extinction of cormorants. first build up, hunters may not high costs where such techniques A coordinated, and appropriately wish to target cormorants for fear are used over a broad geographical regulated, pan-European population of deterring their preferred quarry scale and on a recurrent basis. control plan might allay such (ducks and other waterfowl), concerns. However, there is also even though cormorant predation Acceptability awareness that the killing of any may be significant then. In The acceptability of lethal control wildlife can attract comment and Italy, it has been observed that measures varies considerably, criticism from the general public cormorant shooting may therefore and depends to a large extent on and that killing on a large scale may be restricted to short but intense the viewpoint of the stakeholders not be publicly acceptable. Some periods towards the end of the involved. For a fishery owner or governments are therefore unlikely shooting season — i.e. after fish farmer faced with a cormorant to find such an approach acceptable. the birds have already caused problem, shooting to kill may be considerable damage to fish seen as a particularly acceptable In common with shooting to scare stocks. option. For these it can readily be and other audible deterrents, the
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5 FINANCIAL COMPENSATION
Financial compensation is used other aspects of how cormorant- countries, whereas in others in some countries to offset the fisheries conflicts are perceived compensation is available for consequences of cormorant (e.g. birds will still be eating and/ injured fish and for the associated predation for particular stakeholder or damaging the fish) and might, expenses (disposal of carcases, groups. Such measures are largely, arguably, be considered to make veterinary fees, etc). but not exclusively, restricted to fish the situation worse on the grounds farms and hatcheries, with losses that there might be less incentive Other forms of financial support of fish consumed by cormorants for stakeholders to implement exist under the European Fisheries being covered (though not always any active deterrent measures. Fund (EFF), which forms part of fully) by compensatory payments. There may be a stronger argument, the European Common Fisheries Where compensation is paid for then, for financial support for Policy. Its objective is to provide fish losses to cormorants, the other measures, such as building for exploitation of living aquatic actual loss of fish is seldom, if enclosures, where such approaches resources and aquaculture in the ever, calculated rigorously. Thus, might be realistic. Compensation context of sustainable development, the relationship between financial would undoubtedly be seen as taking account of environmental, payments and the actual fish losses acceptable for some affected economic and social aspects in being incurred is usually no more stakeholder groups. However, it a balanced manner. The support than an estimated guess. This is the seems unlikely that such schemes is available under the ‘aqua- result of the inherent difficulties in will be adopted widely. environmental measures’ and accurately quantifying the impact financed by the EU. It is available to of cormorants on fish stocks or There are active schemes of every Member State of the European catches. In some regions no real financial compensation for damage Union in compliance with Council attempt is made to quantify fish caused by cormorants in several Regulation (EC) No 1198/2006. losses, rather a sum of money is set EU countries — Czech Republic, aside for compensation payments Germany (Saxony), Latvia, The ‘aqua-environmental and this is shared (sometimes Romania, Slovakia, Finland, measures’, which apply under equally, sometimes not) amongst Lithuania and Belgium (Wallonia). Article 30(2)(a) of the EFF, aim to all legitimate claimants. In some The compensation schemes and promote aquaculture production countries it has also been possible procedures vary, and the authority methods that are sensitive to to apply for financial aid for the responsible for this issue may environmental and conservation construction of netting enclosures or differ — in some countries a central issues; they can also be used to help for scaring programmes. government ministry is responsible address cormorant-fishery conflicts. whereas in others the responsibility They cover four different types of Many authorities take the rests with a local authority. measures: view that the cost of managing cormorant conflicts should be Also, there are differences in ▪▪ Forms of aquaculture borne by the affected stakeholders. the legislation regarding what is that provide protection Thus, financial compensation eligible for compensation. In some and enhancement of the arrangements are generally cases, this is available only for fish environment. considered inappropriate. In stocks on fish farms, fish hatcheries ▪▪ Aquaculture operations terms of efficacy, the payment of and fish breeding and keeping that participate in EMAS compensation for fish losses will facilities. Further, compensation (Community eco-management do nothing practical to reduce applies only for dead fish in some and audit system).
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▪▪ Organic aquaculture. along traditional lines. In addition, compensation that should be ▪▪ Sustainable aquaculture compensation may be provided for provided. Because of financial compatible with Natura 2000. especially high damage to fish in constraints, reimbursement for fish ponds. the full economic impacts of pest Compensation under this scheme species has been replaced by may include: costs associated with In the Czech Republic fish contributory compensation, where high or frequent maintenance of losses in ponds are calculated by only part of the estimated costs are farming structures; losses arising multiplying cormorant numbers met. In the case of damage caused from predation by protected wild and the number of days the by protected species, compensatory species (such as cormorants); birds are present — verified payments are provided by the local and loss of revenue due to the by an independent expert or administration, whereas for game requirement to maintain low ornithologist — by an average species this duty is performed by stock densities (on environmental daily food requirement for each the statutory organisations that grounds). Owners of fish pond farms cormorant (500g per day) and manage hunting areas at provincial that fulfill certain environmental the market price of the fish. level, using funds derived from criteria are eligible for annual Compensation is available mostly hunting licences. payments, per hectare of pond area. in the larger fish pond regions located in South Bohemia and In Slovakia, a compensation Under Article 29 of the EFF, South Moravia, and this accounts scheme has applied since 2002 financial support can be also be for up to 85% of the total when a new Nature and Landscape provided to aid investment in the compensation payments for the Protection Act came into force. purchase of equipment used for whole country. This only relates to damage protecting fish pond farms from caused by cormorants at fish wild predators. In Italy, financial compensation rearing and breeding facilities, for cormorant predation on with compensation payments Country Examples fish is provided by regional being provided by the Ministry The number of complaints about administrations, as it is for damage of Environment. Fish losses are cormorant damage from fish pond caused by other protected fauna. estimated by official experts on farmers in Latvia fell to zero in When regional administrations a case by case basis. Between 2008 following the adoption (in delegate this task to provinces 2003 and 2006, 3,696,723 SKK November 2007) of a compensation (e.g. in Emilia-Romagna), the (approximately 122,000 Euro) scheme by the Latvian money is drawn from regional was paid out, representing around Government. sources and has to be shared by 40% of all the money paid out all the provinces in that region. under compensation schemes In Saxony, Germany, fish farmers Provinces may have a duty to for damage caused by protected have been paid compensation carry out bird or animal censuses, species (brown bear, wolf, lynx, since 1996 to help maintain and check for and log complaints otter, European bison, beaver and sustainably manage Carp ponds and calculate the amount of grey heron).
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6 CASE STUDIES
As discussed throughout the Toolbox, cormorant management techniques can be applied over very different temporal and spatial scales. At one extreme there are very localised, short-term, site- specific measures and, at the other, the potential for long-term population control measures at the pan European level. In practice, management quite often applies at scales intermediate to these, with programmes being established, agreed and coordinated over a Fishing station — Lake Kerkini, Greece. wider, but still relatively local area. Photo courtesy of G Catsadorakis.
The following case studies help requires the permanent presence of illustrate the use of cormorant 6.1 Case Study No. 1. management techniques at different at least one person in the area. It is scales and they highlight some of Greece — Local use of visual/ thus relatively costly in manpower the complexities and difficulties that auditory deterrents to protect terms, although is simple to install can affect management programmes. fishing sites on Lake Kerkini and operate and has relatively These range from relatively small low material costs. The method is scale, site-specific examples and For further details contact Savas considered effective for these fishing targeted trials to larger, programmes Kazantzidis ([email protected]) sites close to the shore, with birds coordinated over wider areas and being scared from the area for a national management plans. This A technique has been employed at short period (typically a few hours). section places more emphasis on Lake Kerkini in northern Greece, the larger programmes and plans which combines visual deterrents since much of the site- or technique- (reflectors) with audible deterrents. 6.2 Case Study No. 2. UK specific information has already In this example, preferred fishing (England & Wales) — been incorporated into the main sites close to the shore (<100 m), Protecting a locally section of the report (Section 4) where fishermen place their fishing outlining the various cormorant nets, are protected using a system of endangered species involving management tools. It is also true ropes supported by poles. Reflectors management of a cormorant that where management measures (tin plates and cans) and bells are breeding colony are carried out by individuals or hung along the ropes and, when For further details contact Ian Winfield small organisations at local levels, cormorants approach the fishing ([email protected]) there is rarely sufficient manpower site, fishermen on the shore pull or other resources to fully monitor the rope resulting in the movement the impact of the measures, compile of the bells and the reflectors. This The Schelly (Coregonus lavaretus), data and analyse the effectiveness of technique is used during daylight a species of whitefish, is nationally the techniques. hours throughout the year and rare in the UK. It is subject to
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6.3 Case Study No. 3. Slovenia — An example of collaborative shooting to protect a river fishery
For further details contact Marijan Govedic ([email protected]) or Miha Janc ([email protected])
The River Sava Bohinjka in north- west Slovenia has clear, oligotrophic water which drains from the oligotrophic Lake Bohinj and the surrounding Alpine mountains and flows eastwards to join the Schelly — from Haweswater, UK. Photo courtesy of Ian Winfield. Sava River. It has a water area of approximately 1,000 ha and protection under the UK Wildlife the effects of these measures were the main fish species are: Brown and Countryside Act, 1981 and is limited and did not reduce the Trout, Rainbow Trout, Chub on the List of Priority Species and numbers of adult cormorants at the (Leuciscus cephalus) and Grayling. Habitats under the UK Biodiversity lake, which continued to pose a Due to the presence of dams, Action Plan. The species is restricted threat to the Schelly population. As Nase (Chondrostoma nasus) and to relatively few water bodies in a result, the management measures Danubian Salmon (Hucho hucho) the UK, including Haweswater, a were extended from 2004 to 2007 are rare today. Angling and fly- large reservoir located in the English to include the shooting of adult fishing contribute to the income Lake District (North West England). cormorants. Despite relatively few of the region, both directly from Investigations in the 1990s indicated birds being shot (a total of 29 in angling activities and indirectly from that the status of the Schelly the three years of shooting), with accommodation, food, etc. Reduction population in Haweswater was very progressively fewer birds shot each in the populations of sport fish may poor, both when compared with year, these measures were successful thus cause financial damage. the contemporary status of other in reducing cormorant impact. Schelly populations in England and Within two winters of cormorant Wales and when compared with In 2007, the estimated level of foraging in the Sava Bohinjka its own earlier status in the 1960s. predation over the whole of the (about 200 birds each winter), the This deterioration was attributed to year was only 19% of the 1997 population of Grayling collapsed a number of factors and a range of level (population modelling has dramatically. The number of conservation actions were instigated. indicated that predation impact broodstock electric-fished from from cormorants should be reduced spawning sites on the river for use A cormorant breeding colony started to 10% or less of the 1997 level to in stock enhancement programmes to establish on the lake in 1992 and achieve a significant recovery of the fell from 320 to zero over this subsequent investigations indicated Schelly population in the medium- period. These fish were collected that the feeding activities of these term). Although shooting has not in a fish reserve area where birds were having a significant been undertaken since 2007 due angling had not been permitted negative impact on the population of to the low numbers of cormorants for more than 30 years. Electric Schelly. These concerns led to the present at the lake, further fishing also indicated that the introduction of scaring procedures management of the cormorant total Grayling population had from 1999 onwards to restrict population may be needed, along declined by 95%. Although the nesting and the production of young with continued monitoring of the cormorants’ night roost was outside cormorants at the colony. However, Schelly population. the Sava Bohinjka river valley,
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The Sava Bohinjka River, Slovenia. Photo courtesy of Ian Russell.
a few kilometres downstream of the cormorants and stocking of the birds (in excess of the Radovljica, cormorants fed on the with more fish. allocated totals) is thought to have river because the lakes freeze over taken place. Cormorants are still during the winter period. The legal scaring and shooting of present on the main Sava River cormorants on the Sava Bohinjka every winter, but they continue to Investigations indicated that: over two successive winters be regularly scared away from its cost two angling clubs 12,000€ tributary — Sava Bohinjka. ▪▪ Cormorants were feeding on and 15,000€, respectively, for Grayling. transportation, ammunition and In this conflict a small number ▪▪ None of the other biotic or overheads. During these two of cormorants (about 200) were abiotic parameters changed winters anglers devoted 6,300 perceived as the direct cause of dramatically or varied more volunteer hours per annum to severe damage on a regional scale. than in previous years and none, scaring the birds, and hunters spent Cormorant predation on the Sava could account for the change in 250 and 280 hours, respectively, Bohinjka River represents a quite the fish population. on shooting the birds. Total annual distinct type of conflict, but one ▪▪ There was no evidence of disease costs for these actions in the that commonly occurs on relatively in the Grayling population. whole valley were approximately small, sub-alpine salmonid rivers. ▪▪ The Grayling population 25,000€. Besides legal scaring and Such rivers become favoured improved after the removal of shooting, some illegal shooting cormorant foraging locations, due to
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the freezing over of many adjacent stillwaters, and the common prey species at these sites are of high recreational and amenity value.
6.4 Case Study No. 4. Germany — Wires over Carp ponds
For further details contact Thomas Keller ([email protected])
In one of the more comprehensive and effective tests at a German fish farm, wires deployed in a regular grid pattern (5 m, 7.5 m and 10 m spacing) on a series of eight ponds reduced over-winter fish losses from 88% (in the winter before protection) to about 10% in the following year. During the trial, 113 Parallel wires over a Carp pond, Germany. Photo courtesy of Thomas Keller. cormorants were recorded over a period of 27 days at the farm, but none were observed to land on the is an ecologically important aurata]). The high concentration ponds once wires were in place. In wetland, comprising part of the of fish in these wintering channels another trial, Carp losses were found East Macedonia and Thrace attracts cormorants and can to be 2.5% in a protected pond National Park and one of ten Greek result in substantial losses for (wires spaced at 7.5 m intervals) wetlands protected by the Ramsar the fishermen who harvest these compared with 61% in an adjacent, Convention. It is also of importance channels. unprotected pond. However, no as a fishery, with more than 500 t benefits were apparent for the other of commercially important fish Over the last two decades, fish species in these ponds. In a species landed per year. Market- fishermen have tried various further trial, overhead wires at 10m sized individuals are harvested different techniques (e.g. gun shots, spacing had no apparent effect on during their reproductive migration wires, other audible deterrents) to summer fish losses, which remained to the sea at a specially designed keep cormorants away from the high (>70%) in the vicinity of a trap situated at the southern end channels. However, the current cormorant breeding colony. of the estuarine system. Smaller method is considered the most fish caught in the trap are either successful and cost effective, returned to the lagoon or are placed even though the cost was high. 6.5 Case Study No. 5. in artificial channels where they The channels are now covered are kept for the winter months and completely by nets which are hung Greece — Netting enclosures then released again in the lagoon in from central supports, with some to protect over-winter fish- order to grow until the next harvest supplementary shooting to deter holding facilities period. The wintering channels birds from unprotected areas. The are 1.5–2 km long, 30–40 m wide nets cost about 85,000€ and last For further details contact Manos and 5–6 m deep and typically for about four to six years, with Koutrakis ([email protected]) hold around 300 t of fish (mainly additional annual maintenance Grey Mullet, Mugilidae, but also costs, particularly to repair the part In Greece, the Porto-Lagos Lagoon Sea Bass [Dicentrarchus labrax] of the net that covers the channel and Vistonis Lake estuarine system and Gilthead Sea Bream [Sparus bank, estimated at 10,000€.
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Netting enclosures over fish wintering channels in the Porto Lagos Lagoon, Northern Greece. Photos courtesy of Manos Koutrakis.
6.6 Case Study No. 6. Sweden — Fishery management measures to improve fishery performance on two large lakes in the presence of cormorants
For further details contact Erik Petersen ([email protected]) and Henri fishery by decreasing catches of catches to be processed more Engström ([email protected]) pikeperch and through the ‘theft’ of effectively (trap net and gill net bait fish in the crayfish pots. caught fish were brought to the Lake Hjälmaren is the fourth boat for processing at different largest lake in Sweden (484 km2). In response to the decreasing times) and more rapidly (the Cormorants started to breed on catches, a number of actions were use of a sorting table enabled islands in the lake in the mid taken in June 2001 to improve the undersize Pikeperch and other, 1990’s, with numbers increasing Pikeperch fishery: non-target species to be more rapidly from 23 breeding pairs in rapidly returned to the water, 1996 to 1,278 by 2010 (Figure 5). ▪▪ The minimum landing size was typically in around 30 seconds). The lake supports a commercial increased from 40 cm to 45 cm; fishery, with Pikeperch Sander( ▪▪ The minimum mesh size of the As a result of these measures, the lucioperca) and Signal Crayfish nets was increased from 50 mm Marine Stewardship Council (MSC) (Pacifastacus leniusculus) the two to 60 mm; and certified the Lake Hjälmaren fishery most important species. Cormorants ▪▪ Improved handling methods as a sustainable and well-managed were reported to have affected the were introduced to allow fishery, the first inland fishery in the
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1400 pattern of population development to that seen on Lake Hjälmaren 1200 (Figure 7). The lake supports a similar commercial fishery and 1000 catches on the two lakes have
s historically been more or less ir 800 pa parallel. However, when the new
ng measures were introduced on Lake 600 eedi Hjälmaren, the fishermen on Lake br
# Mälaren refused to adopt similar 400 measures, arguing that the lakes were too dissimilar. 200 The actions taken on Lake Hjälmaren 0 have resulted in an increased yield of Pikeperch, despite the strongly 199 3 199 5 199 7 1999 2001 2003 200 5 200 7 200 9 increasing cormorant population. The Figure 5 Number of cormorant breeding pairs on Lake Hjälmaren, southern mean yearly catch has increased from Sweden, 1996–2010. an average of 59 t in 1996 to 2000 to 153 t per year from 2001 to 2007. In contrast, the catch of Pikeperch world to be recognised in this way. The problem of cormorants stealing on Lake Mälaren only increased However, despite these measures, bait fish from crayfish pots was from 132 t to 142 t over this period. the fishermen found that cormorants found to be largely attributable to In response to the perceived success were proving a particular problem the design of the pots. Switching to of the fishery measures on Lake for smaller 0+ and 1+ Pikeperch in an alternative design that the birds Hjälmaren, the fishermen on Lake the autumn. As a result, the regional were unable to open largely solved Mälaren also introduced a minimum government has given permission this problem. landing size and minimum mesh for birds to be shot during and after size for the Pikeperch fishery in the breeding season. The number The number of breeding cormorant 2008. A transition period of three permitted increased each year up pairs on the nearby Lake Mälaren, years was also agreed, so that the to 2004, but has remained stable at the third largest lake in Sweden new regulations will take full effect 1,650 birds since then (Figure 6). (1,140 km2), showed a similar in 2011. Shooting of cormorants The goal of the shooting has been to protect fish at fishing gear and 2000 to keep the cormorant population 1800 at a low level (250–300 breeding 1600 pairs). However, the shooting has not obviously halted the cormorant 1400 population growth, probably 1200 because only a small proportion 1000 of the shot birds originated from 800 the local breeding population. # shot cormorants 600 Furthermore, the permitted quotas have not been met in most years. 400 The levelling off of the population 200 in the most recent years probably 0 reflects density dependence — i.e. the population being limited by 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 available resources. Figure 6 Number of cormorants shot each autumn on Lake Hjälmaren, 1999–2010.
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3000 provided by up to three fish farmers as necessary. All the ammunition 2500 and fireworks were bought 2000 collectively and monitored to reduce expenses (considered a major part of 1500 the conflict).
1000
# breeding pairs The deterrent actions were initially 500 focused on fish ponds holding Tilapia species rather than more 0 economically important fishes, since earlier experimental trials 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 under controlled conditions Figure 7 Number of cormorant breeding pairs on Lake Mälaren, southern demonstrated these were a Sweden, 1994–2010. preferred prey of cormorants. Subsequent stomach analysis of shot birds revealed that to protect fisheries is also allowed environment, both as a result of approximately 95% of the prey at Lake Mälaren, but on a smaller the release of lead shot and the comprised Tilapia zillii and scale to that on Lake Hjälmaren. presence of bird carcases. indicated that financial losses were One reason for this is the structure far less than those perceived by fish of the lake, which has many In response to this perceived farmers. Tilapia zillii are often seen small, elongated bays. This makes failure, a collaborative partnership as a pest species in carp ponds, coordinated shooting difficult and involving biologists, fish farmers where they can compete with carp means birds can more easily find and NGOs developed a co-operative for oxygen, food and space. safe places to feed and roost when management scheme for the Hula disturbed. Valley that operated from the Over three consecutive winters, winter of 2001–2 to the winter the level of deterrence, manpower of 2004–5. Deterring cormorants and ammunition was progressively 6.7 Case Study No. 7. Israel — from fish ponds was organised reduced, such that by winter Coordinated cormorant in a coordinated manner and was 2003–04 only one professional management on a relatively informed by the best available hunter was employed from mid- large scale in the Hula Valley science and up-to-date information December to mid-February, on both the fish stocks and the assisted by up to three fish farmers For further details contact Tamir Strod cormorant population, in particular, between early December and mid- ([email protected]) total numbers and distribution of January. This saved money and birds at foraging sites. Scaring reduced the use of cartridges by at In the Hula Valley, in northern commenced as soon as the birds first least 60%. Israel, about 8,000–9,000 appeared in the area in late October cormorants used to over-winter and was carried out every morning As a result of these management each year, with the birds causing when the first cormorants arrived to measures over three consecutive major conflicts at fish ponds forage in the fish ponds. Under the winters, the peak seasonal numbers managed for aquaculture. scheme, shooting to scare and the of cormorants feeding at the fish Hundreds of cormorants were use of different types of fireworks ponds declined from about 3,600 shot every winter over a period and pyrotechnic devices, with a birds in December 2001 to around of seven years, but the problem range of effects, largely replaced 200 to 300 in December 2004, essentially remained at about the lethal shooting. Scaring was carried while peak seasonal numbers same intensity. The shooting was out by a team of three professional roosting in the Hula Valley declined costly and seemed to be largely hunters from early December to from 8,150 in December 2001 ineffective. It also polluted the late February, with additional help to 1,250 in December 2004. The
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from the moment cormorants first arrived at the fish ponds.
However, there was some deterioration in the situation subsequently. As a result of the perception, at the end of winter 2004–5, that the problem with cormorants was relatively low, coupled with changes to the fish farmers working in the area, cooperation between farmers and coordination of the management plan became less effective. Consequently, the number of cormorants (both roosting and foraging) increased in the following two winters (2006-07 and 2007-08). This highlights the importance of Mobile gas cannon and shooting, ensuring that the use of deterrents is Israel. Photos courtesy of Ian Russell both sustained and coordinated. and Jonathan Harari.
6.8 Case Study No 8. actions were pre-arranged, Germany, Bavaria — relatively coordinated and monitored over the whole region, to avoid large-scale lethal techniques simply scaring the birds from as examples of cormorant one fish farm to another. The population control in practice birds moved to other foraging and monitoring was carried out on roosting sites well away from the a daily/weekly basis to ensure For further details contact Thomas Keller aquaculture production areas and rapid feedback and effective ([email protected]) losses of fish from the fish ponds targeting of activities. declined markedly. Moreover, the ▪▪ Information — basing decisions Cormorant culling in Bavaria, operating costs (e.g. staff time, on knowledge about cormorant southern Germany (mostly ammunition) for the fish farmers physiology and ecology, during the winter migration in also reduced by about 80%. actual numbers of cormorants August–March) began in 1995 Consequently, the conflict with the and their movements, fish and developed subsequently cormorants was perceived as less of stock assessments, damage through various State regulations an issue each year. assessments, etc. This enabled and legislation from the Bavarian the actions to be focused at the State Government. Although Coupled with the availability ‘hotspots’ — i.e. those fish ponds 2,547–8,724 cormorants were of alternative foraging sites for that were particularly attractive shot each winter — sometimes in cormorants, including the Sea of to cormorants or very sensitive greater numbers than the average Galilee, the key to the success of to damage — instead of over a number counted during regular the Hula Valley scheme was: wider area. surveys — the number of birds ▪▪ Timing — actions started as soon wintering in Bavaria has remained ▪▪ Organisation — coordinating as the cormorants first appeared remarkably stable (Figure 8). interest/expert groups, in the region (late October) and Furthermore, since shooting manpower and resources. All were carried out every morning began, the number of night roosts
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10,000 Shooting is controlled by the 9,000 French national authorities, 8,000 who set annual quotas for each 7,000 administrative area (département). 6,000 Initially, these quotas were set 5,000 at a level that represented about 4,000 12% of the wintering cormorants in mid-January (from official No. Cormorants 3,000 counts), and were only allocated 2,000 where conflicts occurred in fish- 1,000 ponds. Fish farmers also had to 0 declare the number of cormorants shot during the preceding winter 88/89 90/91 92/93 94/95 96/97 98/99 00/01 02/03 04/05 06/07 08/09 Winter in order to qualify for a shooting permit. However, since no effect Cormorants shot Cormorants (winter mean) was observed in the number of Figure 8 Mean cormorant numbers between October and March, and numbers of wintering cormorants, shooting was birds shot in Bavaria in the winters of 1988/89 to 2009/10 (Data: LBV). later extended to other open water bodies, and quotas were allocated to 28 départements by 1997–98. in Bavaria has increased. Most of 6.9 Case Study No 9. Moreover, due to pressure on the the birds were shot at large rivers, France — Large-scale shooting authorities from anglers, quotas followed by ponds, small rivers of wintering cormorants were also allocated for use by and gravel pits. It was concluded anglers on rivers, initially in 9 that this uncoordinated shooting of For further details contact Loïc Marion départements in 1997–98, and cormorants over more than fourteen ([email protected]) then progressively to a large part winters did not reduce the overall, of the country. In 2008–09, 68 nor the regional numbers of birds In less than two decades, France départements allowed shooting at wintering throughout Bavaria. It became the largest wintering fish-ponds or rivers out of a total therefore appears that there must cormorant area in Europe, with most of 93 départements with wintering be a high turnover of migratory of these birds using inland waters. cormorants (77 départements birds through Bavaria, even in mid- This generated strong conflict with allowed shooting in 2006–07). winter. fish farmers in the five main fish- pond areas (Dombes, Forez, Brenne, From 2006–07 the minimum Since cormorant numbers were not Lorraine and Vendée) and with number of cormorants permitted reduced, there was no reason to anglers over a wide area, particularly to be killed in a département under believe that there was a reduction in on rivers. In spite of conflicting quota was increased to 150 from the amount of fish being consumed. views regarding the extent to which 90, with a total of 36,000 birds However, the number of cormorant cormorants were causing serious permitted for the country as a night roosts in Bavaria increased damage at a large geographical scale, whole. The latter was increased during the years of shooting, shooting started in France in 1992 to 41,800 in 2009–10 (Figure 9). suggesting that birds may now during the over-wintering season In reality, not all these birds were be more evenly distributed in (October-March). Initially, this was killed, with numbers actually the area than before. The overall only at a few sites, but it increased shot ranging from 32 to 4,361 in goal of reducing the total amount rapidly from 4,500 birds shot in different départements, totalling of fish consumed by cormorants 1996–97 to 33,000 birds, extending 31,000 cormorants in all in 2006– in Bavaria was not met through over a large part of France, by 07 and 33,000 in 2008–09 and intensive shooting in winter. 2008–09 (Figure 9). France is thus 2009–10. This represents 31% in Similar experiences are reported in currently the area in Europe where 2006–07 and 40% in 2008–09 of France — see Case Study 9. most cormorants are shot. the wintering population counted in
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accorded shot rivers or ponds and allow cormorants to preferentially use large rivers or 45000 lakes where impacts may be less of a 40000 concern. 35000 30000 25000 6.10 Case Study No 10. Czech 20000 Republic — Shooting to 15000 control population growth 10000 and expansion 5000 0 For further details contact Petr Musil ([email protected])
1995-96 1996-97 1997-98 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09 2009-10 Great Cormorants have been breeding in the Czech Republic Figure 9 Numbers of cormorants permitted to be shot in France (‘accorded’) and since the 1980s. In South Moravia numbers of birds shot over the winters 1995/96 to 2009/10. (district of Bˇreclav), the first breeding colony (32 pairs) mid-January, albeit most shooting the past 16 years, few other deterrent established on the Nové Mlýny occurs before this time. measures have been tested except at Reservoirs in 1982. The numbers of a very local scale, with no precise breeding pairs at this site peaked in In spite of this large-scale shooting, data about these. Moreover, shooting 1991 (612 pairs) but decreased in no effect has been observed on the has been carried out throughout the subsequent years, probably due to number of wintering cormorants country (mainly at night roosts in the the falling of some dead trees (roost at a département scale (i.e. no vicinity of large- or medium-sized sites) and the effect of shooting correlation has been demonstrated rivers and, less frequently, at fish- in both the pre- and post-breeding between shooting intensity and ponds during the day), without any period. This colony moved to an trends in bird numbers), and real strategy to protect specific water alternative site near the Kˇrivé progressive levelling-off of the bodies. Thus, no efforts have been Jezero National Nature Reserve in national population since 1999 made to preferentially protect small the late 1990s, with the population appears to be mainly due to natural density-dependent factors. The French national authorities, and 800 4000 many fish-farmers and anglers have breeding pairs 700 3500 come to the conclusion that shooting shot birds is largely ineffective, although 600 3000 they are reluctant to abandon 500 2500 existing lethal control measures pending some other solution. The eeding pairs 400 2000 current favoured proposal is the implementation of a wider pan- 300 1500 European scheme that would limit 200 1000 number of br the cormorant breeding population number of shot Cormorants in northern European countries and 100 500 hence reduce the number of winter 0 0 migrants in France. 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 As a result of the French national plan Figure 10 Numbers of breeding pairs and numbers of birds shot in the Czech focussing on killing cormorants over Republic between 1981 and 2010.
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size increasing from five pairs in accounted for around 70% of all the agencies responsible for fishing, 1997 to 90 pairs in 2007. birds shot in the Czech Republic. hunting and bird protection; fish and The recovery of birds ringed in ornithological research institutes; and In South Bohemia, first breeding Czech colonies has shown that angling, commercial fishing, nature was confirmed in 1983 in the these have a high level of fidelity conservation and bird protection Tˇreboˇn Biosphere Reserve (district to the Czech breeding areas. interests. With the exception of of Jindˇrich˚uv Hradec). The number In total, 104 of 111 recoveries the professional fishermen, all of breeding pairs increased to 142 (93.7%) of Cormorants ringed participants agreed with the 2005 in 1988, fluctuated between 57 and in Czech colonies, which were Action Plan. The Action Plan also 119 pairs between 1989 and 2002, later recorded within the Czech provided the basis for regulating then increased again from 2003 Republic, were found within 30 km the shooting of cormorants by the to 2005 to over 200 pairs. More of the breeding colonies. Thus, various cantons (regions) as, in recently, the breeding population while shooting was originally contrast to the European Union, has been relatively stable (178 to aimed at what were thought to be cormorants can be legally hunted in 217 pairs between 2005 and 2010). migratory cormorants, recovery Switzerland during the normal open The total breeding population in data suggest that shooting probably season for water birds. the whole Czech Republic has has an important effect on the local therefore fluctuated between 288 breeding population. The 1995 Action Plan defined three and 350 pairs between 2005 and types of Swiss waters as a basis for 2010. The population is quite management in the winter: productive, with an annual mean 6.11 Case Study No. 11. production of young of 2.6 to 3.6 Switzerland — National ▪▪ Rivers and small lakes fledglings per nest. with an area of up to 50 ha cormorant management (intervention areas), in which The Great Cormorant is a protected plan — scaring birds and protection of fish has priority species in the Czech Republic, but preventing colonisation and consequently cormorant exemptions permit flushing and/or shooting/scaring is permitted shooting of the birds under licence. For further details contact Verena Keller (with three levels of intensity Shooting is not allowed in the vicinity ([email protected]) depending on the importance of of the breeding colonies during the the resident fish stocks). breeding season (from the end of The Swiss authorities have adopted ▪▪ Lakes with an area of over 50 ha April to mid-July) but is otherwise a programme of measures to and dammed river sections permitted. The number of cormorants safeguard particularly valuable (non-intervention areas), shot increased sharply from 1980 riverine fisheries, in particular the in which the protection of to 2000, but remained relatively locally endangered Grayling. Thus, concentrations of over-wintering consistent after this date before a protection of threatened fish species water birds has priority and further rise in 2009 (Figure 10). was the main argument for taking consequently shooting/scaring Between 2000 and 2009 the number action against cormorants rather of cormorants is controlled/ of birds shot has fluctuated between than damage to fisheries in a wider prohibited to avoid disturbance 2,000 and 3,800. Some fishery context. A Swiss Cormorant Action of water birds (with three levels companies have encouraged shooting Plan was originally established in of intensity, depending on the by paying a sum of about 300CZK 1995, and this was subsequently importance of over-wintering (Czech crowns) (1€ = 24.5CZK) to reviewed and a new plan agreed birds). Exceptions concern hunters for every bird killed. in 2005. A broad-based working shooting, with special permits, group ‘Cormorant and Fisheries’ of cormorants close to fishing The most intensive shooting of set up by the Federal Office for the nets in the case of damage to Great Cormorants has occurred in Environment (FOEN) participated nets. the districts of Jindˇrich˚uv Hradec in drafting the Action Plan and ▪▪ Waters which have overlapping and Bˇreclav, i.e. within 30 km of seeking consensus. This group fishing and bird protection the breeding colonies, and this has comprised: federal and regional interests (overlap areas), leading
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to scaring measures in certain lake areas (e.g. shooting of cormorants near the nets of professional fishermen), but the cessation of scaring measures on certain river sections (e.g. sites of importance for water birds on rivers).
In general, the 1995 Action Plan was considered to have been a success and was implemented in all regions where significant cormorant numbers had occurred. However, maintaining the labour-intensive scaring measures in the long term was considered to pose a problem. As far as achievement of objectives Photograph — Shutterstock was concerned (improving the protection of fish and fisheries by reducing predation by cormorants management) will rise and of over-summering cormorants, in certain water courses while not lead to more widespread and cannot be predicted, and there affecting waterbird conservation) larger breeding colonies in were fears in the fishery sector of the 1995 Action Plan resulted in Switzerland and adjacent areas uncontrolled growth in cormorant fewer cormorants moving onto in neighbouring countries. numbers, a Conflict Resolution river systems, reducing the effect ▪▪ No pan-European Action Committee was set up. This on resident fish stocks, while birds Plan will be applied in the consisted of one representative each over wintering on the large lakes next few years, which would from FOEN, the ‘Schweizerischer were not disturbed by scaring affect cormorant numbers in Fischerei-Verband’ (the Swiss measures against cormorants. Switzerland. Fishing Association), the However, in the overlap area on ‘Schweizer Vogelschutz SVS/ the Upper Rhine, it was felt that Thus, the provisions for continuing BirdLife Schweiz’ (BirdLife greater care was needed to ensure cormorant management during Switzerland) along with regional that deterrent measures (and other the winter were maintained. representatives. This Committee disturbances) did not have negative The 2005 Action Plan laid down was to meet when one of the effects on other waterbirds in this the following as a basis for following trigger criteria applied: internationally important water bird management in the summer: reserve. ▪▪ The number of breeding ▪▪ In intervention areas, colonies in Switzerland has The framework conditions for the cormorants starting to establish increased to five or more, or the 2005 Swiss Action Plan assumed breeding colonies and flying in number of colonies on the same that: to feed are scared away. lake or in the same canton is ▪▪ In non-intervention areas, more than two. ▪▪ The consistently high breeding cormorants are allowed to enter ▪▪ The number of breeding numbers in northern Europe and establish breeding colonies cormorants in Switzerland has risen will continue to lead to a winter undisturbed. to 100 or more breeding pairs. cormorant population of some ▪▪ The damage to nets of 5,500 birds on Swiss waters. As the spatial and temporal commercial fishermen ▪▪ The number of over-summering dynamics of the formation of on a lake has reached an cormorants (without breeding colonies, and the number unacceptably high level, based
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on a joint assessment by the contested by the bird conservation commercial fishermen and the societies who advocated sticking regional fisheries agency. [It with the agreement to apply the is recognised that cormorants system of intervention and non- adversely affect the commercial intervention areas. fishery on certain lakes. The birds take fish from the nets, So far, all breeding colonies thereby tearing holes in them, (six colonies with a total of 547 and professional fishermen have breeding pairs in 2009) have been to alter their working hours in established in non-intervention order to set and recover nets areas and, to date, no measures during periods of the day when have been taken at these sites. cormorants are not active. There However, with the continuing is no obvious means of avoiding increase in the oldest and largest these problems.] colony on Lake Neuchâtel, pressure ▪▪ A member of the working group from the fisheries associations ‘Cormorant and Fisheries’ (both commercial and angling) reports an extraordinary, has increased to destroy part of regional problem in an the colony. In this instance, and in intervention, non-intervention or contrast to the Action Plan, damage overlap area. to fisheries and not protection of threatened fish species is the Full details of the Swiss main argument for taking action. management plan (in German, with There is strong opposition from an English summary) is available nature conservation societies to from the following web address: such action, in particular because http://www.news-service.admin. the colonies are situated in ch/NSBSubscriber/message/ water bird reserves. In 2009, the attachments/371.pdf federal government changed the legislation to allow management The Action Plan as it applies measures (in particular oiling of to the situation in winter has eggs) in federal waterbird reserves not been contested, and around of national and international 6.12 Case Study No. 12. 1,000 cormorants are shot each importance to reduce damage to Denmark — National year. However, the agreed Action fisheries. No intervention has taken cormorant management Plan for summer has come under place so far because in 2011 the pressure and been subject to debate. federal administrative tribunal plan — local actions and Cormorants started to breed in accepted an appeal by nature reduction of breeding output Switzerland in 2001 and when the conservation associations against management plan was adopted in the first authorisation issued by the For further details contact Henrik Lykke 2005, the threshold of 100 breeding department of environment. Sørensen ([email protected]) pairs for convening the Conflict Resolution Committee had already As the revised management plan A cormorant management plan was been reached. The Committee has not been accepted by all first issued in Denmark in 1992 by subsequently met twice but did not parties involved, in particular the Ministry of the Environment come to an agreement. For fishery with regard to management in response to the marked increase stakeholders, the threshold of 100 during the breeding season, the in the breeding population of breeding pairs had often been cited Department of Environment cormorants. This followed the as a level for triggering intervention dissolved the cormorant working introduction of measures to protect at breeding colonies, but this was group in 2009. the species, from 1980 in Denmark
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▪▪ Lays down guidelines for regulation; ▪▪ Identifies the expected effect of the Management Plan; and describes the internal allocation of responsibility within the Danish Nature Agency.
The management plan also includes requirements for the continued monitoring of the cormorant population with a view to ensuring that the conservation status of the species remains satisfactory. The plan provides for a range of management tools to be used in resolving cormorant-fishery conflicts:
Technical measures — Modification of pound nets (Section 4.2.1) in order to make it more difficult for cormorants to catch fish inside the ‘pot’ of the net has been used with some success. However, the technique is not widely applied due to the extra work involved in modifying the nets and the negative effect of the modifications on subsequent catches.
Cormorants on pound net, Denmark. Photo courtesy of Steffen Ortmann. Scaring of birds — Various methods are used to protect migrating smolts and fishing gear and 1981 in the remainder of fisheries, while maintaining the and to prevent the formation of new the EU, subsequent to the Birds cormorant’s protection and survival colonies. Shooting is the method Directive. The increasing population as a Danish breeding bird. The plan is most commonly used, sometimes in led to numerous complaints from designed to provide the Danish Nature combination with other deterrents Danish fishermen and reports of Agency with the best possible tools (e.g. gas cannons, fireworks, and reduced catches and cormorant to manage cormorant populations other audible and visual scaring damage to fishing gear. It resulted in respect of this objective. devices) to reinforce the effect of in the formulation of a national the scaring techniques. cormorant management plan. The plan: Egg oiling — This is used to The current management plan was ▪▪ Describes the present status control unwanted population approved in 2010, with the main of the cormorant population growth in certain defined regions. objective of ensuring that the size in Denmark and the conflicts The effort is concentrated on sites and distribution of the cormorant caused by cormorants; in or close to important areas for population did not cause unacceptable ▪▪ Describes the experiences with fish or fisheries and is only used damage to fish populations and different management tools; on ground-nesting colonies. In
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Photograph — Shutterstock
recent years, the majority of eggs Shooting at pound nets — The management plan and future policy have been oiled in large colonies Danish Nature Agency can issue decisions in Denmark. A brief in Western and Northern Jutland in permits to owners of standing summary of this work is provided an attempt to reduce the number of fishing gear to permit them to in Section 4.5.2. cormorants foraging in the fjords shoot (to kill) cormorants within in West Jutland. Egg oiling is 1000 m of standing fishing gear, Fish farms — The Danish Nature believed to have a long-term effect precluding the breeding period Agency can issue permits to shoot on cormorant numbers at a local or from April to July. Around 4,000 cormorants within fish farm sites. regional level, but the effects can be birds are shot annually near The permit requires that other variable (see Section 4.5.1). standing fishing gear. methods have been tried first. In practice, all the fish farms are Removal of nests to avoid new Shooting in the hunting season protected by nets or wires and only colonies — Nests are removed and (autumn/winter) — A large a few birds are shot at these sites. birds harassed at certain breeding research project on such shooting sites to prevent new colonies from was reported in 2008 and was becoming established. used to inform the review of the
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7 SUMMARY OF MANAGEMENT MEASURES
Cormorant-fishery conflicts are faced with addressing conflicts are resident, migrating) and the complex — they are seen in different strongly encouraged to experiment availability of alternative ways by different stakeholders, and with different techniques and to foraging sites. they affect a range of fishery sectors be creative in devising mitigation ▪▪ The time that can be devoted across a variety of aquatic habitats. programmes to best suit their to addressing the problem Moreover, conflicts are also subject individual needs. (deploying deterrents, to change because of the population coordinating actions, etc.) dynamics of both birds and fish; Many of the available techniques ▪▪ The associated costs (manpower seasonal and annual variations in work by persuading cormorants and equipment) that can be external factors (notably, weather to leave a particular feeding site devoted to addressing the conditions); alterations to the and move elsewhere. The birds’ problem viewed against expected perception of the nature and severity willingness to move will depend on fish losses (i.e. some sort of of the conflicts; and the efficacy of both the severity of the persuasion simple cost-benefit analysis). management measures. to leave a site but also, and perhaps ▪▪ Awareness and adherence to most importantly, on the relative local, national and international Managing such conflicts is also attractiveness of alternative legislation on the use (or complex and influenced by feeding/breeding sites in the area. otherwise) of particular techniques, wide-ranging factors, making it Thus, the effective deployment of and the need to operate safely. impossible to provide specific mitigation techniques at a specific ▪▪ Possible constraints on deterrent recommendations for different location may depend on a good use such as: the proximity of sectors or habitats, or to knowledge of a much wider area. human habitation and sensitive recommend a list of actions that Understanding the nature and extent sites (e.g. airfields); the availability could instantly solve any particular of the problem being addressed will of electrical power; the security problem. therefore be central to devising an of unattended devices against appropriate mitigation programme. possible theft and vandalism; It should also be recognised that accessibility to the land or water potential management tools will Key issues to be considered will areas where deterrents could be not always work to the satisfaction include: deployed; and wider conservation of any or all of those involved concerns (e.g. any designated in a conflict. That said, there are ▪▪ The size of the site to be nature conservation status of a numerous tools available and protected and whether actions site and the potential impact upon ample evidence that these can are to be local and site-specific or other wildlife). prove effective in some places coordinated over a wider area. at some times. Identifying the ▪▪ The nature and size of the Individual managers will probably most appropriate deterrents or problem being addressed also need to consider the timescale other mitigation techniques will (including the type of fishery, over which management measures require careful consideration by time of year, number of birds/ might need to be applied. individual stakeholders, as will the fish involved, trends in bird/fish Relatively few techniques offer decision on whether or not efforts numbers, etc.). potential one-off solutions to may need to be coordinated over ▪▪ The behaviour of the cormorants cormorant conflicts that might be a wider area. In any event, those (e.g. breeding, roosting, effective in the long-term (years).
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The two principle techniques that as the most effective deterrents, coincide as far as possible with the might provide such long term and those that carry biological daily patterns of cormorant use at benefits appear to be: significance and mimic threats a site. Typically, birds feed at first known to birds tend to prove more light and this is likely to be the key 1. The erection or installation of effective and longer-lived than period for applying deterrents, so bird-proof barriers (typically other novelty devices, although this that birds can be scared away from on fish farms and perhaps should not deter experimentation a site before they start to feed and small stillwaters) — techniques and creativity in devising mitigation begin to establish habitual feeding include netting enclosures, programmes. The frequency with patterns. However, birds can feed overhead wires and submerged, which deterrents might need to be at other times of day and may use anti-predator nets. applied will also depend on the a site for other purposes such as 2. Improvements to fish habitat in local situation. More frequent use roosting or loafing. Regular patrols stillwaters and rivers — will be required where there is a to monitor a site are therefore commonly, these may be the result high degree of turnover of birds, to vital in targeting measures most of water quality improvements reinforce the scaring effect on birds effectively. When the potential and general fishery management newly arrived at the site and where for bird predation is at its worst, activities, although this might also there are fewer alternative feeding measures may need to be reinforced include the use of artificial fish sites available for the birds. at regular intervals throughout refuges at some smaller sites. the day from first light to dusk As a general guide, it is likely that a to be most effective. When birds In contrast, a much larger number of cormorant management programme only visit water bodies for certain techniques are effective at deterring will need to be applied consistently periods of the day, such as morning cormorants in the short term, but and aggressively to be successful. and evening, employing scaring they will probably require regular Management measures should efforts only during those periods repetition, reinforcement and be started when birds first arrive, may be sufficient. alteration to remain effective in the before they establish feeding habits longer term. These include many of at the water bodies to be protected. Managing conflicts is also likely the deterrent techniques listed, as Thus, on waters that typically to require striking an appropriate well as local reductions in cormorant experience cormorant depredation balance between the use of non- populations, such as through in winter, a scaring programme lethal deterrents and, where they shooting or the use of management should start in the autumn when the are justifiable and approved, lethal measures at roosting or nesting first birds arrive. Evidence suggests measures. As noted previously, sites. With many deterrents, their that cormorants stop visiting some killing cormorants is very attractive impact is likely to diminish with water bodies for a month or more to some stakeholders and commonly time as habituation tends to occur after initial aggressive scaring seen as taking positive action with any scaring technique that is efforts and, since birds arriving towards solving cormorant-fishery not reinforced by a demonstration of later in the season often follow conflicts — one dead cormorant actual danger. Thus, to be effective birds that are already present to represents one less bird capable of over longer periods, it is advisable feeding areas, conditioning the eating fish. In practice, however, to constantly change the appearance early birds to avoid certain waters such killing may not deliver the and location of devices, and to should help to reduce damage by anticipated ‘instant solution’ or the use combinations of harassment later arrivals. However, control expected benefits. As a number of techniques in a rigorously applied, measures may have to be applied the case studies illustrate, shot birds integrated control strategy. Shooting, consistently throughout the season can be replaced rapidly by birds from too, is thought to be most effective at water bodies located on major elsewhere, especially at attractive where it is used in combination with daily flight paths, migration routes feeding sites or on migration routes, other deterrent measures. or near large roosting areas. and large-scale shooting can prompt birds to become more widely Techniques that require human The application of management distributed, thereby increasing the presence are commonly regarded measures should also be timed to number of sites affected.
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means that there will be no simple relationship between management actions in breeding areas (e.g. in one country) and the consequences of these actions in wintering areas, or vice versa. Further, since numbers and distribution patterns of the birds are partly determined by density- dependent factors operating both within and outside the breeding season, the population as a whole has considerable potential to compensate for reductions in numbers.
For example, our knowledge of cormorant population dynamics The Cormorant’s mobility — between foraging sites and between wintering indicates that a reduction in and breeding areas — and the species’ flexibility — in nesting, roosting and breeding birds in an area often foraging sites — means that protecting a fishery from them is very often not leads to an increase in the numbers easy and may sometimes be impossible. Photograph — Shutterstock. of young birds per nest that are fledged successfully. This is Even at a local scale, the success of management option, with general thought to be a consequence of shooting depends to a large extent support from most stakeholder the reduced competition among on the nature of the local cormorant groups, large-scale population cormorants for food and the greater population, particularly the level control at a national or pan- availability of fish with which they of site fidelity and rate of turnover, European scale is much more can feed their offspring. It is likely but is also influenced by factors contentious. Although this is that the greater the (downwards) such as the site characteristics, the advocated by some stakeholders ‘pressure’ that is applied to reduce shooting strategy and the availability it is strongly contested by others. bird numbers, the stronger will of alternative sites to which the birds In reality, the complexities of be the (upwards) compensatory can move. Both shooting and egg shooting are likely to increase mechanisms that will operate to re- destruction can reduce the size of progressively as the scale of build population sizes. cormorant populations in an area, the shooting increases. Thus, but the level of any reduction can the likelihood of achieving a One way of avoiding the problem vary, the results can be unpredictable successful, pre-determined outcome of constantly fighting these and, where a reduction is seen, this is progressively less likely. compensatory mechanisms would can last for widely differing periods. be to work with density dependence Typically, effects are manifest over Modelling suggests that some form and adopt a management approach the longest term where a local of pan-European population control whereby birds are restricted to a population is relatively discrete, might be feasible, in principle. In particular area and their expansion to with limited turnover. practice, however, there are many other surrounding areas is controlled. biological reasons why attempts to In such a scenario, population size The concept of some form of pan- reduce the continental cormorant in the ‘permitted’ area would, in European cormorant population population, and manage this around effect, become regulated by the control is also attractive to some some lower ‘acceptable’ level, available resources (e.g. food and stakeholders. However, while the would be extremely difficult on breeding sites) and numbers would use of lethal control measures to such a broad scale. For example, the be expected to oscillate about some address localised or short-term large territory, widespread breeding equilibrium or carrying capacity conflict issues is commonly seen populations and further mixing and level. Active measures would be as a necessary and acceptable dispersing of the birds in winter required outside this area — for
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example, preventing new roosts where shooting is the only practical It is anticipated that existing tools establishing and the use of active lethal control measure, whereas the will be refined in the light of deterrents at feeding sites — in control of cormorant populations at experience and that new tools and order to restrict expansion. Of nesting sites is commonly required techniques will emerge. As noted course, preventing such expansion in countries other than where the at the outset of this summary, of the population would not be conflicts actually occur. Control at experimentation and innovation easy, particularly at a larger scale. nesting sites can also be problematic are likely to be the key drivers Nonetheless, such an approach because these may be in inaccessible in developing techniques and may have applications in certain areas or on nature reserves; there may management strategies for use in situations. also be insurmountable, practical different situations. Continuing difficulties — egg oiling is not information exchange will also be Even if successful, any reduction possible where the birds nest in trees, vital in communicating findings and stabilisation of the cormorant for example. and spreading good practice. In population at a lower level would this context, it is hoped that the reduce the overall impact of the birds There are also concerns that should INTERCAFE website (www. on fish stocks and fisheries — fewer unregulated control be permitted, intercafeproject.net) and a planned cormorants across Europe would this could lead to sustained decline new cormorant web site hosted by eat fewer fish. However, it is and possibly local extinction of the European Commission will highly unlikely that this would cormorants. A coordinated, and provide an effective mechanism for result in an even decline in the appropriately regulated, pan- exchanging ideas and experiences pressure on fisheries, as birds are European population control and ensuring ongoing, constructive likely to continue to favour high plan might allay such concerns. dialogue between stakeholder groups. quality habitats that offer the best However, the killing of any wildlife foraging potential. As fisheries that on a large scale will inevitably Finally, it is important to remember offer cormorants the best feeding attract criticism and may not be that because cormorants feed on opportunities are often those that are publicly acceptable, and some fish, the presence of any birds at most valuable or desirable to fisheries governments are unlikely to allow a particular site has the potential stakeholders, there may be little such lethal measures to be initiated to generate conflict between diminution in conflicts even following or extended in their countries. stakeholder groups. This Toolbox a substantial reduction in cormorant This would increase the cormorant describes and evaluates the wide numbers. Thus, although fewer birds quota that would have to be met by variety of techniques that are should mean fewer fisheries with participating countries. available to reduce the impact of problems, conflicts are likely to cormorants on fish communities. persist at many sites, particularly the Regardless of any future initiative in It will help provide the means by ‘best’ ones, unless a major reduction relation to a possible pan-European which impacts can be reduced, in cormorant numbers is achieved. plan, there will be an ongoing need but — ultimately — the resolution to manage cormorant-fishery conflicts of conflict relies on the willingness Aside from the biological issues, over various temporal and spatial of stakeholders to engage in that population reduction through culling, scales. This, in turn, will require process. A range of stakeholders nest destruction or egg oiling raises the use of appropriate management may have legitimate interests, practical, economical, political and tools. It is therefore hoped that this particularly where conflicts ethical issues. Lethal measures are INTERCAFE Toolbox will prove occur at large fisheries or over manpower intensive and costly, and useful to stakeholders and managers extensive areas. The initiation and there are practical issues to address in addressing such conflicts. It continuation of dialogue, and an over who funds any culling and is recognised, of course, that the appreciation and understanding who actually carries it out. This is of Toolbox in no way provides the among stakeholders of others’ particular relevance because conflicts definitive answer to these conflict aspirations and concerns, are pre- tend to occur at bird foraging sites issues. requisites to resolving conflicts.
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8 FURTHER INFORMATION
Worldwide, cormorants are among ▪▪ Review of international ▪▪ EU Cormorant Platform — the most widely studied birds, and research literature regarding a website through which DG there is a huge body of literature on the effectiveness of auditory Environment disseminates their biology, population dynamics bird scaring techniques and information about cormorants, and impacts on fisheries. The links potential alternatives. Bishop, cormorant numbers, below, though far from exhaustive, McKay, Parrott and Allan. management and conflicts provide selected convenient sources Web: http://www.defra.gov.uk/ related to cormorants, fish, of additional information on the environment/noise/research/ fisheries and aquaculture. The methods that have been employed birdscaring/birdscaring.pdf Platform is developed as part of to control, exclude and manage the the work of the EU ‘CorMan’ birds: ▪▪ Controlling Bird Predation project (‘Sustainable at Aquaculture Facilities: Management of Cormorant ▪▪ FACT Wildlife Management Frightening Techniques. Populations’). Web: http:// Group booklet: Protecting Southern Regional ec.europa.eu/environment/ your fishery from Aquaculture Center (USA). nature/cormorants/home_en.htm Cormorants. Web: http:// Follow the ‘Predators’ link on www.naturalengland.org. the ‘SRAC Fact Sheets’ page uk/conservation/wildlife- at https://srac.tamu.edu this is management-licensing/leaflets. document STAC0401 htm#piscivorous ▪▪ Control of Bird Predation ▪▪ Natural England advisory at Aquaculture Facilities: leaflet: Protecting fisheries Strategies and Cost from Cormorants — the Estimates. Southern Regional use of fish refuges. Web: Aquaculture Center (USA). http://www.naturalengland. Follow the ‘Predators’ link on org.uk/conservation/wildlife- the ‘SRAC Fact Sheets’ page management-licensing/leaflets. at https://srac.tamu.edu this is htm#piscivorous document STAC0402
▪▪ Natural England advisory ▪▪ Wetlands International, leaflet: Reducing the impact Cormorant Research Group of fish-eating birds — the official website:http:// use of nets and wires. Web: cormorants.freehostia.com/ http://www.naturalengland. index.htm org.uk/conservation/wildlife- management-licensing/leaflets. htm#piscivorous
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APPENDIX: WORK GROUP 2 MEMBERSHIP
The INTERCAFE Work Group 2 met and undertook work at each of the stakeholder meetings and during the between-meeting periods. Over the four-year span of INTERCAFE, the participants listed below attended some or all of the Group’s meetings and contributed greatly to them. INTERCAFE participants from other Work Groups also made presentations and contributions to Work Group 2 meetings, but they are not named individually here.
Name Affiliation & country Thomas Keller (WG2 Chair) Bavarian State Ministry of Environment, Public Health & Consumer Protection (StMUGV), Germany Kareen Seiche (WG2 Vice-chair) Saxon Ministry of Environment, Germany Michal Adamec State Nature Conservancy, Slovakia Timo Asanti Finnish Environment Institute (SYKE), Finland Bruno Broughton Independent Fisheries Management Consultant, UK Mindaugas Dagys Vilnius University, Lithuania Redik Eschbaum University of Tartu, Estonia Daniel Gerdeaux Institut National de la Recherche Agronomique (INRA), France Robert Gwiazda Polish Academy of Sciences, Poland Jonathon Harari Israel Nature and Parks Authority (INPA), Israel Savas Kazantzidis National Agricultural Research Foundation, Greece Botond Kiss Danube Delta Institute, Romania Ferenc Lévai Aranyponty Zrt., Hungary Linas Ložys Vilnius University, Lithuania Petr Musil Charles University, Czech Republic Ion Navodaru Danube Delta Institute, Romania Oleg Nemenonok Association of Fish Breeders of Latvia, Latvia Ger Rogan Marine Institute, Ireland Nils Røv Norwegian Institute for Nature Research (NINA), Norway Ian Russell Centre for Environment, Fisheries & Aquaculture Science (Cefas), UK Henrik Lykke Sørensen Danish Forest and Nature Agency, Denmark Tamir Strod Border Collie Rescue Inc., Israel
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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.esf.org
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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 Russell, the external websites referred to in I., Broughton, B., Keller, T. and this publication. Carss, D.N. The INTERCAFE Cormorant Management Toolbox — Methods for reducing Cormorant problems at European fisheries. COST Action 635 Final Report III, ISBN 978-1-906698-09-6.
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Published by: NERC Centre for Ecology & Hydrology on behalf of COST
Short Title: COST Action 635 Final Report III
Year of Publication: 2012
ISBN 978-1-906698-09-6
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