TMAP ad hoc Working Group Fish Progress report 2007
Loes J. Bolle, Ulrich Damm, Britta Diederichs, Zwanette Jager, Gerold Lüerßen, Harald Marencic, Thomas Neudecker, Harriët van Overzee, Jörg Scholle, Ralf Vorberg
Report numberC133/07
Client: National Institute for Coastal and Marine Management (RWS RIKZ) PO Box 207 9750 AE Haren The Netherlands Publication Date: 17 December 2007
Report Number C133/07 1 of 62 • Wageningen IMARES conducts research providing knowledge necessary for the protection, harvest and usage of marine and costal areas. • Wageningen IMARES is a knowledge and research partner for governmental authorities, private industry and social organisations for which marine habitat and resources are of interest. • Wageningen IMARES provides strategic and applied ecological investigation related to ecological and economic developments. © 2007 Wageningen IMARES Wageningen IMARES is a cooperative The Management of IMARES is not responsible for resulting damage, as well as for research organisation formed by damage resulting from the application of results or research obtained by IMARES, Wageningen UR en TNO. We are registered its clients or any claims related to the application of information found within its in the Dutch trade record research. This report has been made on the request of the client and is wholly the Amsterdam nr. 34135929, client's property. This report may not be reproduced and/or published partially or BTW nr. NL 811383696B04. in its entirety without the express written consent of the client.
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2 of 62 Report Number C133/07 Contents
Participants & co authors ...... 4
Summary ...... 5
1. Introduction ...... 6
2. Methods ...... 8 2.1 Species lists and selection of priority species ...... 8 2.2 Overview fish monitoring data available to TMAP ...... 9 2.3 Overview environmental data available to TMAP...... 14 2.4 Fish metrics...... 17
3. Results & Discussion ...... 19 3.1 Descriptive analyses of spatial and temporal trends...... 19 3.2 Multivariate analysis: Principal Component Analysis (PCA)...... 38 3.3 Trend analysis ...... 42
4. Recommendations...... 43 4.1 TMAP assessment tool...... 43 4.2 Future work ...... 43
References ...... 45
Referees...... 47
Appendix 1 – Wadden Sea fish fauna...... 49
Appendix 2 – Preliminary reference list Wadden Sea fish fauna...... 53
Appendix 3 – Fishing pressure by the German shrimp fishery ...... 55
Appendix 4 – Review on indicator studies in marine ecosystems ...... 57
Report Number C133/07 3 of 62 Participants & co authors The Netherlands National Institute for Coastal and Marine Management (RWS RIKZ) Postbox 207 9750 AE Haren • Zwanette Jager ( [email protected] ) Wagening IMARES Postbox 68 1970 AB IJmuiden • Loes Bolle ( [email protected] ) • Harriët van Overzee ( [email protected] ) Germany Marine Science Service Fasanenstieg 12 D 21521 Dassendorf • Ralf Vorberg ([email protected]) Landesamt für den Nationalpark Schleswig Holsteinisches Wattenmeer Schloßgarten 1 D 25832 Tönning • Britta Diederichs ([email protected]) Bundesforschungsanstalt für Fischerei Inst. für Seefischerei Palmaille 9 D 22767 Hamburg • Thomas Neudecker ( [email protected] fisch.de ) • Ulrich Damm ( [email protected] fisch.de ) BioConsult Schuchardt & Scholle GbR Klenkendorf 5 27442 Gnarrenburg • Jörg Scholle ( [email protected] ) Trilateral cooperation Common Wadden Sea Secretariat (CWSS) Virchowstr. 1 D 26382 Wilhelmshaven • Harald Marencic ( marencic@waddensea secretariat.org ) • Gerold Lüerßen ( luerssen@waddensea secretariat.org )
4 of 62 Report Number C133/07 Summary Building on previous work done by the TMAP ad hoc Working Group Fish, a meeting and a workshop were held in Hamburg in June and October 2007. The most important aim of both was to come to an agreement on how to proceed with the data preparations and analyses, and to facilitate the exchange of data and analyses procedures. Data from the Demersal Fish Survey (Wageningen IMARES, The Netherlands), the Demersal Young Fish Survey (Bundesforschunganstalt für Fischerei, Germany) and the Schleswig Holstein Survey (Marine Science Service / National Park Agency, Germany) have been taken into account. A number of fish metrics were identified which together are considered to give a good reflection of the fish community in the Wadden Sea. These selected metrics consist of abundance and size metrics for ‘priority species’, and species composition metrics. The priority species were identified previously based on various selection criteria and the occurrence in ongoing monitoring programs. The list was slightly modified this year. The fish metrics were calculated and the (mostly descriptive) analyses were carried out before, during and after the workshop. Mayor progress has been achieved especially for the DYFS data, for which the abundance data are now available for the full time span (although not yet fully quality controlled). Furthermore, the spatial resolution is now at the level of the Wadden Sea sub areas, which gives much more detail than in the last Quality Status Report (2004). The mayor focus of the work in 2007 was getting the fish monitoring data ready for analyses and doing the first (mostly descriptive) analyses. Other work carried out was the development of a (preliminary) reference species list, a literature review on indicator studies in marine ecosystems and compiling an overview (on a meta data level) of the available environmental data. Managers would like to get a conclusion on the status of the Wadden Sea in terms of ‘good’, ‘moderate’ or ‘poor’, but scientists are against giving such qualifications due to the lack of knowledge on the causal factors underlying the observed changes. The most advanced result that we can provide now is to monitor the changes in fish fauna in an effective way by making the best use of the ongoing Wadden Sea surveys and to develop a system by which we can adequately describe trends in a consistent way for future quality status reports. The work of the TMAP ad hoc Working Group Fish is building step by step toward such a system, and will eventually lead to a more complete picture of the status of fish in the Trilateral Wadden Sea area.
Report Number C133/07 5 of 62 1. Introduction Trilateral Cooperation Since 1978, The Netherlands, Denmark and Germany have been working together on the protection and conservation of the Wadden Sea covering management, monitoring and research, and political matters. An important element of the Trilateral Cooperation with regards to monitoring and research is the Quality Status Report (QSR). This report is published every 5 years and it presents the results of various ongoing monitoring programs in the Wadden Sea. Another important element of the Trilateral Cooperation is the Trilateral Monitoring and Assessment Program (TMAP) which aims at providing a scientific assessment of the status and changes in the ecosystem, and the effectiveness of implementing targets set by the Trilateral Wadden Sea Plan. The results of these monitoring and assessment programs are presented in the QSR. Finally, the Trilateral Cooperation with regards to monitoring and research is facilitated and enhanced by means of the International Scientific Wadden Sea Symposia. Fish play (both as predator as well as prey) an important role in the ecology of the Wadden Sea, and the Wadden Sea is an important habitat for (certain life stages of) various fish species. The importance of fish for the Wadden Sea and visa versa has not been recognized sufficiently within the Trilateral Cooperation. Although a chapter on fish was included in the Quality Status Reports of 1999 (De Jong et. al., 1999) and 2004 (Vorberg et. al., 2004), fish are not included in the TMAP, nor is fish mentioned (explicitly) in the Wadden Sea Plan. A closer international cooperation and more focus on fish monitoring and research was recommended by the QSR 2004 and the 11 th International Scientific Wadden Sea Symposium (2005). TMAP ad hoc Working Group Fish The recommendations in the QSR 2004 have led to the instigation of the TMAP ad hoc Working Group Fish. The group reports to the Trilateral Monitoring and Assessment Group (TMAG), through the Common Wadden Sea Secretariat (CWSS). The group met for the first time in Hamburg on 29 30 March 2006. A large group of fish experts was invited, including scientists working in other areas than the Wadden Sea. The nature of the meeting was mainly informative; presentations were given about ongoing monitoring programs and the development of assessment methods and tools (TMAP, 2006a). A sub group of the March meeting reconvened in Wilhelmshaven on July 3 rd , 2006 to draft a report to TMAG. This sub group identified 2 topics which required further attention before submitting the report to TMAG: 1) The preparation of a list of typical/important Wadden Sea fish species and the development of criteria for the selection of ‘priority’ species for TMAP/QSR . 2) The evaluation of the applicability of the fish assessment tool approach that was developed for the Water Framework Directive (WFD) in transitional waters. The follow up work and the report were completed by correspondence. The report was submitted to TMAG in August (TMAP, 2006b), and the evaluation of the WFD was submitted as a separate document (Bioconsult, 2006a). The sub group re convened in Haren on November 20 th , 2006 with the specific goal to jointly discuss the progress and directions taken with regards to the species list, the selection of priority species and the evaluation of the applicability of the WFD approach. Furthermore, a strategy of approach for follow up work to be carried out in 2007 was developed (Bolle, 2006).
6 of 62 Report Number C133/07 Follow up in 2007 The TMAP ad hoc Working Group Fish agreed on 4 of the follow up activities listed below. An additional step, i.e. a literature study, was proposed and carried out by IMARES. 1. Reference list for Wadden Sea fish fauna 2. Selection of priority species 3. Literature study on indicators in marine ecosystems 4. Data analysis 5. Recommendation on TMAP assessment tool A meeting and a workshop were held in Hamburg in 2007 (26 27 June & 22 25 October). The most important aim of both was to come to an agreement on how to proceed with the data preparations and analyses, and to facilitate the exchange of data and analyses procedures. Part of the analyses were carried out during the workshop in October. The work that was carried out by IMARES for the TMAP ad hoc Working Group Fish was commissioned and financed by the National Institute for Coastal and Marine Management (RWS RIKZ). The present report is considered to be a ‘living document’, a preliminary document which can serve as contribution or starting point for a more comprehensive Quality Status Report in 2009.
Report Number C133/07 7 of 62 2. Methods
2.1 Species lists and selection of priority species
Wadden Sea Fish Fauna The Wadden Sea Fish Fauna table is presented in Appendix 1 and lists the typical Wadden Sea fish primarily based on the occurrence in the ongoing monitoring programs in recent years. The table also contains several criteria that can be used to select ‘priority species’. The TMAP ad hoc Working Group Fish had already prepared a this table in 2006 (Bolle, 2006), but minor update of the settings for the selection criteria was carried out this year. The table may will probably be revised again in the following years. Firstly, because the monitoring data can be elaborated if the fyke data collected by the Royal Netherlands Institute for Sea Research are made available. Secondly, the information presented in the selection criteria columns will probably be updated based on new insights due to ongoing research. Selection of priority species In principle, the Wadden Sea Fish Fauna table in Appendix 1 supplies all information required to be able to select priority species. Although a scoring system has been developed, which attempts to provide an objective quantitative tool to select the priority species, it is still necessary that the outcome is reviewed based on expert judgment. The resulting priority species to be included in the analyses are listed in Table 1. The catchability of these species differs between the gear types, therefore the different species were allocated to different gear types. Table 1. Priority species to be included in the spatial and temporal trend analyses (CA=diadromous, ER=estuarine resident, MJ=marine juvenile, MS=marine seasonal) Ecological Species Stratification Beamtrawl Stownet guild Alosa fallax Twaite shad CA Pelagic (x) x Osmerus eperlanus Smelt CA Pelagic (x) x Lampetra fluviatilis River lamprey CA Pelagic - x Platichthys flesus Flounder ER Demersal x (x) Zoarces viviparus Eelpout ER Demersal x - Ammodytes sp. Sand eel ER Pelagic & Burried x - Pleuronectes platessa Plaice MJ Demersal x - Solea vulgaris Sole MJ Demersal x - Limanda limanda Dab MJ Demersal x - Gadus morhua Cod MJ Demersal x - Merlangius merlangus Whiting MJ Demersal x - Clupea harengus Herring MJ Pelagic (x) x Sprattus sprattus Sprat MS Pelagic (x) x Engraulis encrasicolus Anchovy MS Pelagic - x Reference species list Although quantitative historic data is lacking, anecdotal historic data exists on species composition in the Wadden Sea. It was decided to compile a reference list of all species ever encountered in the Wadden Sea. For this list information presented in Fishes and fisheries of the Wadden Sea (Witte and Zijlstra, 1978; Zijlstra, 1978), the Schleswig Holstein Fish Atlas (Vorberg & Breckling 1999) will be used. Furthermore data from various ongoing monitoring programs will be included. A preliminary version of the reference species list is presented in Appendix 2.
8 of 62 Report Number C133/07 2.2 Overview fish monitoring data available to TMAP
Important note : The available data form the various fish monitoring programs will exclusively be used within the framework of this project. The data included in the present analyses and report are from the: Demersal Fish Survey (DFS, Wageningen IMARES, The Netherlands), Demersal Young Fish Survey (DYFS, Bundesforschunganstalt für Fischerei, Germany) Schleswig Holstein Survey (SHS, Marine Science Service / National Park Agency, Germany) The spatial and temporal coverage of the 3 surveys is summarised by the overview of the number of hauls per year and area presented in Table 2. The area codes (QSR areas and D(Y)FS areas) referred to in Table 2 are mapped in Figure 1. A detailed description of the survey designs is given in the following sections.
Figure 1. Map of the Wadden Sea sub areas or QSR areas (as defined within the context of Quality Status Report), and the ICES areas or D(Y)FS areas (as defined in the original DFS/DYFS survey design).
Report Number C133/07 9 of 62 Table 2. Overview fish monitoring data: number of hauls by year, region and survey.
data owner (1) IMARES IMARES IMARES BFA BFA BFA BFA BFA BFA NPA NPA
data collection (1) IMARES IMARES IMARES BFA BFA BFA BFA BFA BFA MSS MSS
survey (2) DFS DFS DFS DYFS DYFS DYFS DYFS DYFS DYFS SHS SHS
gear beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl stownet stownet
1 western 2 eastern NL NL 3 Ems 4 East 8 Dith- 9 North 8 Dith- 9 North QSR area 5 Jade 6 Weser 7 Elbe Wadden Wadden Dollard Frisia marschen Frisia marschen Frisia Sea Sea 610, 612, 617, 618, 408, 409, D(Y)FS area 620 414, 405 413, 405 413, 405 412, 406s 411, 406s 411 408 616 619 410, 406n 1970 47 38 20 1971 49 29 21 21 1972 42 30 20 22 5 8 12 1973 44 29 22 15 7 6 12 1974 49 33 21 18 4 22 24 1975 53 33 21 4 22 24 1976 53 33 21 32 4 22 24 1977 54 34 21 17 7 3 21 22 24 1978 54 33 21 3 22 24 1979 47 30 19 34 18 22 24 1980 54 33 21 25 21 21 21 1981 53 33 21 33 21 24 1982 54 32 21 37 34 22 24 1983 53 32 21 45 25 9 1984 54 31 21 41 28 19 18 1985 54 30 20 46 26 44 1986 54 32 21 45 27 29 25 1987 54 31 23 49 25 15 40 1988 47 30 22 44 26 23 32 1989 47 31 23 53 25 21 24 1990 46 31 23 55 28 28 41 1991 53 33 24 45 27 17 39 8 1992 55 18 28 46 26 27 31 8 1993 50 33 28 34 25 21 37 12 1994 50 28 25 33 25 25 37 9 1995 54 34 26 43 27 48 12 1996 62 34 27 34 25 33 34 12 1997 55 35 27 34 25 51 39 12 1998 62 35 26 30 23 33 60 11 1999 57 36 22 36 25 38 42 12 2000 68 36 26 40 24 32 42 10 2001 53 35 26 35 22 31 37 10 6 2002 53 33 26 27 24 32 36 10 12 2003 55 31 26 26 19 36 39 9 12 2004 61 32 25 19 25 30 27 12 11 2005 60 33 33 33 7 25 21 31 50 11 11 2006 62 32 29 35 6 33 34 28 52 11 11 total 1972 1186 868 1149 32 75 746 832 1087 169 63
(1) NPA = National Park Agency (Germany) (2) DFS = Demersal Fish Survey MSS = Marine Science Service (Germany) DYFS = Demersal Young Fish Survey IMARES = Wageningen IMARES (Netherlands) SHS = Schleswig-Holstein Survey BFA = Bundesforschunganstalt f ür Fischerei (Germany) Beam trawl The Netherlands has started “a census of juvenile fish” in 1969 in the Dutch Wadden Sea and from the Dutch to the Danish coast in offshore areas (Boddeke, 1970). German scientists joined in from 1970 onwards for various parts of the German Wadden Sea (Boddeke et al., 1972). However, comparable survey data for the entire German region are considered to be available only since 1972/1975 depending on region. Furthermore, the German scientists are still in the process of digitising and quality control, especially for the data collected prior to
10 of 62 Report Number C133/07 1996. The survey was initially called the Demersal Young Fish Survey (DYFS) in both countries, but the name was changed to the Demersal Fish Survey (DFS) in the Netherlands at a later stage. The survey gear in both countries is almost identical (WGbeam, 2006). The gear used is a 3 m beam trawl with roller chain (‘bobbin rope’ ) and 20 mm mesh (stretched). The Dutch DFS uses one tickler chain which was omitted in the German DYFS because of the excessive catch of dead shells in many of the German stations (Rauck, pers.com.). Campaigns were carried out in both spring (April May) and autumn (September October), but the spring surveys were terminated in 1986 in the Netherlands and in 2004 in Germany. The main parameters and handling procedures were kept the same over the entire period, e.g. haul duration (15 min.), sorting, counting and measuring all fish by species or genus. The areas investigated mostly remained the same as well. Only minor changes occurred in the setup: the chartering of different vessels with increasing draught, slight shifts of survey weeks due to weather conditions and the intensity of sampling as a result of funding problems. Precision of some data improved over time according to the advances in technology, such as trawled distances (GPS based track recording compared to estimated mean tow distances in the early days of the DYFS), the use of electronic sea going scales for weight measurements instead of the estimation of catch volumes and recently the recording of data for temperature and depths by applying data loggers attached to the gear instead of surface and ship data. The borders of the DYFS code areas were originally not precisely fixed but confined by the gully systems and rough lines drawn in an overview map. Only recently (WGbeam, 2007) distinct borderlines were defined for the purpose of recalculating surface areas of the geographically and depth orientated strata. The DFS / DYFS was initially established entirely for fishery science and stock assessment purposes concerning commercial fish species, in particular plaice and sole. Brown shrimp was soon added to the list of published indices. The young fish indices are used since the eighties by the ICES working group on stock assessments and give a first indication on the year class strengths of the relevant species. As all other fish and many other benthic invertebrate species were recorded within that monitoring programme, it contains one of the most valuable data series for the Wadden Sea and Southern North Sea as well. Therefore the DFS / DYFS data also became relevant for a number of other programmes and conventions besides ICES, either concerning fishes themselves or their habitats. Among these are the European Common Fisheries Policy (CFP) with stock management measures, Oslo Paris Convention (OSPAR) with fish monitoring requirements and EcoQos, TMAP (Trilateral Monitoring and Assessment Programme) preparing to include fish monitoring in coastal and transitional waters into the wide range of other monitoring programmes, Red List of fishes in the North and Wadden Sea (RL), Water Framework Directive (WFD) using fishes as a quality measure for transitional waters, Flora Fauna Habitat Directive (FFHD) monitoring and protecting habitats and their species including fish habitats, European Marine Strategy Directive (EMS) co ordinating the marine environmental monitoring programmes. Many of these programmes are much more recent than the DFS/DYFS programmes and intend to use the data held by the involved governmental agencies. DYFS (Germany) North Frisia and Dithmarschen, i.e. Schleswig Holstein region (DYFS codes 406, 408, 409, 410, 411): The earliest data were gathered in 1970 and are available only in aggregated form (Boddeke et al. 1972). From 1975 onwards a fixed net of 50 stations was established covering all tidal basins from the northern Elbe estuary towards the “Hörnum Tief” which is south of the island of Sylt. For ecological reasons the border line of DYFS region 411 and 412 was shifted to the north transferring some of the southern most stations to the Elbe estuary code. The tidal basin north of Sylt and the Danish part of the Wadden Sea have never been sampled so far by the DYFS programme. Cutter, captain, scientific team and conditions were the same for that region until 1984 and the area was covered twice (spring and autumn) in ten fishing days. Then except for the nets, gear and working procedure everything changed. Other cutters had to be chartered separately for region 411 and the northern most parts of the area 410 and after some years again new and bigger vessels came into the programmes which due to more draught, may possibly have caused the loss of hauls in the shallowest parts fished before. The fixed positions could no longer be kept and the days available were restricted by the available funds to 7 or 6, sometimes 2 days instead of 10. This inevitably led to a variable haul distribution; however, the same tidal
Report Number C133/07 11 of 62 basins were fished. Haul frequency was increased and depth range widened towards some more deeper stations outside the island chain whenever possible according to weather conditions (Neudecker, 2001). The entire region was always fished during daylight, sometimes starting in the dusk. Fishing occurred only with the tidal current leading to a pattern of leaving port in the morning with ebb tide, reaching outer stations normally at low water and returning to port with flood tide or at high water. Exceptions were rare and caused by combinations of daylight, tidal and weather conditions. When the old wooden rollers were worn out, new rubber rollers came into use at the end of the eighties. Mesh size of these standard 3 m beam trawls was always kept the same, but net material changed to thinner threads when new nets had to be put into use. The scientific team always held one DYFS experienced biologist to keep up the quality in fish determination. Nevertheless, problems in distinguishing difficult species remained like e.g. with gobies, sand eels and sea snails. In theses cases the data were stored on genus level. In the early part of the DYFS only numbers and lengths were recorded besides a volume, which was mostly guessed from measuring pitchers as it was generally not possible to make exact measurements by f.e. water replacement. Since 2001 the first of seagoing, marine scales became available with slightly increasing accuracy from 5 to 1 g, and weights were taken for fish and invertebrate groups. It is intended to recalculate weights from recent length weight relationships by species for the older parts of the time series. Elbe estuary (DYFS code 412) The Elbe estuary was always fished from Cuxhaven by the cutter “Ramona” belonging to the same family starting in 1972. Until 1986 another scientific team than that from the North Frisian part did the investigations with the same type of equipment and procedures as applied in the other regions. To keep continuity only part of the team was changed when necessary in later years. Normally two days were spent to cover the region, one day below Cuxhaven towards the outer estuary and another day for the inner part of the estuary. Due to sediment shifts some stations had to be abandoned and were replaced by others in the same area. To give a more stable vessel condition in the stronger currents of the Elbe, always two beam trawls were used; however, only one net was sampled. As a land based laboratory was available in that region, sometimes when adverse weather conditions prevailed samples were collected and analysed later in the lab ashore. The main difference of the investigations in Cuxhaven compared to the northern regions is, however, that about half of the fishing was done at night over dusk to daylight. The day night effect has not been analysed so far for the DYFS data but is known to be significant from the fisheries. It might lead to an increased abundance index for that region and the “Cuxhaven” data, as higher catches of shrimp (and possibly also fish) are taken by commercial fisheries when fishing at night. As mentioned above, the southern most stations of the “Büsum” series fished south of the island “Trischen” were also attributed to the Elbe estuary and DYFS region 412. These were entirely day light hauls. Jade Weser estuaries (DYFS code 413) Except for some hauls in the early seventies, DYFS region 413 was not covered by the DYFS programme until 2005. The extremely tide dependent small harbour of Wremen is the base for the cutter chartered, meaning that fishing is only possible between absolute high water situations. Three days are spent in that region, one for the Jade, one for the fishing ground “Nordergründe” between Weser and Elbe and the third one for the Weser itself. The positions of the hauls were kept the same in these few years. Equipment and procedures are identical to those applied in other regions. East Frisian Wadden Sea (DYFS codes 414 and 405) This part of the Wadden Sea was investigated before the real start of the German DYFS programme by a campaign in 1972, including the entire west east extending tidal systems. Then the “Accumer Ee”, the system between the mainland and the islands Baltrum and Langeoog, was continually visited by the team also investigating the Cuxhaven area until 1993. Therefore in the earlier part of that series part of the hauls was taken at night or dusk, later mainly at daylight which could lead to a day night effect. Cutters have changed over time and became larger in recent years which also could affect the depth distribution of the hauls. One of the problems in this area is the accessibility of the offshore part outside the island chain (DYFS region 405). Quite
12 of 62 Report Number C133/07 often it was not possible to pass the sand barrier and surf between the islands. This fact combined with the small size of area has lead to a relatively high sampling intensity in the tidal channels compared to the other regions of the DYFS campaigns. DFS (The Netherlands) An important source of information on the fish fauna in the Wadden Sea is the Demersal Fish Survey (DFS). This survey was initiated in 1969 (Boddeke et al., 1969) and covers the Dutch Wadden Sea, the Ems Dollard estuary, the Scheldt estuary, and the shallow coastal waters from the Dutch Belgian border to Esbjerg, Denmark. Initially the survey was carried out in spring (April May) and autumn (September October), but since 1987 only the autumn survey has been continued. Slight shifts in the sampling period (depending on the region and vessel) have occurred. In principle a fixed sampling period for an annual survey is optimal because this should minimize variation caused by seasonal patterns, but as inter annual variability in seasonal patterns also occurs, it is impossible to exclude this source of variation alltogether. Sampling is stratified by geographical area (DFS areas) and depth (5m depth classes). Sampling is restricted to water deeper than 2 3 m, because of the draught of the research vessels. Three different research vessels cover the survey area, one for the Scheldt estuary, one for the coastal waters and one for the Wadden Sea + Ems Dollard. The gear used is either a 6m beam trawl (coastal waters) or a 3m beam trawl (Scheldt estuary, Wadden Sea and Ems Dollard). The beam trawls are rigged with a shrimp net, a bobbin rope and a fine meshed cod end (20 mm stretched). Although the DFS was originally designed to provide recruitment indices of commercial flatfish species, all fish and epibenthos species have always been processed, providing valuable information on bottom dwelling species in coastal and estuarine waters. Trawling details such as the position, date, time and depth are recorded for each haul. Since 2002 in the estuarine waters and since 2004 in the coastal waters, sophisticated hydrographic data (temperature, salinity and visibility profiles) are collected with a data logging CTD. Before this only basic hydrographic measurements (surface water temperature and visibility estimates using a secchi disc) were collected by haul on all DFS cruises Only the DFS data collected within the Dutch Wadden Sea and the Ems Dollard (areas 610, 612, 616 620 in Figure 1) are included in the spatial and temporal analyses. The data collected in the coastal waters adjacent to the Wadden Sea (areas 404 407) were not included in theses analyses, but they have been included in the Wadden Sea fish fauna table in Appendix 1 (as a separate survey). The DFS areas in the Wadden Sea correspond to the tidal basins. In the QSR area definitions, the 6 tidal basins in the Dutch Wadden Sea have been combined into 2 larger regions (Figure 1). Stow net In 1991, a fish monitoring program started in the Meldorf Bight (Dithmarschen) using a stow net as standard sampling gear (Vorberg, 2001). Since 2001, a second sampling location has been installed in the Hörnum Deep, a tidal basin between the North Frisian island of Sylt, Amrum and Föhr. Sampling takes place once a year in August. The stow net, operated from an anchored vessel, reached from the water surface down to the bottom and was suitable to obtain quantitative data for pelagic fish (Breckling and Neudecker, 1994). At each site three stations has been installed, and at each sampling station four hauls were made, resulting in a total number of 24 hauls per year.
Report Number C133/07 13 of 62 2.3 Overview environmental data available to TMAP
The TMAP ad hoc Working Group Fish compiled a first basic overview of the environmental data available. This overview is probably far from complete. Only the data sources known to working group participants were included, no further search or literature review was carried out. Most of the information presented here is on a meta data level, i.e. description of what’s available in terms of variables measured, resolution, time span. The information presented for NAO index (this section) and the fishing pressure by the German shrimp fishery (Appendix 3) is more elaborate. Further elaboration of the overview is required, both in terms of sources as well as information collated per source. A future step will be to correlate the fish parameters with relevant environmental parameters, in which the relevance of an environmental factor is based on hypotheses that have been formulated using general ecological knowledge and specific knowledge built up in ongoing research projects. Temperature and salinity Source: BSH (13,500 data sets) Region: German Bight Temporal resolution: monthly mean, min, max, standard deviation Spatial resolution: ? Time span: 1975 2006 Accessibility: ? Source: Royal Netherlands Institute for Sea Research (Royal NIOZ) Region: western Dutch Wadden Sea Temporal resolution: monthly mean Spatial resolution: 1 station in Marsdiep Time span: 1861 2006 Accessibility: freely accessible Oxygen Source: BSH (13,500 data sets) Region: German Bight Temporal resolution: monthly mean, min, max, standard deviation Spatial resolution: ? Time span: 1975 2006 Accessibility: ? Nutrients & Chlorophyll Source: QSR/ TMAP data units Region: Wadden Sea (Netherlands, Lower Saxony, Schleswig Holstein, Denmark) Temporal resolution: ? Spatial resolution: ? Time span: Nutrients in water: NL 1971 2003; LS 1999 2006; SH 1990 2006; DK 1986 2006 Phytoplankton: NL 1971 2006; LS 1999 2005; SH 1999 2002; DK 1990 2006 Accessibility: limited to QSR/TMAP
14 of 62 Report Number C133/07 NAO The North Atlantic Oscillation (NAO) is a well known and key parameter for the climate in our northern hemisphere. Data on the air pressure difference between Iceland and the Azores are gathered daily since 1864 at different stations and are readily available via internet e.g. as monthly means. The Winter (December through March) index of the NAO is based on the difference of normalized sea level pressure (SLP) between Lisbon, Portugal and Stykkisholmur/Reykjavik, Iceland. The SLP anomalies at each station were normalized by division of each seasonal mean pressure by the long term mean (1864 1983) standard deviation. Normalization is used to avoid the series being dominated by the greater variability of the northern station. Positive values of the index indicate stronger than average westerlies over the middle latitudes. A link to various sources is also available, e.g. http://www.cgd.ucar.edu/cas/jhurrell/indices.info.html#naopcdjfm. The NAO has a strong influence on many other parameters like sea surface temperatures, winds and currents and by that influences strongly weather and environmental conditions for flora and fauna. Correlations between these environmental parameters and marine species have been investigated and documented but need to be reviewed. Purps et al. (1999) found a significant effect of the extended NAO winter index (DJFM) on the VPA assessments of plaice 0 group year class strengths and the June NAO index and 0 group sole. Concerning brown shrimp Neudecker et al. (unpublished) could demonstrate a strong correlation of the NAO winter index (DJF) as well as winter SST with the landings of the German shrimping fleet, while Siegel et al. (2005) found significant correlations of the extended NAO winter index (DJFM), winter SST and autumn river runoff on the autumn abundance of brown shrimp investigated by the DYFS. A check whether the extended winter (DJFM), May or June NAO values from 1971 to 2006 would correlate to the DYFS plaice indices for the same period gave no result, however (Neudecker and Damm, pers. comm. 2007). Musselbeds Variable: GIS data on location, size, shape of blue mussel beds Source: QSR / TMAP data units Region: Wadden Sea (Netherlands, Lower Saxony, Schleswig Holstein, Denmark) Temporal resolution: n.a. Spatial resolution: n.a. Time span: subtidal: NL 1999 2003; LS 1999 2006; SH 1999 2006; DK 1999 intertidal: NL 2003 Accessibility: limited to QSR/TMAP Variable: Biomass estimates in survey Source: IMARES Region: Dutch Wadden Sea Temporal resolution: annual survey Spatial resolution: ? hauls Time span: subtidal: 1992 2007 intertidal: 1990 2007 Accessibility: limited to QSR/TMAP Dumping sites Source: QSR2004 Region: Wadden Sea Temporal resolution: n.a. Spatial resolution: n.a. Time span: 1989 2003 Accessibility: freely accessible (http://www.waddensea secretariat.org/QSR/chapters/QSR 02.6 2.11 human activities.pdf)
Report Number C133/07 15 of 62 Source: OSPAR Commission, 2006: Dumping of wastes at sea in 2004 Region: ? Temporal resolution: n.a. Spatial resolution: n.a. Time span: 2004 Accessibility: ? Fishing pressure Variable: Fishing mortality (Fbar) on adult plaice and sole in North Sea Source: ICES WGNSSK Region: North Sea Temporal resolution: annual estimate Spatial resolution: n.a.. Time span: 1957 2006 Accessibility: freely accessible (http://www.ices.dk/iceswork/wgdetailacfm.asp?wg=WGNSSK) Variable: Fishing effort (e.g. fishing days, nr of vessels) by German shrimp trawlers Source: Bundesforschungsanstalt für Fischerei (BFA) Region: German Danish Wadden Sea Temporal resolution: annual estimate Spatial resolution: >2000: ICES rectangles (logbook obligation) <2000: ? Time span: 1952 1958, 1966, 1976, 1986, 1996, 2000 2006 Accessibility: ? Variable: Landings by international shrimp fisheries Source: ICES Region: ? Temporal resolution: annual estimate Spatial resolution: ? Time span: ? Accessibility: ?
16 of 62 Report Number C133/07 2.4 Fish metrics
The approach chosen by the group is mainly driven by work carried out in the estuaries in relation to requirements for the Water Framework Directive for transitional waters (WFD). For the implementation of this Directive an assessment tool was developed, which combines a number of fish metrics. The fish metrics actually are selected variables of the fish community which together are considered to give a good reflection of the fish community in general. In the case of the WFD, the fish metrics consisted of abundance indices of key species and species composition indices based on the number of species in certain ecological guilds (Jager & Kranenbarg, 2004; Bioconsult, 2006b; 2007) The same approach with respect to selecting fish metrics was chosen for the Wadden Sea fish fauna. However for the Wadden Sea it was decided to add mean length of the key species to the fish metrics. Reason for this is that a shift in mean length indicates a change in the (sub )population structure. This can be expected for species like plaice in which trends in abundance in the Wadden Sea are more apparent for one age group than the other. Length (mean, median, maximum) is commonly used as an indicator in marine ecosystems (see literature review in Appendix 4). Fish metrics The group decided to include the following fish metrics in the analyses. Possibly a smaller selection of metrics and/or priority species will be taken on into the next steps, this depends on the results of the analyses. • Mean abundance of priority species by year and region • Mean length of priority species by year and region • Species richness and composition (~ecological guilds) by year and region Priority species The priority species are listed in Table 1 and the choice of these species is discussed in Chapter 2 and Appendix 1. Spatial resolution The spatial resolution for the calculations was set at the level of the so called QSR areas, i.e. the Wadden Sea sub areas which were distinguished in the previous QSR (Figure 1). These QSR areas largely correspond to single or aggregated DFS/DYFS areas (Figure 1 and Table 2). In the DFS/DYFS surveys a distinction is made between the area within the islands and the area outside of the islands. This distinction is not made for the QSR areas. For the present analyses, only the data for the areas within the islands was included. Mean abundance The catch rates per haul were standardized. In the case of the beam trawl catches they were converted to numbers per 1000m 2, in the case of the stow net catches to numbers per 1000000m 3. These abundance estimates were then averaged by year and region. In case of the beam trawl surveys, it was discussed whether or not to weight the averages inversely by the number of hauls per depth class. Argument in favor was that the weighting procedure will eliminate the potential effects of unbalanced sampling over the depth classes (a change in the depth distribution of the sampling may suggest a trend in abundance which does not really exist). Arguments against were that weighting may cause a few hauls to have an extremely high weight and that the depth during one haul can vary strongly in an environment like the Wadden Sea. The group decided against weighting by sample size. The group recommended that in the future weighting by the surface area of the strata should be carried out.
Report Number C133/07 17 of 62 Mean length The mean length was calculated as the Σ(N*length) / ΣN, in which N is number of fish. This formula was used for the mean length by haul calculation and for the mean length by region calculation. In effect, the mean length by region is the average of the mean lengths by haul weighted by the number of fish in the haul. Species richness In this study, species richness is defined as the total number of species observed in a region in a year. Mayor drawback of this parameter is that it is dependent on the number of hauls (in a non linear way). Therefore species richness can not be compared between regions if the number of hauls differ. Furthermore, one should be careful when examining trends in species richness if the number of hauls vary between years. In principle all fish were scored at the species level but due to identification problems a higher taxonomic level was chosen for some groups of species. These were: • Pomatoschistus microps & Pomatoschistus minutus (& Pomatoschistus lozanoi) → Pomatoschistus sp. • Liparis liparis & Liparis montagui → Liparis sp. • Ammodytes tobianus & Ammodytes marinus & Hyperoplus lanceolatus → Ammodytes sp. Species composition In this study, species composition is defined as the total number of species per ecological guild (calculated for each year and region). The ecological guilds considered to be most relevant for the Wadden Sea are CA (diadromous), MJ (marine juvenile) and ER (estuarine resident). The other categories (excluding freshwater species) were grouped into 1 rest group. The name estuarine resident (ER) may be confusing in relation to the Wadden Sea, because some scientists do not consider the Wadden Sea to be a true estuary. In this study we define ER as species that are resident in the Wadden Sea, i.e. they spend the majority of their life span in the Wadden Sea. Whether or not the species also occurs (abundantly) outside of the Wadden Sea is irrelevant for the status of ER. The aggregation of species because of identification problems sometimes causes problems for the calculation of the number of species per ecological guild. Greater sandeel (Hyperoplus lanceolatus) is considered to be a MJ, but the sandeel group (Ammodytes sp.), to which the greater sandeel has been added because of identification problems, is classified as ER. Status of the progress Important note : The calculation of the fish metrics must be considered preliminary. No doubt further corrections of the basic data will follow as a result of systematic quality controls and the ‘running into errors’ when working with the data (please note that the data for non commercial species have not been used much yet). Furthermore, amendments and improvements of the calculation procedures will probably follow after more thought is given to the procedures and results. An example is the surface area weighting of the strata in the beam trawl surveys (DFS/DYFS), which is considered to be better than the current procedure. The taxonomic aggregation levels was only briefly discussed during the workshop in October, and in the process of working up the metrics after the workshop it became clear that further discussions are needed. This is also the case for the classification into ecological guilds of species groups.
18 of 62 Report Number C133/07 3. Results & Discussion
3.1 Descriptive analyses of spatial and temporal trends
The spatial and temporal trends in fish fauna are illustrated by plotting all fish metrics (defined in section 2.4) by year and QSR area. Species richness and species composition As mentioned before, species richness is sensitive to the number of samples. In principle, the number of species will increase curvilinearly with the number of samples until a certain maximum. Figure 2 clearly shows that the number of species encountered in the Dutch DFS increases if the number of hauls increases (per year and region). This relationship, at least partly, explains the differences in species richness between the 3 Dutch QSR areas.
35
30
25
w estern Dutch Wadden Sea
number of species number 20 eastern Dutch Wadden Sea Ems Dollard 15 10 20 30 40 50 60 70 number of hauls Figure 2. Number of species per year and region in relation to the number of hauls per year and region. Overall there appears to be no clear temporal trend in species richness nor in species composition (Figure 3). The number of estuarine residents is remarkably stable, especially in the western and eastern Dutch Wadden Sea. Not much variation is observed in the number of marine juveniles either. Most of the variation in species richness is caused by the number of diadromous species or other (MA & MS) species. A strange dip in species richness is observed in 1995 in the North Frisian area for the DYFS. Although this result can not be explained by an exceptionally low number of hauls in 1995 (Table 1), it seems suspect. Note that the German DYFS data prior to 1996 have not been (sufficiently) quality controlled yet. Abundance of priority species The mean abundance per year for each QSR area and survey is plotted for all priority species in Figures 4.1 – 4.14. Note that the Y axis of the plots are on a log scale (and therefore the zero values have been converted into a small value). The long term average is plotted as a horizontal line in all figures. The trends have been visually classified into 3 groups: • no trend (blue) – flat line or large fluctuations without clear trend on full time scale • up (green) – overall trend is an increase • down (red) – overall trend is a decrease
Report Number C133/07 19 of 62 The classification is indicated in the graphs by the colour of the symbols. The trend descriptions are summarised in Table 3. A fourth description up & down has been used in Table 3 and is further explained in the next paragraph. In these cases the overall trend is still classified as either up, down or no trend depending on the overall pattern. The observed trends differ between species and regions, in which the differences between (adjacent) regions for 1 species are smaller than the differences between species. Overall more downward trends than upward trends are observed. A pattern observed in several species and regions is an increase in abundance in the seventies and a decrease in abundance in the eighties and/or nineties. This effect cannot (only) be ascribed to a survey effect because it is observed in both the DFS and DYFS which are 2 completely independent surveys. The occurrence of this pattern is indicated in Table 3 by the description “up & down”. The time span of the SHS survey is relatively short compared to the DFS and DYFS surveys, especially for the North Frisia area (only 6 years). Therefore caution should be taken when comparing the trends between the SHS and DYFS survey. What appears to be an upward trend in the SHS may be part of an overall downward trend if a longer time span is examined and visa versa. Furthermore note that the area coverage of the stownet sampling (within the QSR area) is limited. Mean length of priority species The mean length has been calculated (according to the procedure described in section 2.4) for all priority species, QSR areas and surveys. A selection of the results (1 area per survey for all priority species) is presented in Figure 5 and all results are summarized in Table 4. Mean length estimates are obviously not available for years and areas with zero catches, and it was decided to only include mean length estimates that were based on at least 5 fish in total. This reduces the number observations for mean length per year and area. Furthermore, the German DYFS data collected prior to 1996 are not included in Figure 5 and Table 4. The data prior to 1996 have not been quality controlled yet and apparently many length records are either missing or not yet available digitally. The classification as defined for the abundance plots (no trend, up, down) was also used for mean length. A classification was only given if estimates for at least 5 years were available. For most species and areas no clear trend in mean length was observed. For plaice a decrease in mean length was observed in the Dutch QSR areas as was expected based on the fact that we know that particularly the abundance of 1+ plaice has decreased (QSR2004). No trend was observed in the east Frisian area and Elbe area, and a slight increase was observed in the north Frisian and Dithmarschen areas. This can possibly be explained by the fact that 1+ group plaice have always been scarce in these areas (pers com. Uli Damm). Based on the trends in abundance by age group for sole (QSR2004) a slight decrease in the mean length was also expected for sole in the Dutch Wadden Sea, but this does not appear to be the case. The mean length of flounder decreases in the Dutch QSR areas, especially the western Dutch Wadden Sea. We were not aware of differential trends for different age groups in the case of flounder, but the mean length results provide a cue to look into this. Based on the present results it seems that the parameter mean length gives sub optimal and indirect indications for the detection of changes in the population structure within the Wadden Sea. A better approach would be to make a distinction between juvenile and adult fish, or (in the case of marine juveniles) between 0 group and 1+ group fish.
20 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea ER MJ DFS (nl) DFS (nl) CA rest
30 30
20 20
10
10 species of number number of species of number
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
3 - Ems Dollard DFS (nl)
30
20
10 number of species of number
0 1970 1975 1980 1985 1990 1995 2000 2005
4 - East Frisia 5 - Jade DYFS (de) DYFS (de)
30 30
20 20
10 10 number of species of number number of species of number
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
6 - Weser 7 - Elbe DYFS (de) DYFS (de)
30 30
20 20
number of species of number 10 10 number of species of number
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
8 - Dithmarschen 9 - North Frisia DYFS (de) DYFS (de)
30 30
20 20
10 10 number of species of number number of species of number
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
8 - Dithmarschen 9 - North Frisia SHS (de) SHS (de)
30 30
20 20
10 10 number of species of number number of species of number
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005 Figure 3. Number of species per year and ecological guild for each region and survey
Report Number C133/07 21 of 62 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea twaite shad - DFS (nl) twaite shad - DFS (nl)
10 10
1 1
0.1 0.1 N / 1000m2 / N N / 1000m2 / N 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard twaite shad - DFS (nl)
10
1
0.1 N / 1000m2 N / 0.01
0.001 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe twaite shad - DYFS (de) twaite shad - DYFS (de) 10 10
1 1
0.1 0.1 N / 1000m2 / N 1000m2 / N 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia twaite shad - DYFS (de) twaite shad - DYFS (de) 10 10
1 1
0.1 0.1 N / 1000m2 / N N / 1000m2 / N 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia twaite shad - SHS (de) twaite shad - SHS (de)
10000 10000
1000 1000
100 100
N / 1000000 m3 1000000 / N 10 m3 1000000 / N 10
1 1 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.1. Mean abundance of twaite shad per year (symbols) and the long term average (line) for each region and survey.
22 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea smelt - DFS (nl) smelt - DFS (nl)
100 100
10 10
1 1 N / 1000m2 / N N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard smelt - DFS (nl) 100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe smelt - DYFS (de) smelt - DYFS (de) 100 100
10 10
1 1 N / 1000m2 / N 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia smelt - DYFS (de) smelt - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia smelt - SHS (de) smelt - SHS (de)
10000 10000
1000 1000
100 100 N / 1000000 m3 1000000 / N m3 1000000 / N
10 10 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.2. Mean abundance of smelt per year (symbols) and the long term average (line) for each region and survey.
Report Number C133/07 23 of 62 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea flounder - DFS (nl) flounder - DFS (nl)
100 100
10 10
1 1 N / 1000m2 / N 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard flounder - DFS (nl)
100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe flounder - DYFS (de) flounder - DYFS (de) 100 100
10 10
1 1 N / 1000m2 / N 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia flounder - DYFS (de) flounder - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia flounder - SHS (de) flounder - SHS (de)
10000 10000
1000 1000
100 100
10 10 N / 1000000 m3 1000000 / N N / 1000000 m3 1000000 N / 1 1
0.1 0.1 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.3. Mean abundance of flounder per year (symbols) and the long term average (line) for each region and survey.
24 of 62 Report Number C133/07
1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea sandeel - DFS (nl) sandeel - DFS (nl)
10 10
1 1
0.1 0.1 N / 1000m2 N / N / 1000m2 / N 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard sandeel - DFS (nl)
10
1
0.1 N / 1000m2 / N 0.01
0.001 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe sandeel - DYFS (de) sandeel - DYFS (de) 10 10
1 1
0.1 0.1 N / 1000m2 N / 1000m2 N / 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia sandeel - DYFS (de) sandeel - DYFS (de) 10 10
1 1
0.1 0.1 N / 1000m2 N / N / 1000m2 N / 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.4. Mean abundance of sandeel per year (symbols) and the long term average (line) for each region and survey.
Report Number C133/07 25 of 62 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea eelpout - DFS (nl) eelpout - DFS (nl)
100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard eelpout - DFS (nl)
100
10
1 N / 1000m2 / N 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe eelpout - DYFS (de) eelpout - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia eelpout - DYFS (de) eelpout - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.5. Mean abundance of eelpout per year (symbols) and the long term average (line) for each region and survey.
26 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea plaice - DFS (nl) plaice - DFS (nl)
1000 1000
100 100
10 10 N / 1000m2 N / N / 1000m2 / N 1 1
0.1 0.1 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard plaice - DFS (nl) 1000
100
10 N / 1000m2 N / 1
0.1 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe plaice - DYFS (de) plaice - DYFS (de) 1000 1000
100 100
10 10 N / 1000m2 N / 1000m2 N / 1 1
0.1 0.1 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia plaice - DYFS (de) plaice - DYFS (de) 1000 1000
100 100
10 10 N / 1000m2 N / N / 1000m2 N / 1 1
0.1 0.1 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.6. Mean abundance of plaice per year (symbols) and the long term average (line) for each region and survey.
Report Number C133/07 27 of 62 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea sole - DFS (nl) sole - DFS (nl)
100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard sole - DFS (nl) 100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe sole - DYFS (de) sole - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia sole - DYFS (de) sole - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.7. Mean abundance of sole per year (symbols) and the long term average (line) for each region and survey.
28 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea dab - DFS (nl) dab - DFS (nl)
1000 1000
100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard dab - DFS (nl) 1000
100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe dab - DYFS (de) dab - DYFS (de) 1000 1000
100 100
10 10
1 1 N / 1000m2 N / 1000m2 N /
0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia dab - DYFS (de) dab - DYFS (de) 1000 1000
100 100
10 10
1 1 N / 1000m2 N / 1000m2 N /
0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.8. Mean abundance of dab per year (symbols) and the long term average (line) for each region and survey.
Report Number C133/07 29 of 62 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea cod - DFS (nl) cod - DFS (nl)
100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard cod - DFS (nl) 100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe cod - DYFS (de) cod - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia cod - DYFS (de) cod - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.9. Mean abundance of cod per year (symbols) and the long term average (line) for each region and survey.
30 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea whiting - DFS (nl) whiting - DFS (nl)
100 100
10 10
1 1 N / 1000m2 N / N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard whiting - DFS (nl) 100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe whiting - DYFS (de) whiting - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia whiting - DYFS (de) whiting - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.10. Mean abundance of whiting per per year (symbols) and the long term average (line) for each region and survey.
Report Number C133/07 31 of 62 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea herring - DFS (nl) herring - DFS (nl)
100 100
10 10
1 1 N / 1000m2 / N N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard herring - DFS (nl) 100
10
1 N / 1000m2 N / 0.1
0.01 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe herring - DYFS (de) herring - DYFS (de) 100 100
10 10
1 1 N / 1000m2 / N N / 1000m2 / N 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia herring - DYFS (de) herring - DYFS (de) 100 100
10 10
1 1 N / 1000m2 N / 1000m2 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia herring - SHS (de) herring - SHS (de)
1000000 1000000
100000 100000
10000 10000
N / 1000000 m3 1000000 / N 1000 m3 1000000 / N 1000
100 100 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.11. Mean abundance of herring per year (symbols) and the long term average (line) for each region and survey.
32 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 2 - eastern Dutch Wadden Sea sprat - DFS (nl) sprat - DFS (nl)
100 100
10 10
1 1
0.1 0.1 N / 1000m2 / N N / 1000m2 / N 0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
3 - Ems Dollard sprat - DFS (nl) 100
10
1
0.1 N / 1000m2 N / 0.01
0.001 1970 1975 1980 1985 1990 1995 2000 2005
year
4 - East Frisia 7 - Elbe sprat - DYFS (de) sprat - DYFS (de) 100 100
10 10
1 1
0.1 0.1 N / 1000m2 / N 1000m2 / N
0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia sprat - DYFS (de) sprat - DYFS (de) 100 100
10 10
1 1
0.1 0.1 N / 1000m2 N / 1000m2 N /
0.01 0.01
0.001 0.001 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
8 - Dithmarschen 9 - North Frisia sprat - SHS (de) sprat - SHS (de)
100000 100000
10000 10000
1000 1000
N / 1000000 m3 1000000 / N 100 m3 1000000 / N 100
10 10 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.12. Mean abundance of sprat per year (symbols) and the long term average (line) for each region and survey.
Report Number C133/07 33 of 62 8 - Dithmarschen 9 - North Frisia river lamprey - SHS (de) river lamprey - SHS (de)
100 100
10 10
1 1 N / 1000000 m3 1000000 N / m3 1000000 N /
0.1 0.1 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.13. Mean abundance of rivier lamprey per year (symbols) and the long term average (line) for each region and survey.
8 - Dithmarschen 9 - North Frisia anchovy - SHS (de) anchovy - SHS (de)
10000 10000
1000 1000
100 100
10 10
1 1 N / 1000000 m3 1000000 N / m3 1000000 N / 0.1 0.1
0.01 0.01 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 4.14. Mean abundance of anchovy per year (symbols) and the long term average (line) for each region and survey.
34 of 62 Report Number C133/07 1 - western Dutch Wadden Sea 8 - Dithmarschen 8 - Dithmarschen twaite shad - DFS (nl) twaite shad - DYFS (de) twaite shad - SHS (de) 20 20 20
15 15 15
10 10 10
5 5 5 mean length (cm) length mean (cm) length mean mean length (cm) length mean
0 0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year year
1 - western Dutch Wadden Sea 8 - Dithmarschen 8 - Dithmarschen smelt - DFS (nl) smelt - DYFS (de) smelt - SHS (de) 20 20 20
15 15 15
10 10 10
5 5
5 (cm) length mean mean length (cm) length mean (cm) length mean
0 0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year year
8 - Dithmarschen river lamprey - SHS (de)
30
25
20
NA NA 15 10
mean length (cm) length mean 5
0 1970 1975 1980 1985 1990 1995 2000 2005
year
1 - western Dutch Wadden Sea 8 - Dithmarschen 8 - Dithmarschen flounder - DFS (nl) flounder - DYFS (de) flounder - SHS (de) 25 25 25
20 20 20
15 15 15
10 10 10
mean length (cm) length mean 5 (cm) length mean 5 (cm) length mean 5
0 0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year year
1 - western Dutch Wadden Sea 8 - Dithmarschen sandeel - DFS (nl) sandeel - DYFS (de) 25 25
20 20
15 15 NA 10 10 mean length (cm) length mean 5 (cm) length mean 5
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
1 - western Dutch Wadden Sea 8 - Dithmarschen eelpout - DFS (nl) eelpout - DYFS (de) 20 20
15 15
10 10 NA
5 5 mean length (cm) length mean (cm) length mean
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
1 - western Dutch Wadden Sea 8 - Dithmarschen plaice - DFS (nl) plaice - DYFS (de) 25 20
20 15 15 10 NA 10 5 mean length (cm) length mean mean length (cm) length mean 5
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year Figure 5. Mean length per year for all priority species, for only 1 region per survey.
Report Number C133/07 35 of 62 1 - western Dutch Wadden Sea 8 - Dithmarschen sole - DFS (nl) sole - DYFS (de) 20 20
15 15
10 10 NA
5
mean length (cm) length mean (cm) length mean 5
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
1 - western Dutch Wadden Sea 8 - Dithmarschen dab - DFS (nl) dab - DYFS (de) 20 20
15 15
10 10 NA
5
mean length (cm) length mean 5 mean length (cm) length mean
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
1 - western Dutch Wadden Sea 8 - Dithmarschen cod - DFS (nl) cod - DYFS (de) 30 30
25 25
20 20
15 15 NA 10 10 mean length (cm) length mean (cm) length mean 5 5
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
1 - western Dutch Wadden Sea 8 - Dithmarschen whiting - DFS (nl) whiting - DYFS (de) 20 20
15 15
10 10 NA
5
mean length (cm) length mean 5 mean length (cm) length mean
0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year
1 - western Dutch Wadden Sea 8 - Dithmarschen 8 - Dithmarschen herring - DFS (nl) herring - DYFS (de) herring - SHS (de) 20 20 20
15 15 15
10 10 10
5 5
mean length (cm) length mean 5 mean length (cm) length mean (cm) length mean
0 0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year year
1 - western Dutch Wadden Sea 8 - Dithmarschen 8 - Dithmarschen sprat - DFS (nl) sprat - DYFS (de) sprat - SHS (de) 20 20 20
15 15 15
10 10 10
5 5
mean length (cm) length mean 5 mean length (cm) length mean (cm) length mean
0 0 0 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005 1970 1975 1980 1985 1990 1995 2000 2005
year year year
8 - Dithmarschen anchovy - SHS (de)
18 16 14 12 10 NA NA 8 6
mean length (cm) length mean 4 2 0 1970 1975 1980 1985 1990 1995 2000 2005
year Figure 5. continued.
36 of 62 Report Number C133/07 Table 3. Summary of spatial and temporal trends in abundance.
survey DFS DFS DFS DYFS DYFS DYFS DYFS SHS SHS
gear beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl stownet stownet 1 western 2 eastern QSR area Dutch Wadden Dutch Wadden 3 Ems Dollard 4 East Frisia 7 Elbe 8 Dithmarschen 9 North Frisia 8 Dithmarschen 9 North Frisia Sea Sea Nyears 37 37 37 33 34 32 32 16 6
Nhauls 1972 1186 868 1149 746 832 1087 169 63 Twaite shad (CA) no trend no trend no trend up no trend no trend no trend no trend no trend
Smelt (CA) no trend no trend no trend no trend up & down up up no trend no trend
River lamprey (CA) ------no trend down
Flounder (ER) no trend no trend up up up up up & down no trend no trend
Sand eel (ER) no trend no trend no trend up & down up & down no trend no trend -- Eelpout (ER) (up &) down (up &) down (up &) down (up &) down (up &) down (up &) down (up &) down --
Plaice (MJ) (up &) down (up &) down (up &) down (up &) down no trend down down --
Sole (MJ) down down down (up &) down down down no trend --
Dab (MJ) down down down (up &) down down down down --
Cod (MJ) (up &) down (up &) down (up &) down (up &) down (up &) down no trend no trend --
Whiting (MJ) (up &) down (up &) down (up &) down up & down up & down (up &) down no trend -- Herring (MJ) up (& down) up (& down) up (& down) up & down up & down no trend no trend down no trend
Sprat (MS) (up &) down (up &) down (up &) down (up &) down (up &) down no trend down down no trend Anchovy (MS) ------no trend no trend Table 4. Summary of spatial and temporal trends in mean length
survey DFS DFS DFS DYFS >1995 DYFS >1995 DYFS >1995 DYFS >1995 SHS SHS
gear beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl beamtrawl stownet stownet 1 western 2 eastern QSR area Dutch Wadden Dutch Wadden 3 Ems Dollard 4 East Frisia 7 Elbe 8 Dithmarschen 9 North Frisia 8 Dithmarschen 9 North Frisia Sea Sea Nyears 37 37 37 11 11 11 11 16 6
Nhauls 1972 1186 868 349 267 375 458 169 63 Twaite shad (CA) up no trend no trend ---- no trend -
Smelt (CA) no trend no trend no trend no trend no trend no trend no trend no trend no trend
River lamprey (CA) ------no trend -
Flounder (ER) down down down no trend no trend no trend no trend no trend -
Sand eel (ER) no trend no trend no trend --- no trend -- Eelpout (ER) down no trend no trend no trend no trend no trend no trend --
Plaice (MJ) down down down no trend no trend up up - -
Sole (MJ) no trend no trend up no trend no trend no trend no trend --
Dab (MJ) no trend no trend no trend no trend no trend no trend no trend --
Cod (MJ) no trend up no trend no trend no trend no trend no trend --
Whiting (MJ) no trend up up no trend no trend no trend no trend -- Herring (MJ) no trend no trend no trend no trend no trend no trend no trend no trend no trend
Sprat (MS) no trend no trend no trend no trend no trend no trend no trend no trend no trend Anchovy (MS) ------no trend
Report Number C133/07 37 of 62 3.2 Multivariate analysis: Principal Component Analysis (PCA)
General remarks Evaluation methods that can structure information determined in the field and thus make results more transparent may be of significance for ecological questions. For this reason an exemplary evaluation by means of PCA – in addition to the central trend analyses (see section 3.1) – was conducted within the framework of the present study with the aim of obtaining indications of possible interrelationships between species abundances and study years and/or of existing time gradients. The exemplary analysis carried out here is based on the catch data (standardized to ind. 1000 m 2) of the Demersal Fish Survey (DFS) from the Ems Dollard area (DFS_Area 620, see Figure 1). Solely the fish species defined here as ‘priority’ for the Wadden Sea region were taken into account in this context (see Table 1). The abundance data were log transformed prior to the analyses. For representation in the form of an ordination the following PCA theoretical variables are depicted on the x and y axis in a linear model. The resulting aligned species values are shown as arrows. The arrow of a species concerned points towards increasing abundance. The longer an arrow belonging to a species is in the ordination, the greater the extent to which this species explains local and/or temporal differences. Results The result of the PCA illustrates a generally large spatial and temporal variability of the priority species in the area examined (Area_620 Eems Dollard). The variability is shown, among other things, by the fact that the hauls scatter relatively far beyond the ordination even within a catch period (here 5 year period, as seen by the haul designations of the same colour) (Figure 6). However, the key result is that a relatively clear time pattern can be identified within the data record in spite of this pronounced variability. For instance, the hauls from the period ‘1970+’ and ‘1980+’ are grouped above or below the 1st main axis while particularly the hauls from the years ‘2000+’ are located to the left of the 2nd axis, clearly separate from the former periods (Figure 6). The interannual differences are based primarily on the fact that maximum catch values in the 1970s and especially in the 1980s as well as a predominantly significant decline in catch figures in the 1990s and/or in the 2000+ period were recorded for nearly all priority species. These findings are indicated by the direction and length of the ‘species arrows’. With the exception of a few species such as flounder and twaite shad, which display a rather indifferent result (multiple R square <0.1), the other species arrows clearly point to ‘1970+’ and ‘1980+’ and thus illustrate the species specific maximum abundance values in these periods. Special weight for structuring the data record and forming a time gradient is primarily given to dab, plaice and sole as well as whiting. The abundance differences between the decades for these species are the most pronounced: all showed a more or less distinct minimum abundance value in the 2000+ period. Figure 7 and Figure 8 depict this result using the example of the temporal and spatial abundance distribution of dab (multiple R square = 0.52) and sole (multiple R square = 0.54). Conclusion The perceptible spatial and temporal variability within the decades (or 5 year periods) examined is predominantly overlapped by interannual differences between the decades with respect to the abundance of the priority fish species. These findings make it appear plausible that relatively significant changes in the fish fauna occurred in the Eems Dollard area in the period from 1970 2006 which very probably cannot be explained by a method related catch variability. The variance is explained quite well, to a degree of approx. 60%, by the first two main axes of the PCA. Indications of species specific development trends can therefore be derived from the analysis.
38 of 62 Report Number C133/07 PCA area620 Ind./1000m2, all hauls, data log-transformed
82_11 axis 2 05_9 87_5 sol 1.0
87_1
79_7
87_2 70_9-s
05_8 87_4 96_12 79_6 06_28 flo 87_9 84_12 80_9 86_7 06_2781-7 81-8 96_7 79_9 71_15 80_13 99_14 70_19 71_11 93_2202_4 86_3 86_16 71_6 05_11 70_10-s89_7 02_11 84_11 96_1380_7 85_3 05_13 96_8 79_871_3 96_4 71_13 80_21 87_3 78_7 05_2906_2906_8 85_7 89_10 71_1097_15 06_6 78_9 80_6 06_2405_10 02_6 97_16 86_6 03_1386_1 osm 87_11 85_6 71_12 99_791_197_2585_9 73_10 85_19 02_101_705_605_3187_2097_1305_7 80_1175_4 02_2 73_6 87_7 96_9 86_11 80_2 04_1772_7 76_20 84_9 78_11 06_26 87_13 87_18 71_189_8 85_1680_3 80_2071_5 91_671_805_2772_8 91_5 vib 71_21 85_18 ple 05_3000_5 97_22 91_206_4 85_17 78_12 97_7 97_9 01_25 70_8- s 89_385_888_2 99_1002_1297_5 81-670_197_27 71_16 00_105_1201_897_1287_6 04_1401_5 81-15 78_18 99_1304_25 02_5 99_2 96_10 85_10 81-9 80_1677_677_7 93_2097_603_2404_1293_2197_23 97_21 91_3 81-21 85_4 99_9 00_289_902_8 82_2104_11 73_996_287_2170_1188_1 86_480_17 87_19 78_8 06_2502_2301_1503_11 71_1482_12 74_1087_803_793_15 96_2371_784_191_121980+82_17 85_14 70_7 00_699_1205_28 99_8 82_13 96_11 85_5 80_1978_3 99_15 93_1871_9 82_103_2691_1002_701_1386_276_1901_2698_201_3 87_15 77_10 97_4 99_397_1093_19 97_1991_4 76_12 87_22 84_4 00_401_1499_6 03_10 01_16 05_3384_1396_5 90_287_12 85_271_17 84_1491_7 77_3 80_4 78_4 06_2202_2601_6 05_2494_7 81-1396_195_1592_11 81-3 86_9 80_15 02_997_887_1000_1799_497_1106_1092_14 84_1088_5 79_389_11 87_17 80_10 99_1602_1502_3 94_973_773_871_497_288_399_1705_1895_2594_1087_1403_23 81-4 81-17 80_8 99_500_2088_470_1872_197_1889_601_401_2397_26 87_2394_500_1479_2 86_10 04_1601_2497_1785_15 74_982_1992_9 93_17 84_396_25 70_14 89_4 83_18 02_10 92_15 92_800_1890_104_370_205_3206_503_1578_103_804_971_1800_13 84_16 98_1371_2 92_10 92_698_1601_17 96_16 74_11 cod 95_11 1990+80_14 78_16 00_7 88_11 91_20 80_18 99_1102_1698_1896_300_1500_1603_1782_1899_104_1301_20 97_2090_3 86_585_1380_5 76_9 04_1097_2403_1272_695_23 06_1194_301_997_1492_16 76_1 88_2181-16 70_3 81-11 84_2 94_8 00_802_1395_1076_17 98_5 78_17 78_1088_14 tws 91_9 03_2297_394_1198_1700_1906_298_1998_676_485_1198_370_12 76_2191_1196_2681-1081-18 90_20 95_14 04_799_2295_2494_606_793_1394_1301_1070_4 94_4 96_18 80_101_2 91_19 98_1005_1905_1498_893_1604_2003_2103_300_2104_2482_1670_2092_1804_596_2401_1 98_2282_4 76_8 81-2080_12 02_2198_1298_1404_803_2594_1298_782_605_1600_1072_10 70_15 95_17 70_5 axis 1 03_5 98_905_2395_903_1403_600_2695_1693_693_179_1504_1981-19 98_2488_604_1886_801_2273_5 73_4 81-2 1970+77_15 98_1503_403_992_704_1502_2492_1271_1982_203_1606_1598_2003_1 96_1502_22 86_18 75_270_13 79_4 78_6 78_19 2000+ 04_2106_1306_398_400_2581-106_1692_1793_14 90_4 84_19 84_1575_1575_14 91_1474_1688_1591_22 75_3 85_1 05_3 79_1372_1302_1802_1492_1395_795_806_12 03_18 82_1599_1873_3 01_1288_789_19 76_2 88_1383_19 02_1972_1100_2385_1293_306_1 72_1289_1 99_1972_1686_1773_1395_3 98_2501_2195_1895_2673_2077_981-5 88_1283_1696_1777_1776_774_15 89_1884_573_19 77_18 94_19 95_1293_579_1005_2006_1706_906_1879_1772_1573_1404_190_19 82_704_2292_370_1694_21 91_2305_4 81-12 83_12 83_20 93_406_2305_202_1706_1402_2500_2200_1103_1971_2099_2004_292_2100_2486_1579_1179_1879_16 95_2003_282_1495_695_2173_1682_1077_2186_2001_1879_193_8 82_2074_3 75_1392_2584_20 91_2477_1383_11 77_14 98_1105_1500_1272_1706_2103_2072_1899_2106_1905_2104_695_184_1897_196_2172_998_2696_19 76_1879_1292_5 76_6 98_23 90_1372_5 90_2196_14 86_19 77_2 92_2305_2672_1406_2076_1693_2593_2696_2000_998_101_1193_792_4 91_1590_2277_174_8 95_1994_1579_1490_504_2394_2075_12 88_8 88_10 92_2 96_2292_2205_2505_105_1700_304_4 81-14 98_2190_1273_1591_873_189_592_2092_2893_992_2782_378_1375_875_6 73_12 78_15 73_18 89_22 92_2493_2793_272_1976_1401_19 94_1676_1390_1579_595_274_773_1782_894_231995+83_5 76_1096_2790_1093_28 84_788_22 74_5 85_20 70_1796_670_693_2376_15 95_494_25 94_188_9 02_2094_17 91_1386_1395_1387_16 92_19 72_277_884_1777_5 76_377_11 73_2274_1973_21 84_874_1789_2 78_20 89_20 90_17 90_1405_2286_2173_1174_182_575_7 95_2286_1472_489_13 91_21 79_19 75_588_1883_17 91_16 88_20 95_577_1993_1077_2090_975_1090_675_2192_194_14 88_19 75_1 05_582_978_576_11 90_2390_8 75_11 83_14 83_13 90_793_24 94_1884_6 78_21 72_1 89_16 89_12 83_10 88_17 90_18 94_2275_16 88_16 86_12 75_17 74_674_1493_12 83_983_875_1974_489_14 75_9 77_1677_4 94_2483_1 91_18 74_13 78_2 dab 89_1572_390_11 92_26 83_7 74_12 84_21 89_21 her 89_23 93_11 77_12 spr94_2 83_2183_15 74_2073_291_17 zsp 90_16 75_20 75_18 83_2 89_1783_474_21 76_5 74_2 83_674_18 whg 83_3 78_14
explanation of variance (species data) 60.4% (axis 1 & 2) -1.0
-1.0 1.0 Figure 6: Ordination diagram of the PCA on the basis of the DFS fishing data (1970 2006, N = 868) from the Ems Dollart area (Area_620). Data log transformed [(ln(Ay+B) transformation of species data. A = 1,000, B = 1,000)]. Hauls in the 1970 1974 period: dark blue, 1975 1979: light blue, 1980 1984: grey, 1985 1989: black, 1990 1994: orange, 1995 1999: red, 2000 2006: light green. Fish: cod = cod, dab = dab, flo = flounder, her = herring, osm = smelt, ple = plaice, sol = sole, spr = sprat, tws = twaite shad, vib = eelpout, zsp = sand eel
Report Number C133/07 39 of 62 PCA area620 ind./1000m2 all hauls, data log transformed
axis 2 2.5 dab multiple R-square = 0.52 82_11 10 05_9 87_5 0 87_1 20
30 79_7 87_2 70_9-s
05_8 40 87_4 96_12 79_6 06_28
80_9 87_9 84_12 06_27 81-8 79_986_7 80_13 81-7 96_7 71_15 60 99_14 70_19 71_11 93_2202_4 70_10-s86_3 86_16 71_6 05_11 89_7 02_1105_13 84_11 96_1380_7 85_3 96_8 79_8 71_3 96_4 71_13 80_21 70 87_3 05_29 78_7 85_7 06_2906_8 06_6 89_10 71_1097_15 78_9 80_6 06_2405_10 02_6 86_6 97_16 87_11 85_6 03_13 86_1 85_9 73_10 71_12 99_791_1 97_25 85_19 02_101_705_605_31 87_2097_1305_7 80_1175_4 80 02_2 96_9 86_11 73_6 04_1787_7 76_20 80_2 72_7 84_9 78_11 90 06_26 87_13 05_2787_18 71_189_8 85_16 80_3 80_2071_2171_5 91_6 71_872_8 91_591_2 85_18 05_3000_5 97_22 06_4 85_17 78_12 97_9 70_8-s 89_385_888_2 97_7 97_5 01_2581-6 70_197_27 71_16 99_1002_1200_105_12 01_8 04_14 97_12 87_6 01_5 81-15 80_1677_6 78_18 99_1304_25 02_5 99_2 96_10 91_3 85_10 81-9 77_7 100 93_2097_603_24 97_23 97_21 81-21 85_4 99_9 00_289_9 04_12 93_2182_2104_11 73_996_287_21 70_1188_1 86_4 80_17 78_8 06_25 02_803_11 82_12 74_1003_7 71_784_1 87_19 85_14 70_7 00_6 99_1202_2301_1505_2871_14 99_8 82_13 87_8 93_1596_1196_23 91_12 85_5 82_1780_1978_3 99_15 71_982_103_2691_1002_7 01_13 86_276_1901_2698_2 01_3 87_15 77_10 97_499_393_1993_18 76_12 87_22 01_14 97_10 05_33 84_1396_597_1991_4 87_12 85_2 71_17 84_1491_7 77_3 80_4 78_4 84_4 00_4 99_606_2202_2603_10 05_2401_16 81-1396_192_1190_2 110 97_899_400_1701_6 94_7 84_1095_1579_3 81-3 86_9 80_15 02_9 87_1097_1171_406_1092_14 88_5 89_11 87_17 80_10 99_1602_1502_3 73_773_894_997_288_399_1705_1895_2594_1087_1403_23 81-4 81-17 80_8 99_52000+88_470_1872_1 01_2301_4 97_2694_5 00_1479_2 86_10 00_2001_2497_17 97_1889_6 87_2392_9 93_17 04_16 85_15 74_9 82_19 84_396_25 70_14 89_4 92_890_100_1870_205_3206_5 78_103_1503_804_9 00_13 04_3 71_18 92_698_1601_17 96_16 84_16 83_18 02_1095_1192_15 80_14 78_16 00_798_1371_296_300_1599_1 74_1188_11 86_5 91_20 80_18 99_1102_1698_18 00_1603_1782_1804_1392_1001_20 97_2090_3 85_1380_5 76_981-11 04_1003_1272_6 94_306_1101_997_1492_16 76_1 88_2181-16 70_3 84_2 00_802_1397_2495_1076_1795_2303_2297_394_1195_2498_1700_19 90_20 98_5 78_17 88_14 94_8 95_14 04_7 91_19 78_10 98_10 98_3 91_9 76_2196_26 06_298_1998_676_485_11 70_12 91_11 81-1081-1801_2 94_699_2206_7 93_1394_1301_1070_4 94_4 96_18 80_1 1980+ 77_15 axis 1 05_14 00_2104_24 76_8 81-2080_12 98_12 05_1998_893_1604_2094_1203_2105_1603_3 82_1670_2004_592_1896_2401_1 98_2282_41990+ 98_14 98_7 03_502_21 04_803_25 82_6 93_600_1079_15 72_10 70_1598_2488_6 86_8 95_17 73_470_5 98_995_904_1505_2303_1403_6 95_1600_26 93_1 81-1904_19 04_1801_2273_5 79_4 81-2 98_15 03_403_992_702_2492_1271_1982_203_1606_1592_1703_198_2096_15 02_2290_4 86_18 75_1575_270_13 78_6 78_19 04_2106_13 06_398_400_2581-106_16 93_14 84_1584_19 75_14 74_1691_1491_2288_15 75_3 85_1 05_3 79_1372_1302_1802_1495_895_792_13 06_12 03_18 82_1599_1877_9 73_3 01_12 88_789_19 76_2 73_19 88_1383_19 02_1972_1100_2393_3 06_1 89_172_12 99_1972_1686_17 73_1395_3 98_2501_2195_1895_2673_2081-5 88_1283_16 96_17 77_17 76_7 74_15 84_5 94_19 95_1293_579_1005_2006_1706_906_1885_1273_1404_190_19 82_7 04_22 70_16 81-12 89_1883_12 77_18 83_20 93_4 00_1102_2503_1999_2092_2186_1500_2472_1579_1779_1695_20 95_21 92_3 79_193_8 94_2174_382_20 91_2375_1305_484_20 91_24 77_13 77_14 06_2372_1705_206_2102_1706_1400_2271_2004_279_1172_979_1896_1998_26 82_1403_2 95_6 73_1682_1077_2186_20 01_18 92_2590_1372_5 83_11 98_1105_2605_1500_1203_2072_1899_2195_104_606_1997_105_2184_1896_21 76_1892_579_12 76_6 94_15 98_2394_20 90_2196_14 86_19 77_2 92_2372_1406_2076_1693_2596_2093_2600_998_101_1193_792_4 91_1577_190_2274_8 95_19 79_1490_5 04_2375_12 88_8 88_10 92_2 96_2205_2592_2200_305_1704_4 81-14 90_1273_15 73_189_5 92_2092_2893_992_27 82_3 75_875_6 73_12 1970+78_15 73_18 05_172_1976_1401_1998_21 91_8 76_1390_1579_595_2 78_13 83_5 76_10 84_7 74_5 89_22 85_20 92_2493_293_2793_23 76_1595_4 94_25 94_16 74_773_17 82_894_23 96_2790_10 93_28 88_2294_1 88_9 70_1794_1702_2096_670_6 91_1386_1387_16 72_277_884_17 77_5 76_3 77_11 73_22 74_1973_21 84_874_17 89_2 90_1790_1405_2286_2195_1373_1174_1 75_792_19 95_22 72_4 79_19 75_588_1883_17 78_20 89_20 95_577_19 93_10 77_2082_5 90_6 75_2192_1 86_14 89_13 88_1991_21 82_9 76_11 90_8 75_11 91_1683_14 88_20 93_24 90_975_10 94_14 75_1 05_5 78_5 90_23 83_13 90_794_22 94_18 84_6 78_21 72_1 89_16 89_12 83_10 88_17 90_18 75_16 88_16 86_12 75_17 74_6 74_14 83_9 83_875_1974_4 89_14 77_1677_493_12 83_1 74_13 75_9 72_3 83_7 5094_24 91_18 78_2 89_15 90_11 74_12 84_21 92_26 89_23 93_11 89_21 83_21 73_2 91_17 77_12 94_2 89_1783_15 74_20 90_16 75_20 75_18 83_2 74_2 83_474_21 76_5 83_674_18
83_3 78_14 -1.0 -1.0 2.5 Figure 7: Temporal spatial abundance distribution of dab in Area_620 (for database see PCA). Hauls in the 1970+ period: blue, 1980+: black, 1990+: red, 2000+: yellow. Visualization: locally weighted scatterplot smoothing.
40 of 62 Report Number C133/07 PCA area620 all hauls, ind./1000m2, data log-trans axis 2 2.5 sole multiple R-square= 0.54 82_11
05_9 55 50 87_5
87_1 45 40 79_7
87_2 70_9-s
05_8 87_4 96_12 79_6 30 06_28
87_9 84_12 80_9 06_27 81-8 79_986_7 80_13 25 81-7 96_7 71_15 99_14 70_19 71_11 93_2202_4 86_16 71_6 05_11 70_10-s86_3 89_784_11 80_7 02_1105_13 96_13 79_8 71_3 85_3 96_8 80_21 87_3 96_4 71_13 05_29 78_7 85_7 06_2906_8 97_15 06_6 89_10 71_10 78_9 80_6 06_2405_10 02_6 97_16 86_6 03_13 86_1 87_11 85_6 71_12 97_2585_9 73_10 85_19 02_105_605_31 99_791_1 35 01_7 87_2097_1305_7 96_9 1980+ 80_1175_4 15 02_2 73_6 87_7 86_11 80_2 04_1772_7 76_20 78_11 85_1684_9 80_3 06_26 87_13 05_2787_18 71_189_8 80_2071_2171_5 85_18 91_6 71_872_8 91_591_2 05_3000_5 97_22 06_4 88_2 85_17 78_12 97_7 97_5 97_9 01_25 70_8-s 89_385_8 71_16 99_1002_12 81-6 70_197_27 00_105_12 01_8 87_6 04_14 04_25 02_5 97_12 01_596_10 85_10 81-15 80_1677_6 78_18 99_13 93_2097_6 97_23 99_2 91_3 81-9 77_7 99_9 03_2404_12 93_2182_21 97_21 70_11 80_17 81-21 85_478_8 00_289_902_8 04_11 73_996_287_21 88_1 86_4 87_19 06_25 02_2303_1171_1482_12 74_1003_7 96_2371_784_1 85_14 70_7 00_6 99_1201_1505_28 03_2699_8 82_13 87_801_2693_1596_1101_3 91_12 87_15 85_5 82_1780_1978_3 99_15 99_3 93_1871_982_1 91_1002_7 01_13 86_276_1998_2 77_10 97_4 97_1093_19 91_4 76_12 87_22 84_4 00_4 01_14 01_1605_33 84_1396_597_19 87_12 85_2 71_17 84_1491_7 77_3 1975+80_4 78_4 99_606_2202_2603_10 05_24 81-1396_192_1190_2 81-3 20 97_899_400_1701_6 94_7 84_1095_1579_3 89_11 86_9 80_15 02_9 87_1097_1171_406_1092_1494_10 03_2388_5 81-17 87_17 80_10 99_1602_1502_370_1873_794_973_897_288_3 99_1705_1895_2587_14 81-4 80_8 99_5 88_4 72_1 89_601_2301_4 97_2687_2394_5 00_1479_2 86_10 00_2001_2497_17 85_1597_18 82_1992_9 93_17 96_25 70_14 04_16 92_800_1870_206_5 78_103_1574_904_9 84_3 89_4 90_104_305_32 03_8 71_1800_13 01_17 83_18 02_10 92_15 80_1492_698_16 96_16 84_16 78_16 95_11 00_798_1371_296_3 74_1188_11 91_20 80_18 99_1102_1698_18 00_1500_1603_1799_182_1804_1392_1001_20 97_2090_3 86_585_1380_5 76_9 axis 1 04_1003_1272_6 94_306_1101_997_1492_16 76_1 88_2181-16 70_3 81-11 84_2 00_802_1397_2495_1076_1795_2397_303_2294_1195_2498_1700_19 90_20 98_5 78_17 88_14 94_8 95_14 2000+04_7 91_19 78_10 98_10 98_3 91_9 76_2196_2691_11 81-18 94_1306_298_1901_1098_676_485_11 70_12 96_18 81-10 01_2 05_14 94_699_2206_7 93_1300_2104_24 70_4 94_4 80_1 76_8 81-2080_12 77_15 98_12 05_1998_894_1293_1604_2003_2105_1603_3 82_1670_2004_592_1896_2401_1 98_2282_4 02_2198_1404_803_25 98_782_6 00_10 72_10 70_15 95_17 70_5 10 03_5 98_995_905_2303_1403_6 95_1600_2693_693_179_1504_19 98_2488_6 04_1886_801_22 73_4 81-2 1970+ 98_15 03_904_1502_24 82_203_1606_1503_198_2081-19 73_5 75_270_13 79_4 78_19 04_21 03_492_798_400_2592_1281-171_1906_16 92_1793_1496_15 02_2290_4 86_18 84_1584_1975_15 74_1691_1488_15 75_3 78_6 06_13 72_1306_302_1495_7 06_12 1990+82_1599_18 73_3 75_1401_12 88_789_19 91_22 83_19 85_1 05_3 00_2379_1302_1893_395_892_13 89_172_12 72_1686_17 73_13 03_1898_2595_18 81-577_9 88_1283_16 76_274_15 73_1984_5 94_1988_13 93_502_1979_1072_1106_1706_985_1206_104_190_19 99_19 04_2295_3 01_2170_1695_2673_20 96_17 77_1781-1276_7 89_18 77_18 83_20 95_1293_405_2000_1103_1992_2186_1506_1879_1772_1573_1479_16 82_7 92_3 79_193_8 94_21 91_2375_1305_484_20 91_24 77_13 83_12 06_2305_202_1706_1402_2500_2271_2004_299_2000_2479_1179_18 95_2082_1403_2 95_695_21 73_1682_1086_20 74_382_20 92_25 83_11 77_14 98_1105_1572_1700_1206_2103_2072_1899_2195_104_606_1905_2172_996_2196_1998_26 76_1879_1277_2176_6 01_18 98_23 90_1372_5 90_2196_14 92_2305_2606_2076_1693_2696_2001_1192_497_184_18 92_574_8 94_1579_1490_5 04_2394_2075_12 88_8 86_19 92_2 77_2 96_2272_1405_2505_1700_393_2504_400_998_193_7 81-14 90_1273_15 89_573_191_1590_2277_192_2092_2893_9 95_1975_875_6 73_12 88_10 73_18 5 05_193_292_2293_2772_1976_1401_1998_21 91_8 76_1390_1579_574_795_292_27 82_378_13 83_5 76_10 84_788_22 74_5 78_15 89_22 85_20 70_1770_696_692_2493_23 76_1595_4 94_25 94_16 73_17 82_894_23 96_2790_10 93_28 94_1 88_9 94_1702_20 91_1386_1387_16 72_277_884_17 77_5 76_3 77_11 73_22 74_1973_21 84_874_17 89_2 90_1790_1405_2286_2195_1373_1174_1 82_575_792_19 95_22 72_4 79_19 75_588_1883_17 78_20 89_20 95_577_19 93_10 77_20 90_6 75_2192_1 86_14 89_13 88_1991_21 05_5 82_9 76_11 90_8 75_11 91_1683_14 88_20 93_24 90_975_10 94_14 78_21 75_1 78_5 90_23 83_13 90_18 90_794_22 94_18 84_686_12 72_1 89_16 89_1289_14 83_10 88_17 75_16 88_16 75_17 74_6 93_1274_14 83_9 75_1983_874_4 77_1677_4 094_2483_1 74_13 75_9 72_3 83_7 91_18 78_2 89_15 90_11 74_12 84_21 92_26 89_23 93_11 89_21 83_21 73_274_2091_17 77_12 94_290_16 75_18 89_1783_15 75_20 83_2 74_2 83_474_21 76_5 83_674_18 83_3 78_14 -1.0 -1.0 2.5 Figure 8: Temporal spatial abundance distribution of sole in Area_620 (for database see PCA). Hauls in the 1970+ period: blue, 1980+: black, 1990+: red, 2000+: yellow. Visualization: locally weighted scatterplot smoothing.
Report Number C133/07 41 of 62 3.3 Trend analysis
During the workshop simple linear regressions were carried out with the intention to examine if the overall trends were significantly increasing or decreasing. However, linear regression is not the appropriate method to analyse temporal trends due to autocorrelation (i.e. violation of the assumption of independence of the observed values for the response variable). Using linear regression when autocorrelation exists will inflate the P values, i.e. insignificant trends may seem significant (Zuur et al, 2007). Therefore, other statistical tools are required to analyse the temporal trends correctly. Two recently developed statistical methods which are currently frequently used in time series analyses are ‘TrendSpotter’ and ‘ Dynamic Factor Analysis’. TrendSpotter is a (univariate) method for trend analyses, in which the autocorrelation problem has been solved (Visser, 2004). To illustrate the possibilities of this method, the data for one of the TMAP priority species (eelpout) in one QSR region (Ems Dollard) has been analysed using TrendSpotter. The results are presented in Figure 9. Dynamic Factor Analysis is a multivariate method for trend analyses is. A feature of this method is that it enables the detection and estimation of common trends in a multivariate time series dataset (Zuur et al., 2007). It is recommended to test and use one or both of these methods in the analyses to be carried out next year.
Figure 9. Results of TrendSpotter analyses for eelpout abundance in Ems Dollard (DFS data). The left panel shows the observed values (annual mean abundance in N per 10000m 2) and the fitted trend with confidence limits. The right panel shows trend difference with confidence limits (transformed data), which indicates the degree of increase or decrease in abundance and the significance of the trend. A significant change (decrease) is only observed in 1989 (i.e. value 0 not in confidence interval).
42 of 62 Report Number C133/07 4. Recommendations
4.1 TMAP assessment tool
The request was put forward to the TMAP ad hoc Working Group Fish to evaluate if the fish metrics can be combined into a ‘tool’ that can be used to describe or maybe even evaluate the Wadden Sea fish fauna, similar to the ‘assessment tool’ developed for the WFD. However, a fundamental discussion is underlying this exercise. Managers would like to get a conclusion on the status of the Wadden Sea in terms of ‘good’, ‘moderate’ or ‘poor’, but scientists are against giving such qualifications due to the lack of knowledge on the causal factors underlying the observed changes. The present level of knowledge is simply not advanced enough to allow this kind of judgement. Scientists can describe temporal and spatial trends in fish abundance and species composition, they can indicate if trends are significant or not, they can analyse if trends are comparable between sub areas and species or not. A choice for scientifically sound metrics can be made and the long term average of these metrics can be calculated. But at present the factors and processes causing changes are still badly understood. Correlative studies between fish metrics and environmental factors have given and will give clues in which direction further (fundamental/process) research is required in order to understand what causes the observed changes. Another aspect which complicates the evaluation in terms ‘good’, ‘moderate’ or ‘poor’, specifically with respect to setting management targets, is the fact that many of the selected fish species are probably strongly influenced by natural variations and/or by processes outside of the Wadden Sea. Furthermore, reference (i.e. historic) conditions are generally not known, but even if they were, you might argue why it would be desirable to go back to the status of hundred (or thousand) years before. The more so, because at present we are experiencing a period of climatic changes, which probably reflects in the fish fauna and may cause ‘regime shifts’ (non linear changes). The most advanced result that we can provide now is to monitor the changes in fish fauna in an effective way by making the best use of the available Wadden Sea surveys and to develop a system by which we can adequately describe trends in a consistent way for future quality status reports. The work of the TMAP ad hoc Working Group Fish is building step by step toward such a system, and will eventually lead to a more complete picture of the status of fish in the Trilateral Wadden Sea area.
Future work
This report presents the results of the analyses carried out in 2007. These results are preliminary and the discussions on data handling, selection of metrics, and trend analyses are still ongoing. Based on the present results, the following is recommended for future work. 1) In the case of the beam trawl surveys, re calculate the means by year and region using the area based weighting factors estimated by the ICES WGbeam (see section 2.4). 2) Continue quality controls and corrections of basic data, specifically in the case of the German DYFS data (see section 2.4). 3) Analyse trends in abundance by using one or more appropriate (state of the art) statistical tools (see sections 3.2 3.3). 4) Analyse trends in abundance by size class, rather than trends in mean length, to examine changes in population structure (see section 3.1 and Figure 5). 5) Maintain current spatial resolution as differences in time series between QSR areas are observed (see Figures 4.1 4.14) 6) Evaluate choice of priority species based on results of trend analyses (e.g. sufficient data available to examine trends?, sampling gear suitable?) (see Figures 4.1 4.14).
Report Number C133/07 43 of 62 7) Evaluate the species richness and species composition metrics in relation to sampling intensity (see section 3.1 and Figures 2 3) 8) Further evaluate applicability of indicators used in marine ecosystems (see Appendix 4). 9) Elaboration of overview of environmental data, both in terms of number of variables (data sources) as well as amount of information per variable. 10) Compile an overview of the hypotheses which have been postulated (in the literature and ongoing projects) on the causal factors underlying the changes in Wadden Sea fish fauna. 11) Analyse the correlations between fish metrics and relevant environmental parameters, in which the relevance of an environmental factor is based on the above mentioned hypotheses.
44 of 62 Report Number C133/07 References Bioconsult, 2006a. Evaluation of fundamental applicability of assessment approach for fish in transitional waters in the Wadden Sea in conformity with Water Framework Directive (WFD). Bioconsult, 2006b. Fischbasiertes Bewertungswerkzeug für Übergangsgewässer der norddeutschen Ästuare. (unveröff.) im Auftrag des Landes Niedersachsen und Schleswig Holstein, Bremen: 88 S. Bioconsult, 2007. Fischbasierter WRRL konformer Bewertungsansatz für das Übergangsgewässer Ems und Ableitung eines Monitoringkonzepts. Kooperation Niederlande Deutschland im Ems Dollart Ästuar. Boddeke R., N. Daan, K.H. Postuma, J.F. deVeen and J.J. Zijlstra, 1970. A census of juvenile demersal fish in the Wadden Sea, the Dutch coastal area and the open sea areas off the coasts of the Netherlands, Germany and the southern part of Denmark. Ann. Biol. 26, 269 275 Boddeke R., R. de Clerck, N. Daan, A. Müller, K.H. Postuma, J.F. de Veen and J.J. Zijlstra , 1972. Young fish and Brown Shrimp survey in the North Sea. Ann.Biol. 27, 183 187 Bolle, L.J., 2006. Follow up on initiatives taken by the TMAP ad hoc working group fish in 2006. IMARES Report Nr. C093/06, 14 pp. Jager, Z. & J. Kranenbarg, 2004. Implementatie KRW vis in overgangswateren, werkdocument RIKZ/OS/2004.606w. In Klinge, M., J. Backx, M. Beers, B. Higler, N. Jaarsma, Z. Jager, J. Kranenbarg, J. de Leeuw, F. Ottburg, M. van der Ven & T. Vrieze, 2004. Achtergronddocument referenties en maatlatten voor vissen. www.stowa.nl. de Jong, P.D., Dahl, K., Neudecker, T., Knust, R., Van Berkel, C.J.M., 1999. Selected fish species and brown shrimp. In: De Jong, F., Bakker, J., Van Berkel, C., Dahl, K., Dankers, N., Gatje, C., Marencic, H., Potel, P. (Eds.). The Wadden Sea Quality Status Report 1999. Wadden Sea Ecosystem No. 9. Neudecker,Th. (2001). Der Demersal Young Fish survey (DYFS) in Schleswig Holstein, Entwicklung und derzeitiger Stand. In: Landesamt für den Nationalpark Schleswig Holsteinisches Wattenmeer (Hrsg.): Wattenmeermonitoring 2000. Schriftenreihe des Nationalparks Schleswig Holsteinisches Wattenmeer, 25832 Tönning, Germany, Sonderheft, 24–30 Purps, M., U. Damm und T. Neudecker, 1999. Der NAO Klimaindex und die Jahrgangsstärke von jungen Schollen (Pleuronectes platessa ) und Seezungen ( Solea solea ). Berichte über Landwirtschaft, Bd 77 (1), 124 127 Siegel V., J. Gröger, T. Neudecker, U. Damm and S. Jansen, 2005. Long term variation in the abundance of the brown shrimp Crangon crangon (L.) population of the German Bight and possible causes for its interannual variability. Fish. Oceanogr. 14:1, 1 16 TMAP, 2006a. Final minutes of the TMAP ad hoc working group fish meeting held in Hamburg on 29 30 March 2006. http:// www.waddensea secretariat.org/workshops/TMAP revision/Fish/fish workshop March06.html . TMAP, 2006b. Report of the TMAP ad hoc working group fish, 25 August 2006. http://www.waddensea secretariat.org/workshops/TMAP revision/Fish/TMAP fish report v5 (06.08.28).doc Visser, H., 2004. Estimation and detection of flexible trends. Atmospheric Environment 38, 4135 4145.
Report Number C133/07 45 of 62 Vorberg, R., Bolle, L., Jager, Z., Neudecker, T. , 2004. Fish. In: Essink, K., Dettmann, C., Farke, H., Laursen, K., Lüerßen, G., Marencic, H., Wiersinga W. (Eds.). The Wadden Sea Quality Status Report 2004. Wadden Sea Ecosystem No. 19. Vorberg, R. and Breckling, P., 1999. Atlas der Fische im schleswig holsteinischen Wattenmeer. Schriftenreihe des Nationalparks Schleswig Holsteinisches Wattenmeer, Heft 10, pp. 178. WGbeam, 2006. Report of the Working Group on BeamTrawl Surveys (WGBEAM), 16–19 May 2006, Hamburg, Germany. ICES CM 2006/LRC:11 WGbeam, 2007. Report of the Working Group on BeamTrawl Surveys (WGBEAM), 12 15 June 2007, Oostende, Belgium. ICES CM 2007/LRC:11 Witte, J.Y. and Zijstra, J.J., 1978. The species of fish occurring in the Wadden Sea. In: Dankers, N.; Wolff, W. J. and Zijlstra, J.J. (Eds.) Fishes and fisheries of the Wadden Sea. Report 5 of the final report of the section ‘Fishes and fisheries’ of the Wadden Sea Working Group. Stichting Veth tot Steun aan Waddenonderzoek, Leiden, 5 19. Zijlstra, J.J., 1978. The function of the Wadden Sea for the members of its fish fauna. In: Dankers, N.; Wolff, W.J. and Zijlstra, J.J. (Eds.). Fishes and fisheries of the Wadden Sea. Report 5 of the final report of the section ‘Fishes and fisheries’ of the Wadden Sea Working Group. Stichting Veth tot Steun aan Waddenonderzoek, Leiden, 20 25. Zuur, A.F., Ieno, E.N., Smith, G.M., 2007. Analysing ecological data. Statistics for Biology and Health. Springer Science + Business Media, New York, 672 pp.
46 of 62 Report Number C133/07 Referees Report C133/07 Project Number: 4392501701 This report has been professionally prepared by Wageningen IMARES. The scientific validity of this report has been internally tested and verified by another researcher and evaluated by the Scientific Team at Wageningen IMARES. Approved: Dr. Ingrid Tulp Scientist Signature: Date: 14 December 2007 Approved: Drs Jakob Asjes Head of Ecology Department Signature: Date: 14 December 2007 Number of copies: 25 Number of pages 62 Number of tables: 4 Number of graphs: 22 Number of appendices: 4
Report Number C133/07 47 of 62 48 of 62 Report Number C133/07 Appendix 1 – Wadden Sea fish fauna Table A1.1 presents a list of the fish fauna of the Wadden Sea. The decision on which species to include in this list was primarily based on the occurrence in the ongoing monitoring programs in recent years. Three species were not caught during the ongoing monitoring programs in recent years, but were nevertheless considered relevant for the Wadden Sea. These species were houting (which is a Habitat Directive species) and the thick lipped and thin lipped grey mullets (both of which are expected to be abundant in fyke catches). The ongoing monitoring programs included in the table are: • The Demersal Fish Survey (DFS) carried out by Wageningen IMARES (formerly known as RIVO, Netherlands) from 1970 onwards • The Demersal Young Fish Survey (DYFS) carried out by the Bundesforschunganstalt für Fischerei (Germany) from 1974 onwards • The Schleswig Holstein Survey (SHS) carried out by the Marine Science Service (Germany) from 1991 onwards A survey which was included in the table despite the fact that it is not an ongoing monitoring program (i.e. it will probably not be continued after 2007) • The Seabird Fish Interactions Survey (SFIS) carried out by the Insitute of Avian Research (Germany) in the years 2005 2007 An ongoing monitoring program for which the data have not been made available to TMAP (yet) is: • The Fyke sampling 't Horntje (NIOZ) carried out by the Royal Netherlands Institute for Sea Research from 1960 onwards The DFS and DYFS are beam trawl surveys, the SHS and SFIS are stownet surveys, and the NIOZ series is a fyke net survey. Both beam trawl surveys have a large spatial coverage, together these 2 surveys cover the entire Dutch and German Wadden Sea and the adjacent coastal waters. The spatial coverage of the stownet and fyke net surveys is limited. Further information on the surveys is given in Report of the TMAP ad hoc working group fish, August 2006. The objective of Table A1.1 was not only to list the Wadden Sea fish species, but also to serve as a basis for the selection of a limited number of species as candidates for monitoring within TMAP. The first part of the table (in shades of yellow to red, named selection criteria) provides information on the ecology of the species, it’s relevance to management and it’s sensitivity to important driving forces. These parameters are important criteria for the selection of species for TMAP monitoring. The second part of the table (in shades of blue, named monitoring) presents the occurrence and abundance of each species in recent years (2001 2005 for the ongoing surveys and 2005 2006 for the SFIS) and the catchability of each species with different gears. These parameters indicate the feasibility of currently monitoring the species within the ongoing monitoring programs. For each fish species a total score was calculated for the selection criteria and for the monitoring parameters separately. For this, each column received a weighting factor indicating the relative importance of each ‘+’ within the column. These weighting factors were based on expert judgement and elaborate discussions within the TMAP ad hoc working group fish. Both scores (i.e. one for the selection criteria and one for the monitoring parameters) are a simple addition of each ‘+’ multiplied by the weighting factor which is listed at the top of the table. Table A1.1 has been sorted by scores, primarily the selection criteria scores and secondarily the monitoring result scores. Fourteen species have a high score (>2) for both selection criteria as well as monitoring results, these are the top 14 species in Table A1.1 and they are listed separately in Table A1.2. Four species have a high score (>2) for the selection criteria but a low score for the monitoring results, they are listed separately in Table A1.3.
Report Number C133/07 49 of 62 Table A1.1: Wadden Sea fish fauna: All fish species caught in recent years in the Wadden Sea or in coastal waters bordering the Wadden Sea, and additional species not caught in recent years but considered relevant for the Wadden Sea. Selection criteria Ecology Relevance for management Sensitivity to driving forces (11) (7) (6) (5) (13) (9) (10) (1) (12) (8) (3) (2) (4) Ecological guilds Stratification Benthic habitat speciesHD speciesWFD for Eems vulnerable or Endangered for birds Food mammalsor Climate change enrichment Nutrient Habitat degradation Fishing mortality (commercial species) Local pressures Score (maximum=11) weight of each "+" n.a. n.a. n.a. 2 2 1 0.5 1 1 1 1 1 Species caught in monitoring programmes in 2001-2005 Pleuronectes platessa Plaice MJ D m-s + + + + + + 6.5 Alosa fallax Twaite shad CA P + + + + + 6.5 Clupea harengus Herring MJ P + ++ + + + 6 Osmerus eperlanus Smelt CA P + ++ + + 5 Solea vulgaris Sole MJ D m-s + + + + + 4.5 Zoarces viviparus Eelpout ER D m-p + + + 4 Platichthys flesus Flounder ER/CA D m-s + + + 3.5 Limanda limanda Dab MJ D s + + + + 3.5 Gadus morhua Cod MJ D + + + + 3.5 Lampetra fluviatilis River lamprey CA P + + 3 Ammodytes sp. Sand eel ER DP s ++ + + 3 Sprattus sprattus Sprat MS P + + + 2.5 Merlangius merlangus Whiting MJ D + + + 2.5 Engraulis encrasicolus Anchovy MS P + + + 2.5 Alosa alosa Allis shad CA P + + + 4 Gymnocephalus cernuus Ruffe FW D + + 3 Petromyzon marinus Sea lamprey CA P + + 3 Myoxocephalus scorpius Bull-rout ER D m-p + + 2 Liparis liparis Sea-snail ER D m-h + + 2 Anguilla anguilla Eel CA D m-s + + 2 Pholis gunnellus Butterfish ER D m-p + + 2 Cyclopterus lumpus Lumpsucker MS D h-p + + 2 Liparis montagui Montaguis sea snail ER D h + + 2 Syngnathus acus Greater pipefish ER D s-p + + 2 Echiichthys vipera Lesser weever MA D m-s + + 2 Syngnathus rostellatus Nilsson's pipefish ER D s-p + + 1.5 Pomatoschistus minutus Sand goby ER D s + + 1.5 Pomatoschistus microps Common goby ER D s + + 1.5 Trachurus trachurus Horse mackerel MA P + + 1.5 Psetta maxima Turbot MJ D s-g + + 1.5 Scophthalmus rhombus Brill MJ D s-g + + 1.5 Belone belone Garfish MS P + + 1.5 Hyperoplus lanceolatus Greater sand-eel MJ DP s + + 1.5 Agonus cataphractus Hooknose ER/MS D m-s + 1 Ciliata mustela Five-bearded rockling ER/MS D m-s + 1 Eutrigla gurnardus Grey gurnard MS D m-s + 1 Callionymus lyra Dragonet MA D m-s + 1 Scomber scombrus Mackerel MA P + 1 Gasterosteus aculeatus Stickleback CA P + 0.5 Trigla lucerna Tub gurnard MJ D m-s 0 Arnoglossus laterna Scaldfish MA D m-s 0 Buglossidium luteum Solenette MA D m-s 0 Trisopterus luscus Bib MJ D 0 Salmo salar Salmon CA P (+) + + 2 Mullus surmuletus Striped red mullet MA D s-h + + 2 Atherina presbyter Sand-smelt MJ P + + 2 Callionymus reticulatus Reticulated dragonet MA D m-s + + 2 Stizostedion lucioperca Pikeperch FW D + + 2 Dicentrarchus labrax Bass MJ D + + 2 Perca fluviatilis Perch FW D + + 2 Entelurus aequoraeus Snake pipefish ER D s-p + 1 Microstomus kitt Lemon sole MA D s-g + 1 Gaidropsarus vulgaris Three-bearded rockling MA D m-s + 1 Callionymus maculatus Spotted dragonet MA D m-s + 1 Galeorhinus galeus Tope MA D + 1 Pollachius pollachius Pollack MA D + 1 Nerophis ophidion Straight-nosed pipefish ER D 0 Enchelyopus cimbrius Four-bearded rockling MA D m-s 0 Trisopterus minutus Poor cod MA D 0
Other species relevant for the Wadden Sea Coregonus oxyrinchus Houting ER P + + + 4 Chelon labrosus Thick-lipped grey mullet MA P 0 Liza ramada Thin-lipped grey mullet MA P 0
50 of 62 Report Number C133/07 Table A1.1: Continued Monitoring (14) Abundance (15) Occurrence (16) Catchability (17) (13) NL: DFS outer area (beamtrawl, 2001-2005) (beamtrawl, NL: DFS area outer 2001-2005) (beamtrawl, NL: area DFS inner DE: DYFS2001-2005) (beamtrawl, DE: SHS (stownet, 2001-2005) DE: SFIS (stownet, 2005-2006) NL: NIOZ (fyke, -) 2001-2005) (beamtrawl, NL: DFS area outer 2001-2005) (beamtrawl, NL: area DFS inner DE: DYFS2001-2005) (beamtrawl, DE: SHS (stownet, 2001-2005) DE: SFIS (stownet, 2005-2006) NL: NIOZ (fyke, -) Beamtrawl Stownet Fyke Score (maximum=12) weight of each "+" 0.5 0.5 1 1 0 0 0.5 0.5 1 1 0 0 n.a. n.a. n.a. Species caught in monitoring programmes in 2001-2005 Pleuronectes platessa Plaice ++ ++ ++ ++ ++ ++ ++ + ++ + + - 11 Alosa fallax Twaite shad + + + ++ ++ - - - ++ + - + 6 Clupea harengus Herring ++ ++ ++ ++ ++ + + + ++ ++ - + 10 Osmerus eperlanus Smelt + ++ ++ ++ ++ + + + ++ ++ - + 9.5 Solea vulgaris Sole + ++ + ++++ + + + + ++ + - 7.5 Zoarces viviparus Eelpout + + + + + - + + + - + - 5.5 Platichthys flesus Flounder + ++ ++ ++ + + + + ++ + + - 9.5 Limanda limanda Dab ++++++ + + ++ + + - - + - 7.5 Gadus morhua Cod + + + + + + + + + + + + 6 Lampetra fluviatilis River lamprey + + + + + - - - + + - + 4 Ammodytes sp. Sand eel + + + + + + + - - + - - 4 Sprattus sprattus Sprat + + + ++ ++ + + + ++ ++ - + 8 Merlangius merlangus Whiting ++ + ++ + + + + + + + + + 7.5 Engraulis encrasicolus Anchovy - - + + + - - - + + - + 3 Alosa alosa Allis shad - - + ------+ 1 Gymnocephalus cernuus Ruffe - + + ------+ + 1.5 Petromyzon marinus Sea lamprey + - - - + ------+ 0.5 Myoxocephalus scorpius Bull-rout + ++ ++ + + + + + + - + - 7.5 Liparis liparis Sea-snail + + + + + + + + - + + - 5 Anguilla anguilla Eel + + + + + - - - + - - - 4 Pholis gunnellus Butterfish + + + + + - + - - + + - 3.5 Cyclopterus lumpus Lumpsucker + - + + + - - - + - + - 3.5 Liparis montagui Montaguis sea snail - - + + + - - - + + + - 3 Syngnathus acus Greater pipefish + + + - - + - - - - + - 2.5 Echiichthys vipera Lesser weever + + + - - + - - - - + - 2.5 Syngnathus rostellatus Nilsson's pipefish ++ ++ ++ ++ ++ + + + ++ ++ + - 10 Pomatoschistus minutus Sand goby ++ ++ ++ ++ ++ + + + + ++ + - 9 Pomatoschistus microps Common goby (18) (18) + + ++ (18) (18) - - ++ + - (18) Trachurus trachurus Horse mackerel + + + ++ ++ + - - + + - + 5.5 Psetta maxima Turbot + + + + + + - - + - + - 4.5 Scophthalmus rhombus Brill + + + + - - - - + - + - 4 Belone belone Garfish + + - + + - - - + + - + 3 Hyperoplus lanceolatus Greater sand-eel + + + - + + - - - + - - 2.5 Agonus cataphractus Hooknose ++ + ++ + + + + + + + + - 7.5 Ciliata mustela Five-bearded rockling + ++ + + + + + + + + + - 6.5 Eutrigla gurnardus Grey gurnard + + + + - - - - + - + - 4 Callionymus lyra Dragonet ++ + + - + + - + - - + - 4 Scomber scombrus Mackerel + + - + + - - - + - - + 3 Gasterosteus aculeatus Stickleback + + + + + - - - + - - + 4 Trigla lucerna Tub gurnard + + + + + + - - + - + - 4.5 Arnoglossus laterna Scaldfish ++ + + - - + - - - - + - 3 Buglossidium luteum Solenette ++ + + - + + - - - - + - 3 Trisopterus luscus Bib + + + - - - + - - - + + 2.5 Salmo salar Salmon - - - + - - - - + - - + 2 Mullus surmuletus Striped red mullet + + + ------+ - 2 Atherina presbyter Sand-smelt + - + - + ------+ 1.5 Callionymus reticulatus Reticulated dragonet + - + ------+ - 1.5 Stizostedion lucioperca Pikeperch - + + ------+ + 1.5 Dicentrarchus labrax Bass + + ------+ 1 Perca fluviatilis Perch - + ------+ + 0.5 Entelurus aequoraeus Snake pipefish + + + - + - - - - + + - 2 Microstomus kitt Lemon sole + + + - + - - - - - + - 2 Gaidropsarus vulgaris Three-bearded rockling + - + ------+ - 1.5 Callionymus maculatus Spotted dragonet - - + ------+ - 1 Galeorhinus galeus Tope + ------+ + 0.5 Pollachius pollachius Pollack - + ------+ + 0.5 Nerophis ophidion Straight-nosed pipefish - - + ------+ - 1 Enchelyopus cimbrius Four-bearded rockling + - - - - + - - - - + - 1 Trisopterus minutus Poor cod + + ------+ + 1
Number of species 48 45 49 34 38 48 45 49 34 38 Number of hauls 295 582 1185 53 19 295 582 1185 53 19
Other species relevant for the Wadden Sea Coregonus oxyrinchus Houting ------+ 0 Chelon labrosus Thick-lipped grey mullet - - - - - + ------+ 0 Liza ramada Thin-lipped grey mullet - - - - - + ------+ 0
Report Number C133/07 51 of 62 Table A1.1: Continued (footnotes)
Footnotes (1) Ecological guildes (2) Stratification (3) Benthic habitat ER = estuarine resident D = demersal m = mud MJ = marine juvenile P = pelagic s = sand MS = marine seasonal migrant DP = sand eels: pelagic or g = gravel MA = marine adventitious buried in bottom h = hard (rocks, musselbeds etc.) CA = diadromous p = plants FW = fresh water
(4) Species included in the Habitats Directive - Annex 1 & 2. Fish species relevant for the Wadden Sea (species relevant for freshwater between brackets) (5) Species abundance monitoring proposed in relation to the Water Framework Directive in transitional waters (all transistional waters except Eider) (6) On any red list (Netherlands, Germany or Denmark) (7) Critical food source as indentified by expert judgement of current group and by Heinis et al., 2005 (8) Publication(s) exist(s) indicating link between abundance/distribution of species and any climate change related factors (9) Publication(s) exist(s) indicating link between abundance/distribution of species and nutrient enrichment or turbidity (10) Publication(s) exist(s) indicating link between abundance/distribution of species and other sources of habitat degradation (11) Species prone to direct fishing mortality (i.e. commercial species). Indirect mortality due to discarding or bottom-disturbance not included (12) Species with a limited dispersal in all life stages, hence suitable indicators of small-scale changes and contaminations (13) Score based on every "+" multiplied by weighting factor (14) Ongoing monitorings programmes and an example of a shorter running survey (SFIS) code = name gear institute country years in table DFS = Demersal Fish Survey beam trawl Wageningen-IMARES (formerly known as RIVO) The Netherlands 1970- 2001-2005 DYFS = Demersal Young Fish Survey beam trawl Bundesforschunganstalt für Fischerei Germany 1974- 2001-2005 SHS = Schleswig-Holstein Survey stownet Marine Science Service Germany 1991- 2001-2005 SFIS = Seabird-Fish-Interactions Survey stownet Insitute of Avian Research Germany 2005-2007 2005-2006 NIOZ = Fyke sampling 't Horntje fyke Royal Netherlands Institute for Sea Research The Netherlands 1960- - (15) Abundance: ++ = top 10 in abundance + = present - = absent (16) Occurrence: ++ = present in 90-100% of the hauls + = present in 10-90% of the hauls - = present in <10% of the hauls (17) Suitability gear for quantitative abundance estimate (18) Identifications unreliable, P. microps and P. minutes pooled
Table A1.2: Species with a high score (>2) on both selection criteria as well as monitoring results. Ecological Benthic Species Stratification guild habitat Alosa fallax Twaite shad CA P - Osmerus eperlanus Smelt CA P - Lampetra fluviatilis River lamprey CA P - Platichthys flesus Flounder ER D m-s Zoarces viviparus Eelpout ER D m-p Ammodytes sp. Sand eel ER DP s Pleuronectes platessa Plaice MJ D m-s Solea vulgaris Sole MJ D m-s Limanda limanda Dab MJ D s Gadus morhua Cod MJ D - Merlangius merlangus Whiting MJ D - Clupea harengus Herring MJ P - Sprattus sprattus Sprat MS P - Engraulis encrasicolus Anchovy MS P -
Table A1.3: Species with a high score (>2) on selection criteria but a low score (<2) on monitoring results. Ecological Benthic Species Stratification guild habitat Alosa alosa Allis shad CA P - Petromyzon marinus Sea lamprey CA P - Coregonus oxyrinchus Houting ER P - Gymnocephalus cernuus Ruffe FW D -
52 of 62 Report Number C133/07 Appendix 2 – Preliminary reference list Wadden Sea fish fauna Author: Ralf Vorberg Main tasks of the TMAP ad hoc working group fish are the development of targets and assessment tools for trilateral Wadden Sea fish. A possible target could be "presence of a typical Wadden Sea fish fauna". As a provisional assessment tool a priority list of Wadden Sea fish species was defined, using data from the existing demersal and pelagic fish surveys. Another tool could be the defintion of a range for species composition and/or species abundances. For this purposes a comprehensive compilation of fish species occurring in the Wadden Sea turned out to be useful. Information derived from running monitoring programmes as the 30 year data sets of the demersal (young) fish survey in the Netherlands and Germany and of the stow net fishery in Schleswig Holstein and Lower Saxony. In addition species lists from the literature were used (Zijlstra et al., 1979; Fricke et al., 1994; Vorberg & Breckling, 1999). The total number of North Sea fish species at the moment is 189 (Fröse & Pauly 2007). The compilation of Wadden Sea fish species yielded a total of 141 proofs, what means that about 75% of all North Sea fish species (can) occur in the Wadden Sea. With regard to a trilateral monitoring and assessment program only one half of all species is of practical importance: 53 species (37,6%) are common, 22 species (15,6%) are fairly common and 66 species (46,8%) have to be regarded as rare or even extremely rare in the Wadden Sea. The priority list created by the TMAP ad hoc working group fish contains 55 species and similarity between these and common species is 93% (after Jaccard's similarity index). Thus, the priority list can be regarded as appropriate for further evaluating trilateral Wadden Sea fish species. References FRICKE, R.; BERGHAHN, R.; RECHLIN, O.; NEUDECKER, T.; WINKLER, H.; BAST, H. D. & HAHLBECK, E. (1994): Rote Liste und Artenverzeichnis der Rundmäuler und Fische (Cyclostomata Pisces) im Bereich der deutschen Nord und Ostsee. IN: NOWAK, E.; BLAB, J. & BLESS, R.: Rote Liste der gefährdeten Wirbeltiere in Deutschland. Kilda Vlg.: 157 176. FROESE, R. and D. PAULY. Editors. 2007.FishBase. World Wide Web electronic publication. www.fishbase.org, version (02/2007). VORBERG, R. & BRECKLING, P. (1999): Atlas der Fische im schleswig holsteinischen Wattenmeer. Schriftenreihe des Nationalparks Schleswig Holsteinisches Wattenmeer, Heft 10: 180 S. WITTE, J.Y. & ZIJLSTRA, J.J. (1979): The species of fish occurring in the Wadden Sea. In. DANKERS, N.; WOLFF, W.J. & ZIJLSTRA, J.J.: Fishes and fisheries of the Wadden Sea. A. A. Balkema, Rotterdam: 10 25.
Report Number C133/07 53 of 62 Witte & stow net S- stow net L- TMAP WG Red List occurrren # scientific name english name german name dutch name Zijlstra DYFS DFS QSR 2004 H S Fish Atlas S-H Ger. counts ce 1 Abramis brama Carp Bream Brasse Brasem x 1 (e)r 2 Acipenser sturio Sturgeon Stör Steur x x 2 (e)r 3 Agonus cataphractus Hook-nose Steinpicker Harnasmannetje x x x x x x x x 8 c 4 Alopias vulpinus Tresher Fuchshai Voshaai x 1 (e)r 5Alosa alosa Allis Shad Maifisch Elft x x x x x x 6 c 6Alosa fallax Twaite Shad Finte Fint x x x x x x x x 8 c 7 Ammodytes tobianus Sand Eel Kleiner Sandaal Zandspiering xx xxxxxx8c 8 Anarhichas denticulatus Northern Wolffish Steinbeißer x 1 (e)r 9Anguilla anguilla Eel Aal Aal x x x x x x x x 8 c 10 Aphia minuta Transparent Goby Glasgrundel Glasgrondel x x x x x x 6 c 11 Argyrosomus regius Meagre Umberfisch Ombervis x 1 (e)r 12Arnoglossus laterna Scaldfish Lammzunge Schurftvis x x x x x x 6 c 13 Aspitrigla cuculus Red Gurnard Seekuckuck Engelse Poon x x 2 (e)r 14 Atherina presbyter Sand-smelt Ährenfisch Koornaarvis x x x x x x x x 8 c 15 Atherina boyeri Big-scale Sand Smelt Kleiner Ährenfisch Kleine Koornaarvis x 1 (e)r 16 Balistes carolinensis Trigger-Fish Grauer Drückerfisch Trekkervis x 1 (e)r 17Belone belone Garfish Hornhecht Geep x x x x x x x x 8 c 18 Blicca bjoerkna White Bream Güster Kolblei x 1 (e)r 19Boops boops Bogue Gelbstrieme Bokvis x x 2 (e)r 20 Brama brama Ray's Bream Brachsenmakrele Braam x x 2 (e)r 21Buglossidium luteum Solenette Zwergzunge Dwergtong x x x x x x x 7 c 22 Galeus melastomus Blackmouth Catshark Fleckhai Hondshaai x 1 (e)r 23 Callionymus lyra Dragonet gestreifter Leierfisch Pitvis x x x x x x x x 8 c 24 Callionymus maculatus Spotted Dragonet gefleckter Leierfisch x x xx 4fc 25 Callionymus reticulatus Reticulated Dragonet Ornament-Leierfisch Rasterpitvis x x x x 4 fc 26 Cetorhinus maximus Basking Shark Riesenhai Reuzehaai x 1 (e)r 27 Cheilopogon heterurus Atlantic Flying-Fish Fliegender Fisch x 1 (e)r 28 Chelon labrosus Thick-lipped Mullet Dicklippige Meeräsche Diklippige Harder x x x x x x x 7 c 29 Ciliata mustela Five-bearded Rockling Fünfbärtelige Seequappe Vijfdradige Meun x x x x x x x x 8 c 30 Clupea harengus Herring Hering Haring x x x x x x x x 8 c 31 Conger conger Conger Eel Meeraal Zeepaling x x 2 (e)r 32Coregonus oxyrinchus Houting Nordseeschnäpel Houting x x x x x 5 fc 33 Crystallogobius linearis Crystal Goby Kristallgrundel x 1 (e)r 34 Ctenolabrus rupestris Goldsinny Klippenbarsch Kliplipvis x 1 (e)r 35Cyclopterus lumpus Lumpsucker Seehase Snotolf x x x x x x x x 8 c 36 Cynoglossus browni Nigerian tonguesole Hundszunge x 1 (e)r 37 Dasyatis pastinaca Common Stingray Stechrochen Pijlstaartrog x x x 3 fc 38 Dentex maroccanus Morocco Dentex Marokkanische Zahnbrasse x 1 (e)r 39 Dicentrarchus labrax Sea Bass Wolfsbarsch Zeebaars x x x x x x 6 c 40 Echiichthys vipera Lesser Weever Kleines Petermännchen Kleine Pieterman x x x x x x 6 c 41 Enchelyopus cimbrius Four-bearded Rockling Vierbärtelige Seequappe Vierdradige Meun x x x x x 5 fc 42Engraulis encrasicolus Anchovy Sardelle Ansjovis x x x x x x x x 8 c 43 Entelurus aequoreus Snake Pipefish Große Schlangennadel Adderzeenaald x x x x x x 6 c 44 Eutrigla gurnadus Grey Gurnard Grauer Knurrhahn Grauwe Poon x x x x x x x x 8 c 45Gadus morhua Cod Kabeljau Kabeljauw x x x x x x x x 8 c 46 Gaidropsarus mediterranaeus Shore Rockling Mittelmeer-Seequappe x 1 (e)r 47 Gaidropsarus vulgaris Three-bearded Rockling Dreibärtelige Seequappe Driedradige Meun x x x x x x 6 c 48 Galeorhinus galeus Tope Shark Hundshai Ruwehaai x x xxx5fc 49 Gasterosteus aculeatus Stickleback Dreistacheliger Stichling Driedoornige Stekelbaars x x x x x x x x 8 c 50 Glyptocephalus cynoglossus Witch Hundszunge Hondstong x x x 3 fc 51 Gobiusculus flavescens Two-spotted Goby Schnappgrundel x 1 (e)r 52 Gymnocephalus cernuus Ruffe Kaulbarsch Pos x x 2 (e)r 53 Hexanchus griseus Bluntnose Sixgill Shark Grauhai Stompsnuitzeskieuwshaai x 1 (e)r 54 Hippocampus hippocampus Sea-Horse Seepferdchen Zeepaardje x 1 (e)r 55 Hippoglossoides platessoidesAmerican Plaice Doggerscharbe Lange Schar x x x 3 fc 56 Hyperoplus lanceolatus Greater Sand Eel Großer Sandaal Groote Zandaal x x x x x x x x 8 c 57 Labrus bergylta Balan Wrasse Gefleckter Lippfisch Gevlekte Lipvis x 1 (e)r 58 Lamna nasus Porbeagle Heringshai Neushaai x 1 (e)r 59 Lampetra fluviatilis River Lamprey Flußneunauge Rivierprik xx xxxxxx8c 60Limanda limanda Dab Kliesche Schar x x x x x x x x 8 c 61 Liparis liparis Sea Snail Großer Scheibenbauch Slakdolf x x x x x x x x 8 c 62 Liparis montagui Montagu's Sea Snail Kleiner Scheibenbauch Montagu's Ringbug x x x x x x x 7 c 63Lipophrys pholis Shanny Schan Slijmvis x x 2 (e)r 64 Liza aurata Golden Grey Mullet Goldmeeräsche Goudharder x x 2 (e)r 65 Liza ramada Thin-lipped Grey Mullet Dünnlippige Meeräsche Dunlippige Harder x x x x 4 fc 66 Lophius piscatorius Angler Seeteufel Zeeduivel x 1 (e)r 67 Maurolicus muelleri Pearlsides Lachshering Lichtend Sprotje x x x 3 fc 68 Melanogrammus aeglefinus Haddock Schellfisch Schelvis x x 2 (e)r 69Merlangius merlangus Whiting Wittling Wijting x x x x x x x x 8 c 70 Merluccius merluccius European Hake Seehecht Stokvis x x x 3 fc 71 Micrenophrys lilljeborgi Norway Bullhead Zwergseeskorpion x 1 (e)r 72 Micromesistius poutassou Blue Whiting Blauer Wittling Blauwe Wijting x x x x 4 fc 73 Microstomus kitt Lemon Sole Limande, Rotzunge Tongschar xx xxxxxx8c 74Mola mola Sunfish Mondfisch Maanvis x x 2 (e)r 75Molva molva Ling Leng Leng x 1 (e)r 76 Mullus barbatus Red Mullet Rote Meerbarbe x 1 (e)r 77Mullus surmelutus Surmullet Streifenbarbe Mul x x x x x x x x 8 c 78 Mustelus mustelus Smooth Hound Glatthai Gladde Haai x 1 (e)r 79 Myoxocephalus scorpius Bull Rout Seeskorpion Zeeonderpad xx xxxxxx8c 80 Nerophis lumbriciformis Worm Pipefish Krummschnauzige Schlangennadel x 1 (e)r 81 Nerophis ophidion Straightnose Pipefish Kleine Schlangennadel x 1 (e)r 82Osmerus eperlanus Smelt Stint Spiering x x x x x x x x 8 c 83 Pagellus acarne Axillary Seabream Achselfleckbrasse Spaanse Zeebrasem x 1 (e)r 84 Pagellus bogaraveo Blackspotted Seabream Graubarsch Zeebrasem x 1 (e)r 85 Pagellus erythrinus Common Pandora Rotbrasse Zeebrasem x 1 (e)r 86 Parablennius gattorugine Tompot Blenny Gestreifter Schleimfisch Gehoornde Slijmvis x x 2 (e)r 87 Perca fluviatilis European Perch Flussbarsch Baars x 1 (e)r 88 Petromyzon marinus Sea Lamprey Meerneunauge Zeeprik x x x x x x 6 c 89Pholis gunellus Butterfish Butterfisch Botervis x x x x x x x 7 c 90 Phrynorhombus norvegicus Norwegian topknot Norwegischer Zwergbutt Dwergtarbot x 1 (e)r 91Platichthys flesus Flounder Flunder Bot x x x x x x x x 8 c 92Pleuronectes platessa Plaice Scholle Schol x x x x x x x x 8 c 93Pollachius pollachius Pollack Pollack Pollak x x x x 4 fc 94Pollachius virens Saithe Seelachs Koolvis x x x x x 5 fc 95 Pomatoschistus lozanoi Lozano's Goby Lozanos Grundel Lozanos Grondel x x 2 (e)r 96 Pomatoschistus microps Common Goby Strandgrundel Brakwatergrondel x x x x x x x x 8 c 97 Pomatoschistus minutus Sand Goby Sandgrundel Dikkopje x x x x x x x 7 c 98 Pomatoschistus pictus Painted Goby Fleckengrundel Kleurige Grondel x x 2 (e)r 99Psetta maxima Turbot Steinbutt Tarbot x x x x x x x x 8 c 100 Pterycombus brama Atlantic Fanfish Silberbrassen x 1 (e)r 101 Pungitius pungitius Ninespine Stickleback Zwergstichling Tiendoornige stekelbaars x x x x 4 fc 102Raja clavata Thornback Nagelrochen Stekelrog x x 2 (e)r 103 Raniceps raninus Tadpole-Fish Froschdorsch Vorskwab x x 2 (e)r 104 Remora remora Common Remora Ansauger x 1 (e)r 105Salmo salar Salmon Lachs Zalm x x x x x x 6 c 106 Salmo trutta Sea Trout Meerforelle Zeeforel x x x x x x 6 c 107 Sardina pilchardus Sardine Sardine Sardien x x x x x x 6 c 108 Scomber japonicus Chub Mackerel Mittelmeermakrele Spaanse Makreel x 1 (e)r 109 Scomber scombrus Mackerel Atlantische E3Makrele Makreel x x x x x x x x 8 c 110 Scomberesox saurus Skipper Makrelenhecht Makreelgeep x 1 (e)r 111Scophthalmus rhombus Brill Glattbutt Griet x x x x x x x x 8 c 112 Scyliorhinus caniculus Lesser spotted Dogfish Kleingefleckter Katzenhai Hondshaai x x 2 (e)r 113 Scyliorhinus stellaris Greater spotted Dogfish Großgefleckter Katzenhai Kathaai x 1 (e)r 114 Scymnodon obscurus Smallmouth Velvet Dogfish Kleinmaulsamthai Fluweelijshaai x 1 (e)r 115 Sebastes marinus Redfish Rotbarsch Noorse Schelvis x 1 (e)r 116 Serranus cabrilla Comber Sägebarsch x 1 (e)r 117Solea solea Sole Seezunge Tong x x x x x x x x 8 c 118 Spinachia spinachia Sea Stickleback Seestichling Zeestekelbaars x x x x x 5 fc 119 Spodyliosoma cantharus Black Sea Bream Streifenbrasse Zeekarper x 1 (e)r 120 Sprattus sprattus Sprat Sprotte Sprot x x x x x x x x 8 c 121 Squalus acanthias Spur-Dog Dornhai Doornhaai x 1 (e)r 122Squatina squatina Monkfish Meerengel Zeeengel x x 2 (e)r 123Stizostedion lucioperca Pike Perch Zander Snoekbaars x x x 3 fc 124 Symphodus melops Corkwing Goldmaid Zwaartooglipvis x 1 (e)r 125 Syngnathus acus Great Pipefish Große Seenadel Grote Zeenaald x x x x x x x7c 126 Syngnathus rostellatus Nilsson's Pipefish Kleine Seenadel Kleine Zeenaald x x x x x x x x 8 c 127 Syngnathus typhle Deep-snouted Pipefish Grasnadel Trompetterzeenaald x x x 3 fc 128 Taractes asper Rough pomfret Kleine Brachsenmakrele x 1 (e)r 129 Taractichthys longipinnis Bigscale Pomfret Langflossen-Brachsenmakrele x 1 (e)r 130 Taurulus bubalis Long-spined Sea ScorpionSeebull Groene Zeeonderpad x x x x 4 fc 131 Trachinotus ovatus Derbio Gabelmakrele x 1 (e)r 132 Trachinus draco Greater Weaver Petermännchen Grote Pieterman x x x 3 fc 133 Trachurus trachurus Horse Mackerel Stöcker Horsmakreel x x x x x x x x 8 c 134 Trigla lucerna Tub Gurnard Roter Knurrhahn Rode Poon x x x x x x x x 8 c 135 Trisopterus esmarki Norway Pout Stintdorsch Kever x x x 3 fc 136Trisopterus luscus Bib Franzosendorsch Steenbolk x x x x x x x 7 c 137 Trisopterus minutus Poor Cod Zwergdorsch Dwergbolk x x x x x 5 fc 138 Xiphias gladius Sword-Fish Schwertfisch Zwaardvis x 1 (e)r 139 Zeugopterus punctatus Topknot Haarbutt Gevlekte Griet x x 2 (e)r 140Zeus faber Dory Heringskönig Zonnevis x 1 (e)r 141Zoarces viviparus Eelpout Aalmutter Puitaal x x x x x x x x 8 c 101 64 0 63 47 52 62 63 112
54 of 62 Report Number C133/07 Appendix 3 – Fishing pressure by the German shrimp fishery Author: Thomas Neudecker The fishing pressure in the Wadden Sea has changed over the last fifty years. While in Germany a great number of smaller boats were active just after the Second World War (approx. 850) the number decreased rapidly during the following years (Table A3.1). Since the nineties the number of shrimpers has not much changed due to the restricted number of licenses. While fishing effort per boat in fishing hours and also fishing power has drastically increased, the area fished remained more or less in the same order of magnitude (Neudecker, 1999) (Table A3.2). Detailed information on the number of fishing days or even more precise effort data is not available until 1999. Only fishing trips were recorded but mostly “shrimp trips” were mixed with “fish trips” until 1994. Since in 2000 the EU log book system became compulsory much better data are available giving fishing hours by boat and ICES area (Figure A2.1). Table A3.1: Some metrics on the German shrimping fleet Years 1952 58 1966 1976 1986 1996
Shrimp cutters ca. 630 407 305 270 247 Engine power 53 82 147 183 227 Per cutter (hp) Boat length (m) 11,5 13,5 15,5 15,9 16,4
Beam length (2x)(m) 12 no data available 17,1 Table A3.2: Figures used for estimating fishing effort in German shrimp fisheries in 1954 and 1996. Years of comparison 1954 1996 (1954 estimated according to different sources) Number of vessels 630 247 Fishing days (1954 as 1996) 137 137 Mean duration of tows [ p.d. in h ] 7 12,15 Aggregated beam length [ m ] 12 17,1 Mean towing speed [ kn ] 2,5 2,7 Total towed area [ km² ] 33 500 35 000 Towed area by boat [ km² ] 52,3 141,7 ICES rectangles are wide compared to the Wadden Sea and do not reflect the spatial fishing situation in an appropriate manner (Figure A2.2). From fishermen’s reports, however, it is known, that in earlier days of the shrimp fishing the boats have hardly left the Wadden Sea proper. Fishing took place in the shallower parts behind the chain of islands and sands, especially in the so called gullies. With the development of larger and technically more sophisticated shrimp boats more distant fishing grounds also in front of the islands were visited and longer trips became possible. That development occurred in the late sixties and seventies and has continued until present days as the remaining smaller boats are sold and are sometimes replaced by new and larger vessels with the latest technical equipment. The ownership also shows changes. In former days the boats were entirely property of local fishermen. Now also companies own sometimes several vessels with hired staff on board. These developments in combination with economic pressures have also changed the traditional seasonal fishing pattern. While there used to be a three months lasting winter period without any fishing which is still valid for many of the vessels, many of the shrimpers
Report Number C133/07 55 of 62 have extended their activity into the winter period as they can meanwhile fish also under fairly windy conditions off shore.
45 0.50
40
35 0.45
30
25 0.40
20
0.35 15 Fishing hours * 1000 Million fishing hours 10 0.30 5
0 1 2 3 4 5 6 7 8 9 101112 0.25 Months 2000 2001 2002 2003 2004 2005 2006 Figure A2.1: Left: Mean monthly fishing hours of German shrimp fleet (2000 2006). Right: Annual fishing hours of German shrimp fleet (2000 2006) One of the most recent observations is that grounds further off shore at depths of about 30 metres and further north, off the Danish coasts are fished during winter and spring time, while the grounds nearer to the coast remain the preferred areas during summer and autumn, still the main fishing season. That development is illustrated by log book data presented in Figure A2.2:
A: Percent landings B: Percent landings C: Percent landings in December 2001 in September 2006 in December 2006 Figure A2.2: Comparison of log book data of fishing areas of the German fleet by ICES rectangle: Winter situation 2001 and 2006 showing the northern directed shift of fishing activity (A and C) and the seasonal shift from summer to winter activity in 2006 (B and C). References Neudecker, Th. (1999). Die Entwicklung des Aufwandes in der deutschen Garnelenfischerei Inf.Fischwirtsch. Fischereiforschung 46 (4) 9 – 13.
56 of 62 Report Number C133/07 Appendix 4 – Review on indicator studies in marine ecosystems Author: Harriët van Overzee Fish communities are continually exposed to anthropogenic influences and variations in natural conditions. The characteristics of fish communities are described by indicators. Different indicators are used when analysing the structure of a fish community, as information is collected at different levels. Variations in these indicators over time imply that changes have taken place in the fish community. These changes are relative as there is no absolute reference point. This literature study reviews indicator studies carried out for marine ecosystems and identifies and discusses indicators that may be used to describe the fish community in the Wadden Sea. As the Wadden Sea is an extension of the North Sea, it is conceivable that the indicators used to describe the fish community in the North Sea may also be applied to the fish community in the Wadden Sea. On the other hand, the geographical connection / vicinity does not automatically mean that the conditions are the same in both regions. It is therefore also useful to look at the specific characteristics of the Wadden Sea. 1. Indicators for species composition of fish communities Various studies have described the species composition of fish communities. The indicators are: (i) the number of rare species (Dulvy et al ., 2006); (ii) life history characteristics; (iii) biodiversity (Perry et al ., 2006; Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Greenstreet & Hall, 1996; Rice & Gislason, 1996); (iv) trophic structure (Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Nicholson & Jennings, 2004; Jennings et al ., 2002); (v) ecological guilds (Breine et al ., 2007; Elliot & Hemmingway, 2002). The species composition may be influenced by both anthropogenic influences and variations in natural conditions. Index of rare species Dulvy et al . (2006) developed a threat indicator based on the population status of 23 different North Sea fish from 1982 to 2001. This indicator responds to changes in the proportion of threatened species in a fish community. The percentage in decline of a species through time was linked to the vulnerability of the species using the World Conservation Union Red List A1 criteria (IUCN, 2004). The species could be classified as no threat = 0, vulnerable = 1 (≥50% decline), endangered = 2 (≥70% decline) and critically endangered = 3 (≥90% decline). From the late 1990s and onwards all the species met the vulnerable criterion and hence were all threatened. Daan (2000) used the number of rare species to detect changes in the fish community in the North Sea. and found that the number of rare species – mostly, warm water species – was increasing. This may be attributable to a rise in the water temperature (van Densen & de Boois, 2000). The ratio between Boreal species (typical North Sea species) and Lusitanian species (southerly species, starting from the English Channel) may therefore serve as an indicator of the species composition of the fish community on the basis of one factor. Variations in indicators describing rare species may illustrate changes that are occurring in a fish community which perhaps cannot be derived from analyses of the dominant part of the community (ICES WGECO, 2007). These indicators may therefore be useful in determining whether changes have occurred in the species composition. Life history characteristics Life history characteristics refer to the life cycle of an organism and can therefore vary between species. Depending on their life history characteristics, the species are sensitive to changes in the environment to different extents. Life history characteristics are therefore used as indicators to describe changes that may have occurred in the species composition.
Report Number C133/07 57 of 62 A trade off between different characteristics enables an organism to survive optimally in a specific environment; for example, K strategists are slow growing, late maturing, long living organisms that live in stable environments, while r strategists are fast growing, early maturing, short living organisms that live in variable environments. K strategists and r strategists stand at opposite ends of the spectrum. All species within the community lie somewhere between the two. Increased fishing mortality is expected to give r strategists an advantage. Life history characteristics are therefore often used as indicators of fish communities that have been exposed to fishing. Age and length at maturity are life history characteristics that have been used as indicators (Perry et al ., 2006; Greenstreet & Rogers, 2006) in studies to detect changes in the fish community of the North Sea. Values of age and length at maturity can be determined by observation either from survey data or from the literature (Jennings et al ., 1999). The number of individuals with the characteristic values can be determined and the mean value for each characteristic can be calculated. Fluctuations in these indicators through time suggest that changes are occurring in the species composition of the community. The life history theory predicts that increased mortality at a certain age and size at maturation selects for earlier maturation. These indicators are therefore used to determine whether fishing has inflicted changes in the life history characteristics of the fish community. The mean maximum length of a fish community has been used as a life history indicator in several studies (Perry et al ., 2006; Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Nicholson & Jennings, 2004) to detect whether changes have occurred within the species composition of the North Sea. This is calculated as follows:
in which L maxj is the maximum length that can be reached by species j, N j is the total number of individuals of species j and N is the total number of individuals. The L max determined from the von Bertalanffy growth equation calculated for each species can be derived from the literature (e.g. Jennings et al ., 2002; Jennings et al ., 1999) whereas the other parameters can be derived from survey measurements. Because fishing inflicts additional mortality, this will bring about changes in the mean maximum length of a fish community. It is therefore not surprising that this indicator is often used to describe changes that fishing inflicts on a fish community. However, Perry et al . (2006) also used this indicator to demonstrate that an increase in water temperature coincided with a northwards shift of species with low maximum length in the North Sea. The life history characteristic, growth rate, has also been used (Greenstreet & Rogers, 2006) as an indicator of the species composition of the North Sea fish community. By using the growth rate of each species derived from the von Bertalanffy growth equation, Greenstreet & Rogers (2006) determined the mean growth rate for the entire fish community. Changes in this indicator through time showed that changes had occurred in the fish community. Both environmental and anthropogenic changes may give species with faster growth rates a selective advantage. Biodiversity Diversity indicators are also used frequently in studies of the North Sea (Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Rice & Gislason, 1996). They provide information on the composition of the community. Biodiversity is a joint construct of species richness and species evenness: the actual number of species in a given area and the distribution of the individuals among the species. A higher number of species as well as a more even distribution among the species points towards higher biodiversity. As species richness or species evenness on its own cannot fully describe the diversity of a community, a combination of the two is used when describing diversity. Several indicators are therefore used when describing the diversity of a fish community. The most common indicators used to describe diversity in the North Sea fish community over the entire range from species richness to species evenness are Hills N 0, N 1 and N 2 (Greenstreet & Rogers, 2006; Piet & Jennings 2005).
Hills N 0 is an indicator of species richness: it is a simple count of the number of species in the community. Hills
N1 is an indicator of species diversity: effectively the number of abundant species. Hills N 2 is also an indicator of species diversity: effectively the number of very abundant species (Indeco, 2006). These indices describe
58 of 62 Report Number C133/07 biodiversity with numbers of species which are derived from samplings of the community. However, it should be noted that these indicators are sensitive to sampling size. Rogers et al . (1998) showed that the number of species that are recorded within an area depends on the intensity of the sampling within the area. A greater effort is required to catch the infrequent species. Variations in natural conditions and anthropogenic activities may both affect the biodiversity of a fish community, but as the mechanism is not understood it is impossible as yet to link these changes to either of these causes. As diversity is a complex indicator that cannot be easily measured (Greenstreet & Piet, manuscript) it is questionable whether it can be used as an indicator of the species composition of any fish community, let alone the Wadden Sea Trophic structure Larger individuals generally, though not always, eat at higher trophic levels. This means that changes in the species composition of a fish community can be linked to changes in the trophic structure of that community. The mean trophic level of a community has been used in different studies (Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Nicholson & Jennings, 2004; Jennings et al ., 2002) as an indicator of the composition of the fish community in the North Sea. This can be calculated as:
in which TL ij and W ij are the trophic level and body mass respectively of species i with length class j. The trophic levels of individuals of different length classes determined by nitrogen stable isotope analysis can be derived from the literature (Jennings et al ., 2002), but large area to area and year to year variations occur. Weight can be derived from survey measurements. This indicator is a measure of the complexity of the food web. A decrease in complexity might cause the system to be less resilient to environmental and/or man induced changes. So far, the results of the different studies have been contradictory. However, more knowledge about the food web is needed to fully understand possible changes in the mean trophic level of the fish community. Different studies on the North Sea fish community (Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Jennings et al ., 2002) have shown that this indicator for species composition did not show interpretable patterns. The mean trophic level is therefore probably not a useful indicator of species composition. Ecological guilds Guilds refer to species that are grouped according to similarities in their characteristics. Guilds are also used as indicators (Breine et al ., 2007). Fish use the Wadden Sea for different purposes. They may therefore be divided into groups that are classified according to the usefulness of the Wadden Sea for the fish. Zijlstra (1978) split the fish species in the Wadden Sea into different groups. The (near )residents who are tolerant of the dynamic environment live their whole life in the Wadden Sea. The diadromous species, which include seasonal visitors who only come into the area when its conditions are suitable and species that only use the Wadden Sea as passageway. The third group consists of the marine juveniles of various North Sea fish species that use the Wadden Sea as a nursery area. Elliot & Hemmingway (2002) use the numbers of species in such groups as ecological guilds of fishes in estuaries. The number of species in an ecological guild may therefore be used as an indicator for describing the fish community of the Wadden Sea. 2. Indicators for size composition of fish communities Various indicators can be used to describe the size composition of a fish community. These are: (i) slope of the size spectra, (ii) mean length, (iii) mean weight, (iv) the proportion of large fish (Rice & Gislason, 1996; Nicholson & Jennings, 2004; Piet & Jennings, 2005; Daan et al ., 2005; Greenstreet & Rogers, 2006). As fishing inflicts size selective mortality, this may be come to light in a decline in size based indicators. However, changing environmental conditions may also affect the growth and recruitment of fish species and hence lead to changes in the size composition. As these two factors are inseparable it is more or less impossible to determine how much each contributes to the changes in the indicators (Shin et al ., 2005).
Report Number C133/07 59 of 62 Slope of the size spectra Size spectra analyses are used to demonstrate that the community shows a log linear decrease in biomass or in the number of individuals with increasing size. The general formula is: ln(y) = a*ln(x) + b in which y is the biomass or number of individuals, x the size, a the slope and b the intercept. Both the slope and the intercept of this relationship are used as indicators in studies on changes in the size composition of the fish community in the North Sea (Rice & Gislason, 1996; Piet & Jennings, 2005; Daan et al ., 2005). The slope is a measure of the decline in numbers in relation to increasing length. The intercept is a measure of the numbers of small fish that have entered the community (recruits). This relationship can be derived from survey data. Depending on the fishing gear and the tow speed of the vessel, certain size classes may be underrepresented in the survey. In these analyses it is therefore necessary to decide on the lower and upper limits of the spectrum. Changes in the slope and intercept through time indicate a change in the size composition of the fish community. Mean length The mean length and mean weight of the North Sea fish community are also used as indicators of the size composition (Greenstreet & Rogers, 2006; Piet & Jennings, 2005; Nicholson & Jennings, 2004). These are calculated as follows:
in which L and W represent the length and weight respectively of each individual and N is the total number of individuals. A change in these indicators in the course of time suggests that a change has occurred in the size composition. Obviously, a community comprising mostly small individuals will have a lower mean length and weight than a community comprising mostly large individuals. These indicators are therefore sensitive to recruitment events. The proportion of large fish The proportion of large fish is also used as an indicator of the size composition of the North Sea fish community (Greenstreet & Rogers, 2006). Greenstreet & Rogers (2006) chose the percentage of fish larger than 30 centimetres as indicator. They used this arbitrary standard because 95 percent of the recorded fish community were shorter than 30 centimetres. A shift in this percentage would imply a change in size composition. ICES WGECO (2007) have redefined this indicator to the percentage of fish larger than 40 centimetres as this seems to reduce the variation (ICES, WGECO, 2007). This size based indicator is used as an Ecological Quality objective (EcoQo) for fish communities in the North Sea. If this indicator is used for the Wadden Sea, analytical procedures are needed to identify the appropriate length threshold (ICES WGECO, 2007).
60 of 62 Report Number C133/07 3. References Breine, J.J., Maes, J., Quataert, P., Bergh, E. van den, Simoens, I., Thuyne, ,G. van, Belpaire, C., 2007. A fish based assessment tool for ecological quality of the brackish Schelde estuary in Flanders (Belgium). Hydrobiologia, 575: 141 159. Daan, N., 2000. De Noordzee visfauna en criteria voor het vaststellen van doelsoorten voor het natuurbeleid. RIVO Rapport C031/00. 90p. Daan, N., Gislason, H., Pope, J.G., Rice, C., 2005. Changes in the North Sea fish community: evidence of indirect effects of fishing? ICES Journal of Marine Science, 62: 177 188. Densen, W.L.T. van & Boois, I.J. de, 2000. Trends in soortendiversiteit van de Noordzeevis. Bruikbaarheid van visserij onafhankelijke surveys 1970 1999. RIVO rapport C049/00. 28p. Dulvy, N.K., Jennings, S., Rogers, S.I., Maxwell, D.L., 2006. Threat and decline in fishes: an indicator of marine biodiversity. Canadian Journal of Fisheries and Aquatic Sciences, 63: 1267 1275. Elliot, M. & Hemingway, K.L., 2002. Fishes in estuaries, London, Blackwell science, pp. 636. Greenstreet, S.P.R. & Hall, S.J., 1996. Fishing and the ground fish assemblage structure in the north western North Sea: an analysis of long term and spatial trends. Journal of Animal Ecology 65: 577 598. Greenstreet, S.P.R. & Rogers, S.I., 2006. Indicators of the health of the North Sea fish community: identifying reference levels for an ecosystem approach to management. ICES Journal of Marine Science, 63: 573 593. Greenstreet, S.P.R. & Piet, G.J., manuscript. Assessing the sampling effort required to estimate α species diversity in the groundfish assemlabe of the North Sea. ICES WGECO Report, 2007. Report of the working group on ecosystem effects of fishing activities (WGECO). Indeco, 2006. Development of indicators of environmental performance of the common fisheries policy. A review of the indicators for ecosystem structure and functioning. IUCN, 2004. Guidelines for using the IUCN Red List categories and criteria. World Conservation Union, Gland, Switzerland. Jennings, S., Greenstreet, S.P.R., Reynolds, J.D., 1999. Structural change in exploited fish community: a consequence of differential fishing effects on species with contrasting life histories. Journal of Animal Ecology, 68: 617 627. Jennings, S., Greenstreet, S.P.R., Hill, L., Piet, G.J., Pinnegar, J.K., Warr, K.J., 2002. Long term trends in the trophic structure of the North Sea fish community: evidence from stable isotope analysis, size spectra and community metrics. Marine Biology, 141: 1085 1097. Jennings, S., 2005. Indicators to support an ecosystem approach to fisheries. Fish and fisheries 6: 212 232. Nicholson, M.D. & Jennings, S., 2004. Testing candidate indicators to support ecosystem based management: the power of monitoring surveys to detect temporal trends in fish community metrics. ICES Journal of Marine Science, 61: 35 42. Perry, A.L., Low, P.J., Ellis, J.R., Reynolds, J.D., 2006. Climate change and distribution shifts in marine fishes. Science, 308: 1912 1915.
Report Number C133/07 61 of 62 Piet, G.J. & Jennings, S., 2005. Response of potential fish community indicators to fishing. ICES Journal of Marine Science, 62: 214 225. Rice, J.R. & Gislason, H., 1996. Patterns of change in the size spectra of numbers and diversity of the North Sea fish assemblage, as reflected in surveys and models. ICES Journal of Marine Science, 53: 1214 1225. Rogers, S.I., Rijnsdorp, A.D., Damm, U., Vanhee, W., 1998. Demersal fish populations in the coastal waters of the UK and continental NW Europe from beam trawl survey data collected from 1990 to 1995. Journal of Sea Research 39: 79 102. Shin, Y., Rochet, M., Jennings, S., Field, J.G., Gislason, H., 2005. Using size based indicators to evaluate the ecosystem effects of fishing. ICES Journal of Marine Science, 62: 384 396. Zijlstra, J.J., 1978. The function of the Wadden Sea for the members of its fish fauna. In: Dankers, N., Wolff, W.J., Zijlstra, J.J. (Editors). Dishes and fisheries in the Wadden Sea. Report 5 of the final report of the section ‘Fishe and fisheries’of the Wadden Sea Working Group. Stichting Veth tot Stean aan Waddenonderzoek, Leiden, pp. 20 25.
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