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The Joint EIFAAC/ICES/GFCM Working group on eels (WGEEL) met by correspondence and video conference from September 7 – 10 September and 27 September – 4 October in 2021 to assess the state of the European eel and its fisheries, investigate the effects of contaminants on the reproductive capacity of the eel stock, discuss the findings of WKFEA, further identify issues specific to the Mediterranean region and report on any updates to the scientific basis of the advice, new and emerging threats or opportunities. For a better integration of the Mediterranean area, new members joined WGEEL, providing data and support as regional experts. This is considered an important step in a continuous process to identify and address Mediterranean-specific issues and harmonize the efforts of WGEEL and the recent ‘GFCM research Programme on European Eel’. The recruitment of European eel strongly declined from 1980 to 2011. The glass eel recruitment compared to that in 1960–1979 in the “North Sea” index area was 0.6% in 2021 (provisional) and 0.9 % in 2020 (final). In the “Elsewhere Europe” index series it was 5.4 % in 2021 (provisional) and 7.1% in 2020 (final), based on available dataseries. For the yellow eel dataseries, recruitment for 2020 was 16% (final) of the 1960–1979 level; the 2021data collection for yellow eel is ongoing. Time-series from 1980 to 2021 show that recruitment has stopped decreasing in 2011 but the trend thereafter is rather unclear.Preliminary analyses of 160 dataseries on yellow or silver eel abundance show the potential of the yellow and silver eels’ series to improve the stock assessment. A comprehensive framework of analyses of the yellow and silver stocks through these series will, however, require many iterations of data collection, analyses and further data needs.Mortality and biomass indicators have been reviewed and visualized, preparing for a future workshop on the evaluation of eel management plans (WKEMP). Spatial overviews and temporal trends show a lack of data for many regions and no evidence yet of a general improvement in stock status for regions with data. Overall silver eel escapement remains low and mortalities high. Doubts remain about the consistency of indicators across countries. The information provided on data and methods used for assessment are not available or sufficiently detailed to ensure transparency and reproducibility of estimates. These limitations and the incomplete reporting impair the use of these data to inform on the status of the stock at a larger scale.A review on the effects of contaminants (in a broader sense: spawner quality) on the reproductive capacity of eel highlighted this as an important, but a frequently lacking, aspect of stock assessment. Monitoring of silver eel quality should be considered as part of new or existing programmes.WGEEL supports the findings WKFEA and the suggested roadmap and agreed to implement the necessary steps towards achieving it. This implies further exploration and analyses of existing as well as the systematic collection of additional data. Implementation will require concerted data collection and assessment, which will require additional support.In summary, the working group has focused on exploring and analysing the data collected in the WGEEL database for their potential use in stock assessment. This included identifying gaps in the available data, defining data requirements for specific analyses in future and developing procedures for the analysis of these data. Furthermore, the group reviewed the effects of contamination on the reproductive potential of eels and renewed their recommendation to consider these in the assessment of effective spawning-stock biomass.

The Joint EIFAAC/ICES/GFCM Working group on eels (WGEEL) met by correspondence and video conference from September 21–28 in 2020 to assess the state of the European eel, investigate the effects of habitat loss on the eel stock and its management, review and update the Stock Annex, prepare the 2021 Data Call and report on any updates to the scientific basis of the advice, new and emerging threats or opportunities. Furthermore, data on fisheries landings, aquaculture and restocking are presented.Analyses were carried out on two glass eel recruitment indices (comprising 28 time-series in the Elsewhere Europe area and 24 time-series in the North Sea) and one yellow recruitment index (comprising 16 time-series). Note, that some data from the current year are always provisional to allow for a small proportion of late reporting series, but this is not considered to materially affect the trends. The potential impacts of COVID-19 on the data collection and quality were noted by the WG and described in detail in the report.The recruitment of European eel strongly declined from 1980 to 2011. The glass eel recruitment compared to that in 1960–1979 in the “North Sea” index area was 0.5% in 2020 (provisional) and 1.4% in 2019 (final). In the “Elsewhere Europe” index series it was 6.5% in 2020 (provisional) and 5.6% in 2019 (final), based on available dataseries. For the yellow eel dataseries, recruitment for 2019 was 17% (final) of the 1960–1979 level; the 2020 data collection for yellow eel is ongoing. Statistical analyses of the time-series from 1980 to 2020 show that recruitment has stopped decreasing in 2011 but the trend thereafter is rather unclear.A Bayesian assessment model (GEREM), structured to allow the existence of potential different trends among regions, and provide absolute recruitment per zone has been run. While still preliminary, this model confirms the trend in recruitment, points out the need of new time-series of recruitment, and could in the future allow a part of the analytical assessment of the stock.The collection of yellow and silver eel series and their biometric data, started last year, has continued and a first analysis has been run. There is a large spatial variability in trends of abundance among locations but the analysis of the long-term time-series shows that current silver eel abundance is low when compared to the pre-1980 levels. The analysis of biometric data allows a first analysis of the biological characteristics of the series and points out missing fields in data collection.Emerging threats and opportunities that have been reported over the past decade were reviewed, and diseases, parasites, contaminants and hydropower were identified as routinely reported and thus established. Climate change was repeatedly reported in the past; yet knowledge remains limited. Moreover, the threat of the EU exit of the UK raised concerns regarding the accessability of glass eels for stocking and the potentially increased availability of glass eel from the UK being traded illegally to Asia The issue of COVID-19 was addressed and impacts were found to fall largely in three categories: i) scientific monitorings, ii) restocking programmes and iii) closures/delays in commercial fishing and loss of markets.The WG has a new standing annual activity to examine quantification of the impacts of nonfishery factors and in 2020 i) reviewed the literature on the effects of habitat loss with a focus on the biological processes operating, ii) the national Eel Management Plans and (latest) triannual assessments identifying whether and to what extent the effects of habitat loss have been taken into account, iii) develop a workplan aiming at the quantification of habitat loss and its effect on eel production in the coming years, and iv) present a number of actual case studies. Due to the lack of appropriate data, a meaningful quantitative assessment is not possible at the moment.Overall, the working group has made progress towards the assessment of the standing stock and spawning–stock biomass (i.e. yellow and silver eel time-series) and the implementation of an additional model for the recruitment data provides towards further analyses (e.g. with respect to regional differences). The WG identified relevant issues for future research, highlighting the limited knowledge on the complex effects of climate change as well as the need for additional and specific data collection to quantify the effects of habitat loss.

The WGEEL has this year adjusted the manner in which it reports data in time-series. First, readers should note that some data reported to the WGEEL in the most recent year are always provisional but are then finalised in the report of the following year. Where data have been updated from those reported in the 2018 report this is indicated in the 2019 report; and provisional data are similarly highlighted. Second, the mean of the previous 5 years data is also presented to help place the data from the most recent year(s) in context of this most recent period. The recruitment of European eel from the ocean remained low in 2019. The glass eel recruitment compared to the 1960–1979 in the ‘North Sea’ index area was 1.4% in 2019 (provisional), 1.9% in 2018 (finalised) and the previous 5-year mean was 1.7% (2012-2016); and in the ‘Elsewhere Europe’ index series it was 6.0% in 2019 (provisional), 8.9% in 2018 (final) and the previous 5-year mean was 8.7%, based on available dataseries. For the yellow eel dataseries, recruitment for 2018 was 26.4% of the 1960–1979 level and the previous 5-year mean was 16.6% (2013–2017); 2019 data collection is ongoing so data not available at time of writing. Statistical analyses of time-series from 1980–2019 show that there was a change in the trend of glass eel recruitment indices in 2011; the recruitment has stopped decreasing and has been increasing in the period 2011–2019 with a rate statistically significantly different from zero. The highest point during the period from 2011–2019 was in 2014. Landings data were updated according to those reported to the WGEEL, either through responses to the 2019 Data call or Country Reports, or integrated by the WGEEL using data from its previous reports. When data are absent and presumed missing for a country or year, a predicted (reconstructed) catch is used to account for non-reporting, but this is not a complete solution and therefore even the raised estimates should be considered as minima. Here we present both reported and reconstructed values. Glass eel fisheries within the EU take place in France, UK, Spain, Portugal and Italy. Glass eel landings have declined sharply from 1980, when reported and reconstructed landings were larger than 2000 tonnes, to 62.2 t in 2018 (final, full reporting), 58.6 t in 2019 (provisional, no reconstruction), and a mean for the previous 5 years (2013–2017) of 56.5 t (full reporting). Yellow and silver eel landings are not always reported separately, so are combined here. The WGEEL has reconstructed the time-series to fill in some gaps in reporting. Reconstructed total commercial landings of yellow and silver eels were around 20 000 t in the 1950s to 2000–3500 t around 2009, most recently being 2393 t in 2017 (final), 2694 t in 2018 (provisional) and a mean of 2729 t for the preceding 5 years (2012–2016). The reported landings were around 10 000 to 12 000 t in the 1950s, declining to 2000 to 3000 t around 2009, and more recently being 2249 t in 2017 (final), 2375 t in 2018 (provisional, only 14 countries reported) and a mean of 2729 t for the preceding 5 years (2012–2016).Recreational catches and landings are poorly reported, so amounts must be treated as minima. Spain reports a recreational fishery for glass eel, with landings estimated as 0.9 t for 2019 (provisional), with a mean of 2 t for the preceding 5 years (2014–2018). Recreational landings for yellow and silver eel combined were 543 t for 2016 (ten countries reporting), 195 t for 2017 (eight countries reported) and 148 t for 2018 (five countries reported). Overall, the impact of recreational fisheries on the eel stock remains largely unquantified although landings can be thought to be at a similar order of magnitude to those of commercial fisheries. Aquaculture production of eel is presented from 1984 onwards. It increased until the mid-2000s, peaking around 8000 t. Production was reported in 2017 (the most recent year of most countries reporting: 10) as 5497 t in 2017 and the preceding 5-year mean was 6429 t (2012–2016). It should be noted that eel aquaculture is based on wild recruits, and part of the production is subsequently released as on-grown eel for stocking. Restocking (the process of capture, translocation and restocking to new locations in the wild) of eel increased after the implementation of management plans in EU Member States in 2009. Although the definition of restocking is clear, the process is complex with a varied and broad sequence of steps and even life stages. As there is still some variation in the way that countries report some of these actions, the WGEEL broadly categorises them as RELEASES, though the term RESTOCKING is still used here for some circumstances. Most recent relatively complete data show 36.3 million glass eel (2017, 15 countries), 14 million yellow eels (2016, six countries) and about 0.25 million silver eels (2018, three countries) were restocked or released (combined). The WG has made substantial progress in developing the use of the Data call and database to refine data submission, checking, analyses and reporting. The Data call for 2020 will request updates for recruitment, landings, aquaculture and releases, plus abundance indices for yellow and silver eels. The emerging threats and opportunities reported by WGEEL in each of the last three years continue to develop/evolve from their initial reporting. In addition, a new eel virus (picornavirus EPV-1) has been detected in eels in several German waters. The WG has a new standing annual activity to examine quantification of the impacts of nonfishery factors, and to review methods for reducing these mortalities. A crude estimate of loss to all non-fishery anthropogenic factors (largely hydropower and pumps) of eel was estimated from reported mortality indicators from approximately half of countries reporting to WG. This amounted to 1625 tonnes annually. Given better and more consistent data, this estimate could be improved in the future. Evidence on the impacts of hydropower facilities and water pumps was reviewed, with new studies ranging from direct measurements of eel mortality at individual facilities, through models to extend empirical data at individual sites to estimate impacts to regional levels, to overarching reviews and national and international advisory reports. Ranges of mortality as eel pass by or through hydropower stations are highly variable, and within previously published ranges. Mitigation measures to reduce eel losses from hydropower and pumping facilities provide clear technical scope for individual site and collective actions to reduce current losses. The WG considered the potential impact of changes to fishery regulations on the time-series used in support of the ICES advice. Many fishery-based time-series are used to assess temporal trends in recruitment and escapement. This is especially true for recruitment in the so-called ‘Elsewhere Europe’ area. New fishery regulations might introduce biases in those time-series and compromise their use in the analyses. Losing fishery-based indices would increase the noise in the stock assessment. As such, it seems worthwhile implementing new fishery-independent time-series. The WG considered the consequences of the Precautionary Approach on advice for European eel. Based on the FAO Code of Conduct, the ICES form of advice, and the EU Eel Regulation, the WG developed a proposal for a coherent framework for advice on eel, consisting of a doubletiered approach: an international tier focused on the status of the whole stock and the long-term objectives (overall stock status, recruitment trends, biomass reference points), and a national (or lower) tier focused on mortality levels and related management actions, addressed per management unit. This proposal suggests adoption of the reference point of the Eel Regulation, as Bmgt = 40% escapement of pristine, and a corresponding mortality limit of ΣAmgt = 0.92. Below Bmgt, mortality should be reduced further, to allow recovery of the stock. It is suggested to adopt a provisional time frame in terms of number of generations for this, which would translate into a corresponding mortality limit for each management unit. Noting that the proposed comprehensive framework for advice deviates from conventional ICES approaches, it is concluded that a followup workshop convened by ACOM might be appropriate, to discuss and evaluate the proposed framework and consider any now unforeseen or unintentional consequences. An international process of Quality Assurance of national assessments and stock indicators is also required as a matter of urgency. The WG considered the challenge of quantifying the effort that is undertaken in the commercial eel fisheries around Europe, based on new data provided by countries through the Data call. It was concluded that for many countries, the licensing of commercial eel fisheries needs to be improved in order to supply fishery managers and WGEEL with the appropriate information to assess the state of the stock. Difficulties encountered include inadequate reporting of levels of effort, lack of recording on number of gears per licence and generic multispecies licensing. The level of reporting can be at the national, regional or local level and this has resulted in some countries having different licence requirements per waterbody. The WGEEL has recommended a workshop on harmonising the reporting of fishing effort.

The fifth World Ocean Review (WOR) explores the coastal habitat and the diverse expectations upon this habitat. It provides a glimpse into millions of years of history, elucidates the theory of continental drift and discusses the many ways in which coasts have changed. It also illustrates how the diverse ecosystem services rendered by the coasts are being subjected to increasing pressure, and profiles measures that will be necessary in the future to respond effectively to the threats from both climate change and natural disasters.

Die fünfte Ausgabe des „World Ocean Review“ (WOR) beschäftigt sich mit dem Lebensraum Küste und den vielfältigen Erwartungen, die an diesen Lebensraum gestellt werden. Der WOR 5 gibt einen Einblik in die über Jahrmillionen zurückreichende Geschichte, erläutert die Theorie der Kontinentalveschiebung und erörtert wie sich das Gesicht der Küsten verändert hat. Er zeigt auf, wie die vielfältigen Ökosystemleistungen der Küsten immer mehr unter Druck geraten und stellt Maßnahmen vor, die in Zukunft notwendig sein werden, um den Bedrohungen durch Klimawandel und Naturkatastrophen Herr zu werden.

In this thesis otolith microchemistry analyses were used to gain insights into the individual life history and stock characteristics of three fish species from the Baltic Sea - the European eel Anguilla anguilla, the Atlantic cod Gadus morhua and the thicklip grey mullet Chelon labrosus. The special hydrographic environment of the world’s largest brackish water system provides promising conditions for the use of otolith elemental analysis to investigate individual migration patterns and stock structures of fish. Here, it was used to gain information with relevance for stock management of fish species that differ widely in their biology, ecology and stock structure. It was investigated whether individual continental migratory history affects health and spawner quality of the European eel. Otolith strontium (Sr) composition was used to identify characteristic migration patterns. Results show that the muscle fat contents of silver eels with strictly catadromous life cycles are significantly reduced compared to silver eels that never entered freshwaters. Furthermore, prevalence and infection intensities of the swimbladder nematode Anguillicoloides crassus are highly increased in catadromous silver eels. Both, a reduced accumulation of fat reserves and intense A. crassus infestations are assumed to impair the successful reproduction of A. anguilla. These results highlight the importance of brackish water habitats for the production of high quality spawners and question the benefit of restocking measures into inland waters. In order to investigate the influence of water temperature and feeding behaviour on the element incorporation into A. anguilla otoliths, two experimental studies were conducted. Results showed that otolith element incorporation is influenced by water temperature, but detected differences between treatments were low to allow an in situ reconstruction of temperature history. In the food experiment no effect on otolith microchemistry was detected between feeding groups. Results indicate that neither temperature changes nor individual dietary behaviour impair the use of otolith Sr concentrations as a tracer of diadromy. Thus the reliability of such migration studies is fundamentally increased. It was further investigated whether multi-element otolith analysis can be used to discriminate Atlantic cod individuals according to their origin. Otolith multi-element concentrations from adult individuals caught at spawning grounds in the North Sea, the western Baltic Sea and the eastern Baltic Sea were analysed. Furthermore, the multi-element composition of the core region of juvenile cod otoliths from western and eastern Baltic areas was examined. Multivariate statistical analyses successfully discriminated between adults from different stocks as well as between western and eastern Baltic Sea juveniles. Significant differences between the eastern Baltic spawning grounds, however, were not detected. These results demonstrate the potential of otolith microchemistry analysis to investigate the structure and connectivity of G. morhua stocks in the Baltic Sea. In a further field study the migratory behaviour of thicklip grey mullet was examined for the first time on individuals caught in the Baltic Sea. By detecting C. labrosus otolith Sr concentrations, this study aimed to gain first insights into preferences and whereabouts of individuals in the Baltic Sea. Results confirmed a preference of brackish habitats for all analysed specimens and suggest a high plasticity of C. labrosus migratory behaviour. The results support the assumption that a considerable fraction of individuals entering the western Baltic Sea regularly migrate to the North Sea. The results presented in this thesis confirm the feasibility of otolith microchemistry analyses for the investigation of a broad range of questions on Baltic Sea fish. Knowledge about investigated species was expanded and opportunities for future studies were indicated. In dieser Arbeit wurden anhand mikrochemischer Otolithenanalysen Erkenntnisse über die individuelle Lebensweise und die Bestandsstruktur von drei Fischarten aus der Ostsee gewonnen – dem Europäischen Aal Anguilla anguilla, dem Atlantischen Kabeljau Gadus morhua und der Dicklippigen Meeräsche Chelon labrosus. Die hydrographischen Besonderheiten der Ostsee als weltgrößtes Brackwassersystem bieten vielversprechende Voraussetzungen für die Anwendung von Otolithen-Elementanalysen zur Untersuchung des individuellen Wanderverhaltens von Fischen und deren Bestandsstrukturen. Hier wurden sie genutzt, um managementrelevante Fragestellungen von Fischarten zu untersuchen, die sich hinsichtlich ihrer Biologie, Ökologie und Bestandsstruktur sehr unterscheiden. Es wurde untersucht, ob das kontinentale Wanderverhalten Europäischer Aale deren Gesundheit und Laicherqualität beeinflusst. Dazu wurden anhand der Otolithen-Strontiumverteilung charakteristische Wandermuster ermittelt. Die Ergebnisse zeigen, dass der Muskelfettgehalt von Blankaalen mit strikt katadromen Wanderverhalten signifikant geringer ist als der von Blankaalen, die niemals ins Süßwasser eingewandert sind. Darüber hinaus sind Prävalenz und Befallsintensität mit dem Schwimmblasen-Nematoden Anguillicoloides crassus bei katadromen Blankaalen stark erhöht. Sowohl eine verringerte Einlagerung von Fettreserven als auch der intensive Befall mit A. crassus stehen im Verdacht, den Reproduktionserfolg von A. anguilla zu vermindern. Die vorliegenden Ergebnisse heben die Bedeutung von Brackwasserhabitaten für die Produktion von gesunden Laichtieren hervor und stellen den Nutzen von Besatzmaßnahmen in Binnengewässer in Frage. Um den Einfluss von Wassertemperatur und Futterverhalten auf die Elementeinlagerung in A. anguilla-Otolithen zu prüfen, wurden zwei experimentelle Studien durchgeführt. Die Ergebnisse zeigen, dass die Einlagerung von Elementen in die Otolithen zwar von der Wassertemperatur beeinflusst wird. Die Unterschiede zwischen den Futtergruppen waren aber so gering, dass eine Rekonstruktion erlebter Temperaturänderungen in situ schwierig erscheint. Im Futterexperiment konnte kein Effekt auf die Elementeinlagerung detektiert werden Die Ergebnisse zeigen, dass weder Temperaturschwankungen noch unterschiedliches Futterverhalten die Verwendung von Sr zur Rekonstruktion diadromen Verhaltens einschränken. Damit wird die Aussagekraft solcher Migrationsstudien deutlich erhöht. Des Weiteren wurde untersucht, ob Otolithen-Multielementanalysen dazu geeignet sind, G. morhua-Individuen ihrer Herkunft zuzuordnen. Dazu wurde die Multielementzusammensetzung von Otolithen adulter Dorsch von Laichplätzen aus der Nordsee, der westlichen und der östlichen Ostsee untersucht. Des Weiteren wurde die Zusammensetzung der Kernbereiche von Otolithen juveniler Dorsche aus der westlichen und der östlichen Ostsee analysiert. Multivariate statistische Analysen konnten sowohl die adulten Bestände erfolgreich trennen, als auch die Juvenilen aus der westlichen und der östlichen Ostsee unterscheiden. Signifikante Unterschiede zwischen den drei östlichen Laichgebieten konnten aber nicht detektiert werden. Die Ergebnisse zeigen das Potential von Otolithen-Multielementanalysen zur Untersuchung der Struktur und Konnektivität von G. morhua-Beständen. In einer weiteren Feldstudie wurde das Wanderverhalten der Dicklippigen Meeräsche C. labrosus erstmals an Individuen aus der Ostsee untersucht. Ziel der Studie war es, mittels der Analyse von Sr-Konzentrationen in C. labrosus-Otolithen grundsätzliche Informationen über Aufenthaltsorte und Habitatspräferenzen der Ostsee-Meeräschen zu erlangen. Die Ergebnisse bestätigen die Präferenz von Brackwasserhabitaten und lassen eine hohe Plastizität des Wanderverhaltens vermuten. Sie stützen die Vermutung, dass ein erheblicher Teil der in die Ostsee einwanderenden Individuen regelmäßig in die Nordsee zurückkehrt. Die Ergebnisse dieser Arbeit bestätigen die gute Eignung mikrochemischer Otolithenanalysen zur Untersuchung unterschiedlichster Fragestellungen an Fischarten aus der Ostsee. Das Wissen über die untersuchten Arten wurde erweitert und neue Wege für zukünftige Studien wurden aufgezeigt.