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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 Working Group on Governance of the Regional Database & Estimation System (WGRDBESGOV) provides the governance function for both the existing Regional Database (RDB) and the new Regional Database & Estimation System (RDBES) that is currently in development. It is composed of representatives from ICES member countries and EU Regional Coordination Groups (RCGs). In this report the WGRDBESGOV reviews the RDBES developments performed during 2021 and plans for the work required in 2022 and beyond. It also considers how RDB data has been used and proposes changes required to the current Data Policy. The RDBES is planned to replace both the existing ICES InterCatch and RDB database systems and has an important part to play in increasing transparency and improving the quality of stock assessment within ICES. To this end three workshops have been planned for 2022 which will help data submitters with the transition to the new system (WKRAISE&TAF-sandeel, WKRDBES-RAISE&TAF and WKINTRO). Additionally, the Working Group on Estimation with the RDBES data model (WGRDES-EST) is continuously engaged to enable the ICES community to move forward with estimation using the RDBES data model. Following on from the RDBES test data calls issued in 2020 and 2021, a full RDBES data call is planned for 2022. It has been a desire since the inception of the RDBES that it can be used to fulfil the FDI (Fisheries Dependent Information) data call. However, it is not a straightforward process, as (1) the FDI data call is issued by the EU and requests different variables than the RDBES, and (2) the FDI includes estimations that need to be first calculated from the RDBES data. Despite these difficulties, both the Joint Research Centre (JRC) and Member States (MS) have expressed their interest in developing this feature of the RDBES, which will reduce MS workload and enhance data consistency in the different databases. During 2022, an intersessional subgroup will look further how to develop this. The need to ensure confidentiality in the data provided to end-users of scientific data and other interested parties, is a relevant issue that all data providers need to address when answering the RDBES Data Call. The essential problem is that at the required level of disaggregation it is common to have small groups of vessels in each segment. During 2022, an intersessional subgroup will address this, in communication with the Commission and the National Correspondents. Recognizing that we have not yet tested the production of stock assessment inputs from RDBES data, it is necessary to revise the roadmap and prolong the planned operations of RDB and InterCatch. We have found that the constraints are different between these databases and that RDB submissions can terminate earlier than InterCatch submissions. Anticipating a gradual adaptation of the RDBES and taking into account the need to utilize historical estimates in the InterCatch formats, it is desirable that the format for national estimates and the format for the stock estimates are compatible with the InterCatch input and output formats, respectively. The RDB and RDBES must ensure that data can be used by the RCGs and authorized groups in ICES whilst ensuring that only permitted users have access to the confidential data – the rules relating to this have previously been defined in the RDB Data Policy. In line with discussions at the ICES Data and Information Group (DIG), the Data Policy is split into two documents: a Data License, and a Data Governance document. It is important to remember that the ultimate success of the RDBES will rely on the effort and contributions from many people in the wider ICES/Data Collection Framework (DCF) community, from data collection to stock assessment, and not just the relatively small groups who attend the WGRDBESGOV or Core Group meetings. The WGRDBESGOV continues to encourage these contributions and recommend some concrete actions to take to enhance further the engagement of the whole ICES/DCF community.

International audience

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.

Aquaculture is the fastest growing sector of the entire food industry. lncreasing demands for seafood in the last decades led to an enormous increase in production of aquatic organisms. Especially the cultivation of prawns and shrimps reached unprecedented yields. Most of the economically important shrimps and prawns are dependent on live feeds, which neither are available in sufficient amounts at all times nor provide consistent quality. For this reason the finding of live feed alternatives had drawn much scientific attention in the recent past. Feeding experiments with larval shrimp and rhabditid nematodes showed promising results. Nevertheless nematodes as live feeds have yet not been adopted by the aquaculture industry. The reasons for this lay in deficiencies of certain nutrients in the nematodes and the abstinence of convenient mass culturing techniques. In the present study, different enrichment techniques of liquid media for the enhancement of fatty acid composition in the nematode Panagrellus redivivus were compared and assessed. Furthermore, the microorganisms Escherichia coli and Saccharomyces cerevisiae were tested for their suitability in nematode production. The present study revealed that the production yields of the free living nematode Panagrellus redivivus were significantly higher when the yeast Saccharomyces cerevisiae was applied, compared to yields achieved with Escherichia coli. Results evidenced that the formulation of liquid media had direct influence on the fatty acid composition as well as the production output of cultivated nematodes. Also, fractions of long-chained, polyunsaturated fatty acids in nematodes were significantly altered by the application of fish oil into the liquid media as well as by the addition of microalgae. Additionally, evidence was provided that larvae of the freshwater prawn Macrobrachium lanchesteri are capable of capturing and ingesting nematodes. The similarities in their larval development to the important aquaculture species Macrobrachium rosenbergii as well as the here discussed attributes qualify this species as an appropriate model organism for dietary studies with prawn larvae.

The small pelagic sprat (Sprattus sprattus) is a key ecologic player in the Baltic Sea. However, there is long-term variability in recruitment which is thought to be influenced by fluctuations in abiotic and biotic conditions experienced during the early life stages. This study concentrates on the influence of different ambient salinities on sprat egg development, egg buoyancy and survival as well as early yolk sac larval morphometric traits. Egg buoyancy significantly decreased with increasing salinity experienced during fertilization and/or incubation experiments. Field egg buoyancy measurements in 2007 and 2008 exhibited annual and seasonal differences in specific gravity, potentially associated with changes in adult sprat vertical distribution. Neither egg development time nor the duration of the yolk sac phase differed among salinity treatments. At eye pigmentation, larval standard length exhibited high variance among individuals but did not differ among treatments. The largest ecological impact of salinity experienced during spawning was the modification the buoyancy of eggs and yolk sac larvae, which determines their vertical habitat in the Baltic Sea. There are strong thermo- and oxyclines in the Baltic Sea, and thus salinity can indirectly impact the survival of these early life stages by modifying the ambient temperatures and oxygen conditions experienced., El espadín (Sprattus sprattus) es un pequeño pelágico que juega un papel ecológico clave en el mar Báltico. No obstante, se considera que la variabilidad a largo plazo en el reclutamiento está influenciada por condiciones bióticas y abióticas experimentadas durante los primeros estadios de desarrollo. Este estudio se concentra en la influencia de diferentes salinidades ambiente sobre el desarrollo de los huevos de espadín, su flotabilidad y supervivencia, así como sobre los rasgos morfométricos de las larvas lecitotróficas. La flotabilidad de los huevos disminuye significativamente con los incrementos de salinidad experimentados durante los experimentos de fertilización y/o incubación. Las medidas de flotabilidad en el medio mostraron diferencias en la gravedad específica de carácter anual y estacionales en 2007 y 2008, potencialmente asociadas a cambios en la distribución vertical de los adultos de espadín. Ni el tiempo de desarrollo de los huevos ni la duración de la fase lecitotrófica difirió entre los tratamientos de salinidad. En el estadio de pigmentación de los ojos la longitud estándar de las larvas mostró importante variabilidad entre individuos, pero no entre tratamientos. El mayor impacto ecológico debido a la salinidad experimentada durante la puesta fue la modificación de la flotabilidad de los huevos y larvas lecitotróficas, lo que determina su hábitat vertical en el mar Báltico. En este mar se dan importantes termo- y oxiclinas y, por tanto, la salinidad puede impactar indirectamente en la supervivencia de estos primeros estadios de desarrollo a través de la modificación de las condiciones ambientales de temperatura y oxígeno en las que se desarrollen.