Report of the Workshop of the Working Group on Eel and the Working Group on Biological Effects of Contaminants (WKBECEEL): ICES WKBECEEL REPORT 2015

The Workshop of the working group on eel and working group on biological effects of contaminants (WKBECEEL) met in Os, Norway, 25–27 January 2016, to discuss the sub-ject “Are contaminants in eels contributing to their decline?”, chaired by Caroline Durif (Norway) and Bjørn Einar Grøsvik (Norway). There were 19 participants representing 10 countries.
The European eel population has been declining since the 1980s. The Working Group on Eel (WGEEL) has been documenting the decline for at least three decades. The causes for the collapse are multiple: overfishing, habitat reduction, pollution, parasites and diseases, and climate change. The role of contaminants is poorly documented because the final migration and reproductive phase of the eel’s life cycle remain unknown. It was therefore recommended to use knowledge from other fish species to evaluate whether it could apply to eels.
The objective of the WKBECEEL was to describe 1) the trends in contaminants in eel, 2) the potential impact of contaminants on lipid metabolism and migration in eel and other species, 3) the impact of contaminants on reproduction in eel and other species, 4) review the impact of contaminants on the genetics of the European eel, and 5) suggest methods to quantify eel quality with regards to contaminants and what could be learned from other species.
Temporal trends of contaminants in eel are still very high, sometimes rendering eels unfit for human consumption. Contaminants clearly remain a health threat for eels now and will remain so for many years because of their long life-cycle and the persistence of lega-cy contaminants in the environment. Analyses of historical samples (pre-1980s) would help in understanding the dynamics of these contaminants and give us a better grasp on the potential effects of emerging contaminants.
Eels in some areas accumulate high concentrations of lipophilic contaminants, all of which may affect their health and fitness. The concentration is likely to increase at the end of their life cycle, as they fast during their transatlantic migration. Thus, contami-nants, as they are released into the blood can cause damage to reproductive organs, affect embryogenesis and larval fitness and survival.
Clear dose-effect relationships for specific contaminants are missing. In other species, contaminants reduce fecundity, lower hatching success and reduce egg quality, induce larval malformation and/or disrupts the endocrine system. Effects on eels are limited to a model which predicts that, depending on eel sensitivity, maternally transferred dioxin-like contaminants (at realistic levels) could cause up to 50% larval mortality.
The limited evidence in other species indicates that there is cause for concern when it comes to the possible effects of contaminants on eel navigation. However, direct research (such as experiments in swim tunnels) is lacking on the effect of contaminants on migration.
Synergistic effects between contaminants and disease agents are very likely. The impact of contaminants at the genomic and transcriptomic level is promising for the develop-ment of tools to evaluate biological effects. Ways to incorporate the effects of contaminants into quantitative assessments were described. Two eel research proposals are de-scribed in the last chapters: a) to standardize fat level measurements in eels, and b) to quantify the effect of contaminants on the reproductive success.