The European eel Anguilla anguilla (L.) is a widespread, panmictic and catadromous fish, widely distributed over Europe, with an important economic value for fisheries. The population is waning, as shown through recruitment monitoring in European rivers. The state of the stock is now considered below safe biological limits and a recent European regulation urges for stock protection measures. Although many potential causes have been suggested, the reasons for this dramatic decline remain unknownAs the eel is a long-lived, carnivorous, benthic and lipid-rich species, it is particularly prone to the accumulation of noxious chemical compounds, especially lipophilic contaminants like polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and brominated flame retardants (BFRs). At the Research Institute for Nature and Forest, we set up a monitoring network (Eel Pollution Monitoring Network, EPMN) and measured contaminants in the eel over Flanders during a 14-year research programme. Between 1994 and 2007 more than 3000 eels from 376 locations were analysed for PCBs, OCPs, heavy metals and some other compounds. We demonstrated that eels in their yellow stage are very suitable chemical bioindicators; contaminant profiles in those eels are fingerprints of the contamination pressure on the site where they grow up. Monitoring of contaminants in Flanders is based on measuring chemicals in water and sediments, but many analytical results of lipophilic compounds like PCBs and OCPs such as DDT, drins or hexachlorobenzene, fall under the detection limit, whereas in eel, those compounds are detectable in nearly all cases. We therefore strongly recommend a critical assessment of the monitoring strategy of chemical substances in our aquatic environment, both at a Flemish and an international scale, within the European Water Framework Directive. Our results generated a status report and distribution maps of eel pollution for some 30 substances. Most substances are present all over Flanders, but there is considerable variation between river basins, dependent on land use. Contaminant analysis in eel is able to pinpoint specific pollution sources, like some volatile organic compounds in very specific locations, very high BFR levels in eels from areas with intensive textile industry, or high lindane levels in some rivers under agricultural pressure. We could demonstrate that banned chemicals like DDT are still in use in some places. Within the study period, trend analysis indicated significant reductions in PCBs and many OCPs. Also for some heavy metals (lead, arsenic, nickel and chromium), concentrations decreased in the eel, but this was not the case for cadmium and mercury. Self-caught eels are much esteemed by fishermen, but considering the eel’s high contaminant body burden, consumption constitutes a potential risk for human health. After reporting our results, several measures were taken, such as a temporary catch and release obligation for eels caught between 2002 and 2006, and the legal enforcement of a maximum concentration for PCBs in fish and fisheries products. On ca 75 % of the sites, PCB levels in eel exceed however this legal upper limit. The intake of PCBs through consumption of eel by recreational fishermen was compared with the intake of a background population through a probabilistic approach. PCB intake seems to be at a level of high concern, and body burden in fishermen in Flanders might reach levels of toxicological relevance. Currently, human health protection is not assured, and we recommended more stringent measures from policy makers. We assessed potential impacts of contaminants on the eel population. Despite a very high internal load of endocrine disrupters, we did not find any effects on vitellogenin levels in immature yellow eel. However, a significant negative correlation between heavy metal pollution load and condition was observed, suggesting an impact of pollution on the health of sub-adult eels. In strongly polluted eels a reduced genetic variability was observed. We further demonstrated that fat stores and condition decreased significantly during the last 15 years in eels in Flanders and The Netherlands, jeopardizing a normal migration and successful reproduction of this long-distance migrator. We hypothesize that pollution is a major driver for this decrease in fat reserves. These findings are of utmost importance for eel management, and may represent a key element in the search for understanding the causes of the decline of the eel. It may well be that the Darwinian evolutionary theory on the survival of the fittest in eel-terms has to be interpreted as the survival of the fattest. |
