The effects of diffuse pollution on the European eel Anguilla anguilla (Linnaeus, 1758)

摘要

In the last 40 years, the population of European eel (Anguilla anguilla L.) has declined dramatically and is now considered to be outside safe biological limits. In 2007 the European Union implemented an “Eel Recovery Plan” regulation, in order to assist in the recovery of the species back to the previous sustainable levels. The major factors regulating eel populations are still unknown and until there is an understanding of the factors causing the low recruitment of eels, the success of any management plans and conservation measures may be limited. One factor considered important in regulating the eel population is pollution.The major aim of these studies was to investigate the impact of environmentalcontaminants on eel throughout their life cycle. Laboratory and field studies were carried out to assess the impact of environmental levels of pesticides (atrazine, fenitrothion, pendimethalin, chlortoluron, flusilazole, copper oxychloride, metaldehyde and chlorpyrifos), metals (copper, lead, zinc and chromium) and flame retardants (tributyl phosphate and hexabromocyclododecane) on the transition of juvenile and adult eels between freshwater and the marine environment and growth and feeding during freshwater residency.Exposure to tributyl phosphate (TBP) in freshwater had some effect on physiological (plasma levels of glucose, sodium and chloride and kidney Na/K ATPase) parameters associated with the silvering process in the eel but not on the morphology or the migratory behaviour during the transition from freshwater to the marine environment. Exposure to a mixture of pesticides (pendimethalin, chlortoluron, flusilazole, copper oxychloride, metaldehyde and chlorpyrifos) did modify the migratory behaviour of eels during the early stages of the freshwater migration but did not have any effects on the physiology of saltwater adaptation. Exposure to atrazine did not impair the olfactory system of eels and they were able to detect compounds released by prey items. Exposure of juvenile (glass eels) to 0.5 μg l of tributyl phosphate did not have an impact on their freshwater adaptation as they were able to survive the movement between salt and freshwater. Glass eels exposed to a range of low concentration of metals (copper, lead, zinc and chromium) all demonstrated significant damage to their DNA. The long term impact of DNA damage is not known or whether this would reduce survival in the eels.The results of the study indicate that exposure to contaminants as the eels migrate between the freshwater and marine environments has probably only a minor role in regulating the eel population.