50. Knights reviewed recent studies of eel contamination by organochlorine compounds and heavy metals (biomonitoring, pathology/toxicity and planned/ongoing). Particularly pertinent long-term biomonitoring data sets have indicated falls in OCs in the Rhine and Meuse. PCB levels have been more stable and data provide evidence of pollution ‘hot spots’. Members were requested to provide information for future reviews.
51. Biomonitoring studies of PCBs in eel as indicators of pollution in a Finnish lake (due to a papermill discharge between 1956 and 1984) were presented by Tulonen. Concentrations decrease downstream and have been diminishing with time, but levels in some eels have exceeded statutory levels for human consumption. Future eel stockings and exploitation might depend on future trends in PCB contamination.
52. Hahlbeck showed that the prevalence of infection of eel swimbladders by Anguillicola crassus on the German Baltic coasts and some inland waters had decreased between 1991 and 1993. Infestation rates varied between 16 to 97%, tending to be lower in outer coastal waters. Although data - and discussions - did not provide any conclusive evidence of deleterious effects on eel stocks and breeding migration, further monitoring was recommended.
53. Holmgren showed that experimental rearing of individually marked elvers produced more females (14%) at 26°C, compared to 7 to 8% females at 17° and 20°C. Rapid initial growth characterized males rather than females. She stressed how several factors might confound an interpretation that the temperature effect on the sex ratios really reflects the effect of temperature on sex determination.
