(Convener: Knights; Rapporteur: Callaghan)
42. In Sweden (Hoglund) the parasite Anguillicola has only been found in yellow eels from areas affected by thermal discharges. Anguillicola infected silver eels have been reported from other areas but as the yellow eels in these areas are not infected, it was suggested that the infected silver eels may have originated from areas affected by thermal discharges. Swedish freshwater eels are as yet uninfected. This may be because of the lower temperature in freshwater and the temperature dependence of the intermediate hosts. More information is needed concerning the role of temperature in the development stages of the parasite.
43. In Denmark (Boetius) Anguillicola infections continue to increase. It was suggested that the growth of yellow eels does not appear to be disturbed by infection with Anguillicola. Silver eels may be more seriously affected and in particular during their migration to the Sargasso. Eels may die before reaching the spawning ground and this was suggested as a possible cause of the decrease in elvers. Desaunay informed the Working Party on some as yet unpublished work under experimental conditions in tanks which suggests that young Anguillicola may die when the eel reaches greater depths. However there is no clear picture of the disturbance effects of the parasite on the migrating silver eel and further research is required.
44. Bosnakovski reported on the death of yellow eels in Lake Ohrid, Yugoslavia, during the summer of 1986. The eels were flabby and swam irregularly towards the surface before dying. On examination the eels were found to be infected with Pseudomonas punctata and 60% were infected by Echinorynchus truttae. Cyprinids, salmonids and healthy eels were not examined but they did not appear to be affected. The cause of eel deaths could be the result of stocking eels from abroad or the unusually high water temperature of 25–26°C as compared with the usual 18–22°C. Anguillicola crassus has recently been found in eels in this lake.
45. Nolan showed an Electricity Supply Board video and gave a presentation outlining a new design for operation of silver eel nets at Killaloe on the River Shannon. The design incorporated hydraulic power systems for raising and lowering the nets. Special consideration was placed on avoiding obstruction of navigation, aesthetic appearance of the bridge and ease of net operation from the fishing boats. He pointed out that close collaboration between engineers and biologists can be quite productive in solving difficult problems.
46. Knights drew attention to the good literature reviews published by Brusle in 1990 and 1991 on organochlorine and heavy metal pollution of eels. He gave examples of the use of eels as indicators of accidental spillages. Much interest and discussion centred around possible relationships between contaminated versus non-contaminated eels, but methodological aspects still need clarification. The whole problem of contamination in eel appears too complex to be handled by the Working Party members. Knights offered to collect information from members and relevant organizations throughout Europe to produce a review for the next Session on the use of eels as indicators and monitors and on sampling and analytical methodologies.
