(Convener: Doering; Rapporteur: Scott)
29. Legault presented a Report for fishery managers on problems of barriers (dams, sluices, conduits, etc.) to migration and the use of eel passes in France. Regional catchment distributions and paucity of stocks were correlated with the degree of impact of the barriers. Some could be made passable by design alterations, others require installation of passes of appropriate design. Traps could be incorporated to provide eels for restocking. In discussion, it was agreed that combined passes for different fish species were desirable, as were means for deflecting silver eels from entering hydro power turbines or pumps in order to aid emigration.
30. Tracking of silver eels in the R. Weser and the Elbe estuary were described by Tesch. Eels possibly swam actively during day and night in deeper parts of the river channels at about 3–4 km/h. In the estuary, eels tended to drift back and forth with the tides, suggesting passive movement, with a relatively long residence time. This correlates with data from other conventional tagging studies.
31. In a second presentation, Tesch described vertical movements of silver eels in the Mediterranean (down to < 600 m) and in the Baltic (down to < 100m). They appeared to be well adapted to diving but concerns were expressed about the possible effects of swim bladder damage due to Anguillicola infestation. It was agreed that more information is needed on the role of the swim bladder in diving.
32. McCarthy described the early results from a study of 1,515 PIT-or externally-tagged silver eels migrating in the Shannon system. About 75% were female, indicating, he believed, that the system is relatively understocked.
33. Petukhov examined the effects of various factors on the patterns of migration from 4 lakes in Belarus. Best correlations were with water temperature and water level, peaks occurring in the 3rd and 4th quarters of the moon and 18th to 24th days of lunar cycles. Spring migrations exceeded those in autumn.
34. Belpaire described some problems faced by eels in the Flandrian River Yser. Recruitment had declined and potential distribution and densities were affected by barriers, habitat loss and agricultural pollution and eutrophication. Silver eel emigration is affected by losses when they are taken into pumps draining the polders. Management measures to help overcome these problems were described.
35. White & Knights gave further information on young eel migrations in the Rivers Severn and Avon. Pass traps appeared efficient although recapture rates of marked eels were low. Speed of migration was up to 1.61 km/day and varied with time of release and season. Some eels caught were larger than expected for their age and were evidence of migration of stocked fish derived from previously cultured stocks.
