(Convener: Wickstrom; Rapporteur: Donnelly)
16. Lecomte-Finiger presented a paper on behalf of Yahyaoui on studies of Moroccan glass eels from Atlantic and Mediterranean coasts, caught in December-January migrations. Optical and SEM otolith studies showed age differences of approximately 1 month, correlating with different migration routes and time of recruitment.
17. Lecomte-Finiger and co-workers discussed otolith ring studies of Stage Vb glass eels from marine and estuarine sites in the Bay of Biscay (February-March 1992). The transition ring had been thought to correlate with the change between marine and estuarine habitats but the studies did not support this. The possibility that some elvers came into freshwater and then returned 100 km out to sea was thought very unlikely. The formation of the transition ring could be related to exhaustion of energy reserves and physiological changes. Further research is needed on this.
18. As part of an on-going long-term study on male/female growth patterns using PIT tags, Holmgren & Wickstrom have shown uncoupling between otolith and somatic growth in fed but initially non-growing elvers. Otolith growth increased with temperature, as expected if otolith growth reflects metabolic rate. Back-calculated length might then be biased during periods with suboptimal conditions for somatic growth. Desaunay observed that otoliths can continue to grow during starvation in other species. Further work, including comparisons between fast and slow growing eels and between the sexes, is progressing and will be reported in the future.
19. Age determinations and back-calculated growth of two eel populations (oligotrophic Burrishoole River system and eutrophic Lough Derg system) were made by Walsh & Moriarty, comparing visual examination and OPRS electronic scanning of otoliths. Both methods require the identification of annual checks by the observer, but the OPRS has the advantage of greatly increased speed in back-calculations.
20. Klein Breteler compared the survival and growth of eels subjected to fin clipping. This method of marking appears to have no effect on the mortality rate and growth rate. Complete (but recognisable) regeneration of the pectoral fin occurred in 14 cases, 3% of the eels. These eels were significantly larger than the others. The causes and implications for eel studies were also discussed.
21. A poster by Robak demonstrated the use of photographs in determining age and growth of eel in the Great Mazuiran Lakes in Poland.
