8. White presented information on recruitment of Severn eels, compiled from direct and indirect sources. Recruitment has declined by 50% over the past 15 years. Oceanic factors are possibly implicated: known changes in position and strength of the Gulf Stream may affect breeding and larval survival and migration. Tesch commented that the Gulf Stream may not be the major transport mechanism.
9. A model for seasonal variation in glass eels was presented by Desaunay for Guerault, based on two years' study. A sample of 140 otoliths of type 3, examined under SEM, indicated some days before start of feeding, 182 days leptocephalus, 85 days glass eel making a total larval life of about 9 months. Larger, winter-caught glass eels (71 mm), would spend the leptocephalus stage in summer and the glass eel starvation stage in autumn, while those hatching in autumn would be leptocephali in spring to summer. They would be caught in autumn at a mean length of 68 mm. Data for the 1920s catches in the Bay of Biscay indicated longer and heavier glass eel than are caught today, suggesting long term, perhaps oceanic, variation. Jellyman suggested that some glass eels may be unable to enter river mouths due to drought, and suffer physiological stress at that time.
10. Lara described glass eel fisheries in the Nalan estuary, NW Spain. Since the increased popularity of these for consumption in the 1960s, the fishing had intensified. Catches were greatest in the 1970s, declining after 1980 to a low of 7 t in 1990. The decline is attributed to poor recruitment, as prices have remained high (max £150 or 30 000 pesetas per kg at Christmas). Tzeng had noted similar peaks in 1977 in Pacific eels, indicating that global factors may be involved. Desaunay stressed the unique scientific importance of eels for studies of global environmental change.
11. Tesch presented material on eel larval captures on his latest cruise of autumn 1991. Captures of 2.8 to 3.25 larvae per towing hour showed younger larvae predominating off Portugal and older, longer ones in the Bay of Biscay, contrary to the hypothesis of transport by the Gulf Stream. He stressed the importance of continuing such cruises.
In response to a suggestion by Moriarty that the Working Group recommended to ICES that Directors of Scientific cruises should be informed of our requirements, Tesch stressed the need for an experienced specialist on eel larvae to take part in such cruises. He mentioned that Strehlow was suitably qualified.
12. Reynolds described the development of a pilot glass eel fishery for the River Shannon in Ireland, to supplement dwindling elver catches for restocking. Glass eels were present only from January to May, with peak catches February to April, depending on water discharges. ‘Robust’ and ‘gracile’ forms were described for samples, the changing proportions of each over time contributing to different sample characteristics.
13. Tesch and Antunes described SEM otolith studies and discussed the problem of quantifying the diffuse zone in larval eel otoliths. Leptocephali never occur on the continental shelf, while glass eels have been found outside it. The duration of metamorphosis is very variable. Desaunay said he believed metamorphosis to be protracted and should be considered as being complete at the start of feeding by the glass eel. Faster transformation may lead to enhanced survival.
14. Lecomte-Finiger gave details of elver otolith SEM studies which indicated egg, leptocephalus, metamorphosis, transition and marginal growth zones. Ontogenetic change is indicated at the end of the leptocephalus daily growth pattern; the glass eel gut is not functional until later. The transition double check suggests physiological or environmental stress. Degree of pigmentation does not always correlate with otolith age history. While the larva may decrease in length, the otolith still continues to grow.
15. Moriarty summarized the present situation with regard to elver supply in Europe from Sweden to Portugal. High catches in the 1970s had been followed by low catches in the 1980s. Statistical tests had indicated significant correlation between rivers. Long-term reductions in catches have been observed in the Baltic and North Sea rivers. There was an indication of an upward change in 1994, including a notable increase to a catch of 90 t in the Loire. For the first time in this regular report, data from the River Severn, UK and the St. Lawrence River, Canada were incorporated. The Canadian data showed an increase for 1994 of juvenile eels mainly from the 1990 glass eel immigration. The improvements in 1994, however, could not be taken as evidence of a reversal of the downward trend. The weight of evidence appeared to favour the hypothesis that the decline in catch had been caused by oceanic rather than anthropogenic effects. It was strongly emphasized, however that, despite the inability to control ocean-based problems, there was scope for significant improvements in the management of recruitment.
16. Svedäng demonstrated that active density dependent migration of eels from Kattegat/Skagerrak into the Baltic was less important than supposed. Unlike the west coasts, Baltic populations had proved to be dominated by one year class.
POSTERS
17. Budimawan (presented by Lecomte-Finiger) showed daily growth increments and age at recruitment of A. marmorata glass eels in four Asian estuaries.
18. Rui Bessa demonstrated the annual changes in the length, weight and width of glass eels caught throughout the year from May 1991 to May 1994 from the Liz river in Portugal.
19. Strehlow illustrated the second and largest known specimen of the very rare congrid larva Leptocephalus pseudomicrocephalus from the northeast Atlantic. The specimen measured 467 mm and characteristics include high number of myomeres and short anal and dorsal fins.
20. Walsh presented SEM otolith studies of glass eel from the Shannon Estuary, Ireland. Diet studies indicated that stomach fullness and prey item diversity increase through the glass eel season.
21. Williamson presented in poster form (i) a request that the Working Group consider a quarterly central Atlantic transect, from the Grand Banks to 30°N 40°W, to investigate oceanic movements and (ii) a proposal for nomenclature of the life stages of the eel.
