SEASONAL AND LONG-TERM CHANGES IN BIOMETRICS OF EEL LARVAE - A POSSIBLE RELATIONSHIP BETWEEN RECRUITMENT VARIATION AND NORTH-ATLANTIC ECOSYSTEM PRODUCTIVITY
Y. Desaunay et D. Guerault, SEASONAL AND LONG-TERM CHANGES IN BIOMETRICS OF EEL LARVAE - A POSSIBLE RELATIONSHIP BETWEEN RECRUITMENT VARIATION AND NORTH-ATLANTIC ECOSYSTEM PRODUCTIVITY, Journal of Fish Biology, 51, 1997, pp. 317-339
The European eel larval life has two stages: the oceanic leptocephalus
, in which growth is dependent on food supply, and the metamorphosis g
lass eel stage, in which feeding and growth are stopped until immigrat
ion in estuarine waters. Data from fisheries and experimental surveys
in European estuaries at different periods between the 1930s and the 1
990s showed a simultaneous decrease of mean length and abundance level
. A monthly survey at the Vilaine estuary (Bay of Biscay) during 2 yea
rs provided a periodical model of seasonal variation in length and wei
ght of newly recruited glass eels. Otolith microstructure was used to
back-calculate larval stage durations and the timing of transatlantic
migration. Glass eels entering the estuary in autumn are longer and mo
re numerous than those arriving in summer. They migrated across the oc
ean during spring and summer, seasons when plankton production is like
ly to reach maximum levels. The proposed hypothesis regarding the dete
rminism of recruitment in the eel, on the seasonal and on the yearly r
ange, is that leptocephalus growth and glass eel survival are partly d
ependent on the plankton production at the oceanic scale. Eel recruitm
ent dynamics could provide an integrated figure of large-scale environ
ment fluctuations. (C) 1997 The Fisheries Society of the British Isles
.