Why Is Recruitment of the American Eel, Anguilla rostrata, Declining in the St. Lawrence River and Gulf?

Abstract

We critically review four potential causes of a drastic decline in juvenile American eels, Anguilla rostrata, recruiting to Lake Ontario (81-fold decline from 1985 to 1992) and in juvenile eel densities in tributaries to the Gulf of St. Lawrence. Silver eels from the St. Lawrence River were much more contaminated and had a high prevalence of deformities and lesions than a reference stock although they were on average less contaminated in 1990 than in 1982 (1.12 versus 4.54 μgg−1 for PCB; 0.025 versus 0.07 μg∙g−1 for mirex). Lethal toxicity from chemical contamination has been known to occur in St. Lawrence River eels for the past 25–30 yr. Major habitat modifications in the St. Lawrence took place in the 1950's (St. Lawrence Seaway and hydroelectric dams), about 30 yr before recruitment started declining; this long delay argues against these perturbations being primary causes of the decline. There is little evidence that commercial fishing and oceanographic changes caused the decline. Overall, we conclude that we do not know what caused the pronounced recruitment decline. We propose research avenues and hypotheses that may advance understanding and emphasize that because of panmixia, the recruitment decline could be species wide.

A synthesis of the ecological processes influencing variation in life history and movement patterns of American eel: towards a global assessment

“…Under panmixis, the number of young eels entering a given river in a given year will not be related to the number of adults that left that river, but to the total number from all geographic areas combined that reached the spawning area in the Sargasso Sea (Castonguay et al 1994a). This disassociation in the stock-recruitment relationship at the local scale will also hold for a quasi-panmictic assemblage of local populations between which differentiation is minimal and only weakly oriented to distance of geographic separation (see Avise and Felley 1979).…”

“…The management of American eel at a global scale has been a persistent idea because of the panmictic (or quasi-panmictic) nature of the species (Castonguay et al 1994a;Haro et al 2000;Casselman 2003;De Leo et al 2009). While site-specific analyses are needed to understand eel life history in the continental phase, the study of the generalized decline of American eel recruitment requires a global assessment (De Leo et al 2009).…”

Fluctuations Des Captures De Civelles (Anguilla Anguilla L.) Et Analyse De La Variation De Leur Capturabilité Dans l'ESTUAIRE De L'adour.

“…Une diminution des prises par sortie en Loire et en Vilaine ou sur la Gironde (CASTELNAUD et al, 1994) est également notée à partir du début des années quatre-vingts. Cette tendance à la baisse est valable pour l'ensemble des pays européens ainsi que sur les côtes américaines (CASTONGUAY et al 1994 ;DEKKER, 1997). …”

“…Sur l'Adour, elle représente la base du chiffre d'affaires pour les professionnels (PROUZET et al, 1994a). On observe pour l'Adour, comme pour l'ensemble des pays européens ainsi que sur les côtes américaines une diminution des prises de civelles (CASTELNAUD et al, 1994 ;CASTONGUAY et al, 1994 ;PROUZET et al, 1994a ;DEKKER, 1997). Les études réalisées sur l'Adour ont pour objectif de quantifier les flux en migration de manière à évaluer les taux d'exploitation.…”

Untitled

“…Malgré des incertitudes sur les causes ou plus exactement sur la hiérarchie des causes de cette diminution (CASTONGUAY et al, 1994), il importe dès à présent de définir une gestion apte à éviter tout risque d'extinction locale, voire générale et à assurer le maintien de l'activité liée à cette espèce.…”