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The stocking of juvenile eels and trap and transport programs of large yellow (American) eels (Anguilla rostrata) were initiated in Ontario to mitigate mortalities observed at hydroelectric dams and to increase escapement from the upper St. Lawrence River and Lake Ontario (Canada). A total of 380 migrating female silver eels (stocked, trapped and transported, and wild) were tagged with acoustic transmitters between 2011 and 2014. Their migration and escapement at the exit of the Gulf of St. Lawrence, the Cabot Strait, were recorded using acoustic receivers. Escapement rates varied between 8.9% and 20.0% annually (mean = 11.4%). A high proportion of stocked eels were detected (N = 27 of 43 detected at Cabot Strait), demonstrating their ability to escape the Gulf. No differences in migration speed or crossing locations at Cabot Strait were found among the three categories. Eels crossing Cabot Strait did not display diel and tidal patterns, but their estimated swimming depth indicated diel vertical migrations. The low escapement rates observed may be related to predation events and (or) the low and variable detection efficiency of the acoustic receivers' line. L'empoissonnement d'anguilles juveniles et des campagnes de piegeage et transport de grosses anguilles jaunes (Anguilla rostrata) ont ete entrepris en Ontario pour contrecarrer la mortalite observee a l'emplacement de barrages hydroelectriques et pour rehausser le nombre d'individus s'echappant du haut fleuve Saint-Laurent et du lac Ontario (Canada). Un total de 380 anguilles argentees femelles en migration (empoissonnees, piegees et transportees et sauvages) ont ete dotees d'un emetteur acoustique de 2011 a 2014. Leur migration et leur echappement a la sortie du golfe Saint-Laurent, dans le detroit de Cabot, ont ete enregistres a l'aide de recepteurs acoustiques. Les taux d'echappement allaient de 8,9% a 20,0% annuellement (moyenne = 11,4%). Une forte proportion d'anguilles empoissonnees ont ete detectees (N = 27 sur 43 detectees dans le detroit de Cabot), ce qui demontre leur capacite de s'echapper du golfe. Aucune difference sur le plan de la vitesse de migration ou des lieux de traversee du detroit n'a ete decelee entre les trois categories. Les anguilles qui traversent le detroit de Cabot ne presentent pas de motifs nycthemeraux ou tidaux, mais leur profondeur de nage estimee indique des migrations verticales nycthemerales. Les faibles taux d'echappement observes pourraient etre associes a des evenements de predation ou a l'efficacite de detection faible et variable de la ligne de recepteurs acoustiques. [Traduit par la Redaction], Introduction Several methods have been employed by fisheries managers and scientists to mitigate fish population declines (Cowx 1994). Two such methods are stocking (in which the early life-history stages are [...]

An international sampling program investigating the causes of the decline of American eels (Anguilla rostrata) and European eels (Anguilla anguilla) in the St. Lawrence (Canada) and Gironde (France) rivers systems provided the opportunity to compare early growth of eels of each species among habitats using back-calculated size-at-age from 1 to 5 years old. Our study supports previous studies showing that the early back-calculated lengths of A. anguilla were higher in downstream and more saline Gironde system habitats than in the upstream fluvial section and provides a new indication that length at 1 year old is twice higher than that reported 10 years earlier. However, our data contradict the current paradigm for A. rostrata by providing evidence that early size-at-age of eels from the upstream St. Lawrence system, most distant from the spawning area, exceeds those of eels sampled downstream, at less distant sites in the estuarine section. Overall, these observations are consistent with the hypothesis that the observed spatial variations in early growth rate of yellow eels sampled in the St. Lawrence and Gironde systems are the consequence of processes occurring in the first year of age, such as genetic selection and (or) genetically dependent habitat choice. Un programme d'echantillonnage international visant a etablir les causes du declin de l'anguille americaine (Anguilla rostrata) et de l'anguille europeenne (Anguilla anguilla) dans les systemes des fleuves Saint-Laurent (Canada) et Gironde (France) s'avere l'occasion de comparer la croissance precoce des anguilles de chaque espece dans differents habitats en utilisant la taille selon l'age retrocalculee pour les individus de 1 an a 5 ans. L'etude appuie des etudes anterieures qui montrent que les longueurs precoces retrocalculees d'A. anguilla etaient plus grandes dans les habitats du reseau inferieur et plus salins de la Gironde que dans le tronqon superieur fluvial, et indique que la longueur a 1 an est deux fois superieure a celle signalee 10 ans plus tot. Nos donnees contredisent toutefois le paradigme actuel pour A. rostrata car elles indiquent que la taille precoce selon l'age des anguilles dans le systeme superieur du Saint-Laurent, le plus distant de l'aire de frai, depasse celle d'anguilles echantillonnees en aval, dans des sites moins distants dans le tronqon estuarien. Globalement, ces observations appuient l'hypothese voulant que les variations spatiales observees du taux de croissance precoce des anguilles jaunes dans les systemes du Saint-Laurent et de la Gironde soient la consequence de processus qui s'operent durant la premiere annee de vie, comme la selection genetique ou le choix d'habitat dependant de la genetique. [Traduit par la Redaction], Introduction A decline of North European and American eel populations (hereinafter called Atlantic eels) has been observed over the last 30 years (Castonguay et al. 1994; Cosewic 2012; Dekker 2003; [...]

Worldwide concerns about declining eel stocks have resulted in the increased use of conservation stocking (i.e. the translocation of early eel life-stages from areas of high recruitment to areas experiencing recruitment declines) as a recovery tool., North Atlantic eels have complicated and incompletely understood life-history strategies with major differences in life-history parameters across the species' broad distributions, and these differences may be important for migrating and spawning successfully., Sex ratio, growth rate and size and age at maturation of American eels ( Anguilla rostrata) stocked into the St. Lawrence River basin from donor areas over 2000 km away with differing life-history characteristics were compared with those of naturally recruited eels to assess the effectiveness of a potential stocking programme in maintaining a sub-population with unique life-history characteristics (largest from across the species range, and exclusively female)., Stocked eels exhibited faster annual growth, had a different sex ratio, and matured and outmigrated at smaller sizes and ages than naturally recruited eels., Conservation stocking should be applied with caution, as stocked eels appear to be following life-history patterns comparable with conspecifics in the geographic range of the donor streams where they were collected. These findings cast doubt on the generally accepted hypothesis that the mechanisms driving eel life-history variation are environmentally induced, and suggest that more care should be taken in assessing and matching the life-history characteristics of donor and recipient sub-populations if conservation stocking is expected to be an important recovery option for eel restoration., © 2014 Her Majesty the Queen in Right of Canada. Aquatic Conservation: Marine and Freshwater Ecosystems © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]