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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; [...]

Downstream migration of silver American eels (Anguilla rostrata) from the St. Lawrence system was examined using acoustic telemetry. One hundred and thirty six silver American eels were tagged, and their passage was recorded using fixed acoustic arrays covering a 420 km distance along the St. Lawrence River and Estuary. Eighty-nine percent of the tagged eels were detected. All migrant eels (111) exhibited unidirectional and downstream movements, but the migration was not completed in one continuous direct movement. High individual variability in migratory longitudinal profiles was documented as well as in individual speed with no apparent relation to river discharge or morphological traits. Migration speed increased over the season. Our observations demonstrated that migrating silver American eels are largely nocturnal and demonstrated the use of nocturnal, ebb tide transport to leave the estuary. With 44 additional eels tagged and released in the maritime estuary, escapement of 180 silver American eels from the Gulf of St. Lawrence system was monitored along a 125 km acoustic line that entirely covered Cabot Strait in 2011. Surprisingly, only four of the tagged eels were recorded escaping the Gulf of St. Lawrence. La migration de devalaison de l'anguille d'Amerique argentee (Anguilla rostrata) a ete etudiee grace a un systeme de telemetrie acoustique. Cent trente-six anguilles argentees ont ete marquees et leur passage ou presence a ete enregistre grace a des lignes acoustiques fixes couvrant une distance de 420 km le long du fleuve et de l'estuaire du St-Laurent. Quatre-vingt neuf pourcent des anguilles marquees ont ete detectees. Toutes les anguilles migrantes (111) montrent des mouvements unidirectionnels vers l'aval mais la migration n'est pas menee d'une seule traite. Une tres grande variabilite individuelle au niveau des profils de migration a ete demontree, ainsi qu'au niveau des vitesses de migration sans que ces dernieres ne puissent etre reliees ni au debit du fleuve ni a des traits morphologiques. La vitesse de migration augmente au cours de la saison. Nos observations suggerent l'utilisation du transport de jusant nocturne pour quitter l'estuaire. Avec 44 anguilles supplementaires marquees et relachees en estuaire maritime, l'echappement de 180 anguilles argentees du systeme St-Laurent a ete suivi grace a une ligne acoustique couvrant les 125 km du detroit de Cabot en 2011. Etonnamment, seulement quatre des anguilles marquees sortant du Golfe du St-Laurent ont ete detectees., Introduction The American eel (Anguilla rostrata) and the European eel (Anguilla anguilla) are facultative catadromous fishes inhabiting continental waters in fresh, brackish, or saltwater environments (e.g., Daverat et al. 2006), [...]

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]

Large-scale habitat use and movements of yellow American eels ( Anguilla rostrata) from the St. Lawrence River were examined using acoustic telemetry from early summer to late fall in 2010 and 2011. Sixty-seven eels were tagged, and their passage or presence was recorded using fixed acoustic arrays covering a 400 km distance along the St. Lawrence River and Estuary. Sixty-four per cent of the 67 tagged eels were detected. Most eels were detected at only one array; the closest to their release location and at several occasions during the tracking period, suggesting a high proportion of freshwater residency in the upstream part of the St. Lawrence River. Downstream movements towards the brackish estuary (63-418 km distance) were demonstrated for 16.4% of the eels, particularly for those caught at the most downstream site that is close to the brackish estuary. Our results strongly suggest a lower activity of freshwater resident yellow eels during summer, a behaviour that may be related to day length, which defines time available for their nocturnal foraging. Indeed, yellow eels were detected primarily at night; no effect of moon phase was revealed. Movements in the vicinity of arrays (up to 116 km in the fluvial estuary) were suggested and smaller-scale movements within Lac St. Louis were demonstrated, highlighting a yellow-eel home range far more extensive than previously reported in smaller systems. Evidence for within-season homing and site fidelity is also reported. [ABSTRACT FROM AUTHOR]

We performed population genetic analyses on the American eel ( Anguilla rostrata) with three main objectives. First, we conducted the most comprehensive analysis of neutral genetic population structure to date to revisit the null hypothesis of panmixia in this species. Second, we used this data to provide the first estimates of contemporary effective population size ( N e) and to document temporal variation in effective number of breeders ( N b) in American eel. Third, we tested for statistical associations between temporal variation in the North Atlantic Oscillation ( NAO), the effective number of breeders and two indices of recruit abundance. A total of 2142 eels from 32 sampling locations were genotyped with 18 microsatellite loci. All measures of differentiation were essentially zero, and no evidence for significant spatial or temporal genetic differentiation was found. The panmixia hypothesis should thus be accepted for this species. N b estimates varied by a factor of 23 among 12 cohorts, from 473 to 10 999. The effective population size N e was estimated at 10 532 (95% CI, 9312-11 752). This study also showed that genetically based demographic indices, namely N b and allelic richness ( Ar), can be used as surrogates for the abundance of breeders and recruits, which were both shown to be positively influenced by variation during high (positive) NAO phases. Thus, long-term genetic monitoring of American glass eels at several sites along the North American Atlantic coast would represent a powerful and efficient complement to census monitoring to track demographic fluctuations and better understand their causes. [ABSTRACT FROM AUTHOR]