No abstract

Telemetry is increasingly being used to estimate population-level survival rates. However, these estimates may be affected by the detectability of telemetry tags and are reliant on the assumption that telemetry data represent the movements of the tagged fish. Predation on tagged fish has the potential to bias survival estimates, and unlike the issue of detectability, methods to correct for the resulting bias (termed "predation bias") are not yet developed. In an acoustic telemetry study on inner Bay of Fundy Atlantic salmon (Salmo salar) smolts during 2008 and 2011, unusual tag detection patterns were indicative that some data may have been representative of the movements of predators rather than smolts. To incorporate predation effects into the resulting survival estimates, a suite of 11 summary migration metrics were compared between Atlantic salmon smolts and striped bass (Morone saxatilis). Cluster analyses revealed that 2.4% to 13.6% of tags implanted in smolts exhibited migration patterns more similar to striped bass than to other smolts, which was interpreted here as evidence of predation. Reassigning the fate of these tags as "depredated-died" reduced estimated survival from 43.5% to 41.1% in 2008 and from 32.6% to 19.0% in 2011 relative to a traditional mark-recapture model, illustrating the effect of predation bias in this case study.Résumé : L'utilisation de la télémétrie pour estimer les taux de survie à l'échelle de la population est de plus en plus répandue. Ces estimations peuvent toutefois être influencées par la détectabilité des étiquettes utilisées et reposent sur le principe que les données de télémétrie rendent compte des déplacements des poissons marqués. La prédation de ces derniers pourrait cependant biaiser les estimations des taux de survie et, contrairement au problème de détectabilité, il n'existe pas encore de méthode permettant de corriger le biais qui en résulte (appelé « biais de prédation »). Dans une étude de télémétrie acoustique portant sur des saumoneaux de saumon atlantique (Salmo salar) de la haute baie de Fundy, menée en 2008 et 2011, des motifs de détection d'étiquettes inhabituels indiquaient que certaines données pouvaient refléter les déplacements de prédateurs plutôt que ceux des saumoneaux. Afin d'intégrer les effets de la prédation dans les estimations des taux de survie en découlant, 11 paramètres sommaires associés à la migration de saumoneaux de saumon atlantique et de bars d'Amérique (Morone saxatilis) ont été comparés. Des analyses typologiques ont révélé que de 2,4 % à 13,6 % des étiquettes implantées dans des saumoneaux témoignaient d'habitudes migratoires plus semblables à celles de bars d'Amérique qu'à celles d'autres saumoneaux, ce qui a été interprété comme une preuve de prédation. La réaffectation du destin de ces étiquettes à des individus « morts-victimes de prédation » s'est traduite par une réduction des taux de survie estimés de 43,5 % à 41,1 % pour 2008, et de 32,6 % à 19,0 % pour 2011, par rapport aux résultats d'un modèle de marquage-recapture tra...

The commercial fishery for Atlantic Sturgeon Acipenser oxyrinchus in the Saint John River, New Brunswick, began in 1880. The early fishery was unregulated, and the adult stock was depleted by 1886 after landings of 712 metric tons. After a 10-year closure the fishery was reopened in 1897 with management regulations, and landings varied from 6 to 20 metric tons/year until 2010. In 2011 an annual quota of 350 adults was established and landings are now stable at 11.3 ± 1.7 (mean ± SD) metric tons/year. Since 2009, fishers have collected biological statistics from adults taken in the fishery and 14-60% of captured individuals have been marked and released each year. During 2009-2015, annual mean values of total length and dressed weight of landed adults were stable, the male : female sex ratio was 1.2:1.0, and mean age of males and females was 27.2 and 34.0 years, respectively. Estimates of instantaneous total mortality ranged from 0.08 to 0.11, and mean annual survival was 90.9%. Of 1,396 marked adults released, 147 were recaptured in the estuary in subsequent years. Tag returns indicated that the modal spawning periodicity of males was 2 years and that of females was 4 years. Valid, modified Schnabel and Jolly-Seber mean annual population estimates for 2013-2015 were 18,179 and 20,798 adults, respectively. The quota in relation to these estimated adult populations represented annual exploitation rates of 1.9% and 1.7%, which are below F 50 and would maintain present stock size. The virgin adult population was determined using 1880-1886 total landings and a mean weight range for adults of 50-30 kg. Estimated range of the 1880 virgin population size was 14,240-23,733 adults. These data suggest that the fishery is sustainable at its current annual yield and that the population is near the carrying capacity of the Saint John River.

Knowledge of the scale of population structure is a prerequisite for designating conservation units. American shad ( Alosa sapidissima ) are of increasing conservation concern, but the scale of population structure within the Canadian portion of the species range is unknown. Using 13 microsatellite loci, we examined the partitioning of genetic variation within four and among 12 Canadian drainages. We detected significant (p < 0.05) and temporally stable genetic differentiation among all drainages, supporting the hypothesis that rivers support genetically distinct populations. However, Bayesian methods identified seven clusters and provided evidence for shad metapopulation structure. We observed a significant (p < 0.01) pattern of isolation by distance (IBD) among all drainages. A strong linear IBD (r = 0.98) was observed among rivers that were outside the Bay of Fundy (BoF). A hypothesized counterclockwise migration route explained a greater proportion of genetic variation (r = 0.87) among BoF rivers than direct route based distances (r = 0.14). Although IBD patterns did not differ regionally (analysis of covariance; p > 0.05), the degree of differentiation among BoF rivers was greater than that among non-BoF rivers, regardless of the geographic scale of comparison. Our results suggest that fisheries managers need to be concerned with the loss of shad genetic diversity on both river and regional scales.