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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. L'utilisation de la telemetrie pour estimer les taux de survie a l'echelle de la population est de plus en plus repandue. Ces estimations peuvent toutefois etre influencees par la detectabilite des etiquettes utilisees et reposent sur le principe que les donnees de telemetrie rendent compte des deplacements des poissons marques. La predation de ces derniers pourrait cependant biaiser les estimations des taux de survie et, contrairement au probleme de detectabilite, il n'existe pas encore de methode permettant de corriger le biais qui en resulte (appele <>). Dans une etude de telemetrie acoustique portant sur des saumoneaux de saumon atlantique (Salmo salar) de la haute baie de Fundy, menee en 2008 et 2011, des motifs de detection d'etiquettes inhabituels indiquaient que certaines donnees pouvaient refleter les deplacements de predateurs plutot que ceux des saumoneaux. Afin d'integrer les effets de la predation dans les estimations des taux de survie en decoulant, 11 parametres sommaires associes a la migration de saumoneaux de saumon atlantique et de bars d'Amerique (Morone saxatilis) ont ete compares. Des analyses typologiques ont revele que de 2,4 % a 13,6 % des etiquettes implantees dans des saumoneaux temoignaient d'habitudes migratoires plus semblables a celles de bars d'Amerique qu'a celles d'autres saumoneaux, ce qui a ete interprete comme une preuve de predation. La reaffectation du destin de ces etiquettes a des individus <> s'est traduite par une reduction des taux de survie estimes de 43,5 % a 41,1 % pour 2008, et de 32,6 % a 19,0 % pour 2011, par rapport aux resultats d'un modele de marquage-recapture traditionnel, illustrant ainsi l'effet du biais de predation dans cette etude de cas. [Traduit par la Redaction], Introduction Quantifying the rate and timing of mortality is important for the conservation planning for many fish populations; however, estimating these rates can be difficult given our inability to directly [...]

Acoustic telemetry is a useful tool to monitor the estuarine survival and behaviour of Atlantic salmon postsmolts. Most frequently, survival is reported as the static fraction of tagged postsmolts detected, and while the timing or location of mortality may be reported, covariates of survival or the relationship between migratory behaviour and survival are less often described. In this study, we used acoustic telemetry to follow Atlantic salmon smolts migrating to sea from four rivers in Nova Scotia, Canada. Further, we tested the relationship between migratory behaviour and survival and used mark-recapture models to examine the role of body length and tag-to-body mass as survival covariates. Survival was most heavily impacted in estuarine habitats closest to head-of-tide. Survival was affected by body length at three of four sites. The shape and spatial variability of the body length--survival relationship provided insight on mortality vectors, highlighting the potential roles of predation and osmotic stress. Survival was not influenced by repeated landward-seaward migratory movements; however, there was a significant correlation between residency and survival. La telemetrie acoustique est un outil utile pour la surveillance de la survie et du comportement en estuaire des post-saumoneaux de saumon atlantique. Dans la plupart des cas, le taux de survie signale est la fraction statique de postsaumoneaux marques detectes et, si le moment et le lieu de la mortalite peuvent etre mentionnes, les covariables du taux de survie ou de la relation entre le comportement migratoire et la survie sont moins souvent rapportees. Dans cette l'etude, nous avons fait appel a la telemetrie acoustique pour suivre des saumoneaux de saumon atlantique en migration de la mer vers quatre rivieres de la Nouvelle-Ecosse (Canada). Nous avons en outre verifie le lien entre le comportement migratoire et le taux de survie et utilise des modeles de marquage-recapture pour examiner la longueur du corps et le rapport entre le poids de la marque et celui du corps comme covariables eventuelles du taux de survie. Les impacts sur ce dernier etaient les plus forts dans les habitats estuariens situes les plus pres de la limite de maree. Dans quatre sites, la longueur du corps avait une incidence sur le taux de survie. La forme et la variabilite spatiale de la relation entre la longueur du corps et le taux de survie ont mis en lumiere des vecteurs de mortalite, faisant ressortir un role possible de la predation et du stress osmotique. Si les deplacements migratoires repetes vers la terre ou vers la mer n'avaient pas d'incidence sur le taux de survie, une correlation significative a cependant ete notee entre le temps de residence et le taux de survie. [Traduit par la Redaction], Introduction Atlantic salmon (Salmo salar L.) populations within the southern portion of their North American range have declined dramatically (Parrish et al. 1998; WWF 2001; COSEWIC 2011), due in large [...]

We developed a Bayesian hierarchical model to estimate annual mortality of repeat-spawning Atlantic salmon, Salmo salar, that distinguishes between mortality rates and the confounding effects of consecutive-year and alternate-year repeat-spawning strategies. The model provides annual estimates of two mortality rates: mortality in the first year (Z1), a time period during which salmon are primarily in freshwater (staging, spawning, and overwintering) followed by a brief period at sea, and mortality in the second year (Z2) when salmon are predominantly at sea. When fit to data for the LaHave River (Nova Scotia, Canada) salmon population, Z1 showed an increasing trend throughout the time series, whereas Z2 also increased but in a single, stepwise manner. Once a time series of mortality rates was separated from the other life-history parameters, we were able to demonstrate how they could be used for examining the influence of environmental conditions by comparing the estimated mortality rate time series with the North Atlantic Oscillation Index (NAOI). This comparison uncovered a statistically significant correlation between the NAOI and the survival in the second year after spawning that would not have been evident had the mortality estimation model not been developed. Nous mettons au point un modele hierarchique bayesien afin d'estimer la mortalite annuelle chez le saumon atlantique, Salmo salar, iteropare qui distingue entre les taux de mortalite et les effets confondants des strategies de fraie aux annees consecutives ou aux deux ans. Le modele fournit des estimations annuelles de deux taux de mortalite, la mortalite durant la premiere annee (Z1), une periode de temps pendant laquelle les saumons sont surtout en eau douce (halte migratoire, fraie et hivernage) suivie par une courte periode en mer, et la mortalite durant la seconde annee (Z2) pendant laquelle les saumons sont surtout en mer. Lorsque le modele est ajuste a des donnees provenant de la population de saumons de la riviere LaHave (Nouvelle-Ecosse, Canada), Z1 suit une tendance croissante dans la serie chronologique, alors que Z2 augmente aussi, mais en un seul palier. Une fois qu'une serie chronologique de taux de mortalite est separee des autres variables du cycle biologique, nous avons pu demontrer comment ces taux de mortalite peuvent servir a examiner l'influence des conditions environnementales en comparant la serie chronologique des taux de mortalite et l'indice de l'oscillation nordatlantique (NAOI). Cette comparaison a revele une correlation statistiquement significative entre le NAOI et la survie dans la seconde annee apres la fraie qui n'aurait pas ete evidente sans la mise au point du modele d'estimation de la mortalite. [Traduit par la Redaction], Introduction Widespread declines in Atlantic salmon (Salmo salar) abundance in North America have not abated since the closure of the commercial fisheries (Friedland et al. 2003a; Gibson et al. 2006; [...]

Abstract: We examined relationships between abundance and habitat use in three age classes of juvenile Atlantic salmon (Salmo salar) in the Stewiacke River, Nova Scotia, Canada. Using stream gradient as [...]

The production of more than one type of young ones within a single species of marine invertebrate is known as poecilogony. A polychaete poecilogonous is used to investigate potential differences in morphogenesis among offspring.

Typically, juvenile survey data are not used explicitly to determine status, trends, or abundance designations for Atlantic salmon Salmo salar, even though they can be the only source of information for many populations. To determine whether juvenile data can be informative about adult abundance and status in Atlantic salmon, we evaluated the similarities in trends among age-classes for two data-rich populations using a nested log-linear model. We found relatively consistent and significant trends for the age-0, adult and egg time series, but the trends in juvenile density data for older age-classes were less consistent with adult abundance trends. A threshold-based analysis demonstrated that relatively low misclassification rates for adult status relative to a set reference level could be obtained from juvenile density estimates. Together, these results suggest that juvenile density data can be an informative proxy for adult abundance and may be useful as an indicator for large changes in population status relative to reference points. This would make data collection via electrofishing an appropriate monitoring method for fisheries management or conservation programs. However, the validity of the idea that dramatic changes in adult abundance will be mirrored in juvenile data partially depends on the specific age-classes monitored, the survey design, and the timing of density dependence in the population. Using juvenile data as an index would necessitate some prior knowledge of the underlying population dynamics before the method could be applied more generally. [ABSTRACT FROM AUTHOR]