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Adult Atlantic salmon (Salmo salar) return to natal rivers several months before spawning and during summer can be subjected to temperatures that exceed their upper temperature tolerance limits. Salmon use thermal refuges to minimize exposure to high temperatures, but little information exists regarding behavioral thermoregulation by adult Atlantic salmon. We examined behavioral thermoregulation by Atlantic salmon during summer in-river residence in a Quebec river with a novel combination of thermal infrared remote sensing, river temperature monitoring, and acoustic telemetry. Adults engaged in behavioural thermoregulation at cooler ambient river temperatures (17-19 [degrees]C) than previously recorded for this species and maintained body temperature within a narrow range (16-20 [degrees]C) via use of cool and warm refuges. Adults used large, stable, stratified pools as refuges, allowing multiple individuals to thermoregulate simultaneously without leaving the pool. Low river discharge and high temperatures can be physical barriers to salmon migration, preventing them from accessing suitable refuges (e.g., pools). Identifying and maintaining connectivity to thermal refuges may be critical for persistence of Atlantic salmon populations as climate changes and rivers warm. Les saumons atlantiques (Salmo salar) adultes reviennent dans leurs rivieres natales plusieurs mois avant le frai et, durant l'ete, peuvent etre exposes a des temperatures depassant leur limite de tolerance thermique superieure. Bien que les saumons utilisent frequemment les refuges thermiques pour minimiser leur exposition aux temperatures elevees, peu d'information existe sur la thermoregulation comportementale des saumons atlantiques adultes. Nous avons examine la thermoregulation comportementale de saumons atlantiques durant leur periode de residence estivale dans une riviere du Quebec en utilisant une combinaison novatrice de teledetection infrarouge thermique, de mesure de la temperature de la riviere et de telemetrie acoustique. Les adultes font preuve de thermoregulation comportementale a des temperatures ambiantes plus faibles (17-19 [degrees]C) que celles observees anterieurement pour cette espece et maintiennent leur temperature corporelle dans une fourchette restreinte (16-20 [degrees]C) en utilisant des refuges frais et chauds. Les adultes utilisent les fosses profondes thermiquement stratifiees comme refuges stables, ce qui permet a de multiples individus de reguler en meme temps leur temperature sans quitter la fosse. Les faibles debits et les temperatures elevees peuvent constituer des barrieres physiques a la migration des saumons, les empechant d'acceder a des refuges convenables (p. ex. fosses). La reconnaissance des refuges thermiques et le maintien de leur connectivite pourraient etre essentiels a la persistance des populations de saumons atlantiques dans un contexte de changements climatiques et de rechauffement des rivieres., Introduction Salmonid species have narrow temperature tolerance ranges, making them highly susceptible to environmental warming resulting from climate change (Brett 1956; Portner and Farrell 2008; Jonsson and Jonsson 2009). Outside [...]

The Gulf of Maine Distinct Population Segment of Atlantic Salmon Salmo salar is listed under the U.S. Endangered Species Act, with dams cited as a key threat to the species. Safe, timely, and efficient passage of emigrating smolts is critical for advancing recovery goals. However, climate change and the earlier (and more variable) onset of smolt migration have challenged the effectiveness of measures designed to protect smolts. Therefore, we used data from four long‐term smolt trapping sites in Maine to characterize run duration, identify a standardized smolt run, and develop a predictive model for the initiation of smolt emigration for natural‐ and hatchery‐origin smolts. We combined these data into a basinwide deterministic model that projects the movement of smolts from their point of origin to estuary entry, which we used to (1) evaluate duration and temperature triggers for supplemental spill periods used at hydroelectric dams to protect smolts and (2) investigate how knowledge of smolt emigration dynamics can guide protective measures in rivers where management actions are being developed. Timing of run initiation varied by over 14 d; however, mean air temperature for the first quarter of the year explained over 60% of the variance in the onset of emigration. Initiation temperature was linked with higher‐elevation rearing areas where smolts originated and not with downstream dams where temperature was monitored. The shape of the smolt wave varied considerably; thus, our standardized smolt wave captured average dynamics but not the specific shape. Overall, 14‐d spill windows are too short. To account for the variable timing and shape of the run, a 54–72‐d protection window would be necessary to protect the earliest and latest emigrants in the absence of physical structures (e.g., turbine screens) and preserve the adaptive variation required for populations to respond to climate‐driven changes in temperature and hydrology. [ABSTRACT FROM AUTHOR]

We examined the role of individual size and origin (wild versus hatchery) to predation risk and marine survival for threatened juvenile steelhead (Oncorhynchus mykiss) in a coastal California watershed. In this study, we found that individual size and origin were strongly associated with increased predation risk of steelhead by a generalist avian predator (western gull, Larus occidentalis) and associated with survival to reproduction by tracking the fate of juvenile steelhead tagged with passive integrated transponder (PIT) tags. Across six cohorts (2005-2010), larger steelhead (>170 mm fork length (FL)) experienced marine survival rates at least 60 times higher than the smallest individuals. Predation risk by western gulls was highest for intermediate-sized fish (145-190 mm FL), which was at least ten times higher than the predation risk of the smallest individuals and four times higher than the predation risk of the largest individuals. Wild steelhead experienced both higher predation risk and higher survival rates than hatchery fish of the same size. Although gulls disproportionately remove intermediate-sized wild steelhead from the population, they also remove large wild individuals that may otherwise experience the highest adult return rates. Instead of focusing on population size alone, conservation measures could also be guided towards the recovery of larger and wild individuals, whose survival is paramount for population recovery. Nous avons examine le lien entre la taille et l'origine (sauvage ou d'ecloserie) des individus, d'une part, et le risque de predation et la survie en mer, d'autre part, pour des truites arc-en-ciel (Oncorhynchus mykiss) juveniles menacees dans un bassin versant de la cote californienne. En suivant des truites arc-en-ciel juveniles dotees de radioetiquettes passives integrees (PIT), nous avons constate que la taille et l'origine des individus etaient fortement associees a un risque de predation accru des truites arc-en-ciel par un predateur aviaire generaliste (le goeland d'Audubon, Larus occidentalis) et etaient associees a la survie jusqu'il la reproduction. A l'echelle de six cohortes (2005-2010), les plus grandes truites (longueur a la fourche (LF) >170 mm) presentaient des taux de survie en mer au moins 60 fois plus eleves que les truites les plus petites. Le risque de predation par des goelands d'Audubon etait le plus eleve pour les individus de taille intermediaire (LF de 145-190 mm), ce risque etant au moins 10 fois plus eleve que pour les individus les plus petits et quatre fois plus eleve que pour les individus les plus grands. Les truites arc-en-ciel sauvages presentaient un risque de predation et des taux de survie plus eleves que les poissons issus d'ecloserie de meme taille. Si les goelands extraient une quantite disproportionnee de truites arc-en-ciel sauvages de taille intermediaire de la population, ils en retirent egalement de grands individus sauvages qui, autrement, pourraient presenter les taux de retour d'adultes les plus eleves. Plutot que d'etre axees exclusivement sur la taille de la population, les mesures de conservation pourraient egalement viser le retablissement d'individus plus grands et sauvages dont la survie est primordiale pour le retablissement des populations. [Traduit par la Redaction], Introduction Individual traits influence ecological parameters such as population dynamics and survival (Palkovacs and Hendry 2010; Bolnick et al. 2011), which necessitates the incorporation of phenotypic variability into fisheries management [...]

Transport of salmonids allows upstream migrating adults to bypass barriers to migration, for example hydroelectric dams or adverse habitats. Downstream movement ("fallback") after transport is common and removes individuals from spawning populations, with possible detrimental consequences for population productivity. Time‐to‐event analysis was used to determine effects of fish characteristics, transport conditions and environmental variables on fallback by adult Atlantic salmon transported to an inaccessible river reach as a population enhancement strategy on the Rivière Sainte‐Marguerite Nord‐Est (Québec, Canada). Of 68 salmon transported, 19 exhibited post‐transport fallback within seven days of transport. Fork length (FL) was the only factor that increased risk of post‐transport fallback; there was a 5% increase in the proportion of large salmon (≥780 mm FL) exhibiting post‐transport fallback relative to individuals of median size (750 mm FL). Although the present study was limited by small sample size, the findings will help inform design of transport programmes in freshwater systems. [ABSTRACT FROM AUTHOR]