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Although telemetry is commonly used to study fishes, researchers rarely design experiments that facilitate in situ quantification of tagging-related impacts to survival. We experimentally applied high (mean burden = 9.6%) and low (2.6%) acoustic tag burdens and gill clip biopsies to migrating juvenile sockeye salmon (Oncorhynchus nerka). Mortality from release to the last marine receiver array was 1.51 times greater for the high tag burden group (25% surviving) compared with the low burden group (40% surviving). A biopsy effect was limited to the first migration segment (14 km), where mortality was 1.86 times greater for biopsied fish. These results demonstrate the importance of quantifying biopsy and tagging effects when survival estimates are prioritized. Bien que la telemetrie soit courammentutilisee pour etudier les poissons, les chercheurs conqoivent rarement des experiences qui facilitent la quantification in situ des impacts de l'etiquetage sur la survie. Nous avons applique experimentalement des fardeaux d'etiquette acoustique eleve (fardeau moyen = 9,6 %) et faible (2,6 %) et des biopsies branchiales a des saumons rouges juveniles (Oncorhynchus nerka) en migration. Le taux de mortalite du moment du lacher jusqu'au dernier reseau de recepteurs marins etait 1,51 fois plus grand pour le groupe au fardeau eleve (25 % de survivants) que pour le groupe au fardeau faible (40 % de survivants). L'effet de la biopsie se limitait au premier segment de la migration (14 km) ou la mortalite etait 1,86 fois plus importante pour les poissons ayant subi une biopsie. Ces resultats demontrent l'importance de quantifier les effets des biopsies et de l'etiquetage quand les estimations de la survie constituent une priorite. [Traduit par la Redaction], The quality of the papers in this journal depends a great deal on the efforts of those who agree to act as critical readers of manuscripts. The editors gratefully acknowledge [...]

For anadromous Pacific salmonid (Oncorhynchus spp.) smolts, the physiological state of individuals can influence migration fate. This critical life stage is typically associated with poor survival and influences population productivity, highlighting the need to identify intrinsic factors associated with outmigration fate. To better understand and identify such factors, we combined acoustic telemetry with nonlethal gill biopsies and used high-throughput real-time quantitative polymerase chain reaction to assess how infectious agents and host gene expression profiles influence migration fate for hatchery steelhead smolts (Oncorhynchus mykiss). Redundancy analyses of gene expression, infectious agent loads, and body condition highlighted gene expression profiles indicative of migratory fate. Smolts never detected after release in the river had significantly elevated expression of the immune genes Il-17D and RPL6, and lower expression of the osmoregulatory gene NKA 1b relative to other individuals. Flavobacterium psychrophilum and 'Candidatus Branchiomonas cysticola' were detected in gill samples, but neither influenced survival. We demonstrate rare evidence of gene expression profiles relating to migration fate in juvenile salmonids and highlight potential mechanisms influencing fate for hatchery steelhead smolts. Pour les saumoneaux de salmonides anadromes du Pacifique (Oncorhynchus spp.), l'etat physiologique des individus peut influencer le resultat de la migration. Cette etape cle du cycle de vie est typiquement associee a une faible survie et elle influence la productivite des populations, d'ou l'importance de cerner les facteurs intrinseques associes au resultat des migrations de sortie. Pour mieux comprendre et cerner ces facteurs, nous avons combine la telemetrie acoustique a des biopsies de branchies non letales et utilise l'amplification en chaine par polymerase quantitative en temps reel et a debit eleve pour evaluer l'influence d'agents infectieux et des profils d'expression genique des hotes sur le resultat de la migration pour des saumoneaux de truite arc-en-ciel (Oncorhynchus mykiss) issus d'ecloseries. Des analyses de redondance de l'expression genique, des charges d'agents infectieux et de l'embonpoint font ressortir des profils d'expression genique qui predisent le resultat de la migration. Les saumoneaux jamais detectes apres leur lacher dans la riviere presentaient une expression significativement elevee des genes de l'immunite Il-17D et RPL6 et une expression plus faible du gene de l'osmoregulation NKA 1b par rapport aux autres individus. Flavobacterium psychrophilum et 'Candidatus Branchiomonas cysticola' ont ete detectes dans les echantillons de branchies, mais ni l'un ni l'autre n'influencait la survie. Nous presentons de rares preuves d'un lien entre les profils d'expression genique et le resultat de la migration chez des salmonides juveniles et decrivons des mecanismes qui pourraient influencer le destin des saumoneaux de truite arc-en-ciel issus d'ecloseries. [Traduit par la Redaction], Introduction Large-scale migrations are an important life history component for Pacific anadromous salmonids (Oncorhynchus spp.). Towards the end of their freshwater residence, individuals undergo dramatic physiological changes prior to migrating [...]

Metabolic scope represents the aerobic energy budget available to an organism to perform non‐maintenance activities (e.g., escape a predator, recover from a fisheries interaction, compete for a mate). Conflicting energetic requirements can give rise to ecologically relevant metabolic trade‐offs when energy budgeting is constrained. The objective of this study was to investigate how aerobic energy is utilized when individual sockeye salmon (Oncorhynchus nerka) are exposed to multiple acute stressors. To indirectly assess metabolic changes in free‐swimming individuals, salmon were implanted with heart rate biologgers. The animals were then exercised to exhaustion or briefly handled as a control, and allowed to recover from this stressor for 48 h. During the first 2 h of the recovery period, individual salmon were exposed to 90 ml of conspecific alarm cues or water as a control. Heart rate was recorded throughout the recovery period. Recovery effort and time was higher in exercised fish, relative to control fish, whereas exposure to an alarm cue had no effect on either of these metrics. Individual routine heart rate was negatively correlated with recovery time and effort. Together, these findings suggest that metabolic energy allocation towards exercise recovery (i.e., an acute stressor; handling, chase, etc.) trumps anti‐predator responses in salmon, although individual variation may mediate this effect at the population level. [ABSTRACT FROM AUTHOR]

Annual migrations by juvenile Pacific salmon Oncorhynchus spp. smolts are predictable, presenting opportunities for predators to exploit these seasonal prey pulses. Directly observing predator–prey interactions to understand factors affecting predation may be possible via dual‐frequency identification sonar (DIDSON) acoustic imaging. Within Chilko Lake, British Columbia, prior telemetry and stomach content analyses suggested that the out‐migration of Sockeye Salmon Oncorhynchus nerka smolts influences the movements and aggregations of Bull Trout Salvelinus confluentus that feed extensively on smolts during their out‐migration. Bull Trout captured at a government‐installed counting fence exhibited high consumption of smolts, but it is only assumed that feeding occurred directly at the fence. We used DIDSON to assess fine‐scale predator–prey interactions between Sockeye Salmon smolts and Bull Trout over 10 d during the 2016 smolt out‐migration. We found that smolt–Bull Trout interactions were correlated with smolt densities at the counting fence, consistent with the prior diet studies in the system. Predator–prey interactions were also coupled with nocturnal migratory behaviors of Sockeye Salmon smolts, presumably to minimize predation risk. These results demonstrate that DIDSON technology can record interactions between predators and migrating prey at a resolution that can identify variability in space and time and provide insight on the role of anthropogenic structures (e.g., counting fences) in mediating such interactions. [ABSTRACT FROM AUTHOR]

We coupled physiological biopsy and positional telemetry to examine survival to reach spawning grounds in relation to water temperature, timing, physiological condition, and holding location (river or lake) in adult migrating sockeye salmon (Oncorhynchus nerka). We tracked 83 fish across a large temperature range (13.5-21.5 °C), which included record highs. Only early-timed migrants that held in Harrison Lake survived to reach spawning grounds (16%, or n = 4). Normal-timed fish, those that migrated at historically observed times, survived at higher levels if they held in Harrison River (72%, or n = 18). Mortalities were identified on the bottoms of both the lake and river. Hypothetical degree-day (DD) accumulation revealed that early-timed river fish would have greatly surpassed (~800 °C DD) a critical disease threshold value (~500 °C DD). There was no difference in hypothetical DD accumulation between normal-timed river fish and early-timed lake fish. Early-timed sockeye had elevated physiological stress (e.g., plasma lactate, glucose, and hematocrit), which may have contributed to high levels of mortality. By using lakes as thermal refugia, early-timed fish likely reduce rates of disease development and may better recover from physiological stress associated with high encountered temperatures. Resume: Nous avons combine des biopsies physiologiques et de la telemetrie de position afin d'etudier la survie jusqu'aux frayeres en fonction de la temperature de l'eau, du calendrier, de la condition physiologique et du lieu de retenue (riviere ou lac) chez des saumons rouges (Oncorhynchus nerka) adultes en migration. Nous avons suivi 83 poissons sur une gamme etendue de temperatures (13,5-21,5 °C) qui comprenait des temperatures exceptionnellement elevees. Seuls les migrateurs a calendrier precoce qui se sont arretes dans le lac Harrison ont survecu jusqu'a leur arrivee sur les frayeres (16 %, ou n = 4). Les poissons a calendrier normal, qui ont migre aux periodes observees dans le passe, ont eu un taux de survie plus eleve s'ils s'etaient arretes dans la riviere Harrison (72 %, ou n = 18). Des mortalites ont ete observees sur le fond du lac et de la riviere. Une accumulation hypothetique de degres-jours (DD) montre que les poissons de riviere a calendrier precoce auraient largement depasse (~800 °C DD) le seuil critique de morbidite (~500 °C DD). Il n'y a pas de diffe rence dans l'accumulation hypothetique de DD entre les poissons de riviere a calendrier normal et les poissons de lac a calendrier precoce. Les poissons a calendrier precoce ont un stress physiologique accru (par ex., le lactate plasmatique, le glucose et l'hematocrite), ce qui peut avoir contribue aux taux eleves de mortalite. En utilisant les lacs comme refuges thermiques, les poissons a calendrier precoce reduisent vraisemblablement leur taux de developpement de maladies et peuvent recuperer plus facilement du stress physiologique associe aux temperatures elevees qu'ils rencontrent. [Traduit par la Redaction], Introduction Migratory Pacific salmon (Oncorhynchus spp.) returning to their natal freshwater spawning grounds initiate freshwater entry when river discharge and temperature are most favourable, matching long-term average environmental conditions (Keefer [...]

Abstract: Since 1995, large segments of the late-run sockeye salmon (Oncorhynchus nerka) stock complex from the Fraser River, British Columbia, Canada, have been initiating spawning migrations several weeks earlier than [...]

Abstract: We assessed the prolonged swimming performance ([U.sub.crit]), metabolic rate (M[O.sub.2-min] and M[O.sub.2-max]), and oxygen cost of transport (COT) for upper Fraser River pink salmon (Oncorhynchus gorbuscha (Walbaum, 1792); 53.5 [...]