The extent and rate of harvest‐induced genetic changes in natural populations may impact population productivity, recovery, and persistence. While there is substantial evidence for phenotypic changes in harvested fishes, knowledge of genetic change in the wild remains limited, as phenotypic and genetic data are seldom considered in tandem, and the number of generations needed for genetic changes to occur is not well understood. We quantified changes in size‐at‐age, sex‐specific changes in body size, and genomic metrics in three harvested walleye (Sander vitreus) populations and a fourth reference population with low harvest levels over a 15‐year period in Mistassini Lake, Quebec. We also collected Indigenous knowledge (IK) surrounding concerns about these populations over time. Using ~9,000 SNPs, genomic metrics included changes in population structure, neutral genomic diversity, effective population size, and signatures of selection. Indigenous knowledge revealed overall reductions in body size and number of fish caught. Smaller body size, a small reduction in size‐at‐age, nascent changes to population structure (population differentiation within one river and homogenization between two others), and signatures of selection between historical and contemporary samples reflected coupled phenotypic and genomic change in the three harvested populations in both sexes, while no change occurred in the reference population. Sex‐specific analyses revealed differences in both body size and genomic metrics but were inconclusive about whether one sex was disproportionately affected. Although alternative explanations cannot be ruled out, our collective results are consistent with the hypothesis that genetic changes associated with harvesting may arise within 1–2.5 generations in long‐lived wild fishes. This study thus demonstrates the need to investigate concerns about harvest‐induced evolution quickly once they have been raised.

In young temperate zone fishes, conflicting energy demands lead to variability in growing season and winter survival. Growing season survival is driven by size-dependent predation risk whereas winter survival is constrained by autumn body size, energy storage and winter duration. We developed a model of the seasonality of energetics coupled to empirical measures of resource availability, size-dependent predation and temperature seasonality for rainbow trout (Oncorhynchus mykiss) in two sets of lakes in British Columbia, Canada, representing endpoints of a gradient of temperature, growing season duration and winter duration. This model was used to determine the energy allocation strategy which maximized first-year survival across these gradients. Survival was sensitive to the timing of the switch from somatic to storage strategies in cold, short growing season, low resource environments. A broader range of energy allocation strategies were viable in warmer, longer growing season and higher resource lakes. We used empirical observations of autumn energy storage and our modeled values for size-dependent minimal lipid levels needed to survive winter in each system to estimate winter survival for juvenile rainbow trout. Winter survival estimates were 6% in cold lakes with low resources, 82% in warm, lakes with low resources and 100% in warm lakes with high resources. Fish in warm lakes with ample resources allocated substantially more to storage than the minimum required to survive winter generated from our model, suggesting additional selection pressures for increased storage when there was ample surplus energy. We concluded that growth-survival trade-offs, modified by seasonality of the environment, influenced the growing season energy allocation strategies for young-of-the-year fish, and suggested this may be important for understanding population viability across environmental gradients.

Catch-and-release regulations designed to protect fisheries may fail to halt population declines, particularly in situations where fishing effort is high and when multiple stressors threaten a population. We demonstrate this claim using Alberta’s Bow River, which supports a high-effort rainbow trout (Oncorhynchus mykiss) fishery where anglers voluntarily release >99% of their catch. We examined the population trend of adult trout, which were tagged and recaptured using electrofishing surveys conducted intermittently during 2003–2013. We constructed Bayesian multisession capture–recapture models in Stan to obtain abundance estimates for trout and regressed trend during two periods to account for variation in sampling locations. General patterns from all models indicated the population declined throughout the study. Potential stressors to this system that may have contributed to the decline include whirling disease (Myxobolus cerebralis), which was detected for the first time in 2016, notable floods, and release mortality. Because disease and floods are largely uncontrollable from a management perspective, we suggest that stringent tactics such as angler effort restrictions may be necessary to maintain similar fisheries.

We contrast catchability of walleye (Sander vitreus) and northern pike (Esox lucius) populations with angling fisheries across regions that differ twofold in growing-degree-days and productivity and sixfold in fish diversity. Populations of both species in Alberta, Wisconsin, Minnesota, and Oneida Lake, New York, had density-dependent catchability with approximately tenfold higher catchability in Alberta than in the other regions when density was controlled for. There is no evidence that the higher catchability estimates for Alberta walleye and northern pike are due to differential spatial distributions, enhanced hook avoidance due to catch and release or to differential size structure of the populations, or to differences in harvest regulations. We argue that the most likely explanation for the tenfold higher catchability is increased hunger resulting in enhanced foraging activity in the region with a substantially shorter growing season, lower prey productivity, and lower prey community diversity. Regardless of the proximate causes, higher catchability of fish harvested in recreational fisheries in Alberta substantially increases their vulnerability to overharvest and collapse if angling effort is unabated.Résumé : Nous comparons la capturabilité de populations de doré jaune (Sander vitreus) et de grand brochet (Esox lucius) dans la pêche sportive dans diverses régions présentant des différences du simple au double du nombre de degrés-jour de croissance et de la productivité, et du simple au sextuple en ce qui concerne la diversité des poissons. Des populations des deux espèces en Alberta, au Wisconsin, au Minnesota et dans le lac Oneida (New York) présentaient des capturabilités dépendantes de la densité, celle de l'Alberta étant environ dix fois supérieure à celles des autres régions quand la densité était prise en considération. Aucune observation ne porte à croire que les estimations de capturabilité plus élevées pour les dorés jaunes et les grands brochets en Alberta découlent de répartitions différentielles, d'un plus grand évitement des hameçons en raison de la pêche avec remise à l'eau, de différences sur le plan de la structure de tailles des populations ou de différences touchant à la réglementation des prises. Nous postulons que l'explication la plus vraisemblable pour la capturabilité dix fois plus élevée en Alberta est la faim plus intense se traduisant par une activité de quête de nourriture accrue dans cette région caractérisée par une période de croissance sensiblement moins longue, la productivité plus faible des proies et la plus faible diversité des communautés de proies. Quelles qu'en soient les causes immédiates, à défaut d'une réduction de l'effort de pêche sportive, la plus grande capturabilité des poissons visés par cette pêche en Alberta accroît considérablement leur vulnérabilité à la surexploitation et à l'effondrement. [Traduit par la Rédaction]