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Walleye (Sander vitreus) populations in Alberta, Canada, collapsed by the mid-1990s and were a case study in the paper Canada's Recreational Fisheries: The Invisible Collapse? Here we fit age-structured population dynamics models to data from a landscapescale monitoring program to assess walleye population status and reconstruct recruitment dynamics following the invisible collapse. Assessments indicated that populations featured low [F.sub.msy] values of approximately 0.2-0.3 under conservative assumptions for the stock-recruitment relationship but that many populations were lightly exploited during 2000-2018. Recruitment reconstructions showed that recovery from collapse in 33/55 lakes was driven in part by large positive recruitment anomalies that occurred during 1998-2002. Additionally, 15/55 lakes demonstrated cyclic recruitment dynamics. The documented recruitment anomalies and cyclic fluctuations could be due to environmental effect(s) or cannibalism, and experimentation is likely necessary to resolve this uncertainty. These findings contribute new information on the recovery dynamics of walleye following the invisible collapse and demonstrate the effectiveness of coupling traditional fisheries science models with broad-scale monitoring data to improve understanding of population dynamics and sustainability across landscapes. Au milieu des annees 1990, les populations de dore jaune (Sander vitreus) en Alberta (Canada) s'etaient effondrees, constituant une etude de cas dans l'article intitule Canada's Recreational Fisheries: The Invisible Collapse? Nous calons des modeles de dynamique de la population structures par age sur des donnees issues d'un programme de surveillance a l'echelle du paysage dans le but d'evaluer l'etat des populations de dore jaune et de reconstituer la dynamique du recrutement dans la foulee de l'effondrement invisible. Des evaluations indiquent que les populations presentent de faibles valeurs de [F.sub.msy] d'environ 0,2-0,3 pour des hypotheses prudentes concernant la relation de recrutement au stock, mais que de nombreuses populations ont ete legerement exploitees durant la periode de 2000 a 2018. Les reconstitutions du recrutement montrent que le retablissement suivant l'effondrement dans 33 lacs sur 55 etait partiellement mu par d'importantes anomalies positives du recrutement qui se sont produites durant la periode de 1998 a 2002. En outre, 15 lacs sur 55 presentaient une dynamique de recrutement cyclique. Les anomalies de recrutement et les fluctuations cycliques documentees pourraient etre dues a un ou des effets environnementaux ou au cannibalisme, et des experiences sont probablement necessaires pour lever cette incertitude. Ces constatations fournissent de nouveaux renseignements sur la dynamique du retablissement du dore jaune dans la foulee de l'effondrement invisible et demontrent l'efficacite du jumelage de modeles traditionnels issus des sciences halieutiques a des donnees de surveillance a grande echelle pour ameliorer la comprehension de la dynamique et de la perennite des populations a l'echelle du paysage. [Traduit par la Redaction], Introduction The invisible collapse of inland recreational fisheries is among the most influential papers published in fisheries science (hereinafter 'invisible collapse'; Post et al. 2002 in Sass and Allen 2014). [...]

We develop a mechanistically motivated von Bertalanffy growth model to estimate growth rate and its predictors from spatial-temporal data and compare this model's performance with a suite of commonly used mixed-effects growth models. We test these models with simulated data and then apply them to test whether concerns that high density is causing growth suppression of walleye (Sander vitreus) in Alberta, Canada, are supported using data collected during 2000-2017. Simulation experiments demonstrated that models that failed to account for complex dependency structures often resulted in growth rate estimates that were less accurate and biased low as judged by median absolute relative error and median relative error, respectively. The magnitude of this bias depended on the parameter values used for simulation. For the case study, a spatial-temporal model was more parsimonious and had higher predictive performance relative to simpler models and did not support the slow-growing walleye hypothesis in Alberta. These findings demonstrate the importance of considering spatial-temporal correlation in analyses that rely on surveillance-style monitoring datasets, particularly when examining relationships between life-history traits and environmental characteristics. Nous developpons un modele de croissance de von Bertalanffy a relations mecanistes pour estimer le taux de croissance et ses variables predictives a partir de donnees spatiotemporelles et comparons la performance de ce modele a une serie de modeles de croissance a effets mixtes couramment utilises. Nous mettons ces modeles a l'essai en utilisant des donnees simulees et les appliquons ensuite pour verifier si des donnees recueillies de 2000 a 2017 appuient l'interpretation proposee qu'une forte densite causerait une suppression de la croissance de dores jaunes (Sander vitreus) en Alberta (Canada). Des experiences de simulation demontrent que les modeles qui ne tiennent pas compte de structures de dependance complexes produisent souvent des estimations des taux de croissance moins exactes et biaisees vers le bas, comme indique par l'erreur relative mediane absolue et l'erreur relative mediane, respectivement. La magnitude de ce biais depend des valeurs des parametres utilisees pour la simulation. Pour l'etude de cas, un modele spatiotemporel s'avere plus parcimonieux et presente une meilleure performance predictive que les modeles plus simples et n'appuie pas l'hypothese des dores a croissance lente en Alberta. Ces resultats demontrent l'importance de tenir compte des correlations spatiotemporelles dans les analyses qui reposent sur des ensembles de donnees de type surveillance, en particulier pour l'examen des relations entre des caracteres du cycle biologique et des caracteristiques du milieu ambiant. [Traduit par la Redaction], Introduction Inland recreational fisheries are embedded in complex social-ecological systems (see Carruthers et al. 2019), generate ~US$51 billion * [year.sup.-1] in North America (Funge-Smith 2018), and support important ecosystem services [...]

Pinniped populations around the world increased rapidly after hunting and culling during the nineteenth and twentieth centuries ended. Some believe that pinnipeds are now preventing the recovery of certain fish populations, and that controlling pinniped population abundance using lethal measures such as harvesting or by non‐lethal means like contraception could recover fish populations. It is unclear, however, how effective and how long it would take for such methods of population control to bring numbers of pinnipeds down to target levels. We used sex‐ and age‐structured population models to estimate how quickly harbor seal (Phoca vitulina) abundance in British Columbia, Canada, could be reduced by 50%, through combinations of lethal removals and sterilization of adult females. Models were fit to seal abundance, demographic, and harvest data collected between 1879 and 2014. Simulation modeling suggests reliance on contraception exclusively is unlikely to reduce the current harbor seal population (numbering ~100,000) by 50% within 25 years, and would result in more variable outcomes, compared to lethal removals. Contraception could be combined with harvesting to maintain a target abundance of harbor seals (although captive studies with harbor seals are needed to confirm the efficacy of contraception). Our simulation modeling approach provides a useful framework to assess how non‐lethal measures could be integrated into policies that promote active population control of harbor seal numbers. [ABSTRACT FROM AUTHOR]

Predation risk and competition among conspecifics significantly affect survival of juvenile salmon, but are rarely incorporated into models that predict recruitment in salmon populations. Using densities of harbour seals (Phoca vitulina) and numbers of hatchery-released Chinook salmon (Oncorhynchus tshawytscha) smolts as covariates in spatially structured Bayesian hierarchical stock-recruitment models, we found significant negative correlations between seal densities and productivity of Chinook salmon for 14 of 20 wild Chinook populations in the Pacific Northwest. Changes in numbers of seals since the 1970s were associated with a 74% decrease (95% CI: -85%, -64%) in maximum sustainable yield in Chinook stocks. In contrast, hatchery releases were significantly correlated with Chinook productivity in only one of 20 populations. Our findings are consistent with recent research on predator diets and bioenergetics modeling that suggest there is a relationship between harbour seal predation on juvenile Chinook and reduced marine survival in parts of the eastern Pacific. Forecasting, assessment, and recovery efforts for salmon populations of high conservation concern should thus consider including biotic factors, particularly predatorprey interactions. Le risque de predation et la concurrence entre individus d'une meme espece ont une incidence significative sur la survie des saumons juveniles, mais sont rarement integres dans les modeles qui predisent le recrutement dans les populations de saumons. En utilisant la densite de phoques communs (Phoca vitulina) et le nombre de saumoneaux relaches d'ecloseries comme covariables dans des modeles bayesiens hierarchiques spatialement structures de recrutement au stock, nous avons constate la presence de correlations negatives significatives entre la densite de phoques et la productivite de saumons quinnats (Oncorhynchus tshawytscha) pour 14 des 20 populations de saumons quinnats sauvages dans le Pacific Northwest. Des variations des nombres de phoques depuis les annees 1970 sont associees a une baisse de 74 % (IC a 95 % : -85 %, -64 %) du rendement equilibre maximal dans les stocks de saumons quinnats. En revanche, le nombre de saumoneaux relaches d'ecloseries n'est significativement correle a la productivite des saumons quinnats que dans 1 des 20 populations. Nos constatations concordent avec celles de travaux recents sur les regimes alimentaires de predateurs et la modelisation bioenergetique qui donnent a penser qu'il existe une relation entre la predation de saumons quinnats juveniles par les phoques communs et une survie en mer reduite dans certaines parties de l'est de l'ocean Pacifique. La prediction, l'evaluation et les efforts de retablissement de populations de saumons dont la conservation est tres preoccupante devraient donc integrer des facteurs biotiques, en particulier les interactions predateurs-proies. [Traduit par la Redaction], Introduction The abundance of predators and intensity of competition within a spatial arena give rise to risks associated with foraging activities that may ultimately affect the survival rates of juvenile [...]

Most stocks of Atlantic cod (Gadus morhua) in the Northwest Atlantic collapsed in the early 1990s, with little sign of recovery since then. In the southern Gulf of St. Lawrence (sGSL), the failed recovery is due to severe increases in the natural mortality of adult Atlantic cod. We examined the role of predation by grey seals (Halichoerus grypus) in this failed recovery by directly incorporating grey seal predation in the population model for Atlantic cod via a functional response. Estimated predation mortality of adult Atlantic cod increased sharply during the cod collapse and has continued to increase, comprising the majority of mortality since the late 1990s. While predation by grey seals appeared to play a minor role in the collapse of Atlantic cod, we found it to be the main factor preventing recovery. Our results are consistent with the hypothesis that failed recovery is due to predation-driven Allee effects, a demographic effect due to the decline in cod abundance and an emergent effect resulting from increasing grey seal abundance. Under current conditions, extirpation of sGSL Atlantic cod appears likely unless there is a large decline in the abundance of grey seals.La plupart des stocks de morue (Gadus morhua) dans le nord-ouest de l'ocean Atlantique se sont effondres au debut des annees 1990, montrant peu d'indices de retablissement depuis. Dans la partie sud du golfe du Saint-Laurent (sGSL), cette absence de retablissement est due a d'importantes augmentations de la mortalite naturelle des morues adultes. Nous examinons le role de la predation par les phoques gris (Halichoerus grypus) dans ce processus en incorporant directement cette predation dans le modele demographique pour la morue sous la forme d'une reaction fonctionnelle. La mortalite par predation estimee des morues adultes a connu une augmentation marquee durant l'effondrement des stocks de morue et continue d'augmenter, expliquant la majorite de la mortalite depuis la fin des annees 1990. Si la predation par les phoques gris semble avoir joue un role limite dans l'effondrement de la morue, nous constatons qu'il s'agit du principal facteur empechant son retablissement. Nos resultats concordent avec l'hypothese voulant que l'absence de retablissement soit due a des effets d'Allee induits par la predation, un effet demographique decoulant de la baisse d'abondance des morues et un effet emergent decoulant de l'abondance croissante des phoques gris. Dans les conditions actuelles, la disparition de la morue du sGSL semple probable a moins d'une importante diminution de l'abondance des phoques gris. [Traduit par la Redaction], IntroductionMost stocks of Atlantic cod (Gadus morhua) in the Northwest Atlantic collapsed to very low levels of abundance in the late 1980s and early 1990s. Since then, abundance of these [...]

We introduce a Lagrangian movement model that can be used to characterize cyclic migrations of iteroparous fish populations. We demonstrate how movement parameters can be estimated using conventionally available catch-at-age data and provide a description of the potential bias that may arise from model misspecification, data aggregation, and nonstandardized sampling effort. The model can be extended to incorporate covariates representing biological and environmental forces that alter the distribution and migration range of exploited populations. We expect that this movement model will be a useful tool to model fish migration, to illustrate how fisheries dynamics are affected by fish migration, and to be used as an operating model in closed loop simulations to test the robustness of management frameworks to spatial structure and connectivity. Nous presentons un modele de deplacement lagrangien qui peut etre utilise pour caracteriser les migrations cycliques de populations de poissons iteropares. Nous montrons comment des parametres de deplacement peuvent etre estimes en utilisant des donnees generalement disponibles de capture selon l'age et presentons une description du biais potentiel qui peut decouler de la mauvaise definition de parametres du modele, du regroupement de donnees et d'un effort d'echantillonnage non normalise. Le modele peut etre elargi pour y inclure des covariables representant des forces biologiques et environnementales qui modifient la repartition et l'aire de migration de populations exploitees. Nous nous attendons a ce que ce modele de deplacement soit utile pour modeliser la migration de poissons et illustrer l'incidence de cette migration sur la dynamique des peches et qu'il pourrait etre utilise comme modele operatoire dans des simulations en boucle fermee pour evaluer la robustesse de cadres de gestion quand il y a presence de structure ou de connectivite spatiale. [Traduit par la Redaction], Introduction Two of the main drivers of cyclic migration in marine fish species are seasonal availability of food and spawning behavior (Walters and Martell 2004). In many iteroparous species, these [...]