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Mature thorny (Amblyraja radiata), winter (Leucoraja ocellata), and smooth (Malacoraja senta) skates have declined to very low abundance in the southern Gulf of St. Lawrence (SGSL) and on the eastern Scotian Shelf (ESS). We used stage-structured state-space models to examine decadal patterns in mortality rates in these skates. Mortality at early life stages (embryos in egg cases, hatchlings, and (or) small juveniles) appeared to decrease between the 1970s and the 2000s. In contrast, estimated mortality rates increased for larger individuals over this period. Although potentially confounded in models with effects of any changes in juvenile growth, the estimated increases in mortality could not instead be attributed solely to changes in growth. Increases in the mortality of large individuals appeared to reflect increases in natural mortality, possibly due to predation by grey seals. Increases in natural mortality were not evident for skates on the neighbouring western Scotian Shelf, where grey seal abundance has remained lower. Even in the absence of fishing, recovery of skates is unlikely under current ecosystem conditions in the SGSL and on the ESS. Les raies epineuses (Amblyraja radiata), tachetees (Leucoraja ocellata) et a queue de velours (Malacoraja senta) matures sont devenues tres peu abondantes dans le sud du golfe du Saint-Laurent (SGSL) et l'est du plateau neo-ecossais (ESS). Nous avons utilise des modeles d'espaces d'etats structures selon les etapes du cycle de vie afin d'examiner les patrons decennaux des taux de mortalite chez ces raies. La mortalite durant les premieres etapes du cycle de vie (embryons dans les capsules d'oeufs, alevins vesicules et petits juveniles) semble diminuer entre les annees 1970 et les annees 2000. En revanche, pour les individus plus grands, les taux de mortalite estimes ont augmente au cours de cette periode. Si, dans les modeles, les augmentations estimees de la mortalite peuvent potentiellement se confondre avec les effets de changements de la croissance des juveniles, elles ne peuvent toutefois etre entierement attribuees a de tels changements. Les augmentations de la mortalite des grands individus semblent refleter des augmentations de la mortalite naturelle possiblement dues a la predation par les phoques gris. Aucune augmentation claire de la mortalite naturelle n'a ete notee pour les raies de la partie ouest du plateau neo-ecossais, ou l'abondance des phoques gris est demeuree plus faible. Meme en l'absence de peche, un retablissement des raies est peu probable dans les conditions ecosystemiques actuelles dans le SGSL et le ESS. [Traduit par la Redaction], Introduction Elasmobranch fishes, especially the larger species, are considered to be among the most vulnerable fishes to exploitation because of their life-history characteristics, in particular late maturation, large adult size, [...]

Cusk (Brosme brosme) was designated as 'threatened' by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2003, based on an estimated 93% decline between 1970 and 2001 from the Fisheries and Oceans Canada (DFO) Scotian Shelf summer bottom trawl survey index. We combined this index with a fishery-dependent longline index in a Bayesian surplus production state-space model to estimate population trends and the recovery potential of western Scotian Shelf cusk. We tested for index nonproportionality using a power curve function in the observation model and identified potential hyperdepletion for cusk in the trawl survey index. We estimate a 59% decline in cusk biomass between 1970 and 2001, and a 64% decline from 1970 to 2007. Although population projections indicate the current landing limit should lead to population recovery, robustness tests suggest the biomass projections and recovery time lines are overly optimistic. Simulations showed that incorporating multiple indices increases power to recapture model parameters and failure to account for index nonproportionality results in biased parameter estimates. We suggest that nonproportionality of fishery-independent indices must be considered when determining the population status of data-poor species. Le brosme (Brosme brosme)aete designe espece menacee par le Comite sur la situation des especes en peril au Canada (COSEPAC/COSEWIC) en 2003 en se basant sur un declin estime de 93 % de 1970 a 2001 d'apres l'indice de l'inventaire par chalutage de fond en ete sur la plate-forme Neorecossaise de Peches et Oceans Canada (MPO/DFO). Nous combinons cet indice avec un indice base sur la peeche commerciale a la palangre dans un modele bayeesien etat-espace de production exceedentaire afin d'estimer les tendances de la population et le potentiel de recuperation des brosmes de l'ouest de la plate-forme Neo-ecossaise. Nous avons verifie l'absence de proportionnante de l'indice a l'aide d'une fonction de courbe de puissance dans le modele d'observation et avons decele un epuisement exagere dans l'indice base sur l'inventaire au chalut. Nous estimons un declin de 59 % de la biomasse des brosmes de 1970 a 2001 et un declin de 64 % de 1970 a 2007. Bien que les projections deemographiques indiquent que la limite actuelle des debarquements devrait permettre une recuperation de la population, des tests de robustesse montrent que les projections de biomasse et les echeanciers de recuperation sont trop optimistes. Des simulations revelent que l'incorporation de plusieurs indices augmente le pouvoir de recapture des parametres du modele et que la negligence de l'absence de proportionnante des indices entraine une erreur dans l'estimation des parametres. Nous suggerons qu'il est necessaire de tenir compte de l'absence de proportionnalite dans les indices indeependants de la pieche quand on determine le statut d'especes pour lesquelles on possede peu de donnees. [Traduit par la Redaction], Introduction Fisheries stock assessments are frequently based on data intensive population dynamics models, and thus are generally limited to the target species of large-scale commercial fisheries (Davis 2002; Kelly and [...]

Marine and freshwater ecosystems are increasingly at risk of large and cascading changes from multiple human activities (termed "regime shifts"), which can impact population productivity, resilience, and ecosystem structure. Pacific salmon exhibit persistent and large fluctuations in their population dynamics driven by combinations of intrinsic (e.g., density dependence) and extrinsic factors (e.g., ecosystem changes, species interactions). In recent years, many Pacific salmon have declined due to regime shifts but clear understanding of the processes driving these changes remains elusive. Here, we unpacked the role of density dependence, ecosystem trends, and stochasticity on productivity regimes for a community of five anadromous Pacific salmonids (Steelhead, Coho Salmon, Pink Salmon, Dolly Varden, and Coastal Cutthroat Trout) across a rich 40‐year time‐series. We used a Bayesian multivariate state‐space model to examine whether productivity shifts had similarly occurred across the community and explored marine or freshwater changes associated with those shifts. Overall, we identified three productivity regimes: an early regime (1976–1990), a compensatory regime (1991–2009), and a declining regime (since 2010) where large declines were observed for Steelhead, Dolly Varden, and Cutthroat Trout, intermediate declines in Coho and no change in Pink Salmon. These regime changes were associated with multiple cumulative effects across the salmon life cycle. For example, increased seal densities and ocean competition were associated with lower adult marine survival in Steelhead. Watershed logging also intensified over the past 40 years and was associated with (all else equal) ≥97% declines in freshwater productivity for Steelhead, Cutthroat, and Coho. For Steelhead, marine and freshwater dynamics played approximately equal roles in explaining trends in total productivity. Collectively, these changing environments limited juvenile production and lowered future adult returns. These results reveal how changes in freshwater and marine environments can jointly shape population dynamics among ecological communities, like Pacific salmon, with cascading consequences to their resilience. [ABSTRACT FROM AUTHOR]