Search

Coastal hypoxia around the world has raised concerns about its sublethal effects on juvenile demersal fishes. We examined the growth rate of juvenile English sole (Parophrys vetulus) under 15 combinations of temperature and dissolved oxygen levels. We found interactive effects of temperature and hypoxia on fish growth. Fish exposed to moderate hypoxia and normoxia exhibited similar growth responses to increasing temperature; however, a threshold effect was evident under severe hypoxia, which caused a significant reduction in growth. Further, a generalized additive mixed model was applied to simulate fish growth off the Oregon coast during a climate transition from the 2009 El Nino to the 2010-2011 La Nina. Model simulations indicated that habitat quality varied significantly between estuarine (high quality) and coastal (low quality) nurseries. Coastal habitats may remain moderately suitable during El Nino years, while estuarine refuges are more preferred during La Nina years. This study contributes to the assessment of climate change and hypoxic disturbance on demersal fisheries by providing an analytical framework to evaluate synergistic temperature-hypoxia interactions on juveniles in their nursery habitats. L'hypoxie littorale partout sur terre suscite des inquietudes quant a ses effets subletaux sur les poissons demersaux juveniles. Nous examinons les taux de croissance de carlottins anglais (Parophrys vetulus) juveniles exposes a 15 combinaisons de temperature et de teneurs en oxygene dissous. Nous relevons des effets interactifs de la temperature et de l'hypoxie sur la croissance des poissons. La croissance de poissons exposes a une hypoxie moderee et a une normoxie reagit de maniere similaire a une hausse de temperature; un effet de seuil est toutefois evident en situation de forte hypoxie, qui entraine une baisse significative de la croissance. Un modele additif generalise mixte est en outre utilise pour simuler la croissance des poissons au large des cotes de l'Oregon durant la transition climatique de l'episode El Nino de 2009 a l'episode La Nina de 2010-2011. Des simulations du modele indiquent des differences significatives de qualite de l'habitat entre les aires de croissance estuariennes (de bonne qualite) et cotieres (de faible qualite). Les habitats cotiers pourraient demeurer moderement convenables durant les annees El Nino, alors qu'il y a une preference accrue pour des refuges estuariens durant les annees La Nina. L'etude est utile pour l'evaluation des effets des changements climatiques et des perturbations hypoxiques sur les ressources halieutiques demersales, car elle fournit un cadre analytique pour l'evaluation des effets d'interactions synergistes de la temperature et de l'hypoxie sur les poissons juveniles dans leurs habitats de croissance. [Traduit par la Redaction], Introduction Global expansion of coastal hypoxia (dissolved oxygen (DO) < 1.4 mL [O.sup.2] * [L.sup.-1]) has resulted in deleterious consequences to ecosystem functions and services (Chan et al. 2008; Ekau [...]

Changes to Earth's climate affect organisms globally; in marine systems, these impacts are seen through warming water temperatures, ocean acidification, hypoxia and frequent marine heatwaves. These effects may lead to the movement of species to more favourable conditions. While climate‐driven movement is well studied at the adult stage, how the early life stages of marine fish will respond to future variability is less clear. Many fish species are constrained by specific spawning locations or phenology. Spawning in certain locations allows for local retention of offspring, while precise timing can facilitate transport of offspring to nursery locations through seasonal circulation patterns. Our research investigates how changing oceans impact the location and timing of spawning of Bering Sea groundfishes over the next century. We used ROMS SST and SSS model output and NOAA survey data in species distribution models to hindcast and project distributions and centre of gravity for eggs and larvae of six groundfish species. Our analyses found that most of our study species exhibit flexible geography. However, the speed and direction of egg and larval movement did not track the speed and direction of their respective thermal niches. Hence, the projected distributional patterns of adult stages may be limited by their early life stages. This response is likely to be mirrored globally by other species with planktonic eggs and larvae. These results indicate that life history considerations are critical for the management of commercially important species, as effects on early life stages are strongly connected to the success or failure of adult populations. [ABSTRACT FROM AUTHOR]

Age composition is defined as the proportion of a fish population belonging to each age class and is an informative input to stock assessment models. Variations in somatic growth rates may lead to larger errors in age composition estimates. To reduce this source of error, we compared the performance of four methods for estimating age compositions of a simulated fish population: two methods based on age-length keys (ALK, pooled and annual) and two model-based approaches (generalized additive models (GAMs) and continuation ratio logits (CRLs)). CRL was the most robust and precise method, followed by annual ALKs, particularly when significant growth variability was present. We applied these methods to survey age subsample data for Pacific cod (Gadus macrocephalus) in the eastern Bering Sea, estimating age compositions that were then incorporated in its stock assessment model. The model that included age compositions estimated by CRL displayed the highest consistency with other data in the model. CRL approach has utility for estimating age compositions employed in stock assessment models, especially when substantial variation in somatic growth is present. La composition selon l'age designe la proportion d'une population de poissons appartenant a chaque classe d'age et constitue un intrant informatif dans les modeles d'evaluation de stocks. Des variations des taux de croissance somatique peuvent accroitre l'erreur associee aux estimations de la composition selon l'age. Pour reduire cette source d'erreur, nous avons compare la performance de quatre methodes d'estimation de la composition selon l'age d'une population de poissons simulee, dont deux methodes basees sur des cles age-longueur (CAL, regroupees et annuelles) et deux approches basees sur des modeles (modeles additifs generalises, ou MAGs, et modeles logistiques des cotes de continuite, ou MLCCs). La methode MLCC s'avere la plus robuste et precise, suivie des CAL annuelles, particulierement quand une variabilite significative de la croissance est presente. Nous avons applique ces methodes a des donnees d'evaluation sous-echantillonnees pour l'age pour la morue du Pacifique (Gadus macrocephalus) dans la mer de Behring orientale, pour estimer des compositions selon l'age qui ont ensuite ete incorporees dans le modele d'evaluation du stock de l'espece. Le modele qui comprend les compositions selon l'age estimees par MLCC presente la plus grande coherence avec d'autres donnees dans le modele. L'approche MLCC est utile pour estimer les compositions selon l'age employees dans les modeles d'evaluation de stocks, particulierement en presence de variations considerables de la croissance somatique. [Traduit par la Redaction], Introduction Marine fish populations inhabit a changing environment, where oceanographic, ecological, and fishery drivers affect vital rates, including somatic growth, sexual maturation, natural mortality, and spatial distribution (Gertseva et al. [...]

We tested the hypothesis that ocean temperature effects on productivity for northeast Pacific pink (Oncorhynchus gorbuscha), sockeye (Oncorhynchus nerka), and chum salmon (Oncorhynchus keta) changed after 1988-1989, coincident with a decline in Aleutian Low variance. Nonstationary temperature effects were tested with three different analytical methods (correlation, mixed-effects models, and variable coefficient generalized additive models) applied to spawner-recruit time series from 86 wild runs between Puget Sound and the northern Bering Sea. All three methods supported the hypothesis, with evidence for change in temperature effects that was strongest in the Gulf of Alaska, British Columbia, and Washington and weakest in the Bering Sea. Productivity for all three species showed generally positive responses to ocean temperature in Alaska before 1988-1989, but generally neutral responses after 1988-1989. British Columbia and Washington salmon showed either neutral responses to temperature (pink), negative responses that weakened after 1988-1989 (sockeye), or a switch from neutral to negative responses (chum). We conclude that the inverse response of Alaskan and more southern salmon populations to temperature variability is a time-dependent phenomenon. Nous avons teste l'hypothese selon laquelle les effets de la temperature de l'ocean sur la productivite des saumons roses (Oncorhynchus gorbuscha), sockeye (Oncorhynchus nerka) et keta (Oncorhynchus keta) du nord-est de l'ocean Pacifique ont change apres 1988-1989, coincidant avec une diminution de la variance de la depression des Aleoutiennes. La presence d'effets non stationnaires de la temperature a ete verifiee par trois methodes analytiques differentes (correlation, modeles a effets mixtes et modeles additifs generalises a coefficients variables) appliquees a des series chronologiques geniteurs-recrues pour 86 migrations de saumons sauvages du Puget Sound a la mer de Behring septentrionale. Les trois methodes appuient l'hypothese, les indices de variations des effets de la temperature etant les plus importants pour le golfe d'Alaska, la Colombie-Britannique et l'Etat de Washington, et les plus faibles pour la mer de Behring. La productivite des trois especes presentait des reactions generalement positives a la temperature de l'ocean en Alaska avant 1988-1989, mais des reactions generalement neutres par la suite. Les saumons de la Colombie-Britannique et l'Etat de Washington presentaient des reactions a la temperature soit neutres (roses), negatives et diminuant apres 1988-1989 (sockeye) ou une transition de reactions neutres a negatives (keta). Nous concluons que les reactions inverses des populations de l'Alaska et des populations plus au sud a la variabilite de la temperature constituent un phenomene dependant du temps. [Traduit par la Redaction], Introduction The Pacific Decadal Oscillation (PDO) was first recognized in relation to inverse production regimes between Pacific salmon (Onchorynchus spp.) in Alaska and more southern areas (Mantua et al. 1997; [...]

Scientific surveys are widely used for stock assessment, but the estimated population parameters are based on the size-at-age relationship and age structure derived from a small subsample of the catch that is aged. This calls for an assessment of subsampling strategies, especially when population's life history traits are spatially structured. In the Eastern Bering Sea, Pacific cod (Gadus macrocephalus) size and age are spatially structured, with younger and smaller individuals being more abundant at shallower depths. We conducted parallel subsamplings during Pacific cod surveys to compare two contrasting subsampling strategies: length-stratified and random. Geographical heterogeneity of Pacific cod length resulted in divergent estimates of ages between subsampling strategies. When this spatial variability was taken into account to estimate population parameters, random strategy provided more accurate mean and modal size-at-age and estimated age structure. Bias in the length-stratified subsampling arises from the poor efficacy in capturing the geographical patterns of size observed in the population. However, combining age data samples from multiple years helps to minimize the divergences between the two strategies. Des releves scientifiques sont abondamment utilises pour l'evaluation de stocks, mais les parametres demographiques estimes reposent sur la relation de la taille selon l'age et la structure d'ages obtenues a partir d'un petit sous-ensemble des prises pour lesquelles les ages ont ete determines. Il convient donc d'evaluer les strategies de sous-echantillonnage utilisees, particulierement dans les cas ou des caracteres associes au cycle biologique dans une population presentent une structure spatiale. Dans la partie orientale de la mer de Behring, les tailles et les ages des morues du Pacifique (Gadus macrocephalus) sont structures dans l'espace, les individus plus jeunes et plus petits etant plus abondants a plus faibles profondeurs. Nous avons realise des sous-echantillonnages paralleles durant des releves de morues du Pacifique pour comparer deux strategies de sous-echantillonnage distinctes, soit une approche stratifiee selon la longueur et une approche aleatoire. L'heterogeneite geographique de la longueur des morues du Pacifique se traduit par des estimations divergentes des ages obtenues par les differentes strategies. Quand cette variabilite spatiale est prise en compte dans l'estimation de parametres demographiques, la strategie aleatoire fournit des structures moyennes et modales de tailles selon l'age et une structure d'ages estimee plus exactes. Un biais dans les sousechantillons stratifies selon la longueur resulte de la faible capacite de rendre compte des motifs geographiques des tailles observes dans la population. L'utilisation d'echantillons combines de donnees sur l'age pour plusieurs annees aide toutefois a minimiser les differences entre les deux strategies. [Traduit par la Redaction], Introduction Scientific surveys are widely recognized as a primary source of data inherently less prone to population parameter bias and imprecision due to the standardization procedures. However, the high cost [...]

We investigate how the reproductive strategy in a migratory marine fish may be influenced by spatial variations in mortality in early life stages. In particular, we examine how spawning time and location affect offspring survival and growth. A drift model for early life stages (eggs to age 1) of the Barents Sea cod (Gadus morhua) is combined with empirical estimates of spatial variation in mortality at two different life stages. We examine seasonal and interannual differences in survival and growth in offspring originating from two spawning grounds, with the central site requiring higher migration distance, and hence cost, than the northern site. When accounting for spatially explicit mortality fields, central and northern spawned offspring have about equal survival, as do early and late spawned offspring. Furthermore, central spawned offspring grow faster and are likely to reach a larger size compared with northern spawned offspring. Our results indicate that the fitness benefit of southward migration in the Barents Sea cod is not mainly due to higher early survival of offspring, but rather due to effects of offspring acquiring a larger size. Nous examinons l'influence potentielle des variations spatiales de la mortalite aux premieres etapes du cycle de vie sur la strategie de reproduction chez un poisson marin migrateur. Nous nous penchons plus particulierement sur l'effet du moment et de lieu du frai sur la survie et la croissance de la progeniture. Un modele de derive pour les premieres etapes du cycle biologique (des oeufs a l'age de 1 an) de la morue (Gadus morhua) de la mer de Barents est combine a des estimations empiriques de la variation spatiale de la mortalite a deux etapes differentes du cycle de vie. Nous examinons les variations saisonnieres et interannuelles de la survie et de la croissance de progenitures issues de deux lieux de frai, un site central necessitant une plus grande distance de migration et donc un cout de migration plus important que l'autre site, plus septentrional. En tenant compte de champs de mortalite spatialement explicites, les progenitures issues des sites central et septentrional presentent des taux de survie a peu pres egaux, tout comme les progenitures produites vers le debut et la fin de la periode de frai. En outre, la progeniture issue du site central grandit plus rapidement et est plus susceptible d'atteindre de plus grandes tailles que la progeniture issue du site septentrional. Nos resultats indiquent que l'avantage sur le plan de l'aptitude que confere la migration vers le sud chez la morue de la mer de Barents ne decoule pas principalement d'un taux de survie precoce plus important de la progeniture, mais plutot des effets de l'atteinte d'une plus grande taille par la progeniture. [Traduit par la Redaction], Introduction Conditions experienced during early life stages may result in long-lasting effects on individuals and may have important implications at the population level (Metcalfe and Monaghan 2001; Beckerman et al. [...]