Search

In the past four decades, summer flounder (Paralichthys dentatus) abundance in the Northwest Atlantic shifted with no definitive explanation for this shift. Here, we extract patterns in population-level size variability from summer flounder mean length-at-age data from 1992 to 2015 using an autoregressive state-space modeling approach and annual fishing and oceanographic covariates. We found that summer flounder length-at-age varies annually, suggesting that productivity can vary annually due to variable sizes. We found that location and depth of the observed fish, exploitation, and the Gulf Stream appeared to influence the magnitude of length-at-age variation, whereby lengths-at-age were above the mean length at greater depth, northern latitudes, and during periods characterized by a northerly Gulf Stream position or higher fishing exploitation. These factors should be considered as indicators to track size and more accurately understand productivity as the summer flounder population changes and the fishery adapts in response. This study brings us closer to annual proxies for summer flounder length-at-age variation, an important tool for fisheries managers and stock-assessment scientists to more accurately predict fish stock abundances and productivity. Au cours des quatre dernieres decennies, l'abondance du cardeau d'ete (Paralichthys dentatus) dans le nord-ouest de l'ocean Atlantique a change sans que cela puisse etre explique de maniere definitive. Nous extrayons des motifs de variabilite des tailles a l'echelle de la population de donnees sur la longueur moyenne selon l'age de cardeaux d'ete pour la periode de 1992 a 2015 en utilisant une approche de modelisation d'espace d'etats autoregressive et des covariables annuelles relatives a la peche et aux conditions oceanographiques. Nous constatons que la longueur selon l'age des cardeaux d'ete presente des variations annuelles, donnant a penser que la productivite peut varier annuellement en raison de la variabilite des tailles. Nous relevons que l'emplacement et la profondeur des poissons observes, l'exploitation et le Gulf Stream semblent influer sur la magnitude des variations des longueurs selon l'age, ces dernieres etant superieures a la longueur moyenne a plus grande profondeur, a haute latitude et durant des periodes caracterisees par le deplacement vers le nord du Gulf Stream ou une plus forte exploitation par peche. Ces facteurs devraient etre pris en compte comme indicateurs pour suivre les variations des tailles et etablir une comprehension plus exacte de la productivite au fil des variations des populations de cardeaux d'ete et de l'adaptation des peches a ces variations. L'etude est un pas vers l'etablissement de variables substitutives annuelles pour decrire les variations de la longueur selon l'age des cardeaux d'ete, qui constituent, pour les gestionnaires des peches et les chercheurs s'interessant a l'evaluation des stocks, un important outil pour predire avec plus d'exactitude l'abondance et la productivite de stocks de poissons. [Traduit par la Redaction], Introduction Fluctuations in fish productivity occur due to variability in demographic processes, including recruitment, mortality, and somatic growth. It is often difficult to disentangle the effects of these sources of [...]

Forage fish support the largest fisheries in the world but also play key roles in marine food webs by transferring energy from plankton to upper trophic-level predators, such as large fish, seabirds, and marine mammals. Fishing can, thereby, have far reaching consequences on marine food webs unless safeguards are in place to avoid depleting forage fish to dangerously low levels, where dependent predators are most vulnerable. However, disentangling the contributions of fishing vs. natural processes on population dynamics has been difficult because of the sensitivity of these stocks to environmental conditions. Here, we overcome this difficulty by collating population time series for forage fish populations that account for nearly two-thirds of global catch of forage fish to identify the fingerprint of fisheries on their population dynamics. Forage fish population collapses shared a set of common and unique characteristics: high fishing pressure for several years before collapse, a sharp drop in natural population productivity, and a lagged response to reduce fishing pressure. Lagged response to natural productivity declines can sharply amplify the magnitude of naturally occurring population fluctuations. Finally, we show that the magnitude and frequency of collapses are greater than expected from natural productivity characteristics and therefore, likely attributed to fishing. The durations of collapses, however, were not different from those expected based on natural productivity shifts. A risk-based management scheme that reduces fishing when populations become scarce would protect forage fish and their predators from collapse with little effect on long-term average catches.

Understanding demographic variation in recruitment and somatic growth is key to improving our understanding of population dynamics and forecasting ability. Although recruitment variability has been extensively studied, somatic growth variation has received less attention, in part because of difficulties in modeling growth from individual size-at-age estimates. Here we develop a Bayesian state-space approach to test for the prevalence of alternative forms of growth rate variability (e.g., annual, cohort-level, or in the first year recruited to the fishery) in size-at-age data. We apply this technique to 29 Pacific groundfish species across the California Current, Gulf of Alaska, and Bering Sea--Aleutian Islands marine ecosystems. About 40% of modeled stocks were estimated to exhibit temporal growth variation. In the majority of stocks, growth trends fluctuated annually across ages in a single year, suggesting that either there are shared environmental features that dictate growth across multiple ages or the presence of some systematic (within-year) observation errors. This method represents a novel way to use size-at-age data from fishery or other sources to test hypotheses about growth dynamics variability. La comprehension des variations demographiques du recrutement et de la croissance somatique est centrale a l'amelioration de la comprehension et de la capacite de prevision de la dynamique des populations. Si la variabilite du recrutement a fait l'objet de nombreuses etudes, celle de la croissance somatique a recu moins d'attention, en raison notamment des difficultes que presente la modelisation de la croissance a partir d'estimations de la taille selon l'age. Nous presentons une approche bayesienne d'espaces d'etat pour evaluer la prevalence de differentes formes de variabilite du taux de croissance (p. ex. annuelle, au niveau de la cohorte ou dans l'annee suivant le recrutement dans la ressource halieutique) dans les donnees de taille selon l'age. Nous avons applique cette technique a 29 especes de poissons de fond du Pacifique des ecosystemes marins du courant de Californie, du golfe d'Alaska et de la mer de Behring--des iles Aleoutiennes. Il est estime qu'environ 40 % des stocks modelises presentent des variations temporelles de la croissance. Dans la majorite des stocks, les tendances de croissance variaient annuellement selon le groupe d'ages dans une annee donnee, ce qui donne a penser qu'il existe des elements partages du milieu qui dictent la croissance selon l'age ou qu'il y a presence d'erreurs d'observation systematiques (durant une meme annee). La methode represente une nouvelle maniere d'utiliser les donnees de taille selon l'age tirees des peches ou d'autres sources pour verifier des hypotheses concernant la variabilite de la dynamique de croissance. [Traduit par la Redaction], Introduction Marine fish productivity varies because of fluctuations in demographic processes such as recruitment, mortality, and somatic growth. Therefore, quantifying causes of variability in these processes and corresponding effects on [...]

Understanding population fluctuations is a major goal of population ecology. In unpredictable marine environments, population variation is thought to be caused primarily by varying survival rates through a critical early life‐history stage. However, there is increasing evidence that somatic growth variation is common and causes population fluctuations.We examine the relative effects of empirically validated variability in somatic growth and recruitment on two response metrics across eight different life‐history archetypes of marine fish. We evaluate how much variation is propagated into mature biomass (MB), a proxy for population resilience, and population production, a measure of population rebuilding capacity. Production is defined as the biomass produced by the stock above what is needed to sustain the population at a constant level.We used empirical estimates of reproductive success and somatic growth rate, coupled with a population model, to evaluate the relative role of both types of variation in population fluctuations. The effects of this variation on population production and MB were examined across three variation scenarios, in which somatic growth only, reproduction only or both processes varied temporally. We also examined three levels of age truncation to explore whether modified population age structure altered these dynamics.The contribution of somatic growth to biomass variability exceeded that of recruitment for some species (2/8), while in others (5/8 species), recruitment variation was more influential. When population production was examined, somatic growth variation contributed more to population variation for three species. The relative importance of the two processes was not clearly correlated with key life‐history traits (i.e., growth and mortality rates), but instead was determined by time‐series characteristics of growth and recruitment variation. Increasing age truncation slightly increased the relative effect of recruitment variation on MB variation for three species.These results suggest somatic growth variation can be as important as early life‐history survival in driving population fluctuations in some marine fish species. This analysis provides a counterexample to the commonly held assumption of many marine population dynamics models: That population variability is induced primarily through variation in reproductive success. This paper overturns a commonly held perception that fish population stochasticity is caused primarily by recruitment variation, instead showing somatic growth variation can be equally influential for some species. [ABSTRACT FROM AUTHOR]

Consumers and regulators influence conservation of marine finfish by controlling harvest demand and availability. Consumer power to choose sustainably-harvested species is threatened by seafood mislabeling, which may be a product of fraud or human error. Here we examined the prevalence of mislabeling, and its financial and ecological implications, by compiling and analyzing an international dataset of DNA barcoding studies of marine finfish ( n = 43). On average, DNA-identified species sold were less expensive (−2.98% ex-vessel price) and more sustainable (+3.88% IUCN status) than species listed on their label; thus, mislabeling had a net positive impact on the conservation status of sold species. However, ecological impacts of some frequently mislabeled taxa were potentially severe, suggesting eco-conscious consumers may want to avoid certain genera. Mislabeling may be reduced by increasing traceability and identification of seafoods, particularly at points in the chain-of-custody beyond ports, where the majority of mislabeling occurred. [ABSTRACT FROM AUTHOR]