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Spatial and temporal synchrony in abundance or survival trends can be indicative of whether populations are affected by common environmental drivers. In Atlantic salmon (Salmo salar), return rates to natal rivers have generally been assumed to be affected primarily by shared oceanic conditions, leading to spatially synchronous trends in mortality. Here, we investigated the existence of parallel trends in salmon sea survival, using data on migrating smolts and returning adults from seven Canadian populations presumed to share feeding grounds. We analysed sea survival, using a Bayesian change-point model capable of detecting nonstationarity in time series data. Our results indicate that while salmon have experienced broadly comparable patterns in survival, finer-scale temporal shifts are not synchronous among populations. Our findings are not consistent with the hypothesis that salmon populations consistently share the same mortality-related stressors in the marine environment. Although populations may have shared greater synchrony in survival patterns in the past, this synchrony may be breaking down. It may be prudent to direct greater attention to smaller-scale regional and population-level correlates of survival. Le synchronisme spatial et temporel des tendances d'abondance ou de survie peut indiquer si differentes populations sont influencees par les memes facteurs environnementaux. Il est generalement presume que, chez les saumons atlantiques (Salmo salar), les taux de retour aux rivieres natales sont principalement influences par des conditions oceaniques communes, ce qui mene a des tendances de mortalite synchrones dans l'espace. Nous examinons l'existence de tendances paralleles de survie en mer des saumons en utilisant des donnees sur les saumoneaux migrants et les adultes retournant dans leur riviere natale de sept populations canadiennes presumees avoir les memes aires d'alimentation. Nous analysons la survie en mer en utilisant un modele bayesien de points de changement pouvant detecter la presence de non-stationnarite dans les donnees de series chronologiques. Nos resultats indiquent que, bien que les saumons presentent des motifs de survie generalement semblables, des changements temporels a echelle plus fine ne sont pas synchrones d'une population a l'autre. Nos resultats ne concordant pas avec l'hypothese voulant que les populations de saumons aient toujours en commun les memes facteurs de stress relies a la mortalite dans le milieu marin. Si les motifs de survie des populations peuvent avoir presente un plus grand synchronisme par le passe, ce synchronisme pourrait etre en train de s'effriter. Il peut etre prudent d'accorder plus d'attention aux correlats de la survie a des echelles regionales ou populationnelles plus fines. [Traduit par la Redaction], 1. Introduction The viability of a species depends on the resistance and resilience of its constituent populations to natural and human-induced environmental change. Reduced viability reflects reductions in the abundance [...]

Trophic cascade studies often rely on linear food chains instead of complex food webs and are typically measured as biomass averages, not as biomass variation. We study trophic cascades propagating across a complex food web including a measure of biomass variation in addition to biomass average. We examined whether different fishing strategies induce trophic cascades and whether the cascades differ from each other. We utilized an allometric trophic network (ATN) model to mechanistically study fishing-induced changes in food web dynamics. Different fishing strategies did not trigger traditional, reciprocal trophic cascades, as measured in biomass averages. Instead, fishing triggered a variation cascade that propagated across the food web, including fish, zooplankton and phytoplankton species. In fisheries that removed a large amount of top-predatory and cannibalistic fish, the biomass oscillations started to decrease after fishing was started. In fisheries that mainly targeted large planktivorous fish, the biomass oscillations did not dampen but slightly increased over time. Removing species with specific ecological functions might alter the food web dynamics and potentially affect the ecological resilience of aquatic ecosystems. Les etudes de cascades trophiques reposent souvent sur des chaines alimentaires lineaires plutot que sur des reseaux trophiques complexes, ainsi que sur des mesures de la biomasse moyenne, plutot que des variations de la biomasse. Nous etudions la propagation de cascades trophiques a travers un reseau trophique complexe en integrant une mesure de la variation de la biomasse en plus de la moyenne de cette derniere. Nous tentons de determiner si differentes strategies de peche induisent des cascades trophiques et si ces dernieres different les unes des autres. Nous utilisons un modele de reseau trophique allometrique (RTA) pour etudier de maniere mecaniste les modifications induites par la peche de la dynamique du reseau trophique. Differentes strategies de peche ne declenchent pas de cascades trophiques reciproques traditionnelles, telles que mesurees par la biomasse moyenne. La peche declenche plutot une cascade de variations qui se propage dans tout le reseau trophique, incluant des especes de poissons, de zooplancton et de phytoplancton. Dans les peches qui prelevent une grande quantite de poissons cannibales et predateurs de niveau superieur, les oscillations de la biomasse commencent a diminuer apres le debut de la peche. Dans les peches qui ciblent principalement de grands poissons planctonivores, les oscillations de la biomasse ne s'attenuent pas, mais augmentent plutot legerement au fil du temps. Le retrait d'especes ayant des fonctions ecologiques precises pourrait modifier la dynamique des reseaux trophiques et avoir une incidence sur la resilience ecologique des ecosystemes aquatiques. [Traduit par la Redaction], Introduction The widespread importance of trophic cascades ('indirect species interactions that originate with predators and spread downward through food webs' sensu Ripple et al. 2016) has become increasingly recognized since [...]

Animals with different life‐history types vary in their stress‐coping styles, which can affect their fitness and survival in changing environments. We studied how chronic exposure to manganese sulfate (MnSO4), a common aquatic pollutant, affects life‐history traits, physiology, and behavior of zebrafish (Danio rerio) with two life‐history types: fast (previously selected for fast juvenile growth, early maturation, and small adult body size) and slow life histories (selected for slow juvenile growth, late maturation, and large adult body size). We found that MnSO4 had negative effects on growth and condition factors, but the magnitude of these effects depended on the life‐history type. Individuals with fast life histories were more susceptible to MnSO4 than fish with slow life histories as they had lower growth rate, condition factor and feeding probability in high MnSO4 concentrations. Our results demonstrate that MnSO4 can impair fish performance, and life‐history variation can modulate the stress‐coping ability of individuals. Animals with different life‐history types vary in their stress‐coping styles, which can affect their fitness and survival in changing environments. We found that MnSO4 had negative effects on growth and condition factors, but the magnitude of these effects depended on the life‐history type. Individuals with fast life histories were more susceptible to MnSO4 than fish with slow life histories as they had lower growth rate, condition factor and feeding probability in high MnSO4 concentrations. [ABSTRACT FROM AUTHOR]

Key life‐history data, such as growth and age, are necessary to effectively manage and conserve threatened freshwater mussel species. Traditionally growth and age studies require large yet destructive sample sizes covering all age classes. Such methods pose a risk to populations of conservation concern, and therefore, alternative methods that need only limited sample sizes are necessitated to prevent further threats to such populations. We applied retrospective shell growth at age reconstructions to 98 critically endangered freshwater pearl mussel (FPM) individuals from 34 populations across Finland and Sweden, enabling the use of extremely small sample sizes (n = 1–6 per population). We compared the performance of six different growth models with the reconstructed size‐at‐age data across FPM juvenile (<20 years old) and adult life stages. The growth reconstruction model showed reasonable skill in reconstructing FPM growth patterns. The von Bertalanffy model showed to be a good general descriptor of growth for FPM, but it systematically underestimated the asymptotic size. The power law model was the most accurate in estimating juvenile growth (lowest deviances from the size‐at‐age data). FPM showed great variability in longevity (Amax = 54–254 years) and growth constant k (0.018–0.057 year−1). Our results show that reasonable estimates of growth can be attained even when sample sizes are extremely limited. The results can be further applied to gain knowledge on the population's age structure, size at maturation, and recovery potential. The methodology is applicable to other freshwater mussel species of conservation concern. [ABSTRACT FROM AUTHOR]

Many generalist predators, including fish, insects and mammals, temporarily focus on their search behaviour and can switch between prey species. Flexible and rapid behavioural plasticity enables a predator to forage optimally, as guided by search image formation and prey switching in response to changing prey abundances.More than half a century of studies have used Holling type III functional response to model the impact of this feeding behaviour on population dynamics, yet a mechanistic understanding for the pathway between individual behaviour and feeding rates remains poorly understood.To understand this common feeding behaviour, we developed three mechanistic models using first‐principles to provide direct derivations for the relationship between observed individual behaviour and feeding rates.The derived models yield three novel, generalised functional responses for predators characterised by prey switching and mutually exclusive feeding (i.e. feeding is limited to one prey species at a time). We show how these functional responses act as Holling type III response, and how they can be used to predict predators' diet compositions.Our results demonstrate that several behavioural forms of prey switching, as displayed in a wide range of predator species, consistently produce type III conforming functional responses. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Marine ecosystems can undergo regime shifts, which result in nonstationarity in the dynamics of the fish populations inhabiting them. The assumption of time-invariant parameters in stock-recruitment models can lead to severe errors when forecasting renewal ability of stocks that experience shifts in their recruitment dynamics. We present a novel method for fitting stockrecruitment models using the Bayesian online change point detection algorithm, which is able to cope with sudden changes in the model parameters. We validate our method using simulations and apply it to empirical data of four demersal fishes in the southern Gulf of St. Lawrence. We show that all of the stocks have experienced shifts in their recruitment dynamics that cannot be captured by a model that assumes time-invariant parameters. The detected shifts in the recruitment dynamics result in clearly different parameter distributions and recruitment predictions between the regimes. This study illustrates how stock-recruitment relationships can experience shifts, which, if not accounted for, can lead to false predictions about a stock's recovery ability and resilience to fishing. Les ecosystemes marins peuvent subir des changements de regime, entrainant une non-stationnarite de la dynamique des populations de poissons qu'ils renferment. L'hypothese de l'invariabilite dans le temps des parametres de modeles de recrutement au stock peut mener a de graves erreurs dans la prevision de la capacite de renouvellement de stocks caracterises par des changements de la dynamique de recrutement. Nous presentons une nouvelle methode de calage de modeles de recrutement au stock qui fait appel a un algorithme bayesien en ligne de detection de points de changement, capable d'integrer des changements brusques des parametres de modelisation. Nous validons la methode a l'aide de simulations et l'appliquons a des donnees empiriques pour quatre poissons demersaux du sud du golfe du Saint-Laurent. Nous demontrons que tous les stocks ayant subi des changements de dynamique du recrutement ne peuvent etre representes par un modele reposant sur l'hypothese de parametres invariables dans le temps. Les changements detectes de la dynamique de recrutement se traduisent par des differences evidentes des distributions de parametres et predictions du recrutement entre les regimes. L'etude illustre les changements qui peuvent caracteriser les relations de recrutement au stock qui, s'ils ne sont pas pris en consideration, peuvent mener a de fausses predictions concernant la capacite de retablissement et la resilience a la peche d'un stock. [Traduit par la Redaction], Introduction Reproduction forms a vital link between current and future generations. The sustainability of fishing is largely attributable to the ability of a fish stock to renew itself such that [...]

Barriers to migration can negatively affect population persistence. To explore how dams can influence the viability of a diadromous fish, we developed an empirically based stochastic model to estimate per-capita population growth rate (r) and probability of population decline (Pr(r < 0)). Our simulations incorporated life-history parameters common for many populations of Atlantic salmon (Salmo salar L., 1758), particularly in the southern part of the species range. Additionally, we explored the influence of individuals that reproduce more than once, i.e., 'kelts', on r and Pr(r < 0). For the life-history scenarios examined here, dams are forecast to negatively affect persistence, even at the comparatively high per- dam smolt survival rate of 90%. As the number of dams increases from one to four, the probability of negative population growth increases four-fold from 10% to 47%. Kelt survival rate, number of dams, and smolt dam-passage survival were all found to be significant factors in predicting population persistence. The present study suggests two primary conclusions: (1) dams are likely to have a negative influence on Atlantic salmon and (2) kelts can have considerable and positive influence on population viability. Our work provides compelling support for the hypothesis that mortality attributable to dam facilities can adversely affect survival, persistence, and recovery of depleted migratory fish populations. Key words: viability, migration barrier, life history, per-capita growth, kelt. Les obstacles a la migration peuvent avoir une incidence negative sur la persistance de populations. Afin d'explorer l'influence des barrages sur la viabilite d'un poisson anadrome, nous avons mis au point un modele stochastique base sur des donnees empiriques pour estimer le taux de croissance de la population par individu (r) et la probabilite d'une baisse de la population (Pr(r < 0)). Nos simulations integrent des parametres du cycle biologique qu'ont encommunde nombreuses populations de saumons atlantiques (Salmo salar L., 1758), particulierement dans la partie meridionale de l'aire de repartition de l'espece. Nous avons en outre explore l'influence des individus qui se reproduisent plus d'une fois, c'est-a -dire les ' charognards ', sur r et Pr(r < 0). Pour les scenarios de cycle biologique examines, il est predit que les barrages ont un effet negatif sur la persistance, meme a un taux de survie par barrage des saumoneaux relativement eleve de 90 %. L'augmentation du nombre de barrages d'un a quatre se traduit par la multiplication par quatre de la probabilite de croissance negative de la population, qui passe de 10 % a 47 %. Le taux de survie des charognards, le nombre de barrages et le taux de survie des saumoneaux apres le passage d'un barrage s'averent tous etre d'importants facteurs de prediction de la persistance de la population. Deux conclusions principales ressortent de l'etude, a savoir que (1) les barrages exercent probablement une influence negative sur le saumon atlantique et (2) les charognards exercent une influence considerable et positive sur la viabilite des populations. Ces travaux appuient l'hypothese voulant que la mortalite attribuable aux barrages ait une incidence negative sur la survie, la persistance et le retablissement de populations decimees de poissons migrateurs. [Traduit par la Redaction] Mots-cles : viabilite, obstacle a la migration, cycle biologique, croissance par individu, charognard., Introduction Threats to species persistence originate primarily as a result of human activity. Among the most prominent of these is anthropogenic habitat destruction or modification. Barriers to migratory species (e.g., [...]

Estimation of population abundances in the absence of good observational data are notoriously difficult, yet urgently needed for biodiversity conservation and sustainable use of natural resources. In the field of fisheries research, management regulations have long demanded population abundance estimates even if data available are sparse, leading to the development of a range of fish stock assessment methods designed for data-poor populations. Here, we present methods developed within the context of fisheries research that can be applied to conduct population abundance estimations when facing data-limitations. We begin the review from the less data-demanding approaches and continue with more data-intensive ones. We discuss the advantages and caveats of these approaches, the challenges and management implications associated with data-poor stock assessments, and we propose the implementation of the Bayesian hierarchical framework as the most promising avenue for future development and improvement of the current practices. Key words: Bayesian statistics, conservation, data-poor stock assessment, small populations, sustainable harvesting. De facon notoire, l'estimation des abondances des populations en absence de donnees observees est difficile ; pourtant il y a un besoin urgent de telles estimations pour la conservation de la biodiversite et l'utilisation durable des ressources naturelles. Dans le domaine de recherche des pecheries, les reglements de gestion attendent depuis longtemps des estimes de l'abondance des populations, meme si les donnees disponibles sont clairsemees, conduisant au developpement d'une gamme de methodes d'evaluation des stocks de poissons, conques pour les populations en manque de donnees. Les auteures presentent des methodes developpees dans le contexte de la recherche en pecheries pouvant etre utilisees pour conduire des estimations d'abondance des populations, lorsque les donnees sont limites. Elles commencent la revue avec les approches demandant peu de donnees et continuent avec celles demandant plus de donnees. On discute des avantages et des mises en garde de ces approches et les defis des implications en amenagement, associes avec les estimations des stocks en manque de donnees puis on propose la mise en place du cadre hierarchique bayesien comme constituant l'avenue la plus prometteuse pour le developpement futur et l'amelioration des pratiques actuelles. [Traduit par la Redaction] Mots-cles : statistiques bayesiennes, conservation, estimation des stocks en manque de donnees, petites populations, recolte durable., Introduction Humans have been consistently depleting natural resources, for example, through habitat losses, environmental changes, and consumption. During the past two centuries, the growing human population has intensified the pressure [...]