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Fish recruitment is complex, regulated by environmental factors that induce high mortality early in life. Additionally, age-0 fish can be difficult to sample, making recruitment difficult to detect. We used a robust design occupancy model to evaluate the effects of biotic (age-0 and adult common carp (Cyprinus carpio), bluegill (Lepomis macrochirus), walleye (Sander vitreus), and northern pike (Esox lucius) relative abundance, prey availability, age-0 carp length) and abiotic (water level, temperature) factors on age-0 carp occupancy, detection, and extinction in 13 lakes in South Dakota, USA, for July-April 2008-2010. Age-0 carp occupancy decreased with increasing adult carp abundance and increased with increasing water levels. Age-0 carp detection probability was high during summer (>0.75) but decreased in fall and spring (0.34). Most lakes were occupied in July but overwinter extinction probability was high (59%), resulting in 51% occupancy probability by April. Other environmental factors were not supported, suggesting they had little effect on reproduction and survival. Our results indicate reproduction was universally successful but difficult to detect and that overwinter mortality often resulted in recruitment failure. Le recrutement de poissons est un phenomene complexe module par des facteurs environnementaux qui induisent une forte mortalite au debut du cycle de vie. L'echantillonnage de poissons d'age 0 peut en outre s'averer difficile, ce qui rend le recrutement difficile a detecter. Nous avons utilise un modele d'occupation a conception robuste pour evaluer les effets de facteurs biotiques (abondance relative de carpes communes (Cyprinus carpio), crapets arlequins (Lepomis macrochirus), dores jaunes (Sander vitreus) et grands brochets (Esox lucius) d'age 0 et adultes, disponibilite de proies, longueur des carpes d'age 0) et abiotiques (niveau d'eau, temperature) sur l'occupation, la detection et la disparition de carpes d'age 0 dans 13 lacs du Dakota du Sud (Etats-Unis), de juillet a avril 2008-2010. L'occupation de carpes d'age 0 diminuait avec l'augmentation de l'abondance de carpes adultes et augmentait a mesure qu'augmentaient les niveaux d'eau. La probabilite de detection de carpes d'age 0 etait forte durant l'ete (>0,75), mais diminuait a l'automne et au printemps (0,34). La plupart des lacs etaient occupes en juillet, mais la probabilite de disparition hivernale etait elevee (59 %), se traduisant par une probabilite d'occupation en avril de 51 %. Les modeles n'appuient pas d'autres facteurs environnementaux, donnant a penser que ces facteurs avaient peu d'effet sur la reproduction et la survie. Nos resultats indiquent un succes de reproduction generalise bien que difficile a detecter et que la mortalite hivernale entrainait souvent un echec du recrutement. [Traduit par la Redaction], Introduction Elucidating complex, interrelated biotic and abiotic factors that dynamically interact to regulate fish recruitment has challenged and perplexed fisheries scientists for decades. In freshwater systems, predation is often cited [...]

Electrofishing is a commonly used technique to assess freshwater fish population abundance, and in many programs, there has been a shift in the sampling methodologies towards less laborious techniques. These new techniques usually only provide an index of abundance and require calibration with other sampling methods such as successive removal to be used for absolute abundance estimation. Using data for juvenile Atlantic salmon (Salmo salar) collected in 400 sites sampled over 21 years in two large Canadian river catchments with a single sampling protocol, we developed a hierarchical Bayesian model to account for effort, day of sampling, area of the site, and catchment effects on the relationship between the single-pass index of abundance and the fish densities, thereby illustrating the importance of carrying out a calibration exercise on a regular basis. Our work indicates that calibration relationships can change over time even with standardized sampling protocols and that these directional changes in important components of the sampling procedure can bias the estimate of population abundance and misinform the understanding of population dynamics. La peche electrique est une methode couramment utilisee pour evaluer l'abondance de populations de poissons d'eau douce et, dans de nombreux programmes, une transition s'est operee dans les methodologies d'echantillonnage vers des methodes moins laborieuses. Ces nouvelles methodes ne fournissent en general qu'un indice de l'abondance et, pour qu'elles puissent estimer l'abondance absolue, doivent etre etalonnees en utilisant d'autres methodes d'echantillonnage comme le retrait successif. Sur la base de donnees sur les saumons atlantiques (Salmo salar) juveniles recueillies dans 400 sites echantillonnes sur une periode de 21 ans dans deux grands bassins versants canadiens en utilisant un seul protocole d'echantillonnage, nous avons developpe un modele bayesien hierarchique pour rendre compte de l'effort, du jour d'echantillonnage, de la superficie du site et des effets du bassin versant sur la relation entre l'indice d'abondance pour une seule passe et les densites de poissons, illustrant ainsi l'importance de proceder regulierement a un etalonnage. Nos travaux indiquent que les relations d'etalonnage peuvent changer au fil du temps meme pour des protocoles d'echantillonnage normalises et que ces variations directionnelles de composants importants de la procedure d'echantillonnage peuvent biaiser l'estimation de l'abondance de populations et faire en sorte que la comprehension de la dynamique de populations repose sur de l'information erronee. [Traduit par la Redaction], Introduction Our understanding of population and ecosystem responses to extrinsic and intrinsic controlling factors are best informed by experiments and data collected over long time scales. Otherwise, inferences of status [...]

We developed state-space models for inferring movements and behaviors of fish implanted with acoustic transmitters and detected within a spatial array of stationary acoustic receivers. In these models, fish movements and behavior switching are specified using a hidden Markov model of the changes in an individual's latent activity center. The observed number of detections at each acoustic receiver is modeled as a function of the distance between the receiver and a fish's activity center. To illustrate these models, we analyzed the detections of individual Gulf sturgeon (Acipenser oxyrinchus desotoi) that moved within a spatial array of acoustic receivers placed in the Suwannee River, Florida. Our models of these detections provided estimates of the locations of individual sturgeon and the periods when individuals switched between spawning and resting behaviors. We anticipate that these models will be used to analyze acoustic surveys of other species and help design new surveys. Nous avons developpe des modeles d'espace d'etats pour inferer les deplacements et comportements de poissons dotes d'etiquettes acoustiques et detectes a l'interieur d'un reseau spatial de recepteurs acoustiques stationnaires. Dans ces modeles, les deplacements et les changements de comportements des poissons sont specifies a l'aide d'un modele de Markov cache des changements du centre d'activite latent de l'individu. Le nombre de detections observe a chaque recepteur acoustique est modelise en tant que fonction de la distance entre le recepteur et le centre d'activite du poisson. Pour illustrer ces modeles, nous avons analyse les detections d'esturgeons noirs du golfe (Acipenser oxyrinchus desotoi) se deplacant au sein d'un reseau spatial de recepteurs acoustiques place dans le fleuve Suwannee (Floride). Nos modeles de ces detections fournissent des estimations des emplacements d'esturgeons individuels et des periodes durant lesquelles les individus passent de comportements de frai a des comportements de repos ou vice versa. Nous anticipons que ces modeles seront utilises pour analyser les releves acoustiques d'autres especes et pour aider a concevoir de nouveaux releves. [Traduit par la Redaction], Introduction Direct observation of an animal's movements over ecologically relevant space and time scales is challenging. For this reason, animal movements are often studied by applying a physical tag to [...]

Genetic stock identification (GSI) estimates stock proportions and individual assignments through comparison of genetic markers with reference populations. It is used widely in anadromous fisheries to estimate the impact of oceanic harvest on riverine populations. Here, we provide a formal, explicit description of Bayesian inference in the conditional GSI model, documenting an approach that has been widely used in the last 5 years, but not formally described until now. Subsequently, we describe a novel cross-validation method that permits accurate prediction of GSI accuracy when making Bayesian inference from the conditional GSI model. We use cross-validation and simulation of genetic data to confirm the occurrence of a bias in reporting-unit proportions recently reported in Hasselman et al. (2016). Then, we introduce a novel parametric bootstrap approach to reduce this bias, and we demonstrate the efficacy of our correction. Our methods have been implemented as a user-friendly R package, rubias, which makes use of Rcpp for computational efficiency. We predict rubias will be widely useful for GSI of fish populations. L'identification genetique des stocks (IGS) estime les proportions de stocks et les affectations d'individus en comparant des marqueurs genetiques a ceux de populations de reference. L'approche est largement utilisee dans les peches aux especes anadromes pour estimer l'incidence de la peche oceanique sur les populations de rivieres. Nous presentons une description explicite formelle d'inference bayesienne dans le modele d'IGS conditionnel, qui documente une approche largement utilisee au cours des 5 dernieres annees, mais dont une description formelle n'avait pas encore ete faite. Nous decrivons ensuite une nouvelle methode de validation croisee qui permet la prediction exacte de l'exactitude de l'IGS quand une inference bayesienne est faite a partir du modele d'IGS conditionnel. Nous utilisons la validation croisee et la simulation de donnees genetiques pour confirmer la presence d'un biais dans les proportions d'unites de rapport recemment rapportees dans Hasselman et al. (2016). Nous presentons ensuite une nouvelle approche d'autoamorcage parametrique pour reduire ce biais et demontrons l'efficacite de cette correction. Nos methodes ont ete mises en application dans un progiciel en R, rubias, qui utilise Rcpp a des fins d'efficacite computationnelle. Nous predisons que rubias sera tres utile pour l'IGS de populations de poissons. [Traduit par la Redaction], Introduction Over 35 years ago, models were introduced for genetic stock identification (GSI) of Pacific salmon (Grant et al. 1980; Milner et al. 1981). These models permit the use of [...]

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 [...]

In modern fishery stock assessments, the productivity of exploited stocks is frequently summarized by a scaleinvariant 'steepness' parameter. This parameter, which describes the slope of the spawner--recruit curve, determines resilience of a stock to exploitation and is highly influential when estimating maximum sustainable yield. In this study, we examined conditions under which steepness can be estimated reliably. We applied a statistical catch-age model to data that were simulated over a broad range of stock characteristics and exploitation patterns and found that steepness is often estimated at its upper bound regardless of underlying productivity. The ability to estimate steepness reliably was most dependent on the true value of steepness, the exploitation history of the stock, natural mortality, duration of the time series, and quality of an index of abundance; this ability was relatively unaffected by levels of stochasticity in recruitment and sampling intensity of age compositions. We further explored the method of inverse prediction to improve estimates of steepness and conclude that this approach holds promise. We illustrate the utility of simulation and inverse prediction methods with two fish stocks located off the southeastern United States, greater amberjack (Seriola dumerili) and gag grouper (Mycteroperca microlepsis). Resume: Dans les evaluations modernes des stocks, la productivite du stock exploite est souvent resumee par un parametred'≪ inclinaison ≫ qui est invariable a toutes les echelles. Ce parametre, qui decrit la pente de la courbe reproducteurs--recrues, de termine la re silience d'un stock a l'exploitation et est tres important dans la determination du rendement maximum durable. Notre etude examine les conditions dans lesquelles l'inclinaison peut etre estimee de facon fiable. Nous avons utilise un modele statistique des captures en fonction de lage avec des donnees simulees presentant un vaste eventail de caracteristiques des stocks et de patrons dexploitation et avons decouvert que linclinaison est souvent estimee a sa limite superieure, quelle que soit la productivite sous-jacente. La possibilite destimer linclinaison de maniere fiable depend surtout de la valeur reelle de linclinaison, de lhistoire dexploitation du stock, de la mortalite naturelle, de la duree de la serie chronologique et de la qualite de lindice dabondance; cette possibilite est relativement peu affectee par les niveaux de stochasticite dans le recrutement et lintensite de lechantillonnage de la composition en age. Nous avons eprouve en plus la methode de prediction inverse pour ameliorer les estimations de linclinaison et concluons que la methode est prometteuse. Nous illustrons lutilite de la simulation et de la prediction inverse a laide de deux stocks de poissons du large du sud-est des E tats-Unis, ceux de la grande seriole (Seriola dumerili) et de la bade che baillou (Mycteroperca microlepis). [Traduit par la Redaction], Introduction Estimating the parameters of a spawner--recruit function is one of the most vexing challenges in fisheries stock assessment. Ultimately, these parameters control the productivity and resilience of modeled fish [...]

ABSTRACT. Urban areas have suffered from declines in environmental quality and biodiversity; however, there is a lack of long-term studies examining these issues because people rarely collect data from a [...]

Estimation of fish abundance from acoustic surveys requires the estimation of total acoustic backscatter of the target species in the sampled region. Although the arithmetic mean of acoustic backscatter is an unbiased estimator of the mean backscatter for regular or random sampling designs, under the presence of spatial structure, its use leads to a loss of information and the estimation of its variance is not trivial. Here, we tackle these shortcomings by building a spatial model of acoustic backscatter using spline-based generalized additive models (GAMs). GAMs were used to provide local and global estimates of acoustic backscatter, and their precision was calculated by statistical simulations of the models' parameters. For a series of surveys performed off the western and southern Iberian Peninsula, GAM estimates were unbiased and more precise than the arithmetic mean estimates. Simulations of the acoustic backscatter fields were combined with resampling of the trawls to provide confidence intervals for fish numbers and biomass. The relative standard errors of the estimates were within 13% and 46% (average 22%) for numbers and within 12% and 35% (average 19%) for biomass. Acoustic sampling error was the major contributor to the overall variance. Resume: Afin d'estimer l'abondance des poissons a partir des inventaires acoustiques, il est necessaire d'obtenir une estimation de la retrodiffusion acoustique totale de l'espece cible dans la region echantillonne. La moyenne arithmetique de la retrodiffusion acoustique est un estimateur sans distorsion de la retrodiffusion moyenne pour les plans d'echantillonnage reguliers ou aleatoires; cependant, en presence de structure spatiale, son utilisation mene a une perte d'information et l'estimation de la variance est difficile. Nous abordons ici ces lacunes en construisant un modele spatial de la retrodiffusion acoustique a l'aide de modeles additifs generalises (GAM) bases sur les splines. Les GAM ont servi a fournir des estimations locales et globales de la retrodiffusion acoustique et leur precision a ete calculee par des simulations statistiques des parametres du modele. Dans une serie d'inventaires realises au large de l'ouest et du sud de la peninsule iberique, les estimations par GAM ne montrent aucune distorsion et elles sont plus precises que les estimations arithmetiques moyennes. Les simulations des champs de retrodiffusion acoustique ont ete combinees a des re-echantillonnages des donnees de chalutage afin d'obtenir des intervalles de confiance pour la densite et la biomasse des poissons. Les erreurs types relatives des estimations varient de 13 a 46 % (en moyenne 22 %) pour la densite et de 12 a 35 % (en moyenne 19 %) pour la biomasse. L'erreur de l'echantillonnage acoustique est la source principale de la variance globale. [Traduit par la Redaction], Introduction Acoustic surveys are commonly used to estimate indices of abundance at age for many stocks of pelagic fish worldwide (Simmonds and MacLennan 2005). As in every estimation procedure, estimates [...]

The size of the regional species pool may influence local patterns of diversity. However, it is unclear whether certain spatial scales are less sensitive to regional influences than others. Additive partitioning was used to separate coral-dwelling fish diversity to its alpha and beta components, at multiple scales, in several regions across the Indo-Pacific. We then examined how the relative contribution of these components changes with increased regional diversity. By employing specific random-placement null models, we overcome methodological problems with local--regional regressions. We show that, although alpha and beta diversities within each region are consistently different from random-placement null models, the increase in beta diversities among regions was similar to that predicted once heterogeneity in coral habitat was accounted for. In contrast, alpha diversity within single coral heads was limited and increased less than predicted by the null models. This was correlated with increased intraspecific aggregation in more diverse regions and is consistent with ecological limitations on the number of coexisting species at the local scale. These results suggest that, apart from very small spatial scales, variation in the partitioning of fish diversity along regional species richness gradients is driven overwhelmingly by the corresponding gradients in coral assemblage structure. Key words: additive partitioning; coral reefs; fish; gamma diversity; scale; similarity; species diversity.

We tested three hypotheses used to explain the increase in young-of-the-year (YOY) Atlantic salmon (Salmo salar) density with habitat complexity: the territory-size, predator-refuge, and foraging-benefits hypotheses. We manipulated habitat complexity in three different treatments (boulder-removed, control, and boulder-added) at eight sites in Catamaran Brook and the Little Southwest Miramichi River, New Brunswick. The density of juvenile salmon was two times higher in the boulder-added treatment than in the other treatments. Our data were consistent with the territory-size hypothesis; visual isolation was highest and territory size was smallest in the boulder-added treatment, and salmon selected microhabitats to maximize their field of view. Our results showed partial support for the predator- refuge hypothesis; salmon in the boulder-added sites were closer to cover and showed a reduced reaction distance to a novel stimulus, but did not preferentially select microhabitats closer to cover. We found no direct support for the foraging-benefits hypothesis; however, there is indirect evidence that boulders may improve the growth potential of instream habitat. Our results suggest that YOY Atlantic salmon may be attracted to complex environments for the increased cover and that the decreased visibility of these sites causes a reduction in territory size, allowing a higher density of fish. Nous verifions trois hypotheses qui servent a expliquer l'augmentation de la densite de jeunes de l'annee (YOY) en fonction de la complexite des habitats chez le saumon atlantique (Salmo salar), soit les hypotheses de la taille du territoire, des refuges contre les predateurs et des avantages alimentaires. Nous avons manipule la complexite des habitats par trois traitements experimentaux (retrait de blocs rocheux, temoin, ajout de blocs rocheux) a huit sites dans Catamaran Brook et la riviere Little Southwest Miramichi, Nouveau-Brunswick. La densite de jeunes saumons etait deux fois plus importante dans les sites d'ajout de blocs rocheux que dans les autres situations experimentales. Nos donnees s'accordent avec l'hypothese de la taille du territoire; l'isolement visuel est maximal et la taille des territoires minimale dans les conditions d'ajout de blocs et les saumons choisissent les microhabitats de facon a maximiser leur champ visuel. Nos resultats appuient en partie l'hypothese des refuges contre les predateurs; les saumons dans les sites d'ajout de blocs sont plus pres d'un abri et ils ont une distance de reaction plus courte a un nouveau stimulus, mais ils ne choisissent pas leurs microhabitats preferentiellement en fonction de la proximite des abris. Nous ne trouvons aucun appui direct pour l'hypothese des avantages alimentaires; il y a cependant des indications indirectes que les blocs rocheux peuvent ameliorer le potentiel de croissance des habitats dans le cours d'eau. Nos resultats indiquent que les YOY du saumon atlantique peuvent etre attires par les habitats complexes pour un meilleur abri et que la visibilite reduite de ces sites entraine une diminution de la taille des territoires, ce qui permet une plus grande densite de poissons. [Traduit par la Redaction], Introduction The structural complexity of a habitat has long been implicated as a major determinant of both species richness (MacArthur and MacArthur 1961) and the local abundance of particular species [...]

This study explored the extent to which variation in habitat factors related to growth and density influence selfthinning patterns in stream-living brown trout (Salmo trutta). Analysis of 110 cohorts at 12 sites of four contrasting streams revealed density-mass relationships in two phases. Density of survivors decreased little during the first half of their lifetime. A second phase commenced as individuals attained a threshold mass upon which density declined linearly with increased mass. The slopes of the second phase were greater than predicted by space and food demands. Among sites, these slopes were related to threshold densities at the beginning of the second phase. In turn, elevations, threshold densities, and slopes depicted concave trajectories against site depth, whereas threshold masses increased linearly. Apparently, cohorts remain below the carrying capacity during the first half of their lifetime and self-thin during the second half. Space-limited habitats impose site-specific carrying capacities and site-specific self-thinning coefficients, suggesting a common mechanism underlying self-thinning and an unanticipated, emerging property: two-phase patterns with far more variation in self-thinning coefficients. Variability in growth and density exhibited by brown trout and other salmonids across regions suggests that two-phase patterns may occur broadly, and self-thinning coefficients may vary widely. La presente etude explore dans quelle mesure la variation des facteurs de l'habitat relies a la croissance et la densite influence les patrons d'auto-eclaircie chez des truites brunes (Salmo trutta) vivant en eau courante. L'analyse de 110 cohortes a 12 sites dans quatre cours d'eau bien differents indique deux phases dans les relations densite-masse. La densite des survivants diminue peu durant la premiere moitie de la vie des poissons. Une deuxieme phase debute lorsque les individus atteignent une masse seuil au-dela de laquelle la densite diminue en fonction lineaire de l'accroissement de masse. Les pentes de cette seconde phase sont plus fortes que ne permettent de le predire les besoins en espace et en nourriture. Parmi les sites, ces pentes sont reliees aux densites seuils au debut de la seconde phase. En sequence, l'altitude, la densite seuil et la pente decrivent des trajectoires concaves en fonction de la profondeur du site, alors que la masse seuil augmente de facon lineaire. Il semble que les cohortes demeurent sous le stock limite durant la premiere moitie de leur cycle et procedent a une auto-eclaircie durant la seconde moitie. Les habitats limites en espace imposent des stocks limites et des coefficients d'auto-eclaircie specifiques au site, ce qui laisse croire a un mecanisme commun sous-jacent a l'autoe claircie et une caracteristique emergente inattendue, soit des patrons biphasiques avec beaucoup plus de variation dans les coefficients d'auto-eclaircie. La variabilite de la croissance et de la densite observee chez la truite brune et d'autres salmonide s dans les diverses regions indique que les patrons biphasiques peuvent se produire sur une grande echelle et que les coefficients d'auto-eclaircie peuvent varier considerablement. [Traduit par la Redaction], Introduction The importance and implications of body size to the structure and dynamics of populations composed of individuals with indeterminate and flexible growth have been well documented (Peters 1983; Lomicki [...]

Precise, unbiased estimates of population size are an essential tool for fisheries management. For a wide variety of salmonid fishes, redd counts from a sample of reaches are commonly used to monitor annual trends in abundance. Using a 9-year time series of georeferenced censuses of Chinook salmon (Oncorhynchus tshawytscha) redds from central Idaho, USA, we evaluated a wide range of common sampling strategies for estimating the total abundance of redds. We evaluated two sampling-unit sizes (200 and 1000 m reaches), three sample proportions (0.05, 0.10, and 0.29), and six sampling strategies (index sampling, simple random sampling, systematic sampling, stratified sampling, adaptive cluster sampling, and a spatially balanced design). We evaluated the strategies based on their accuracy (confidence interval coverage), precision (relative standard error), and cost (based on travel time). Accuracy increased with increasing number of redds, increasing sample size, and smaller sampling units. The total number of redds in the watershed and budgetary constraints influenced which strategies were most precise and effective. For years with very few redds ( La gestion des peches requiert comme outils essentiels des estimations precises et non faussees de la taille des populations. Chez une grande diversite de poissons salmonides, le decompte des frayeres dans un echantillon de sections de cours d'eau sert couramment a suivre les tendances annuelles d'abondance. En utilisant une serie chronologique de 9 annees d'inventaires georeferences de frayeres de saumons chinook (Oncorhynchus tshawytscha) dans le centre de l'Idaho, E.-U., nous testons une gamme etendue de strategies courantes d'inventaire pour l'estimation de l'abondance totale des frayeres. Nous evaluons deux tailles d'unites d'echantillonnage (sections de 200 et de 1000 m), trois proportions echantillonnees (0,05, 0,10 et 0,29), ainsi que six strategies d'echantillonnage (echantillonnage par indices, echantillonnage aleatoire simple, echantillonnage systematique, echantillonnage stratifie, echantillonnage par groupements adaptatifs et un plan equilibre spatialement). Nous evaluons les strategies d'apres leur exactitude (couverture de l'intervalle de confiance), leur precision (erreur type relative) et leur cout (temps de deplacement). L'exactitude augmente en fonction directe du nombre de frayeres et de la taille des echantillons et en fonction inverse de la taille des unites d'echantillonnage. Le nombre total de frayeres dans le bassin versant et les contraintes budgetaires determinent quelles strategies sont les plus precises et les plus efficaces. Les annees avec tres peu de frayeres ( [Traduit par la Redaction], Introduction Chinook salmon (Oncorhynchus tshawytscha) populations are important for the economy, recreation, and culture of the Pacific Northwest (Lichatowich 1999). Over the last century, these populations have experienced substantial declines [...]

Abstract: The combined model produced a tool for evaluating effects on fish populations from passage through hydro-power turbines at dams. Mean blade-strike mortality was higher for adult Atlantic salmon (Salmo [...]

Abstract: Growth, size at maturity. gonadosomatic index (GSI), egg size. and absolute fecundity of Nile tilapia (Oreochroinis niloticus) were significantly affected by oxygen levels (1.5 [+ or -] 1.0, 2.8 [...]

Abstract: Introduced species can cause economic and environmental harm. Researchers have developed risk assessment models for exotic species based on biological characteristics. However, few have quantified propagule pressure despite its [...]

Abstract: It is often assumed that visual survey data provide more accurate fish counts than conventional extractive gear. As a result, use of underwater vehicles to assess the abundance and [...]

While there is great interest in the degree to which local interactions 'scale-up' to predict regional patterns of abundance, few studies in marine systems have simultaneously examined patterns of abundance at both the large scale (tens of kilometers) typical of larval movement and the small scale (meters) typical of post-settlement interactions. We addressed this gap by monitoring larval supply, adult survivorship, and giant kelp (Macrocystis pyrifiera, a primary habitat-forming species) abundance for 13 populations of kelp bass (Paralabrax clathratus) spread over ~200 km in the Santa Barbara Channel, California, USA. At the small, within-site scale, both recruitment and adult survivorship of kelp bass were density-dependent and positively related to kelp abundance. At the larger, among-site scale, the spatial pattern of adult kelp bass abundance was predicted well by the pattern of kelp bass larval supply, but there was a consistent negative spatial relationship between kelp abundance and kelp bass larval supply despite the positive effects of kelp on kelp bass at the smaller spatial scale. This large-scale negative relationship was likely a product of a channel-wide spatial mismatch between oceanographic conditions that favor kelp survival and those that concentrate and distribute fish larvae. These results generally support the recruit adult hypothesis: kelp bass populations are limited by recruitment at low recruit densities but by density-dependent competition for food resources and/or predator refuges at high recruit densities. At the same time, spatial variation in kelp abundance produced substantial spatiotemporal heterogeneity in kelp bass demographics, which argues for a multispecies, metacommunity approach to predicting kelp bass dynamics. Key words: density dependence; giant kelp; kelp bass; larval supply; Macrocystis pyrifera; Paralabrax clathratus; population dynamics; recruitment; Santa Barbara Channel, California, USA; spatial scale; survivorship; temperate reef fish.

Abstract: Native salmonid fishes often face simultaneous threats from habitat fragmentation and invasion by nonnative trout species. Unfortunately, management actions to address one may create or exacerbate the other. A [...]

Understanding the causes and consequences of species extinctions is a central goal in ecology. Faced with the difficult task of identifying those species with the greatest need for conservation, ecologists have turned to using predictive suites of ecological and life,history traits to provide reasonable estimates of species extinction risk. Previous studies have linked individual traits to extinction risk, yet the nonadditive contribution of multiple traits to the entire extinction process, from species rarity to local extirpation to global extinction, has not been examined. This study asks whether trait synergisms predispose native fishes of the Lower Colorado River Basin (USA) to risk of extinction through their effects on rarity and local extirpation and their vulnerability to different sources of threat. Fish species with 'slow' life histories (e.g., large body size, long life, and delayed maturity), minimal parental care to offspring, and specialized feeding behaviors are associated with smaller geographic distribution, greater frequency of local extirpation, and higher perceived extinction risk than that expected by simple additive effects of traits in combination. This supports the notion that trait synergisms increase the susceptibility of native fishes to multiple stages of the extinction process, thus making them prone to the multiple jeopardies resulting from a combination of fewer individuals, narrow environmental tolerances, and long recovery times following environmental change. Given that particular traits, some acting in concert, may differentially predispose native fishes to rarity, extirpation, and extinction, we suggest that management efforts in the Lower Colorado River Basin should be congruent with the life-history requirements of multiple species over large spatial and temporal scales. Key words: dams; functional diversity; life history; Lower Colorado River Basin (USA); native fishes; river regulation; species attributes; species invasions.

Abstract: We examined the relationship between multiple spatial scales of fish assemblage structure and land cover in streams of a northern Great Plains ecoregion. We used regional richness measurements, an [...]

Abstract: We present a hierarchical Bayesian modelling (HBM) framework for estimating riverine fish population size from successive removal data via electrofishing. It is applied to the estimation of the population [...]

Abstract: Survey indices play an important role in stock assessments as they provide information on stock trends. In certain cases, large interannual variations have been observed that are unlikely to [...]

Abstract: Rainbow smelt (Osmerus mordax) are invaders of inland lakes in the Laurentian Great Lakes region of North America and have negatively affected native fish populations. Walleye (Sander vitreus) comprise [...]

Abstract: A method for using age-composition data to determine stock-specific migration timing and abundance in a mixed-stock salmon fishery is developed. The Chignik sockeye salmon (Oncorhynchus nerka) fishery has two [...]

Quantifying the effects of density-dependent and density-independent factors in demographic and dispersal processes remains a major challenge in population ecology. Based on unique long-term capture--mark--recapture (CMR) data (1949-2000) on pike (Esox lucius) from Windermere, United Kingdom, we provide estimates of density-dependent and density-independent effects, under the influence of individual size and sex, on natural survival, fishing mortality, and dispersal. Because survival is expected to be related to the individual growth process, we also explore the degree of parallelism between the two processes by applying the best-supported survival model structure to individual growth data. The CMR data were analyzed using sex- and age-structured multistate models (two lake basins: north and south) assuming no seasonal variation in survival and dispersal. Total survival and dispersal probabilities were insensitive to this assumption, and capture probability was shown to be robust to assumptions about intra-annual variation in survival and dispersal. The analyses revealed that large pike (>55 cm) displayed marked basin-specific differences in survival and dispersal responses to the abundance of conspecifics in which pike from the south basin show high density dependence in survival and a low degree of density dependence in dispersal, whereas the opposite was found for those of the north basin. Both large- and small-pike dispersals were found to be dependent upon the between-basin gradient in perch (Perca fluviatilis, the main prey) abundance, but most so for north-to-south dispersal. The strength and pattern of density-dependent mortality in small pike was influenced by temperature in a peculiar way: at low summer temperatures survival was lowest at high small-pike abundances and low perch abundances; at low temperatures, survival was lowest at high small-pike abundances and high perch abundances. Analyses of individual small-pike growth trajectories showed a similar modulation of the positive perch abundance effect on growth rate when temperature increases. The growth analysis also indicated that cannibalism may be biased in favor of rapidly growing individuals or at least increased growth rate for the surviving individuals. Altogether, this study provides evidence of a complex interplay between density-dependent and density-independent factors affecting survival, dispersal, and individual growth of an aquatic top predator. Key words: cannibalism; capture--mark--recapture: demography,' density dependence; Esox lucius; growth; harvesting; Perca fluviatilis; predator-prey, interaction; temperature; Windermere, United Kingdom.

Abstract: The objective was to uncover the roles of environmental, density-independent, and intrinsic, density-dependent factors as drivers of population size in stream-resident brown trout (Salmo trutta) across space and time. [...]

Abstract: We examined the effects of predator species on yellow perch (Perca flavescens) from lakes in the Sudbury mining region (Ontario, Canada), where fish communities are just beginning to recover [...]

Abstract: Reproductive activity of seven species representing three divergent life history strategies was monitored monthly for 2 years in channel and floodplain habitats of the Brazos River, Texas, USA, to [...]

Abstract: An exploited bull trout, Salvelinus confluentus, population experienced a 28-fold increase in adult density during a 10-year period from a minimum of 60 individuals. This demonstrates the extent to [...]

HOW FAR WILL POLICY BEND TO SAVE THE SALMON? These days, folks in the Pacific Northwest may be excused if they're experiencing a little deja vu. Just a decade ago, […]

Since 1984, annual bottom trawl surveys of the west coast (California--Washington) upper continental slope (WCUCS) have provided information on the abundance, distribution, and biological characteristics of groundfish resources. Slope species of the deep-water complex (DWC) are of particular importance and include Dover sole, Microstomus pacificus; sablefish, Anoplopoma fimbria; shortspine thornyhead, Sebastolobus alascanus; and longspine thornyhead, S. altivelis. In the fall of 1994, we conducted an experimental gear research cruise in lieu of our normal survey because of concerns about the performance of the survey trawl. The experiment was conducted on a soft mud bottom at depths of 460-490 m off the central Oregon coast. Treatments included different combinations of door-bridle rigging, ground-gear weight, and scope length. The experimental design was a 2 x 2 x 2 factorial within a randomized complete-block. Analysis of variance was used to examine the effects of gear modifications on the engineering performance of the trawl (i.e. trawl dimensions, variation in trawl dimensions, and door attitude) and to determine if catch rates in terms of weight and number of DWC species and invertebrates were affected by the gear modifications. Trawl performance was highly variable for the historically used standard trawl configuration. Improvements were observed with the addition of either a 2-bridle door or lighter ground gear. Changes in scope length had relatively little effect on trawl performance. The interaction of door bridle and ground gear weight had the most effect on trawl performance. In spite of the standard trawl's erratic performance, catch rates of all four DWC species and invertebrates were not significantly different than the 2-bridle/heavy combination, which did the best in terms of engineering performance. The most important factor affecting DWC catch rates was ground gear. Scope length and the type of door bridle had little effect on DWC catch rates. Subsequent revisions to survey gear and towing protocol and their impact on the continuity of the slope survey time series are discussed., Introduction Bottom trawl surveys are an important source of fishery-independent data for assessing, monitoring, and managing groundfish populations. NOAA's National Marine Fisheries Service (NMFS) has been conducting groundfish bottom trawl [...]