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Managers and stakeholders increasingly ask whether predation is a driving force behind the poor status of many species, and whether predator control is likely to be a successful management action to intervene. We review existing literature on Atlantic salmon Salmo salar predation and predator control, as well as general ecological theory on the role of predation in the life cycle of this iconic fish. Many bird, mammal, and fish predators target salmon at different life stages. In healthy salmon populations, predation is likely compensated for by reduced intraspecific competition during the freshwater stage. There is little evidence that predation alone has been an underlying mechanism for driving salmon populations below conservation limits. However, depending on the predator's response to salmon abundance, predation may keep decimated populations from recovering, even when the actual causes of decline have been removed. Under such a scenario, predation control may contribute to recovery, but there are no strong examples that clearly demonstrate the efficacy of managing predators to recover threatened salmon populations, challenging further applications. Key words: predators, predation impact, predator species, Salmo salar, stock recovery, Introduction Few species on the planet inspire as much fascination and sympathy as the Atlantic salmon Salmo salar. Salmon is a symbol of the native ecosystems in the North Atlantic [...]

Juvenile sockeye salmon (Oncorhynchus nerka) in British Columbia migrate past numerous Atlantic salmon (Salmo salar) farms from which they may acquire infectious agents. We analyse patterns of molecular detection in juvenile sockeye for the bacterium Tenacibaculum maritimum, known to cause disease in fish globally and to cause mouthrot disease in farmed Atlantic salmon in British Columbia. Our data show a clear peak in T. maritimum detections in the Discovery Islands region of British Columbia, where sockeye migrate close to salmon farms. Using well-established differential equation models to describe sockeye migration and bacterial infection, fit to detection data, we assessed support for multiple hypotheses describing farm- and background-origin infection. Our best models (with 99.8% empirical support) describe constant background infection pressure, except around Discovery Islands salmon farms, where farm-origin infection pressure peaked at 12.7 (approximate 95% CI: 4.5 to 31) times background levels. Given the severity of associated disease in related species and the imperilled nature of Fraser River sockeye, our results suggest the need for a more precautionary approach to managing farm-wild interactions in sockeye salmon. Durant leurs migrations, les jeunes saumons rouges (Oncorhynchus nerka) en Colombie-Britannique passent a proximite de nombreux elevages de saumons atlantiques (Salmo salar) qui peuvent leur transmettre des agents infectieux. Nous analysons les motifs, chez les jeunes saumons rouges, de detection moleculaire de la bacterie Tenacibaculum maritimum, pathogene des poissons a l'echelle planetaire qui cause la pourriture de la bouche chez les saumons atlantiques d'elevage en Colombie- Britannique. Nos donnees montrent une pointe tres nette de detections de T. maritimum dans la region des iles Discovery de cette province, ou les saumons rouges passent pres d'elevages de saumons durant leur migration. En utilisant des modeles d'equations differentielles bien etablis pour decrire la migration des saumons rouges et l'infection bacterienne, cales sur des donnees de detection, nous evaluons differentes hypotheses qui decrivent les infections associees aux elevages et aux conditions de reference. Les meilleurs modeles (appuyes a 99,8% par les donnees empiriques) decrivent une pression d'infection de reference constante, sauf autour d'elevages de saumons des iles Discovery, ou la pression d'infection associee aux elevages atteint une pointe de 12.7 fois (IC approximatif a 95% : 4,5 a 31) les valeurs de reference. Etant donne les graves effets de la maladie associee chez des especes apparentees et le caractere menace des saumons rouges du fleuve Fraser, nos resultats soulignent la necessite d'une approche plus prudente de gestion des interactions des saumons rouges sauvages avec les elevages. [Traduit par la Redaction], Introduction Across taxa, long-distance migrations likely evolved to exploit resources, avoid predation, and--in some species--evade infectious disease (Altizer et al. 2011). Recent human agricultural practices, however, can result in elevated [...]

Passage of hydropower plants by upstream-migrating salmonid spawners is associated with reduced migration success, and the need for knowledge of fish behavior downstream of dams is widely recognized. In this study, we examined fishway passage of landlocked Atlantic salmon (Salmo salar) in River Klaralven, Sweden, and brown trout (Salmo trutta) in River Gudbrandslagen, Norway, and the influence of prior experience on passage success in 2012 and 2013. Fishway trap efficiency varied from 18% to 88% and was influenced by river discharge. Most salmon (81%) entered the fishway trap on days without spill, and salmon moved from the turbine area to the spill zone when there was spill, with small individuals showing a stronger reaction than large fish. Analysis of fish with and without prior trap experience showed that a higher percentage of the 'naive' fish (70% of salmon and 43% of the trout) entered the fishway traps than the 'experienced' ones (25% of the salmon and 15% of the trout). Delays for fish that entered the trap ranged from 3 to 70 days for salmon and 2 to 47 days for trout. Le passage a travers des centrales hydroelectriques par des salmonides en montaison de frai est associe a une reduction du succes de migration, et il est largement reconnu que des connaissances sur le comportement des poissons en aval de barrages sont necessaires. Nous examinons le passage dans des passes migratoires de ouananiches (Salmo salar) dans le fleuve Klaralven (Suede) et de truites brunes (Salmo trutta) dans le fleuve Gudbrandsdalslagen (Norvege), et l'influence de l'experience anterieure sur le succes de passage en 2012 et 2013. L'efficacite de piegeage des passes migratoires variait de 18 % a 88 % et etait influencee par le debit du fleuve. La plupart des saumons (81 %) entraient dans le piege de la passe durant des jours sans deversement et les saumons se deplaqaient de la zone de turbinage a la zone de deversement quand il y avait un deversement, les petits specimens presentant une reaction plus forte que les gros poissons. L'analyse des poissons avec et sans experience de pieges anterieure montre qu'un plus grand pourcentage de poissons <> (70 % des saumons et 43 % des truites) que de poissons <> (25 % des saumons et 15 % des truites) entrait dans les pieges des passes. Les retards des poissons qui entraient dans un piege allaient de 3 a 70 jours pour les saumons et de 2 a 47 jours pour les truites. [Traduit par la Redaction], Introduction Habitat fragmentation is a major threat to biodiversity worldwide and an important topic in conservation biology (Nilsson et al. 2005; Noss and Daly 2006). Hydroelectric development, in which dams [...]

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 [...]

Abstract: Individuals travelling through landscapes may use the presence of conspecifics to evaluate habitat quality. Juvenile Atlantic salmon (Salmo salar L., 1758) are usually territorial and exhibit some degree of [...]

In stream-living salmonids, an underlying mechanism for the critical period after emergence has generally been assumed to be size-dependent swimming capacity constraining fry (age-0) to low-velocity habitats with reduced food availability and intense competition. A further plausible mechanism is that intercohort habitat exclusion confines fry to marginal habitats. This possibility was tested using a seminatural stream with 16 test arenas, each comprising one high-velocity, deep habitat and one low-velocity, shallow habitat. We observed groups of newly emerged Atlantic salmon (Salmo salar) fry, either alone or in sympatry with one or two age-1 salmon. Salmon fry used high-velocity areas (42.2 ± 0.4 cm-[s.sup.-1]) most extensively in the absence of intercohort competition, where they obtained more food than in low-velocity areas (3.3 ± 0.3 cm-[s.sup.-1]), even though foraging efficiency was lower (though not significantly so). In sympatry with older cohorts, fry increased their use of the low-velocity habitat, with a reduced foraging activity, suggesting that strong older cohorts in natural populations may have the potential to influence the strength of the recruiting cohort by negative density dependence due to interference competition for habitat. Il a generalement ete presume que, chez les salmonides vivant dans les cours d'eau, le fait que les alevins (0 an) sont limites par leur capacite natatoire dependante de la taille a des habitats de faible velocite caracterises par une faible disponibilite de nourriture et une concurrence intense constituait un mecanisme sous-jacent pour la periode critique apres l'emergence. Un autre mecanisme plausible veut que l'exclusion inter-cohorte de l'habitat confine les alevins a des habitats marginaux. Cette possibilite a ete verifiee en utilisant un cours d'eau semi-naturel comptant 16 arenes d'essai comprenant chacune un habitat d'eau profonde de forte velocite et un habitat peu profond de faible velocite. Nous avons observe des groupes d'alevins de saumon atlantique (Salmo salar) nouvellement emerges, seuls ou en sympatrie avec un ou deux saumons d'un an. Les alevins utilisaient les zones de forte velocite (42,2 ± 0,4 cm*[s.sup.-1]) plus intensement en l'absence de concurrence inter-cohorte, ou ils y obtenaient plus de nourriture que dans les zones de faible velocite (3,3 ± 0,3 cm*[s.sup.-1]), meme si l'efficacite d'approvisionnement y etait plus faible (mais pas significativement). En sympatrie avec des cohortes plus vieilles, les alevins faisaient un usage accru de l'habitat de faible velocite et reduisaient leur activite d'approvisionnement, ce qui donne a penser que les cohortes fortes plus vieilles dans les populations naturelles pourraient influencer la force de la cohorte qui recrute par une dependance negative sur la densite decoulant de la concurrence pour l'habitat. [Traduit par la Redaction], Introduction In an environment with limited food supply, growth of organisms may be associated with increased per capita demands, resulting in a progressive reduction in their total number. Such progressive, [...]

Telemetry is increasingly being used to estimate population-level survival rates. However, these estimates may be affected by the detectability of telemetry tags and are reliant on the assumption that telemetry data represent the movements of the tagged fish. Predation on tagged fish has the potential to bias survival estimates, and unlike the issue of detectability, methods to correct for the resulting bias (termed 'predation bias') are not yet developed. In an acoustic telemetry study on inner Bay of Fundy Atlantic salmon (Salmo salar) smolts during 2008 and 2011, unusual tag detection patterns were indicative that some data may have been representative of the movements of predators rather than smolts. To incorporate predation effects into the resulting survival estimates, a suite of 11 summary migration metrics were compared between Atlantic salmon smolts and striped bass (Morone saxatilis). Cluster analyses revealed that 2.4% to 13.6% of tags implanted in smolts exhibited migration patterns more similar to striped bass than to other smolts, which was interpreted here as evidence of predation. Reassigning the fate of these tags as 'depredated-died' reduced estimated survival from 43.5% to 41.1% in 2008 and from 32.6% to 19.0% in 2011 relative to a traditional mark-recapture model, illustrating the effect of predation bias in this case study. L'utilisation de la telemetrie pour estimer les taux de survie a l'echelle de la population est de plus en plus repandue. Ces estimations peuvent toutefois etre influencees par la detectabilite des etiquettes utilisees et reposent sur le principe que les donnees de telemetrie rendent compte des deplacements des poissons marques. La predation de ces derniers pourrait cependant biaiser les estimations des taux de survie et, contrairement au probleme de detectabilite, il n'existe pas encore de methode permettant de corriger le biais qui en resulte (appele <>). Dans une etude de telemetrie acoustique portant sur des saumoneaux de saumon atlantique (Salmo salar) de la haute baie de Fundy, menee en 2008 et 2011, des motifs de detection d'etiquettes inhabituels indiquaient que certaines donnees pouvaient refleter les deplacements de predateurs plutot que ceux des saumoneaux. Afin d'integrer les effets de la predation dans les estimations des taux de survie en decoulant, 11 parametres sommaires associes a la migration de saumoneaux de saumon atlantique et de bars d'Amerique (Morone saxatilis) ont ete compares. Des analyses typologiques ont revele que de 2,4 % a 13,6 % des etiquettes implantees dans des saumoneaux temoignaient d'habitudes migratoires plus semblables a celles de bars d'Amerique qu'a celles d'autres saumoneaux, ce qui a ete interprete comme une preuve de predation. La reaffectation du destin de ces etiquettes a des individus <> s'est traduite par une reduction des taux de survie estimes de 43,5 % a 41,1 % pour 2008, et de 32,6 % a 19,0 % pour 2011, par rapport aux resultats d'un modele de marquage-recapture traditionnel, illustrant ainsi l'effet du biais de predation dans cette etude de cas. [Traduit par la Redaction], Introduction Quantifying the rate and timing of mortality is important for the conservation planning for many fish populations; however, estimating these rates can be difficult given our inability to directly [...]

Weak levels of acidification (pH < 6.6) inhibit the ability of fishes to assess predation risk via interference with damage-released chemical alarm cues. While survival benefits associated with behavioural responses to alarm cues have been demonstrated under laboratory conditions, it remains largely unknown whether fishes under natural conditions experience similar benefits. Using hatchery-reared juvenile Atlantic salmon (Salmo salar) as a model organism, we conducted a tethering experiment in reaches of neutral (pH ≥ 6.6) and acidic (pH < 6.6) salmon nursery streams, plus one additional stream that varied between pH classes. Despite exposure to fewer predatory fish species, similar availability of physical refugia, and similar threat from terrestrial predators, tethered fish in acidic streams were significantly more likely to be predated over the course of a trial than their counterparts in neutral streams. These results suggest that (i) in the absence of compensatory mechanisms, juvenile Atlantic salmon under acidic conditions may experience greater rates of predation as a result of impaired chemosensory risk assessment, and (ii) brook trout (Salvelinus fontinalis) appear to play the greatest role in limiting the survival of young-of-theyear (0+) salmon. De faibles niveaux d'acidification (pH < 6,6) inhibent la capacite des poissons d'evaluer le risque de predation en entravant les signaux chimiques d'alarme liberes en cas de lesions. Si des avantages pour la survie associes aux reactions comportementales a des signaux d'alarme ont ete demontres en laboratoire, de tels avantages pour les poissons en situation naturelle restent generalement a demontrer. En utilisant le saumon atlantique (Salmo salar) juvenile issu d'aleviniere comme organisme modele, nous avons mene une experience avec des individus attaches dans des tron^ons neutres (pH ≥ 6,6) et acides (pH < 6,6) de cours d'eau natals, en plus d'un cours d'eau qui oscillait entre les deux categories de pH. Bien qu'ils aient ete exposes a moins d'especes de poissons predateurs, a une disponibilite semblable de refuges physiques et a une menace similaire de predateurs terrestres, les poissons attaches dans les cours d'eau acides presentaient une probabilite de predation significativement plus grande que leurs congeneres en rivieres neutres durant la periode de l'essai. Ces resultats donnent a penser que (i)en l'absence de mecanismes compensatoires, les saumons atlantiques juveniles en conditions acides pourraient presenter des taux de predation plus eleves en raison de leur plus faible capacite d'evaluation chimiosensorielle des risques et (ii) les ombles de fontaine (Salvelinus fontinalis) constitueraient le facteur limitatif le plus important en ce qui concerne la survie des saumons de l'annee 0+. [Traduit par la Redaction], Introduction Predator-prey interactions are one of the most studied topics in ecology, particularly with regard to prey that are likely to incur greater fitness costs during a predation event than [...]

We have constructed a statistical model to forecast, with uncertainty, the stock of Norwegian farmed Atlantic salmon (Salmo salar). The model provided good predictions of future biomass of Norwegian farmed salmon and can also be used to perform 'what-if' analysis exploring the impact of varying scenarios for stocking and slaughtering. The model is based on the number of fish in each mass class (0-1, 1-2, ..., 10+ kg) and their average mass. The model, which is related to standard size-structured models, computes the number of fish growing into the next mass class the next month and the number of fish remaining in the same mass class. In addition, the number of new fish stocked, fish lost, slaughtered, and wasted, as well as the sea temperature related to the growth, were modelled. All the model parameters were estimated based on monthly data from 2002 to 2007, and the model was validated statistically. Any animal production involving cycles may benefit from this forecasting tool. Nous avons construit un modele statistique pour predire, avec l'incertitude, le stock des saumons atlantiques (Salmo salar) norvegiens d'elevage. Le modele fournit de bonnes predictions de la biomasse future des saumons norvegiens d'elevage et peut aussi servir a faire une analyse de simulation (<< qu'arrive-t-il si? >>) qui explore l'impact de divers scenarios d'empoissonnement et de recolte. Le modele est base sur le nombre de poissons dans chaque classe de masse (0-1, 1-2, ..., 10+ kg) et leur masse moyenne. Le modele, qui est apparente aux modeles standard structures en fonction de la taille, calcule le nombre de poissons qui passent par croissance dans la classe de masse superieure le mois suivant et le nombre de poissons qui demeurent dans la meme classe de masse. De plus, il y a modelisation du nombre de nouveaux poissons empoissonnes, des poissons perdus, tues et gaspilles, de meme que de la temperature de la mer en relation avec la croissance. Tous les parametres du modele ont ete estimes a partir de donnees mensuelles de 2002 a 2007 et le modele a ete valide statistiquement. Cet outil de prediction peut etre utile pour toute production animale comportant des cycles. [Traduit par la Redaction], Introduction Thanks to its extraordinary geographical characteristics, Norway became the first country to actively promote the development of salmon farming. Today, Norwegian interests play an important role in global salmon [...]

We report how aquaculture may negatively alter a critical phenological trait (developmental rate) linked to survival in wild fish populations. At the southern limit of the species range in eastern North America, the persistence of small Atlantic salmon (Salmo solar) populations may be constrained by interbreeding with farmed salmon that escape regularly from intensive aquaculture facilities. Using a common-garden experimental protocol implemented over an 8-year period, we show that embryos of farmed salmon and multigenerational farmed-wild hybrids ([F.sub.1], [F.sub.2], wild backcrosses) had slower developmental rates than those of two regional wild populations. In certain cases, our data suggest that hybrid developmental rates are sufficiently mismatched to prevailing environmental conditions that they would have reduced survival in the wild. This implies that repeated farmed-wild interbreeding could adversely affect wild populations. Our results therefore reaffirm previous recommendations that based on the precautionary principle, improved strategies are needed to prevent, or to substantially minimize, escapes of aquaculture fishes into wild environments. Resume: Nous demontrons comment 1'aquaculture peut affecter negativement un trait phenologique essentiel (le taux de developpement) lie a la survie des populations sauvages de poissons. A la limite sud de l'aire de repartition de l'espece dans Test de l'Amerique du Nord, la persistance de petites populations de saumons atlantiques (Salmo salar) peut etre res-treinte par des croisements avec des saumons d'elevage qui s'echappent regulierement des installations d'aquaculture intensive. A l'aide d'un protocole experimental de jardin commun maintenu sur une periode de 8 annees, nous montrons que les embryons de saumons d'elevage et des hybrides de plusieurs generations de saumons sauvages et eleves (retrocroise-ments en nature de [F.sub.1] et de [F.sub.2]) ont des taux de developpement plus lents que les poissons de deux populations regionales sauvages. Dans certains cas, nos donnees indiquent que les taux de developpement des hybrides sont suffisamment mesap-paries aux conditions prevalentes de l'environnement qu'ils auraient reduit la survie en nature. Ceci donne a entendre que des croisements repetes entre des poissons d'elevage et des poissons sauvages pourraient affecter negativement les populations sauvages. Nos resultats nous amenent done a reaffirmer les recommandations anterieures basees sur le principe de precaution voulant que des strategies ameliorees soient necessaires pour empecher, ou reduire a un strict minimum, la fuite de poissons d'elevage vers les environnements sauvages. [Traduit par la Redaction], Introduction Unparalleled declines of many wild fish populations, coupled with growing aquaculture production, have made it critical to assess the potential risks associated with interactions between wild and escaped farmed [...]

Apparent within-site survival of Atlantic salmon (Salmo salar) parr, individually tagged with passive integrated transponders, was not constant throughout the winter period in a 3-year study (2003-2006) in Catamaran Brook, New Brunswick, Canada. Highest decline in apparent survival (19.4%-33.3% of the study population) occurred prior to any ice formation and coincided with early winter acclimatization period (dynamic temperature and discharge regime). Stream discharge and parr maturity were identified to be relevant factors explaining emigration prior to ice formation. Apparent survival was improved during the period affected by subsurface ice and considerably better when surface ice was prevailing, with a decline in population size between 0% and 15.4%. Overall, observed within-site winter mortality was low (4.4%), and the majority of the loss of tagged salmon parr occurred because of emigration. On average, the within-site population of tagged salmon parr declined by 31.7% over the whole winter (November-April). Our data suggest that anthropogenic impacts, like climate change or river regulation, are likely to affect the apparent survival rate and distribution of juvenile Atlantic salmon because of their effects on natural ice regime in streams. Resume: La survie apparente dans un meme site de tacons du saumon atlantique (Salmo salar) porteurs d'un transpon-deur passif integre, ne s'est pas revelee constante au cours de la periode hivernale pendant une etude de trois ans (2003-2006) a Catamaran Brook, Nouveau-Brunswick, Canada. Le declin le plus marque de la survie apparente (19,4-33,3 % de la population etudiee) se produit avant toute formation de glace et coincide avec la periode d'acclimatation du debut de l'hiver (temperature et regime d'ecoulement dynamiques). Nous avons identifie l'ecoulement du cours d'eau et la maturite des tacons comme les facteurs pertinents pour expliquer l'emigration avant la formation de la glace. La survie apparente s'ameliore durant la periode marquee par la formation de glace dans la colonne d'eau et elle est considerablement meil-leure quand la glace de surface predomine; le declin de la taille de la population varie alors de 0 et 15,4 %. Globalement, la mortalite hivernale observee dans un meme site est faible (4,4 %) et la majorite des pertes de tacons de saumons marques sont dues a l'emigration. En moyenne, la population de tacons de saumons marques dans un meme site a baisse de 31,7 % durant l'ensemble de l'hiver (novembre-avril). Nos donnees indiquent que les impacts anthropiques, comme le changement climatique ou la regularisation du debit, affectent vraisemblablement le taux de survie apparente et la repartition des jeunes saumons atlantiques par leurs consequences sur le regime naturel des glaces dans les cours d'eau. [Traduit par la Redaction], Introduction Winter is recognized to be a critical period for survival of freshwater fishes (Hurst 2007). In fluvial systems, the 'winter bottleneck' has typically been associated with energetic imbalance (Finstad [...]

Adaptive responses to environmental heterogeneity may vary among populations. Genetic variability in reaction norms might account for population differences in the ability to respond to environmental change and may reflect local adaptation. Reaction norms for early life history traits were compared among three population crosses of Atlantic salmon (Salmo salar). Two comprised second-generation backcrosses introgressed with either farmed or wild genes; the third comprised individuals from a second-generation, pure wild cross. Using a common-garden experimental protocol, each cross was exposed to three temperature regimes. Plasticity in embryonic development, growth, survival, and body size was measured from fertilization up to 24 weeks of exogenous feeding. Reaction norms differed markedly among crosses, irrespective of whether individuals interbred with those whose genes originated from another wild population or from a cultured population. We find that introgression involving individuals with comparatively few genetic differences can change reaction norms. If plasticity represents an adaptive response to local environments, then changes to reaction norms resulting from interbreeding between populations are unlikely to have a beneficial effect on fitness. Les reactions adaptatives a l'heterogeneite de l'environnement peuvent varier d'une population a une autre. La variabilite genetique des normes de reaction peut expliquer les differences entre les populations dans leur capacite a reagir aux changements environnementaux et peut representer une adaptation locale. Nous avons compare les normes de reaction des traits du debut du cycle biologique chez trois populations croisees de saumons atlantiques (Salmo salar). Deux des populations comprenaient des individus retrocroises de seconde generation avec introgression de genes de pisciculture ou de genes sauvages; la troisieme comprenait des individus de seconde generation issus d'un croisement sauvage pur. Dans un protocole experimental de jardin commun, chaque croisement a ete expose a trois regimes thermiques. Nous avons mesure la plasticite du developpement embryonnaire, de la croissance, de la survie et de la taille corporelle depuis la fecondation jusqu'apres 24 semaines d'alimentation exogene. Les normes de reaction varient de facon marquee d'un croisement a l'autre, independamment du fait que les individus aient ete croises avec d'autres dont les genes provenaient d'une autre population sauvage ou d'une population d'elevage. Nous observons que l'introgression, qui implique des individus avec comparativement peu de differences genetiques, peut modifier les normes de reaction. Si la plasticite represente une reaction adaptative aux environnements locaux, alors les changements de normes de reaction dus aux croisements entre les populations sont peu susceptibles d'avoir un effet benefique sur la fitness. [Traduit par la Redaction], Introduction Phenotypic plasticity reflects the ability of individuals to respond to environmental change (Bradshaw 1965), a characteristic of presumed fundamental importance to the persistence of natural populations (Schlichting and Pigliucci [...]

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 [...]

Research | Facilities | Publishing | People | Environment | Business | Trend watch RESEARCH Science results emerge from US eclipse A total solar eclipse http://www.nature.com/news/mysteries-of-sun-s-corona-on-view-during-upcoming-eclipse-1.22434 on 21 August, delighting [...]

Abstract: Many prey fishes rely on damage-released chemical alarm cues to detect and avoid predators. The ability to use these cues has been shown to confer considerable survival benefits to [...]

Abstract: Atlantic salmon (Salmo salar) males may mature early in life in freshwater, rather than maturing after a migration to sea, if their size is above a threshold value. We [...]

Research has been conducted on male sneaking behavior of Atlantic salmon which leads to interspecific hybridization. Results demonstrate that this behavior helps sneaking Atlantic salmon males to fertilize brown trout ova in absence of brown trout males and that brown trout male aggressiveness towards sneaking salmon males and low survival of salmon sneaker hybrids are interspecific barriers.

A study assesses the role of temperature on the maintenance of Major Histocompatibility Complex (MHC) gene diversity along a latitudinal gradient in wild Atlantic salmon. Results suggest that genetic diversity at MHC class II represents local adaptation to cope with pathogen diversity in rivers associated with different thermal regimes.

Field experiments are conducted to test ontogenic sequence of density dependence by manipulating local density at two life-history stages in juvenile Atlantic salmon. The results indicate that density-dependent effects are partitioned amongst survival, growth and dispersal changes throughout ontogeny and these changes occur in correlation with changes in individual mortality risks and dispersal abilities, and suggest a general paradigm for the way in which juvenile density dependence is manifest in spatially structured populations of highly fecund organisms.

The wild Atlantic salmon is an imperiled species and is being covered by Endangered Species Act since November 2000. Involvement of schools, informing the public and implementation of WA Wetland Nursery are some of the measures taken to save the salmon.

The interaction of genetic and environmental components that acted on size and on the reproductive tactic in Atlantic salmon is examined by determining the moment of divergence of conditions between future mature and immature males. It was concluded that the genotype determining the threshold value, the size at emergence and intrinsic characteristics of the individual interacted with environmental condition in determining the reproductive phenotype expressed by an individual.

The endocrine system is responsible for the transmission of environmental cues to physiological response. The thyroid system has been implicated in behavioral changes that occur during the parr-smolt transformation of salmonids. The direct relationship between circulating thyroid hormone levels and downstream movements of individuals has not been explored. We demonstrated that when Atlantic salmon smolts are not provided an increase in daylength there is no expression of downstream migration and when provided with a prolonged cold spring the expression of downstream migration is extended. There is a close relationship between extended migration and physiological condition. Gill Na+, K+-ATPase activity and plasma T4 levels remained elevated in cold late springs compared to control groups. However, a dirct relationship between these physiological parameters and the photoperiod control of migration is not evident. Increases in thyroid hormone levels early in spring are likely to be necessary for the transmission of environmental cues for migration, but alone are not sufficient.

The Aysen region in southern Chile--a key habitat for several endangered marine species--is under enormous pressure from the country's powerful salmon industry. Chile should follow the lead of nations such [...]

Acid rain coupled with resulting increased aluminum (Al) is a potential cause of Atlantic salmon decline in many North American rivers. Smolts appear to be the most sensitive of the salmon lifestages to acid/Al (AA), however the mechanisms underlying increased sensitivity are unknown. Our goals were: to confirm that smolts are more sensitive to AA than parr, and to determine the mechanisms underlying increased sensitivity. In the lab, parr and smolts were exposed to either control or AA water, and sampled after 2 and 6 days. In AA smolts, plasma chloride decreased 11% and plasma glucose increased 3-fold after 6 days, however, in parr plasma chloride and glucose were unaffected. Gill Na+, K+ ATPase activity (NKA) and hematocrit of both lifestages were unaffected by AA. Gill Al increased > 7-fold after 2 and 6 days of treatment in both lifestages. After 6 days, parr gill Al was 2-fold > than smolts. In the field, caged parr and smolts were placed in either a reference (RS) or an AA impacted stream (AAS) and sampled after 2 and 6 days. Plasma chloride decreased 8.3% in AAS parr and 27% in smolts after 2 days. After 6 days, plasma chloride in AAS parr continued to decline, but partially recovered in AAS smolts. Plasma glucose increased 2.7- and 2.2-fold in AAS parr and smolts, respectively, and remained levated after 6 days. Gill NKA decreased 45% in both AAS parr and smolts after 6 days. Gill Al increased &gt 8-fold after 2 and 6 days of treatment in both lifestages. After 6 days, parr gill Al was 2-fold &gt than smolts. Our results confirm that smolt ionoregulatory ability is more sensitive to AA than that of parr, however neither decreased gill NKA nor elevated gill Al appear to be the mechanism of increased smolt sensitivity.