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Juvenile fish winter mortality, whether through starvation, predation, or disease, depends in part on feeding history. Assessing mortality risk thus requires metrics that can distinguish well-fed from poorly fed individuals. To investigate the effects of winter feeding and spring re-feeding after winter fasting on young-of-the-year Pacific herring (Clupea pallasii), captive herring were maintained on different feeding rations for 20 weeks under ambient winter and spring conditions and evaluated for differences in size, gut mass, RNA/DNA ratio, body composition, and swimming performance. Lipid and moisture levels were inversely related indicators of feeding history, differing most between full-ration and fasted herring. Fasted herring that were re-fed in spring had evidence of compensatory growth without impacting swimming performance. Minimal growth and reduced gut mass observed even among fully fed herring suggest limits to winter feeding benefits. Metabolically processing stored fat rather than foraging and incurring greater predation risk may thus be an advantageous strategy regardless of winter food availability. Mortalities due to starvation and possibly disease were highest among small herring across rations, supporting the importance of size-dependent winter mortality. La mortalite hivernale des poissons juveniles, par privation de nourriture, predation ou maladie, depend en partie de l'historique d'alimentation. Ainsi, l'evaluation du risque de mortalite necessite la mesure de parametres pouvant distinguer les individus bien nourris et mal nourris. Afin d'examiner les effets de l'alimentation hivernale et de la reprise de l'alimentation au printemps apres le jeune hivernal sur de jeunes harengs du Pacifique (Clupea pallasii) de l'annee, differentes rations ont ete donnees a des harengs captifs pendant 20 semaines dans des conditions ambiantes hivernales et printanieres, et les differences de taille, de masse du tube digestif, de rapport ARN/ADN, d'embonpoint et de performance de nage ont ete evaluees. Les teneurs en lipides et l'humidite ponderale sont des indicateurs inversement relies de l'historique d'alimentation, leurs differences etant les plus grandes entre les harengs nourris de rations completes et ceux ayant jeune. Les harengs ayant jeune en hiver qui ont ensuite ete nourris au printemps presentaient des signes de croissance compensatoire sans incidence sur la performance de nage. Une croissance tres limitee et une baisse de la masse du tube digestif observees meme chez les harengs nourris de rations completes indiqueraient qu'il y a des limites aux avantages de l'alimentation hivernale. Le traitement metabolique de graisses emmagasinees plutot que la quete de nourriture engendrant un plus grand risque de predation pourrait donc constituer une strategie avantageuse, peu importe la disponibilite de nourriture en hiver. La mortalite causee par la privation de nourriture et, possiblement, par la maladie est la plus grande chez les petits harengs, peu importe la ration, ce qui souligne l'importance de la mortalite hivernale dependante de la taille. [Traduit par la Redaction], Introduction For high-latitude juvenile fishes, winter feeding is commonly believed to be insufficient to achieve metabolic demands, resulting in caloric deficits and corresponding declines in condition, though winter starvation mortality [...]

The Arctic nearshore surrounding Point Barrow, Alaska, is a dynamic system with complex oceanographic and meteorological processes that drive community composition to change rapidly in space and time. Nearshore fish and zooplankton communities were sampled in the summers of 2013-2015. Spatial, temporal, environmental, and biological drivers of fish community structure in the Arctic nearshore surrounding Point Barrow were investigated using multivariate canonical correspondence analysis (CCA). A CCA model using the 13 most explanatory variables (three environmental, one spatial, four temporal, and five zooplankton abundances) explained 73% of the variance in community structure in this region. Distinct fish communities were identified within the three waterbodies that were studied (Chukchi Sea, Beaufort Sea, and Elson Lagoon), and these distinctions were largely driven by salinity. Species move into the nearshore at various times after landfast ice breaks up, creating an annual succession of species that can be found in these nearshore habitats. Low-latitude species tend to become abundant later in the summer season, whereas true Arctic species are present under the ice or move in shortly after breakup. Arctic species are also more abundant in colder years, whereas low-latitude species dominate during warmer years. The increasing abundance of low-latitude species in the Arctic nearshore may have serious implications for the food webs in these ecosystems as climate change continues. Le littoral arctique entourant la pointe Barrow (Alaska) est un systeme dynamique caracterise par des processus oceanographiques et meteorologiques complexes qui engendrent des changements rapides de la composition des communautes dans le temps et l'espace. Les communautes littorales de poissons et de zooplancton ont ete echantillonnees durant les etes 2013 a 2015. Les facteurs spatiaux, temporels, environnementaux et biologiques qui modulent la structure des communautes de poissons dans la zone littorale arctique entourant la pointe Barrow ont ete examines en utilisant l'analyse canonique des correspondances (ACC) multivariee. Un modele d'ACC integrant les 13 variables les plus explicatives (trois variables environnementales, une spatiale, quatre temporelles et cinq d'abondance du zooplancton) explique 73 % de la variance dans la structure des communautes dans cette region. Differentes communautes de poissons ont ete cernees dans les trois plans d'eau etudies (la mer des Tchouktches, la mer de Beaufort et la lagune d'Elson), ces distinctions etant majoritairement modulees par la salinite. Des especes entrent dans la zone littorale a divers moments apres la debacle de la glace de rive, creant une succession annuelle d'especes pouvant etre observees dans ces habitats littoraux. Les especes de faibles latitudes ont tendance a devenir abondantes plus tard durant l'ete, alors que les especes veritablement arctiques sont presentes sous la glace ou arrivent peu apres la debacle. Les especes arctiques sont aussi plus abondantes durant les annees plus froides, alors que les especes de faibles latitudes predominent durant les annees plus chaudes. Avec la poursuite des changements climatiques, l'augmentation de l'abondance d'especes de faibles latitudes dans la zone littorale arctique pourrait entramer de graves consequences pour les reseaux trophiques dans ces ecosystemes. [Traduit par la Redaction], Introduction Environmental scientists have shifted attention to polar regions where the effects of climate change occur most rapidly (Johannesson et al. 2004). In addition to environmental changes, decreasing sea ice [...]

Walleye pollock (Theragra chalcogramma) is an important component of the eastern Bering Sea ecosystem and subject to major fisheries. The Oscillating Control Hypothesis (OCH) predicted that recruitment of pollock year classes should be greatest in years with early ice retreat and late blooms in warm water, because more energy would flow into the pelagic (vs. benthic) community. The OCH further predicted that, with pollock population growth, there should be a shift from bottom-up to top-down regulation. New data support the predictions that in those years with early ice retreat, more primary production accrues to the pelagic compartment and that large numbers of age-0 pollock survive to summer. However, in these years, production of large crustacean zooplankton is reduced, depriving age-0 pollock of lipid-rich prey in summer and autumn. Consequently, age-0 pollock energy reserves (depot lipids) are low and predation on them is increased as fish switch to age-0 pollock from zooplankton. The result is weak recruitment of age-1 recruits the following year. A revised OCH indicates bottom-up constraints on pollock recruitment in very warm periods. Prolonged warm periods with decreased ice cover will likely cause diminished pollock recruitment and catches relative to recent values. © 2011 International Council for the Exploration of the Sea.

In Southeast Alaska, overwintering Pacific herring (Clupea pallasii) form large conspicuous schools that are preyed upon by an abundance of mammalian and avian predators, thus leading to the question of why herring adopt a strategy that appears counterproductive to predator avoidance during these periods. We examined the spatial and temporal dynamics of overwintering Pacific herring and associations with predators through monthly hydroacoustic surveys during two consecutive winters. Large variation was observed through the winter season in herring distribution, school morphology, and density. Herring school characteristics and biomass estimates were negatively correlated with humpback whale (Megaptera novaeangliae) abundance patterns during both winters, and as whales departed towards the end of winter, herring distributions shifted from dispersed schools in the water column toward deep, dense schools. We postulate that the schooling patterns observed in Lynn Canal overwintering herring are likely to be mediated by predation threat rather than energetics or feeding activities. An additional consequence of humpback whales dispersing herring in the water column may be an increased threat of predation by other surface-oriented predators. Dans le sud-est de l'Alaska, lors de periodes d'hivernage les harengs du Pacifique (Clupea pallasii) se regroupent dans des zones bien precises ou ils forment de grands bancs tres visibles, predates par de nombreuses especes de mammiferes et d'oiseaux marins. Ceci souleve la question de savoir pourquoi les harengs adoptent une telle strategie qui semble etre contre-productive en terme de survie durant ces periodes. Nous avons examine les comportements de bancs de harengs du Pacifique et leurs relations avec la presence de predateurs au cours de releves acoustiques effectues lors de deux hivers consecutifs. Nos resultats demontrent une variation significative des caracteristiques des bancs, ainsi que des biomasses estimees, negativement correlees avec l'abondance de baleines a bosse (Megaptera novaeangliae) au cours des deux hivers. Le depart de ces predateurs de la zone d'etude est suivi d'un changement de distribution des bancs de harengs passant de disperses dans la colonne d'eau, a denses et profonds typiques des periodes d'hivernage. Les comportements des harengs du Pacifique observes dans la zone d'etude ne seraient pas induits par des considerations energetiques ou d'alimentation, mais refleteraient plutot une reponse directe a la pression de predation. La presence de baleines a bosse semble forcer les bancs de harengs a se disperser dans la colonne d'eau, avec comme possible consequence d'augmenter leur vulnerabilite face a d'autres predateurs de surface., Introduction Predator avoidance is the prime explanation for why many pelagic fishes aggregate to form large-scale schools (Magurran 1990; Rieucau et al. 2015a). Although schooling is commonly considered as an [...]

We examined how marine-derived nutrients (MDN), in the form of spawning Pacific salmon, influenced the nutritional status and δ[sup.15]N of stream-dwelling fishes. We sampled juvenile coho salmon (Oncorhynchus kisutch) and Dolly Varden (Salvelinus malma) during spring and fall from 11 south-central Alaskan streams that ranged widely in spawning salmon biomass (0.1-4.7 kg x [m.sup.-2]). Growth rate (as indexed by RNA-DNA ratios), energy density, and δ[sup.15]N enrichment in spring-sampled fishes increased with spawner biomass, indicating the persistence of spawner effects more than 6 months after salmon spawning. Point estimates suggest that spawner effects on nutrition were substantially greater for coho salmon than Dolly Varden (268% and 175% greater for growth and energy, respectively), indicating that both species benefitted physiologically, but that juvenile coho salmon accrued more benefits than Dolly Varden. Although the data were less conclusive for fall- than spring-sampled fish, they do suggest spawner effects were also generally positive during fall, soon after salmon spawned. In a follow-up analysis where growth rate and energy density were modeled as a function of δ[sup.15]N enrichment, results suggested that both increased with MDN assimilation, especially in juvenile coho salmon. Our results support the importance of salmon runs to the nutritional ecology of stream-dwelling fishes. Nous examinons comment les nutriments d'origine marine (MDN), que representent les saumons du Pacifique en fraie, influencent le statut nutritif et le δ[sup.15]N des poissons des cours d'eau. Nous avons echantillonne des jeunes saumons coho (Oncorhynchus kisutch) et Dolly Varden (Salvelinus malma) durant le printemps et l' automne dans 11 cours d' eau du centre-sud de l'Alaska qui differaient considerablement par la biomasse de saumons en fraie (0,1-1,7 kg x [m.sup.-2]). Le taux de croissance (mesure par les rapports ARN-ADN), la densite energetique et l'enrichissement de δ[sup.15]N chez les poissons preleves au printemps augmentent tous en fonction de la biomasse des reproducteurs en fraie, ce qui indique une persistance des effets des reproducteurs plus de 6 mois apres la fraie des saumons. Des estimations ponctuelles laissent penser que l'effet des reproducteurs sur la nutrition est substantiellement plus important pour le saumon coho que pour la Dolly Warden (respectivement 268 % et 178 % superieur pour la croissance et l'energie), ce qui indique que les deux especes profitent du point de vue physiologique, mais que les jeunes saumons cohos accumulent plus d'avantages que les Dolly Warden. Bien que les donnees soient moins claires chez les poissons echantillonnes a l'automne que chez ceux du printemps, elles indiquent que les effets des reproducteurs sont aussi generalement favorables durant l'automne, peu apres la fraie des saumons. Lors d' une etude subsequente, nous avons modelise le taux de croissance et la densite energetique en fonction de l' enrichissement de δ[sup.15]N; les resultats indiquent que les deux augmentent avec l'assimilation des MDN, particulierement chez les jeunes saumons cohos. Nos resultats soulignent l'importance des montaisons de saumons pour l'ecologie de l'alimentation chez les poissons qui habitent les cours d'eau. [Traduit par la Redaction], Introduction Ecosystems are linked through movements of material, and these spatial subsidies can greatly affect community interactions and enhance productivity (Polis et al. 1997; Wipfli and Baxter 2010). Many subsidies [...]

Abstract--New technologies can be riddled with unforeseen sources of error, jeopardizing the validity and application of their advancement. Bioelectrical impedance analysis (BIA) is a new technology in fisheries research that [...]

Abstract--In this study, phase angle (the ratio of resistance and reactance of tissue to applied electrical current) is presented as a possible new method to measure fish condition. Condition indices [...]

A first-order loss-rate kinetic model of polynuclear aromatic hydrocarbon (PAH) weathering prove useful in determining the petroleum spilled from the oil tanker T/V Exxon Valdez in the environment. Around 1541 field samples were found to contain adequate concentration of PAH to validate the application of the model. Results indicated that the rate of weathering of petroleum depends on the ratio of surface area to volume of petroleum in the environment.