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Salmonid populations are often regulated by territorial competition among juveniles for food and space. In the canonical view, salmonid territories are spaced horizontally across the river bottom in a two-dimensional mosaic. However, some juveniles instead feed in tight, three-dimensional (3-D) social groups. To investigate whether territoriality is possible within such groups, we applied a new concept--the momentary home range--to quantify the size, exclusivity, and temporal dynamics of 3-D space use by juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Chena River, AK. Individual strategies spanned a broad continuum of exclusivity and stationarity. However, some of the largest, most dominant fish in each group aggressively defended stationary, exclusive feeding spaces and thus were unambiguously territorial. Transient floaters entered and left the group quickly. A majority of fish were not aggressive but nevertheless occupied exclusive, stationary spaces that probably function as territories with regard to resource distribution and population regulation. The presence of territoriality within social groups, in a 3-D configuration, expands the known domain of this important behavior. Key words: territoriality, home range, Chinook salmon, schooling, salmonids, drift foraging, Introduction Patterns of space use are among the most fundamental relationships between animals and their environment, and competition for space strongly affects population dynamics in many species (Adams 2001). For [...]

Applications of video in fisheries research range from simple biodiversity surveys to three-dimensional (3D) measurement of complex swimming, schooling, feeding, and territorial behaviors. However, researchers lack a transparently developed, easy-to-use, general purpose tool for 3D video measurement and event logging. Thus, we developed a new measurement system, with freely available, user-friendly software, easily obtained hardware, and flexible underlying mathematical methods capable of high precision and accuracy. The software, VidSync, allows users to efficiently record, organize, and navigate complex 2D or 3D measurements of fish and their physical habitats. Laboratory tests showed submillimetre accuracy in length measurements of 50.8 mm targets at close range, with increasing errors (mostly Les applications de la video en recherche sur la peche vont de simples etudes de la biodiversite a la mesure en trois dimensions (3D) des complexes comportements territoriaux, de nage, de rassemblement en bancs et d'alimentation. Les chercheurs ne disposent toutefois pas d'un outil convivial a usage general developpe de maniere transparente pour la mesure video en 3D et la consignation d'evenements. Nous avons donc mis au point un nouveau systeme de mesure comprenant un logiciel gratuit et convivial et du materiel facile a obtenir, qui repose sur des methodes mathematiques souples pouvant produire des resultats de grandes exactitude et precision. Le logiciel, VidSync, permet aux usagers de consigner, d'organiser et de consulter des mesures 2D ou 3D complexes des poissons et de leurs habitats physiques. Des essais en laboratoire ont demontre une exactitude submillimetrique des mesures de la longueur de cibles de 50,8 mm prises a faible distance, l'erreur augmentant (generalement, Introduction Video-based methods to observe and measure animals and their behavior have diverse applications in fish research (Shortis et al. 2009), and they are especially useful for species sensitive to [...]

Most studies of cross-ecosystem resource subsidies have demonstrated positive effects on recipient consumer populations, often with very large effect sizes. However, it is important to move beyond these initial addition-exclusion experiments to consider the quantitative consequences for populations across gradients in the rates and quality of resource inputs. In our introduction to this special issue, we describe at least four potential models that describe functional relationships between subsidy input rates and consumer responses, most of them asymptotic. Here we aim to advance our quantitative understanding of how subsidy inputs influence recipient consumers and their communities. In the papers following, fish were either the recipient consumers or the subsidy as carcasses of anadromous species. Advancing general, predictive models will enable us to further consider what other factors are potentially co-limiting (e.g., nutrients, other population interactions, physical habitat, etc.) and better integrate resource subsidies into consumer-resource, biophysical dynamics models. La plupart des etudes des apports de ressources entre ecosystemes ont demontre des effets positifs sur les populations de consommateurs recepteurs, dont, bien souvent, de tres grands effets sur la taille. Il importe toutefois d'aller au-dela de ces experiences initiales d'ajout-exclusion pour examiner les consequences quantitatives sur les populations le long de gradients du taux et de la qualite des apports de ressources. Dans notre article d'introduction au present numero special, nous decrivons au moins quatre modeles potentiels qui decrivent les relations fonctionnelles entre les taux d'apports de ressources et les reactions de consommateurs, la plupart etant asymptotiques. Nous tentons ainsi d'accroitre la comprehension quantitative de l'influence des apports sur les consommateurs recepteurs et les communautes dont ils font partie. Dans les articles suivants, des poissons representent soit des consommateurs recepteurs ou des apports, sous forme de carcasses d'especes anadromes. Le developpement de modeles predictifs generaux permettra d'evaluer quels autres facteurs pourraient etre colimitants (p. ex. nutriments, autres interactions de populations, habitat physique) et de mieux integrer les apports de ressources aux modeles biophysiques de la dynamique consommateurs-ressources. [Traduit par la Redaction], Introduction The importance of cross-ecosystem resource subsidies has been recognized in a variety of ecosystems for decades. Leaf detritus or dissolved organic matter entering freshwater food webs, sea wrack decomposing [...]

Contributions of terrestrial-, freshwater-, and marine-derived prey resources to stream fishes vary over time and space, altering the energy pathways that regulate production. In this study, we determined large-scale use of these resources by juvenile Chinook and coho salmon (Oncorhynchus tshawytscha and Oncorhynchus kisutch, respectively) in the glacial Susitna River, Alaska. We resolved spatial and temporal trophic patterns among multiple macrohabitat types along a 97 km segment of the river corridor via stable isotope and stomach content analyses. Juvenile salmon were supported primarily by freshwater-derived resources and secondarily by marine and terrestrial sources. The relative contribution of marine-derived prey to rearing salmon was greatest in the fall within off-channel macrohabitats, whereas the contributions of terrestrial invertebrate prey were generally greatest during midsummer, across all macrohabitats. No longitudinal (upstream-downstream) diet pattern was discernable. These results highlight large-scale spatial and seasonal patterns of energy flow and the dynamic interplay of pulsed marine and terrestrial prey subsidies to juvenile Chinook and coho salmon in a large, complex, and relatively pristine glacial river. Les apports de ressources de proies issues de sources terrestres, marines et d'eau douce aux poissons de cours d'eau varient dans le temps et l'espace, modifiant les voies energetiques qui regissent la production. Nous avons determine l'utilisation a grande echelle de ces ressources par des saumons quinnats et cohos (Oncorhynchus tshawytscha et Oncorhynchus kisutch, respectivement) juveniles dans la riviere Susitna, une riviere glaciaire en Alaska. Nous avons defini les motifs trophiques spatiaux et temporels dans differents types de microhabitats le long d'un troncon de 97 km du corridor de la riviere a l'aide d'analyses d'isotopes stables et des contenus stomacaux. Les saumons juveniles etaient supportes principalement par des ressources provenant de sources d'eau douce et deuxiemement par de sources marines et terrestres. La contribution relative de proies de sources marines a la croissance des saumons etait la plus forte a l'automne dans les microhabitats hors du chenal, alors que les contributions des proies invertebrees terrestres etaient generalement les plus grandes au milieu de l'ete, dans tous les microhabitats. Aucun motif longitudinal (de l'amont vers l'aval) d'alimentation n'a ete decele. Ces resultats font ressortir des motifs spatiaux et saisonniers a grande echelle des flux d'energie, ainsi que l'interaction dynamique d'apports ponctuels de proies marines et terrestres aux saumons quinnats et cohos juveniles dans une grande riviere glaciaire complexe et relativement vierge. [Traduit par la Redaction], Introduction Riverine landscapes are complex assemblages of dynamic habitats in which aquatic consumers receive energy and nutrients from a number of ecologically distinct sources (Polis et al. 1997). Salmon-bearing river [...]

The spread of invasive species in riparian forests has the potential to affect both terrestrial and aquatic organisms linked through cross-ecosystem resource subsidies. However, this potential had not been explored in regards to terrestrial prey subsidies for stream fishes. To address this, we examined the effects of an invasive riparian tree, European bird cherry (EBC, Prunus padus), spreading along urban Alaskan salmon streams, by collecting terrestrial invertebrates present on the foliage of riparian trees, their subsidies to streams, and their consumption by juvenile coho salmon (Oncorhynchus kisutch). Riparian EBC supported four to six times less terrestrial invertebrate biomass on its foliage and contributed two to three times lower subsidies relative to native deciduous trees. This reduction in terrestrial invertebrate biomass was consistent between two watersheds over 2 years. In spite of this reduction in terrestrial prey resource input, juvenile coho salmon consumed similar levels of terrestrial invertebrates in stream reaches bordered by EBC. Although we did not see ecological effects extending to stream salmonids, reduced terrestrial prey subsidies to streams are likely to have negative consequences as EBC continues to spread. La propagation d'especes envahissantes dans les forets ripisylves a le potentiel d'influencer les organismes terrestres et aquatiques relics par l'entremise d'apports de ressources entre ccosystemes. Ce potentiel n'a toutefois pas ctc explorce en ce qui concerne les apports de proies terrestres pour les poissons de cours d'eau. Nous avons donc examinc les effets de la propagation d'un arbre riverain envahissant, le cerisier a grappes d'Europe (Prunus padus, CGE), le long de rivieres a saumons en Alaska en caractcrisant les invertcbrcs terrestres prcsents dans le feuillage d'arbres riverains, leurs apports aux cours d'eau et la consommation qu'en font les saumons cohos (Oncorhynchus kisutch) juvcniles. Les CGE riverains a soutenu une biomasse d'invertcbrcs terrestres sur leur feuillage de quatre a six fois infcrieure et a contribuc des apports de deux a trois fois infcrieurs a ceux d'arbres feuillus indigenes. Une telle reduction de la biomasse d'invertcbrcs terrestres a ctc observce dans deux bassins versants et sur deux annces. Malgrc cette rcduction des apports de ressources de proies terrestres, les saumons cohos juvcniles consommaient des quantitcs semblables d'invertcbrcs dans les troncons de cours d'eau bordcs par des CGE. Bien qu'aucun effet ccologique n'ait ctc observc sur les salmonidcs lotiques, il est probable que la reduction des apports de proies terrestres dans les cours d'eau aura des conscquences ncgatives a mesure qu'avance la propagation des CGE. [Traduit par la Rcdaction], Introduction Stream and riparian ecosystems are linked through resource subsidies that extend beyond ecosystem boundaries, supporting adjacent species and food webs (Polis et al. 1997; Nakano and Murakami 2001; Power [...]

Yukon River Chinook salmon (Oncorhynchus tshawytscha) populations are declining for unknown reasons, creating hardship for thousands of stakeholders in subsistence and commercial fisheries. An informed response to this crisis requires understanding the major sources of variation in Chinook salmon productivity. However, simple stock-recruitment models leave much of the variation in this system's productivity unexplained. We tested adding environmental predictors to stock-recruitment models for two Yukon drainage spawning streams in interior Alaska--the Chena and Salcha rivers. Low productivity was strongly associated with high stream discharge during the summer of freshwater residency for young-of-the-year Chinook salmon. This association was more consistent with the hypothesis that sustained high discharge negatively affects foraging conditions than with acute mortality during floods. Productivity may have also been reduced in years when incubating eggs experienced major floods or cold summers and falls. These freshwater effects--especially density dependence and high discharge--helped explain population declines in both rivers. They are plausible as contributors to the decline of Chinook salmon throughout the Yukon River drainage. Les populations de saumons quinnats (Oncorhynchus tshawytscha) du fleuve Yukon sont en baisse pour des raisons inconnues, ce qui entraine une situation difficile pour des milliers de parties prenantes des peches de subsistance et commerciales. Une reponse eclairee a cette crise requiert la comprehension des grandes sources de variation de la productivite du saumon quinnat. Les modeles simples de recrutement aux stocks n'arrivent toutefois pas a expliquer une bonne partie des variations de productivite dans ce systeme. Nous avons teste la pertinence d'ajouter des variables environnementales predictives aux modeles de recrutement aux stocks pour deux cours d'eau de frai du bassin versant du fleuve Yukon dans l'interieur de l'Alaska, les rivieres Chena et Salcha. Une faible productivite etait fortement associee a des debits eleves durant l'ete de la residence en eau douce des saumons quinnats de l'annee. Cette association correspondait mieux a l'hypothese selon laquelle un debit eleve soutenu a une incidence negative sur les conditions d'approvisionnement qu'avec l'hypothese d'une mortalite aigue durant les crues. Il se peut aussi qu'une reduction de la productivite ait eu lieu durant des annees ou les oeufs en incubation ont ete exposes a de grandes crues ou des etes et automnes froids. Ces effets associes au milieu d'eau douce, particulierement la dependance sur la densite et les debits eleves, contribuent a expliquer les baisses des populations dans les deux rivieres. Il s'agit de facteurs plausibles du declin du saumon quinnat dans tout le bassin versant du fleuve Yukon. [Traduit par la Redaction], Introduction The Yukon River Chinook salmon (Oncorhynchus tshawytscha) population historically supported commercial and subsistence fisheries harvesting over 140 000 fish annually (Evenson et al. 2009). It is a culturally and [...]

Salmon provide an important resource subsidy and linkage between marine and land-based ecosystems. This flow of energy and nutrients is not unidirectional (i.e., upstream only); in addition to passive nutrient export via stream flow, juvenile emigrants actively export nutrients from freshwater environments. In some cases, nutrient export can exceed import. We evaluated nutrient fluxes in streams across central Idaho, USA, using Chinook salmon (Oncorhynchus tshawytscha) adult escapement and juvenile production data from 1998 to 2008. We found in the majority of stream-years evaluated, adults imported more nutrients than progeny exported; however, in 3% of the years, juveniles exported more nutrients than their parents imported. On average, juvenile emigrants exported 22% ± 3% of the nitrogen and 30% ± 4% of the phosphorus their parents imported. This relationship was density-dependent and nonlinear; during periods of low adult abundance, juveniles were larger and exported up to 194% and 268% of parental nitrogen and phosphorus inputs, respectively. We highlight minimum escapement thresholds that appear to (i) maintain consistently positive net nutrient flux and (ii) reduce the average proportional rate of export across study streams. Our results suggest a state shift occurs when adult spawner abundance falls below a threshold to a point where the probability of juvenile nutrient exports exceeding adult imports becomes increasingly likely. Les saumons assurent un transfert des ressources et un lien importants entre les ecosystemes marins et terrestres. Ce flux d'energie et de nutriments n'est pas unidirectionnel (c.-a-d. uniquement vers l'amont); en plus de l'exportation passive de nutriments assuree par l'ecoulement de l'eau, les emigrants juveniles exportent activement des nutriments hors des milieux d'eau douce. Dans certains cas, l'exportation de nutriments peut surpasser leur importation. Nous avons evalue les flux de nutriments dans des cours d'eau du centre de l'Idaho (Etats-Unis) a partir de donnees sur l'echappement d'adultes et la production de juveniles de saumon quinnat (Oncorhynchus tshawytscha) recueillies de 1998 a 2008. Nous avons constate, pour la majorite des annees-cours d'eau evaluees, que les adultes importaient plus de nutriments que leur descendance en exportait. Cela dit, pour 3 % des annees, les juveniles exportaient plus de nutriments que leurs parents en importaient. En moyenne, les emigrants juveniles exportaient l'equivalent de 22% ± 3%del'azote et 30%[+ or -]4%duphosphore importes par leurs parents. Cette relation dependait de la densite et etait non lineaire; durant les periodes de faible abondance d'adultes, les juveniles etaient plus grands et exportaient jusqu'a 194 % et 268 % des apports parentaux d'azote et de phosphore, respectivement. Nous mettons en lumiere des seuils d'echappement minimums qui semblent (i) maintenir un flux net de nutriments uniformement positif et (ii) reduire le taux d'exportation proportionnel moyen dans les cours d'eau etudies. Nos resultats suggerent qu'un changement d'etat se produit quand l'abondance des geniteurs adultes tombe sous un seuil au-dela duquel la probabilite que les exportations de nutriments par les juveniles depassent les importations par les adultes est de plus en plus grande. [Traduit par la Redaction], Introduction Migratory salmonids are important vectors of energy (carbon (C)) and nutrients (nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca)) between marine and freshwater ecosystems (Lyle and Elliot 1998; [...]

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: This study examined the influence of fall-spawning coho salmon (Oncorhynchus kisutch) on the density, growth rate, body condition, and survival to outmigration of juvenile coho salmon on the Copper [...]

Abstract: Factors (riparian stand condition, management regimes, and channel properties) affecting distributions of wood, detritus (leaves and branches), and sediment were examined in headwater streams draining young-growth red alder (Alnus [...]

PACIFIC SALMON SUBSIDIZE FRESHWATER AND TERRESTRIAL ECOSYSTEMS THROUGH SEVERAL PATHWAYS, WHICH GENERATES UNIQUE MANAGEMENT AND CONSERVATION ISSUES BUT ALSO PROVIDES VALUABLE RESEARCH OPPORTUNITIES Salmon runs in the Pacific Northwest have [...]

Predation on anadromous salmon can have important consequences for both predators and prey. Salmon provide large seasonal pulses of energy and nutrients via carcasses, eggs and juveniles to many freshwater consumers, and conversely, predation can represent a significant source of mortality for juvenile salmon. Recent declines of Chinook salmon (Oncorhynchus tshawytscha) populations in Alaska have raised concern that predation might inhibit their recovery. Here, we quantify patterns of predation by freshwater fishes on juvenile salmon across seasons, habitats, predator sizes and streamflow levels in the Arctic‐Yukon‐Kuskokwim region of Alaska. We analysed piscivore stomach contents and identified prey using DNA sequence "barcoding." In coastal rivers, juvenile pink (O. gorbuscha) and chum (O. keta) salmon contributed heavily to Arctic grayling (Thymallus arcticus) and Dolly Varden char (Salvelinus malma) diets, coho salmon (O. kisutch) prey were rare, and Chinook salmon were not detected. In interior rivers, Arctic grayling, burbot (Lota lota) and northern pike (Esox lucius) consumed small numbers of Chinook salmon. Predation on Chinook salmon was documented disproportionately in sloughs during a summer of exceptionally high streamflow. Dietary and distributional patterns suggested northern pike and burbot may exclude salmon from sloughs in low‐gradient river reaches that would otherwise provide suitable rearing habitat. The data also provided tentative support for the hypothesis that high streamflow induces juvenile Chinook salmon to move from mainstem habitats into sloughs, where they face an increased risk of mortality. Incorporating predation risk into climate adaptation, fisheries management and habitat restoration decisions may help to facilitate Chinook salmon recovery. [ABSTRACT FROM AUTHOR]