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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 [...]

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 [...]

Studies examining species occurrence often fail to account for false absences in field sampling. We investigate detection probabilities of five gear types for six fish species in a sample of lakes on the North Slope, Alaska. We used an occupancy modeling approach to provide estimates of detection probabilities for each method. Variation in gear- and species-specific detection probability was considerable. For example, detection probabilities for the fyke net ranged from 0.82 (SE = 0.05) for least cisco (Coregonus sardinella) to 0.04 (SE = 0.01) for slimy sculpin (Cottus cognatus). Detection probabilities were also affected by site-specific variables such as depth of the lake, year, day of sampling, and lake connection to a stream. With the exception of the dip net and shore minnow traps, each gear type provided the highest detection probability of at least one species. Results suggest that a multimethod approach may be most effective when attempting to sample the entire fish community of Arctic lakes. Detection probability estimates will be useful for designing optimal fish sampling and monitoring protocols in Arctic lakes. Les etudes sur l'occurrence des especes ne tiennent souvent pas compte des fausses absences dans l'echantillonnage sur le terrain. Nous nous sommes penches sur les probabilites de detection associees a cinq types d'engins pour six especes de poissons dans un echantillon de lacs de la North Slope, en Alaska. Nous avons utilise une approche de modelisation de l'occupation pour obtenir des estimations des probabilites de detection pour chaque methode. Les variations de la probabilite de detection selon l'engin et l'espece etaient considerables. Par exemple, les probabilites de detection pour le verveux allaient de 0,82 (ET = 0,05) pour le cisco sardinelle (Coregonus sardinella)a 0,04 (ET = 0,01) pour le chabot visqueux (Cottus cognatus). Des variables propres au site avaient egalement une incidence sur la probabilite de detection, dont la profondeur du lac, l'annee, le jour d'echantillonnage et la connexion du lac a un cours d'eau. A l'exception de l'epuisette et de la nasse a vairons placee sur la rive, chaque type d'engins offrait la probabilite de detection la plus elevee pour au moins une espece. Ces resultats suggerent que le recours a plusieurs methodes pourrait etre l'approche la plus efficace pour l'echantillonnage de la communaute entiere de poissons d'un lac arctique. Les estimations de la probabilite de detection seront utiles a l'elaboration de protocoles optimaux d'echantillonnage et de surveillance des poissons dans les lacs arctiques. [Traduit par la Redaction], Introduction The study of how species' distributions vary over time, space, and environmental heterogeneity has long been a central theme in ecology (e.g., Elton 1927; Krebs 1978). Studies of these [...]

Abstract: Generalist feeding strategies are favoured in stressful or variable environments where flexibility in ecological traits is beneficial. Species that feed across multiple habitat types and trophic levels may impart stability on food webs through the use of readily available, alternative energy pools. In lakes, generalist fish species may take advantage of spatially and temporally variable prey by consuming both benthic and pelagic prey to meet their energy demands. Using stomach content and stable isotope analyses, we examined the feeding habits of fish species in Alaska's Arctic Coastal Plain (ACP) lakes to determine the prevalence of generalist feeding strategies as a mechanism for persistence in extreme environments (e.g. low productivity, extreme cold and short growing season). Generalist and flexible feeding strategies were evident in five common fish species. Fish fed on benthic and pelagic (or nektonic) prey and across trophic levels. Three species were clearly omnivorous, feeding on fish and their shared invertebrate prey. Dietary differences based on stomach content analysis often exceeded 70%, and overlap in dietary niches based on shared isotopic space varied from zero to 40%. Metrics of community‐wide trophic structure varied with the number and identity of species involved and on the dietary overlap and niche size of individual fishes. Accumulation of energy from shared carbon sources by Arctic fishes creates redundancy in food webs, increasing likely resistance to perturbations or stochastic events. Therefore, the generalist and omnivorous feeding strategies employed by ACP fish may maintain energy flow and food web stability in extreme environments. [ABSTRACT FROM AUTHOR]