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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 [...]

Salmonids frequently adapt their feeding and movement strategies to cope with seasonally fluctuating stream environments. Oncorhynchus mykiss tend to drift-forage in higher velocity habitat than other salmonids, yet their presence in streams with seasonally low velocity and drift suggests behavioral flexibility. We combined 3D videogrammetry with measurements of invertebrate drift and stream hydraulics to investigate the drivers of O. mykiss foraging mode and movement during the seasonal recession in a California stream. From May to July (2016), foraging movement rate increased as prey concentration and velocity declined; however, movement decreased in August as pools became low and still. In May, 80% of O. mykiss were drift-foraging, while by July, over 70% used search or benthic-foraging modes. Velocity and riffle crest depth were significant predictors of foraging mode, while drift concentration was a poor univariate predictor. However, topranked additive models included both hydraulic variables and drift concentration. A drift-foraging bioenergetic model was a poor predictor of foraging mode. We suggest that infall and benthic prey, as well as risk aversion, may influence latesummer foraging decisions. Les salmonides adaptent frequemment leurs strategies d'alimentation et de deplacement selon les fluctuations saisonnieres des milieux des cours d'eau. Si les Oncorhynchus mykiss ont tendance a s'alimenter d'organismes a la derive dans des habitats de plus grande vitesse d'ecoulement que d'autres salmonides, leur presence dans des cours d'eau qui, en certaines saisons, presentent de faibles vitesses d'ecoulement et de faibles concentrations de la derive indiquerait une certaine souplesse comportementale. Nous avons combine la videogrammetrie en 3D a des mesures de la derive d'invertebres et de l'hydraulique du cours d'eau pour etudier les facteurs qui modulent le mode de quete de nourriture et les deplacements des O. mykiss durant la recession saisonniere d'un cours d'eau californien. De mai a juillet (2016), la frequence des deplacements de quete de nourriture augmentait a mesure que la concentration de proies et la vitesse du courant diminuaient; les deplacements ont toutefois faibli en aout, alors que l'eau dans les fosses etait devenue basse et stagnante. En mai, 80 % des O. mykiss s'alimentaient de la derive, alors qu'en juillet, plus de 70 % utilisaient des modes de recherche ou d'approvisionnement benthique. La vitesse d'ecoulement et la profondeur des cretes de seuil etaient des indicateurs significatifs du mode d'approvisionnement, alors que la concentration de la derive etait un pietre indicateur univarie. Les modeles additifs les plus performants integrent toutefois des variables hydrauliques et la concentration de la derive. Un modele bioenergetique de consommation d'organismes a la derive ne predit pas bien le mode d'approvisionnement. Nous proposons que les proies qui tombent dans le cours d'eau et les proies benthiques, ainsi que l'aversion pour le risque, pourraient influencer les decisions d'approvisionnement a la fin de l'ete. [Traduit par la Redaction], Introduction Substantial work has examined the fitness consequences of foraging behavior for juvenile salmonids. Much has focused on the energetics and position choices of drift-foraging, where fish hold at stations [...]

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 [...]

Habitat selection is an important phenomenon that may greatly affect individual fitness. Using an artificial stream, we examined the relationship between the percentage of prey captured, reactive distance, dominance, and water velocity for juvenile Chinook Salmon (Oncorhynchus tshawytscha) from the Chena River, Alaska, and tested the fitness-based microhabitat selection model of Grossman et al. (Ecol Freshw Fish 11:2-10, 2002). Recent declines in the abundance of Chinook accentuate our need for habitat selection studies on this species. We conducted three experiments: two with single fish (1st N = 27, fish SL 58-84 mm, 2nd N = 14, fish SL 49-56 mm) and one with pairs of dominant and subordinate fish (N = 10 pairs, 64-96 mm, mean difference in SL = 7 mm). We placed individual or pairs of fish in an artificial flume and recorded reactive distance and the percent prey capture with individual dead brine shrimp (Artemia spp.) as prey. Prey were presented at 10 cm/s velocity intervals ranging from 10 to 60 cm/s; velocities found in the natural habitat. Mean reactive distance in single fish experiments (henceforth SFE) averaged 33 and 29 cm respectively, and was not related to velocity. We detected a negative, curvilinear relationship between velocity and percent prey capture. Holding velocities for juvenile Chinook were significantly lower than prey capture velocities. The Grossman et al. (Ecol Freshw Fish 11:2-10, 2002) model yielded an optimal focal-point velocity prediction of 35 cm/s for juvenile Chinook, however focal-point velocities occupied by juveniles in the Chena River averaged 12 cm/s. Predicted optimal velocities were present in the Chena River; hence, this discrepancy suggests that other factors such as distraction from drifting debris or predation risk influenced habitat selection. There were no differences in reactive distances or holding velocity/capture velocity relationships for dominant and subordinate fish; however, dominants captured significantly more prey than subordinates. Being subordinate resulted in a decrease of 61% in mean percent prey capture (the difference between what was captured by the fish alone versus the difference with a dominant), whereas the mean cost to fish with dominant rank was a 21% decline between the percentage captured alone versus that with a subordinate. [ABSTRACT FROM AUTHOR]