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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 [...]

Multispecies risk assessments have developed within many international conservation programs, reflecting a widespread need for efficiency. Under the United States Endangered Species Act (ESA), multispecies assessments ultimately lead to species‐level listing decisions. Although this approach provides opportunities for improved efficiency, it also risks overwhelming or biasing the assessment process and would benefit from clear guidance for practitioners. We reviewed multispecies assessments conducted between 1993 and 2019 for ESA listing decisions to identify the ecological basis for combining species, the assessment approach used, and the policy factors influencing their efficacy. We identified 42 cases covering 359 species. Most assessments (81%) included two to five species, although the maximum was 82. A common theme involved grouping narrow endemics or habitat specialists based on taxonomic relatedness, similar distributions, and common threats to persistence. All assessments included a combined threats analysis, but few employed a common species' response model or expert elicitation process. Although ESA risk assessments are distinct from policy decisions, most assessments (50%) supported decisions that all species warranted endangered status. Available guidance has generally emphasized ecological similarity as the key attribute leading to successful multispecies assessments. The challenge with consistently selecting species based on qualitative proxies such as common distributions or threats to persistence is that ecological patterns and processes are scale dependent. Focusing instead on the assessment methods and their potential for bias and increased efficiency may provide a stronger basis for developing consistent and transparent guidance. [ABSTRACT FROM AUTHOR]

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]

Surface water connectivity can influence the richness and composition of fish assemblages, particularly in harsh environments where colonisation factors and access to seasonal refugia are required for species persistence., Studies regarding influence of connectivity on Arctic fish distributions are limited and are rarely applied to whole assemblage patterns. To increase our understanding of how surface water connectivity and related hydrologic variables influence assemblage patterns, we investigated species richness and composition of Arctic lake fishes over a large region, 8500 km2, of the central Arctic Coastal Plain, Alaska., We collected fish presence/non-detection data from 102 lakes and used a hierarchical multispecies occupancy framework to derive species richness and inform species composition patterns. Our mean estimate of regional richness was 12.3 ( SD 0.5) species. Presence of a permanent channel connection was an overriding factor affecting species richness (mean 3.6, 95% CI 3.1-4.9), presumably driving lake colonisation potential. In lakes without a permanent channel connection, data suggest richness (mean 2.0, 95% CI 1.7-3.3) increased with the availability of in-lake winter refugia and with the potential of ephemeral connections during spring floods., Fish species functional traits and environmental faunal filters contributed to patterns of richness and assemblage composition. Composition corresponded with richness in a coherent manner, where each successive level of richness contained several discrete assemblages that showed similar responses to the environment. Lakes with permanent channel connections contained both widespread and restricted species, while the species-poor lakes that lacked a connection contained mainly widespread species., This work provides useful baseline information on the processes that drive the relations between patch connectivity and fish species richness and assemblage composition. The environmental processes that organise fish assemblages in Arctic lakes are likely to change in a warming climate. [ABSTRACT FROM AUTHOR]

For six fish species sampled from 86 lakes on the Arctic Coastal Plain, Alaska, we examined whether lake occupancy was related to variables representing lake size, colonisation potential and/or the presence of overwintering habitat., We found the relative importance of each factor for a given species could be related to its ecology and adult size. The three large-bodied migratory species, least cisco ( Coregonus sardinella), broad whitefish ( Coregonus nasus) and arctic grayling ( Thymallus arcticus), were influenced by factors associated with the likelihood of fish recolonising lakes, including whether the lakes had a stream connection. Of the large-bodied species, least cisco had the highest likelihood of occupancy (0.52 ± 0.05) and models provided evidence that least cisco exhibit both migratory and resident forms., Models for small-bodied fish differed among species, indicating different niches. Ninespine stickleback ( Pungitius pungitius) were the most widespread and ubiquitous of the species captured (occupancy probability = 0.97 ± 0.01); they were captured in lakes that freeze to the bottom, suggesting that they disperse widely and rapidly after the spring freshet, including colonisation of sink habitats. Alaska blackfish ( Dallia pectoralis) had a lower occupancy (occupancy probability = 0.76 ± 0.05) with a distribution that reflected tolerance to harsh conditions. Slimy sculpin ( Cottus cognatus) had an occupancy probability of 0.23 ± 0.06, with a distribution indicating its marine origin., Based on these patterns, we propose an overall model of primary controls on the distribution of fish on the Arctic Coastal Plain of Alaska. Harsh conditions, including lake freezing, limit occupancy in winter through extinction events while lake occupancy in spring and summer is driven by directional migration (large-bodied species) and undirected dispersal (small-bodied species). [ABSTRACT FROM AUTHOR]

The article discusses the importance of nest site selection to determine the breeding survival of Pacific and Yellow-billed loons which dwell sympatrically in Arctic regions. Study results using logistic regression analysis show that both species select breeding sites, such as lakes with small islands, to minimize the risk of predation and exposure to strong waves and ice patterns. The study recommends that land managers focus on lake sheltered areas to protect the nests from potential hazards.

For Pacific salmon, estuaries are typically considered transitional staging areas between freshwater and marine environments, but their potential as rearing habitat has only recently been recognized. The objectives of this study were two-fold: (1) to determine if Coho SalmonOncorhynchus kisutchwere rearing in estuarine habitats, and (2) to characterize and compare the body length, age, condition, and duration and timing of estuarine occupancy of juvenile Coho Salmon between the two contrasting estuaries. We examined use of estuary habitats with analysis of microchemistry and microstructure of sagittal otoliths in two watersheds of south-central Alaska. Juvenile Coho Salmon were classified as estuary residents or nonresidents (recent estuary immigrants) based on otolith Sr : Ca ratios and counts of daily growth increments on otoliths. The estuaries differed in water source (glacial versus snowmelt hydrographs) and in relative estuarine and watershed area. Juvenile Coho Salmon with evidence of estuary rearing were greater in body length and condition than individuals lacking evidence of estuarine rearing. Coho Salmon captured in the glacial estuary had greater variability in body length and condition, and younger age-classes predominated the catch compared with the nearby snowmelt-fed, smaller estuary. Estuary-rearing fish in the glacial estuary arrived later and remained longer (39 versus 24 d of summer growth) during the summer than did fish using the snowmelt estuary. Finally, we observed definitive patterns of overwintering in estuarine and near shore environments in both estuaries. Evidence of estuary rearing and overwintering with differences in fish traits among contrasting estuary types refute the notion that estuaries function as only staging or transitional habitats in the early life history of Coho Salmon. Received December 5, 2012; accepted June 10, 2013 [ABSTRACT FROM AUTHOR]

Fish maturity status, sex ratio, and age and size at first maturity are important parameters in population assessments and life history studies. In most empirical studies of these variables, fish are sacrificed and dissected to obtain data. However, maturity status and the sex of mature individuals can be determined by inserting an endoscope through a small incision in the body cavity wall and viewing the gonads. The objective of this study was to evaluate endoscopy in a field setting for gonadal assessment of stream-resident forms of salmonids that mature at small sizes. Ninety-one brook trout (60-210 mm fork length [FL]) were obtained via electrofishing and anesthetized. Maturity status and sex of mature individuals were determined with an endoscope. After recovery, individuals were euthanized with anesthetic and were dissected to validate the endoscopic classification. Endoscopy correctly determined the maturity status and sex of mature individuals for 96% of the brook trout; the highest accuracy was observed for the smallest (60-70 mm FL) and largest (>140 mm FL) individuals examined. In the misclassifications, visceral fat hampered visibility and was mistaken for mature testes. Immediate postprocedure mortality was 3.3% and was limited to individuals smaller than 70 mm FL. Endoscopy is a useful technique that can be used in field settings to assess maturity status and sex of mature fish with a low rate of immediate mortality. [ABSTRACT FROM AUTHOR]

Estimation of fish abundance in streams using the removal model or the Lincoln-Peterson Mark-recapture model is a common practice in fisheries. These models produce misleading results if their assumptions are violated. We evaluated the assumptions of these two models via electrofishing of rainbow trout Oncorhynchus mykiss in central Idaho streams. For one-, two-, three-, and four-pass sampling effort in closed sites, we evaluated the influences of fish size and habitat characteristics on sampling efficiency and the accuracy of removal abundance estimates. We also examined the use of models to generate unbiased estimates of fish abundance through adjustment of total catch or biased removal estimates. Our results suggested that the assumptions of the mark-recapture model were satisfied and that abundance estimates based on this approach were unbiased. In contrast, the removal model assumptions were not met. Decreasing sampling efficiencies over removal passes resulted in underestimated population sizes and overestimates of sampling efficiency. This bias decreased, but was not eliminated, with increased sampling effort. Biased removal estimates based on different levels of effort were highly correlated with each other but were less correlated with unbiased mark-recapture estimates. Stream size decreased sampling efficiency, and stream size and instream wood increased the negative bias of removal estimates. We found that reliable estimates of population abundance could be obtained from models of sampling efficiency for different levels of effort. Validation of abundance estimates requires extra attention to routine sampling considerations but can help fisheries biologists avoid pitfalls associated with biased data and facilitate standardized comparisons among studies that employ different sampling methods. [ABSTRACT FROM AUTHOR]