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Individual growth can exert strong control on population dynamics but is constrained by resource acquisition rates. Difficulty in accurately quantifying resource availability over large spatial extents and at high temporal frequencies often limits attempts to understand the extent to which resources limit individual growth. Daily estimates of stream metabolism, including gross primary productivity (GPP), are increasingly available but have not, to our knowledge, been linked to fish growth. Here we examine how environmental variables such as GPP, water temperature, turbidity, and high-flow releases from a dam are linked to spatiotemporal variation in the growth of flannelmouth sucker (Catostomus latipinnis) in the Colorado River within the Grand Canyon. We fit state-space growth models to 6 years of mark-recapture data collected in four river reaches spanning 300 river kilometers. Consistent with past research in this system, we find that all four environmental variables influence growth in length of a native primary consumer fish. GPP and temperature have a positive influence on growth, while turbidity and high-flow events have a negative influence. Water temperature is the dominant driver of spatiotemporal variation in growth, while the link between high-frequency GPP and fish growth is relatively novel. Fish growth is likely to be linked to stream metabolism in other systems where overall productivity, not the quality of primary producers, limits the food webs that support fish growth. Key words: stream metabolism, temperature, turbidity, primary consumer, resource availability, Introduction Growth of individual animals can be constrained by both environmental conditions and rates of resource acquisition. In turn, growth can exert strong control on population dynamics via impacts on [...]

River ecosystems have been altered by flow regulation and species introductions. Regulated flow regimes often include releases designed to benefit certain species or restore ecosystem processes, and invasive species suppression programs may include efforts to restrict access to spawning habitat. The impacts of these management interventions are often uncertain. Here, we assess hypotheses regarding introduced brown trout (Salmo trutta) movement in a regulated river. We model mark- recapture data in a multistate framework to assess whether movement was affected by the operation of a tributary weir (restricting access to spawning habitat), experimental releases of fall-timed high flow experiments (Fall HFEs), or simply increased during the fall, spawning season. Our results suggest that the presence of the weir led to reduced tributary homing and the release of Fall HFEs stimulated upstream movement and straying. Both effects are of a similar magnitude, however the Fall HFE effect is more certain. Our results suggest the expansion of an invasive species was stimulated by management interventions, and demonstrate the potential for unanticipated outcomes of restoration in highly altered river ecosystems. Key words: ecological flows, designer flows, salmonids, adaptive management, invasion, barriers, Introduction River discharge regulation and water diversions that alter flow regimes and favor invasive fishes have led to the widespread homogenization of freshwater fish communities (Poff et al. 2007; Comte [...]

Flows released from reservoirs are often modified to mitigate the negative ecosystem effects of dams. We estimated the effects of two experimental flows, fall-timed floods and elimination of sub-daily variation in flows on weekends, on growth rates of rainbow trout (Oncorhynchus mykiss) in the Colorado River downstream from Glen Canyon Dam. Experimental flow effects were compared to effects of water temperature, phosphorous concentration, solar insolation, and competition, by fitting mixed effect von Bertalanffy models to ~ 10 000 observations of growth from mark-recapture between 2012 and 2021. There was strong support for models predicting faster growth during intervals with higher solar insolation, and lower water temperature and competition for prey. Effects of phosphorus and experimental flows were small and uncertain. Drought-related increases in dam release temperatures during summer and fall were predicted to result in severe weight loss for larger trout and could eventually threaten the viability of the population and the fishery it supports. The effects of water temperature and competition on fish growth substantially exceeded the effects of controlled floods and steadier flows. Key words: Drought, fish growth, water quality, controlled floods, hydropeaking, water temperature, Introduction Dams and river regulation have fundamentally altered flow regimes of the world's rivers (Petra and others 2009). Environmental flows (e-flows) seek to replicate aspects of the quantity, timing, or [...]

Autonomous passive integrated transponder (PIT) tag antennas are commonly used to detect fish marked with PIT tags but cannot detect unmarked fish, creating challenges for abundance estimation. Here we describe an approach to estimate abundance from paired physical capture and antenna detection data in closed and open mark-recapture models. Additionally, for open models, we develop an approach that incorporates uncertainty in fish size, because fish size changes through time (as fish grow bigger) but is unknown if fish are not physically captured (e.g., only detected on antennas). Incorporation of size uncertainty allows for estimation of size-specific abundances and demonstrates a generally useful method for obtaining state-specific abundances estimates under state uncertainty. Simulation studies comparing models with and without antenna detections illustrate that the benefit of our approach increases as a larger proportion of the population is marked. When applied to two field data sets, our approach to incorporating antenna detections reduced uncertainty in abundance substantially. We conclude that PIT antennas hold great potential for improving abundance estimation, despite the challenges they present. Les antennes pour etiquettes a transpondeurs passifs integres (PIT) autonomes sont frequemment utilisees pour la detection de poissons dotes de PIT, mais elles ne peuvent detecter les poissons non etiquetes, ce qui presente des difficultes pour l'estimation de l'abondance. Nous decrivons une approche d'estimation de l'abondance a partir de donnees jumelees de capture physique et de detection par antenne dans des modeles de marquage-recapture fermes et ouverts. Pour les modeles ouverts, nous presentons en outre une approche qui incorpore l'incertitude associee a la taille des poissons, puisque cette derniere change au fil du temps (au fil de la croissance des poissons), mais est inconnue si les poissons ne sont pas captures physiquement (p. ex. seulement detectes par des antennes). L'incorporation de l'incertitude associee a la taille permet d'estimer l'abondance de poissons de differentes tailles et demontre l'utilite generale d'une methode permettant d'obtenir des estimations de l'abondance pour des etats precis auxquels une incertitude est associee. Des etudes de simulation comparant des modeles avec et sans detection par des antennes indiquent que plus la proportion etiquetee de la population est grande, plus l'approche proposee est avantageuse. Appliquee a deux ensembles de donnees de terrain, l'approche d'incorporation des detections par antennes reduit considerablement l'incertitude des estimations d'abondance. Nous concluons que les antennes a PIT presentent un grand potentiel pour ce qui est d'ameliorer les estimations d'abondance, malgre les difficultes qui leur sont associees. [Traduit par la Redaction], Introduction Managers regularly require abundance estimates to assess population status and trends (Maxwell and Jennings 2005), inform management decisions (Walters 1986; Williams et al. 2002), trigger management actions (Bair et [...]

Recovering endangered species populations when confronted with the threat of invasive species is an ongoing natural resource management challenge. While eradication of the invasive species is often the optimal economic solution, it may not be a feasible nor desirable management action in other cases. For example, when invasive species are desired in one area, but disperse into areas managed for endangered species, managers may be interested in persistent, but cost-effective means of managing dispersers rather than eradicating the source. In the Colorado River, a nonnative rainbow trout (Oncorhynchus mykiss) sport fishery is desired within Glen Canyon National Recreation Area, however, dispersal downriver into the Grand Canyon National Park is not desired as rainbow trout negatively affect endangered humpback chub (Gila cypha). Here, we developed a bioeconomic model incorporating population abundance goals and cost-effectiveness analyses to approximate the optimal control strategies for invasive rainbow trout conditional on achieving endangered humpback chub adult population abundance goals. Model results indicated that the most cost-effective approach to achieve target adult humpback chub abundance was a high level of rainbow trout control over moderately high rainbow trout population abundance. Adult humpback chub abundance goals were achieved at relatively low rainbow trout abundance and control measures were not cost-effective at relatively high rainbow trout abundance. Our model considered population level dynamics, species interaction and economic costs in a multi-objective decision framework to provide a preferred solution to long-run management of invasive and native species.

Choosing whether or not to migrate is an important life history decision for many fishes. Here we combine data from physical captures and detections on autonomous passive integrated transponder (PIT) tag antennas to study migration in an endangered fish, the humpback chub (Gila cypha). We develop hidden Markov mark-recapture models with and without antenna detections and find that the model fit without antenna detections misses a large proportion of fish and underestimates migration and survival probabilities. We then assess survival and growth differences associated with life history strategy and migration for different demographic groups (small male, small female, large male, large female). We find large differences in survival according to life history strategy, where residents had much lower overwinter survival than migrants. However, within the migratory life history strategy, survival and growth were similar for active migrants and skipped migrants for all demographic groups. We discuss some common challenges to incorporating detections from autonomous antennas into population models and demonstrate how these data can provide insight about fish movement and life history strategies. La decision de migrer ou non est une importante decision du cycle de vie de nombreux poissons. Nous combinons des donnees de captures physiques et de detections par des antennes autonomes pour transpondeurs passifs integres (etiquettes PIT) afin d'etudier la migration chez un poisson en voie de disparition, le chevesne a bosse (Gila cypha). Nous developpons des modeles de Markov caches de marquage-recapture avec et sans detections par antenne et constatons que le calage du modele sans detections par antenne ne releve pas une grande proportion des poissons et sous-estime les probabilites de migration et de survie. Nous evaluons ensuite les differences sur le plan de la survie et de la croissance associees a la strategie de survie et a la migration pour differents groupes demographiques (petits males, petites femelles, grands males, grandes femelles). Nous relevons de grandes differences sur le plan de la survie selon la strategie de survie, la survie hiemale etant bien plus faible pour les individus residents que pour les migrants. Cela dit, parmi les poissons adoptant une strategie migratoire, la survie et la croissance sont semblables entre les migrants actifs et ceux qui sautent une migration, et ce, pour tous les groupes demographiques. Nous abordons certaines des difficultes courantes associees a l'incorporation de detections par antenne autonome a des modeles demographiques et demontrons comment ces donnees peuvent fournir des renseignements utiles sur les deplacements et les strategies de survie des poissons. [Traduit par la Redaction], Introduction An individual's decision to migrate, or not, is an important life history strategy decision faced by many organisms. The impetus for migration can be better forage (Holdo et al. [...]

Drift-feeding fish are typically considered size-selective predators. Yet, few studies have explicitly tested which aspect of prey 'size' best explains size selection by drift-foraging fish. Here, we develop a Bayesian discrete choice model to evaluate how attributes of both prey and predator simultaneously influence size-selective foraging. We apply the model to a large dataset of paired invertebrate drift (n = 784) and rainbow trout (Oncorhynchus mykiss) diets (n = 1028). We characterized prey 'size' using six metrics (length, width, area, hemispherical area, volume, mass) and used pseudo-[R.sup.2] to determine which metric best explained observed prey selection across seven taxa. We found that rainbow trout are positively size-selective, they are selecting prey based upon differences in prey width, and size-selectivity increases with fish length. Rainbow trout demonstrated strong selection for the adult and pupae stages of aquatic insects relative to their larval stages. Our study provides strong empirical evidence for size-selective foraging in rainbow trout and demonstrates prey selection is based primarily upon width, not length or area as has been widely reported. Les poissons qui s'alimentent d'organismes a la derive sont typiquement consideres comme etant des predateurs selectifs selon la taille. Peu d'etudes ont toutefois verifie explicitement quel aspect de la << taille >> des proies explique le mieux la selection des tailles par ces poissons. Nous developpons un modele bayesien de choix discrets pour evaluer l'influence d'attributs tant des proies que des predateurs sur l'alimentation selective selon la taille. Nous appliquons le modele a un grand ensemble de donnees jumelees sur les invertebres a la derive (n = 784) et les regimes alimentaires de truites arcen-ciel (Oncorhynchus mykiss) (n = 1028). Nous caracterisons la << taille >> des proies a l'aide de six parametres (longueur, largeur, aire, aire hemispherique, volume et masse) et utilisons le pseudo-[R.sup.2] pour determiner quel parametre explique le mieux la selection de proies entre sept taxons. Nous constatons que les truites arc-en-ciel font preuve de selection positive en fonction de la taille, qu'elles selectionnent leurs proies sur la base de differences de largeur des proies et que la selectivite de la taille augmente avec la longueur des poissons. Les truites arc-en-ciel presentent une forte propension a selectionner les adultes et pupes d'insectes aquatiques plutot que leurs larves. L'etude fournit de preuves empiriques solides d'une alimentation selective selon la taille chez les truites arc-en-ciel et demontre que la selection de proies est principalement basee sur la largeur, non sur la longueur ou l'aire, comme cela a ete largement rapporte. [Traduit par la Redaction], Introduction Foraging is essential to animal survival and reproduction (Stephens et al. 2008). Because of the fundamental role that foraging decisions play in the dynamics of animal populations, foraging ecology [...]

Recovery of imperiled fishes can be achieved through suppression of invasives, but outcomes may vary with environmental conditions. We studied the response of imperiled desert fishes to an invasive brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) suppression program in a Colorado River tributary, with natural flow and longitudinal variation in thermal characteristics. We investigated trends in fish populations related to suppression and tested hypotheses about the impacts of salmonid densities, hydrologic variation, and spatial-thermal gradients on the distribution and abundance of native fish species using zero-inflated generalized linear mixed effects models. Between 2012 and 2018, salmonids declined 89%, and native fishes increased dramatically (~480%) once trout suppression surpassed ~60%. Temperature and trout density were consistently retained in the top models predicting the abundance and distribution of native fishes. The greatest increases occurred in warmer reaches and in years with spring flooding. Surprisingly, given the evolution of native fishes in disturbance-prone systems, intense, monsoon-driven flooding limited native fish recruitment. Applied concertedly, invasive species suppression and efforts to mimic natural flow and thermal regimes may allow rapid and widespread native fish recovery. Le retablissement d'especes de poissons en peril peut se faire par la suppression d'especes envahissantes, mais les resultats peuvent dependre des conditions ambiantes. Nous avons etudie la reaction de poissons de regions desertiques en peril a un programme de suppression des truites brunes (Salmo trutta) et des truites arc-en-ciel (Oncorhynchus mykiss) envahissantes dans un affluent du fleuve Colorado, en fonction de l'ecoulement naturel et des variations longitudinales des caracteristiques thermiques. Nous avons examine les tendances au sein de populations de poissons associees a la suppression et avons teste des hypotheses concernant les effets de la densite de salmonides, des variations hydrologiques et des gradients thermiques sur la repartition et l'abondance d'especes de poissons indigenes en utilisant des modeles lineaires generalises a effets mixtes avec inflation du zero. De 2012 a 2018, les salmonides ont connu une baisse de 89% et les poissons indigenes, une augmentation marquee (~480%) une fois que la suppression des truites a depasse ~60%. La temperature et la densite des truites etaient des variables uniformement retenues dans les modeles predisant le mieux l'abondance et la repartition de poissons indigenes. Les augmentations les plus importantes se sont produites dans les tronqons plus chauds et durant des annees d'inondations printanieres. Etonnamment, vu Devolution des poissons indigenes dans les systemes frequemment perturbes, des inondations intenses associees a la mousson limitaient le recrutement de poissons indigenes. Appliques de maniere concertee, la suppression d'especes envahissantes et des efforts visant a reproduire l'ecoulement et les regimes thermiques naturels pourraient permettre le retablissement rapide et repandu d'especes de poissons indigenes., Introduction Freshwater ecosystems are heavily modified world-wide, and consequently native fishes are threatened by a variety of persistent and emerging factors, including invasive species, hydropower generation and river regulation, climate [...]

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