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Although submerged macrophyte (hereafter, "macrophyte") communities are globally prevalent in low-gradient rivers, the net reach-scale effect of macrophytes on drift-feeding fish microhabitat preference is poorly understood. We used snorkeling and bioenergetics to study fish habitat selection for rainbow trout (Oncorhynchus mykiss) in the Henrys Fork, ID, USA, investigating microhabitat preference across a reach-scale gradient of macrophyte growth. Fish preferred microhabitats with deep water, low velocity, and low macrophyte coverage. Preferences for microhabitats with higher net rate of energy intake (NREI) were modulated by reach-scale macrophyte coverage, higher coverage increasing preferences for higher NREI. Macrophyte coverage was a weak positive predictor for depth and NREI, and a weak negative predictor for water velocity and median substrate. Our results suggest trade-offs between fish predation risk and bioenergetic food intake, with macrophytes modulating these trade-offs across scales by affecting reach-scale geomorphology, bioenergetics, and predation risk. As such, this study highlights the important and dynamic role that macrophytes can play in fish population dynamics in rivers, with important implications for management decisions. [ABSTRACT FROM AUTHOR]

Reservoirs are examples of novel ecosystems that have developed into popular sport fisheries; these systems are also becoming seasonal refuges for migratory birds, including the piscivorous American white pelican (Pelecanus erythrorhynchos). We (1) investigated the proportion of cutthroat trout (Oncorhynchus clarkii utah) and other species consumed by pelicans, (2) compared whether pelicans have an adverse effect on cutthroat trout spawning movement, and (3) determined the importance of pelican predation relative to other sources of fish mortality in Strawberry Reservoir, Utah, USA. Pelican diet samples consisted of >85% Utah sucker (Catostomus ardens), 6% Utah chub (Gila atraria), and 3% cutthroat trout. Based on bioenergetics, we estimated that pelicans consumed 384–3020 individual cutthroat trout (0.17%–1.3% of population), in contrast to 14 166–27 196 nongame sucker and chub. Bird-related mortality rate ranged from 1% to 6% for stocked, PIT (passive integrated transponder)-tagged adult cutthroat trout and from 4% to 16% for subadult cutthroat trout. Based on these results, any management action taken to control pelican predation would need to be weighed against the benefits of nongame fish removal and the protected status of pelicans. [ABSTRACT FROM AUTHOR]

Increasing water demand, water development, and ongoing climate change have driven extensive changes to the hydrology, geomorphology and biology of arid-land rivers globally, driving an increasing need to understand how annual hydrologic conditions affect the distribution and abundance of imperiled desert fish populations. We analyzed the relationship between annual hydrologic conditions and the endangered Rio Grande silvery minnow (Hybognathus amarus) in the Middle Rio Grande, New Mexico, USA, using hurdle models to predict both presence and density as a function of integrated annual hydrologic metrics. Both presence and density were positively related to spring high flow magnitude and duration and negatively related to summer drying, as indicated by an integrated flow metric. Simulations suggest hydrologic conditions near the wettest observed in the data set would be required to meet recovery goals in a single year in all reaches. We demonstrate how the models developed herein can be used to examine alternative water management strategies, including strategies that may currently be socially and logistically infeasible to implement, to identify strategies minimizing trade-offs between conservation and other management goals. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The inclusion of passive interrogation antenna (PIA) detection data has promise to increase precision of population abundance estimates (--> N ^ -->). However, encounter probabilities are often higher for PIAs than for physical capture. If the difference is not accounted for, --> N ^ --> may be biased. Using simulations, we estimated the magnitude of bias resulting from mixed capture and detection probabilities and evaluated potential solutions for removing the bias for closed capture models. Mixing physical capture and PIA detections (pdet) resulted in negative biases in --> N ^ -->. However, using an individual covariate to model differences removed bias and improved precision. From a case study of fish making spawning migrations across a stream-wide PIA (pdet ≤ 0.9), the coefficient of variation (CV) of --> N ^ --> declined 39%–82% when PIA data were included, and there was a dramatic reduction in time to detect a significant change in --> N ^ -->. For a second case study, with modest pdet (≤0.2) using smaller PIAs, CV (--> N ^ -->) declined 4%–18%. Our method is applicable for estimating abundance for any situation where data are collected with methods having different capture–detection probabilities. [ABSTRACT FROM AUTHOR]

Temporal symmetry models (TSM) represent advances in the analytical application of mark-recapture data to population status assessments. For a population of char, we employed 10 years of active and passive mark-recapture data to quantify population growth rates using different data sources and analytical approaches. Estimates of adult population growth rate were 1.01 (95% confidence interval = 0.84-1.20) using a temporal symmetry model ( λTSM), 0.96 (0.68-1.34) based on logistic regressions of annual snorkel data ( λA), and 0.92 (0.77-1.11) from redd counts ( λR). Top-performing TSMs included an increasing time trend in recruitment ( f) and changes in capture probability ( p). There was only a 1% chance the population decreased ≥50%, and a 10% chance it decreased ≥30% ( λMCMC; based on Bayesian Markov chain Monte Carlo procedure). Size structure was stable; however, the adult population was dominated by small adults, and over the study period there was a decline in the contribution of large adults to total biomass. Juvenile condition decreased with increasing adult densities. Utilization of these different information sources provided a robust weight-of-evidence approach to identifying population status and potential mechanisms driving changes in population growth rates. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In reservoirs, seasonal drawdown can alter the physical environment and may influence predatory fish performance. We investigated the performance of lake trout ( Salvelinus namaycush) in a western reservoir by coupling field measurements with visual foraging and bioenergetic models at four distinct states (early summer, mid-summer, late summer, and fall). The models suggested that lake trout prey, juvenile kokanee ( Oncorhynchus nerka), are limited seasonally by suitable temperature and dissolved oxygen. Accordingly, prey densities were greatest in late summer when reservoir volume was lowest and fish were concentrated by stratification. Prey encounter rates (up to 68 fish·day−1) and predator consumption are also predicted to be greatest during late summer. However, our models suggested that turbidity negatively correlates with prey detection and consumption across reservoir states. Under the most turbid conditions, lake trout did not meet physiological demands; however, during less turbid periods, predator consumption reached maximum bioenergetic efficiency. Overall, our findings demonstrate that rapid reservoir fluctuations and associated abiotic conditions can influence predator-prey interactions, and our models describe the potential impacts of water level fluctuation on valuable sport fishes. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We compared sources of variability and cost in paired stomach content and stable isotope samples from three salmonid species collected in September 2001-2005 and describe the relative information provided by each method in terms of measuring diet overlap and food web study design. Based on diet analyses, diet overlap among brown trout, rainbow trout, and mountain whitefish was high, and we observed little variation in diets among years. In contrast, for sample sizes n ≥ 25, 95% confidence interval (CI) around mean δ15Ν and δ13C for the three target species did not overlap, and species, year, and fish size effects were significantly different, implying that these species likely consumed similar prey but in different proportions. Stable isotope processing costs were US$12 per sample, while stomach content analysis costs averaged US$25.49 ±$2.91 (95% CI) and ranged from US$1.50 for an empty stomach to US$291.50 for a sample with 2330 items. Precision in both δ15Ν and δ13C and mean diet overlap values based on stomach contents increased considerably up to a sample size of n = 10 and plateaued around n = 25, with little further increase in precision. Nous avons comparé les sources de variabilité et les coûts dans des échantillons appariés de contenus stomacaux et d'isotopes stables récoltés en septembre 2001-2005 chez trois espèces de salmonidés; nous décrivons l'information relative apportée par chaque méthode en ce qui a trait au chevauchement des régimes alimentaires et au plan d'étude des réseaux trophiques. D'après les analyses des régimes alimentaires, le chevauchement est élevé entre la truite brune, la truite arc-en-ciel et le ménomini de montagnes et il y a peu de variation de régime entre les années. En revanche, pour des tailles d'échantillon de n ≥ 25, les intervalles de confiance (IC) à 95 % autour des valeurs moyennes de δ15N et de δ13C pour les trois espèces ciblées ne se chevauchent pas et les effets de l'espèce, de l'année et de la taille du poisson sont significativement différents, ce qui implique que ces espèces consument vraisemblablement des proies semblables, mais dans des proportions différentes. Le coût de traitement des analyses d'isotopes stables est de 12 $US par échantillon, alors qu'une analyse de contenu stomacal coûte en moyenne 25,49 ±2,91 $US (IC à 95 %) et varie de 1,50 $US pour un tube digestif vide à 291,50 $US pour un échantillon contenant 2330 proies. La précision du chevauchement moyen des régimes alimentaires basé sur les valeurs de δ15N et de δ13C et sur les contenus stomacaux augmente considérablement jusqu'à une taille d'échantillon de n = 10 et atteint un plateau vers n = 25 avec peu d'augmentation de précision par la suite. [ABSTRACT FROM AUTHOR]

Using empirical field data for bull trout (Salvelinus confluentus), we evaluated the trade-off between power and sampling effort–cost using Monte Carlo simulations of commonly collected mark–recapture–resight and count data, and we estimated the power to detect changes in abundance across different time intervals. We also evaluated the effects of monitoring different components of a population and stratification methods on the precision of each method. Our results illustrate substantial variability in the relative precision, cost, and information gained from each approach. While grouping estimates by age or stage class substantially increased the precision of estimates, spatial stratification of sampling units resulted in limited increases in precision. Although mark–resight methods allowed for estimates of abundance versus indices of abundance, our results suggest snorkel surveys may be a more affordable monitoring approach across large spatial scales. Detecting a 25% decline in abundance after 5 years was not possible, regardless of technique (power = 0.80), without high sampling effort (48% of study site). Detecting a 25% decline was possible after 15 years, but still required high sampling efforts. Our results suggest detecting moderate changes in abundance of freshwater salmonids requires considerable resource and temporal commitments and highlight the difficulties of using abundance measures for monitoring bull trout populations. [ABSTRACT FROM AUTHOR]

We demonstrate that invasion success, through the introduction and establishment stages, can generally be predicted based on biological characteristics of the organisms and physical aspects of the environment; however, predicting subsequent effects during integration is more challenging, especially for omnivorous fish species in large, heterogeneous systems. When gizzard shad (Dorosoma cepedianum) were incidentally introduced into Lake Powell, Utah–Arizona (2000), we predicted they would be successful invaders and would have food-web effects ranging from neutral to negative. As predicted, gizzard shad successfully established and dispersed throughout this large reservoir (300 km) within just 4 years, and their density was positively correlated with productivity. Also as predicted, gizzard shad exhibited fast growth rates, and striped bass (Morone saxatilis) predators were thus gape-limited, obtaining little gizzard shad forage. Contrary to our predictions, however, competition over zooplankton resources between gizzard shad and both threadfin shad (Dorosoma petenense) and juvenile striped bass appeared limited because of spatial segregation and diet preference. In sum, gizzard shad will continue to be successful invaders, but with limited effects on the established predator–prey cycle. [ABSTRACT FROM AUTHOR]

Temperature-mediated competition (i.e., dominance shifts between species depending on temperature) may explain the segregation of salmonid species along altitudinal stream gradients. We evaluated this hypothesis for exotic brown trout (Salmo trutta) and native Bonneville cutthroat trout (Oncorhynchus clarkiiutah) by rearing them in experimental sympatry and allopatry using enclosures constructed at six sites spaced along a 45-km segment of a mountain stream. For both species, we compared condition and growth between allopatric and sympatric treatment groups. We found that brown trout negatively affected cutthroat trout performance, whereas cutthroat trout failed to impart an effect in the reverse direction, regardless of temperature. Thus, we documented asymmetric competition between these species but found little evidence indicating that its outcome was influenced by temperature. Brown trout – cutthroat trout segregation is therefore unlikely to be due to temperature-mediated competition. Instead, brown trout may have displaced cutthroat trout from downstream areas through competition or other mechanisms, while abiotic factors preclude their (brown trout) invasion of upper elevations. Given the magnitude of effect observed in our study, we recommend that brown trout receive greater consideration in cutthroat trout conservation. La compétition reliée à la température, dans laquelle la dominance passe d'une espèce à une autre en fonction de la température, peut probablement expliquer la ségrégation des espèces de salmonidés le long de gradients d'altitude dans les cours d'eau. Nous avons éprouvé cette hypothèse chez des truites brunes (Salmo trutta) exotiques et des truites fardées Bonneville (Oncorhynchus clarkiiutah) indigènes en les élevant ensemble (sympatrie expérimentale) ou séparément (allopatrie) dans des enclos construits à six sites échelonnés sur un segment de 45 km d'un cours d'eau de montagne. Chez les deux espèces, nous avons comparé la condition et la croissance des groupes de poissons élevés dans des conditions de sympatrie et d'allopatrie. La truite brune affecte négativement la performance de la truite fardée, alors que la truite fardée n'arrive pas à avoir d'impact sur la truite brune, quelle que soit la température. Il y a donc une compétition asymétrique entre ces deux espèces, mais il y a peu d'indications que l'issue de la compétition est influencée par la température. La ségrégation entre la truite brune et la truite fardée n'est vraisemblablement pas due à la compétition reliée à la température. Il est possible que la truite brune élimine la truite fardée des zones d'aval par compétition ou par un autre mécanisme, alors que les facteurs abiotiques empêchent l'invasion des altitudes plus élevées par la truite brune. Étant donné l'ampleur des effets observés dans notre étude, nous recommandons de porter plus d'attention à la truite brune dans les travaux de conservation de la truite fardée.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Nutrients can load directly to either the epilimnion or metalimnion of lakes via either differential inflow depths of tributaries or intentional fertilization of discrete strata. We evaluated the differential effects of epilimnetic versus metalimnetic nutrient loading using 17-m-deep mesocosms that extended into the deep chlorophyll layer of oligotrophic Pettit Lake in the Sawtooth Mountains of Idaho. Addition of nitrogen plus phosphorus stimulated primary production nearly identically (2.4- to 4-fold on different dates) in both treatments, with the production peaks occurring in the strata where nutrients were added. The metalimnetic fertilization, however, resulted in equal or greater stimulation of chlorophyll a and phytoplankton biovolume than when nutrients were added directly to the epilimnion. Periphyton growth was stimulated 10–100 times more by epilimnetic fertilization than by metalimnetic fertilization and diverted nutrients from the planktonic autotrophs. These results suggest that the development of deep chlorophyll layers may be influenced by plunging river inflows that carry nutrients to the metalimnion and that metalimnetic lake fertilization may be useful as a tool for increasing lake productivity while reducing the impact on water quality.Les nutriments peuvent s'insérer directement soit dans l'épilimnion, soit dans le métalimnion des lacs selon les différentes profondeurs d'arrivée des eaux des tributaires ou à la suite d'une fertilisation délibérée d'une strate particulière. Nous avons comparé les effets de l'entrée des nutriments dans l'épilimnion et dans le métalimnion à l'aide de mésocosmes de 17 m de profondeur qui atteignaient la couche profonde de chlorophylle dans le lac oligotrophe Pettit dans les monts Sawtooth en Idaho. L'addition d'azote et de phosphore stimulait la production primaire presque de la même façon dans les deux traitements (d'un facteur de 2,4 à 4 aux différentes dates) et le maximum de production se produisait dans la strate dans laquelle les nutriments avaient été ajoutés. La fertilisation du métalimnion stimulait autant sinon plus la chlorophylle a et le biovolume du phytoplancton qu'une addition des nutriments directement à l'épilimnion. La croissance du périphyton était activée de 10–100 fois plus par une fertilisation de l'épilimnion plutôt que du métalimnion et elle détournait les nutriments des autotrophes planctoniques. Ces résultats laissent croire que la formation des couches profondes de chlorophylle peut être influencée par l'influx en profondeur des eaux de rivière qui apportent des nutriments au métalimnion et que la fertilisation du métalimnion peut être un outil commode pour augmenter la productivité d'un lac, tout en minimisant l'impact sur la qualité de l'eau.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]