Philip M. Harrison

Diel vertical migration hypotheses explain size-dependent behaviour in a freshwater piscivore

In aquatic organisms, diel vertical migration (DVM) is typically characterized as ascent at dusk and decent at dawn. Often several hypotheses are required to explain the sensory-mechanisms and ultimate causes of DVM. Currently, most of the research focused at the individual level has identified DVM functions as a response to light, feeding opportunities, predator avoidance and bioenergetics in small planktivores. However, there are no studies examining whether DVM hypotheses can explain and predict individual behavioural characteristics in top-level predators. In this study, we test whether bull trout, Salvelinus confluentus, a cold-water pelagic-cruising piscivore, show size-dependent daily and seasonal patterns in DVM consistent with light levels (proximate trigger) and feeding opportunities, predator avoidance and bioenergetics hypotheses. To test these hypotheses, free-swimming bull trout (N ¼ 187, 358e881 mm total length) in a large, temperate reservoir were implanted with depth-sensing acoustic transmitters for 1 year. We found that swimming depths of bull trout were shallowest at night, deepest during the day and showed clear patterns of DVM across all seasons. In line with the predator avoidance hypothesis, large and small bull trout occupied different depths in all seasons except the spring, while the likelihood of depth change for large and small fish varied depending on season and diel period. The greatest depth difference among large and small bull trout occurred in the summer and less so in autumn. In the summer, small bull trout remained at greater depths (w15 m) than larger fish (w 7m ) regardless of diel period. Our results indicate that light is a proximate trigger, and since there is no clear temperature-related bioenergetic advantage to changing depths during winter, feeding opportunities and predator avoidance are the most parsimonious DVM hypotheses to explain body-size-dependent behaviour in this top-level predator.

Temporal plasticity in thermal-habitat selection of burbot Lota lota a diel-migrating winter-specialist.

In this study, animal-borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter-specialist diel-migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12-14° C) optimal for hunting and feeding during non-reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non-reproductive periods, respectively, active selection was limited to selection for 4-6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night-time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal-habitat selection was a good predictor of night-time habitat occupancy in a diel-migrating species. Together, these results show that thermal-habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.

Behavioral attributes of turbine entrainment risk for adult resident fish revealed by acoustic telemetry and state-space modeling

BackgroundFish entrainment through turbine intakes is one of the major issues for operators of hydropower facilities because it causes injury and/or mortality and adversely affects population abundance. Entrainment reduction strategies have been developed based on the behavior of downstream migrating fishes, particularly diadromous species. However, knowledge of the behavior of migratory fishes has very limited application for reducing the entrainment of resident fishes, including several species that represent important recreational and aboriginal fishery resources in reservoirs. In this study, we used fine-scale acoustic telemetry and state-space modeling to investigate behavioral attributes associated with entrainment risk of resident adult bull trout (Salvelinus confluentus) in a large hydropower reservoir in British Columbia, Canada.ResultsWe found that adult bull trout resided longer in the vicinity of the powerhouse and moved closer to the turbine intakes in the fall and particularly in the winter. Bull trout were more likely to engage in exploratory behavior (characteristic of foraging or reduced activity) during periods when their body temperature was lower or higher than 6°C. We also detected diel changes in behavioral attributes, with bull trout distance to intakes and probability of exploratory behavior slightly increasing at night.ConclusionsWe hypothesize that the exploratory behavior in the forebay is associated with foraging for kokanee (nonanadromous form of Oncorhynchus nerka), which have been shown to congregate near the dams of hydropower reservoirs in the winter. Our study findings should be applicable to bull trout populations residing in other reservoirs and indicate that entrainment mitigation (for example, use of deterrent devices) should be focused on the fall and winter. This work also provides a framework for combining acoustic telemetry and state-space models to understand and categorize movement behavior of fish in reservoirs and, more generally, in any environment with fluctuating water levels.

Individual isotopic specializations predict subsequent inter-individual variation in movement in a freshwater fish

Despite many similarities and intuitive links between individual dietary specialization and behavioral inter-individual variation, these phenomena have been studied in isolation, and empirical data confirming relationships between these intraspecific variance sources are lacking. Here we use stable isotope analysis and acoustic telemetry to test the hypothesis that individual specialization in trophic (δ15 N) and littoral/pelagic prey reliance (δ13 C) covary with inter-individual variation in movement in a group of 34 free-swimming burbot (Lota lota). By performing stable isotope analysis on tissues with differing isotopic turnover rates (anal fin and dorsal muscle), in 24 lethally sampled burbot, we demonstrate that individual specialization in trophic niche (δ15 N) and littoral/pelagic prey reliance (δ13 C) occurred within the population. By performing stable isotope analysis on anal fins of a group of telemetry tagged burbot, we were able to show that interactions between trophic niche and littoral/pelagic prey reliance, explained a significant proportion of the subsequent between-individual variance in mean movement rates. These findings demonstrate an empirical connection between behavioral inter-individual variation and dietary specialization, thus providing a substantial expansion of our understanding of the wider ecological consequences of these interesting phenomena.

What are the consequences of fish entrainment and impingement associated with hydroelectric dams on fish productivity? A systematic review protocol

BackgroundThis systematic review will address the need for a better understanding of the impacts of fish entrainment and impingement associated with hydroelectric dams on fish productivity in freshwater temperate environments. As the number of dams continues to increase worldwide, so too has concerns for their effects on fish populations. Fish injury and mortality at hydroelectric facilities may have serious consequences for fish populations, which are generally the result of three main sources: (1) fish passage through hydroelectric facilities (i.e., turbines, spillways, sluiceways, and other passage routes) during downstream migration for migratory fish; (2) the entrainment of resident fish; and (3) the impingement of fish (migratory or resident) against screens/trash racks. Most studies on the impacts of entrainment and impingement at hydroelectric facilities on fish have primarily focused on: (1) how fish injury and mortality occurs; and (2) evaluations of the effectiveness of various management strategies used to mitigate harm during downstream passage. Given the contributions of migratory and resident adults and juveniles to fish production, a necessary extension is to evaluate the impacts of fish injury and mortality from hydropower dam entrainment and impingement on fish productivity. Therefore, to ensure the sustainability of fishes dependent on our freshwater ecosystems, a better understanding of the impacts of fish entrainment and impingement associated with hydroelectric dams on fish productivity is needed.MethodsThis systematic review will search for, compile, summarize and synthesize evidence on the impacts of fish entrainment and impingement associated with hydroelectric dams on fish productivity in freshwater temperate environments. Considered studies will include (but not be limited to): (1) those that report a metric related to mortality and injury as an indication of the effect on fish productivity; (2) the change in a metric related to mortality and injury relative to an appropriate control; and (3) articles that scale-up the evaluation to include some estimate of a change in a component of fish productivity (e.g., articles that include an estimate of fish loss from the population due to entrainment/impingement by comparing a metric related to mortality or injury to an estimate of population size or biomass). Only studies where the causal relationship between intervention and outcome is made clear to allow for the effects of entrainment and impingement to be isolated from other potential impacts of hydroelectric power production (e.g., barriers to migration and/or habitat degradation), will be included. The review will use public search engines and specialist websites, and will include both primary and grey literature. Potential effect modifiers will be identified to obtain a better understanding of the factors that are associated with variation in effects among studies, given differences in: (1) site-specific factors (e.g., turbine type, size, power output); (2) methodologies and study designs used to assess impacts; and (3) biological factors (e.g., fish life history stage, body size and morphology). Study quality will be assessed to allow for critical evaluation, including study design, confounding factors and statistical analysis. Data will be compiled into a narrative synthesis and a meta-analysis will be conducted where data availability and quality allow.