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.

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.