Summer differences in behavioural feeding habits and use of feeding habitat among brown trout (Pisces) age classes in a temperate area

Abstract

Field studies were conducted to examine intra-specific diet variation in a population of brown trout (Salmo trutta L.) in a temperate area (River Tormes, Central Spain) during the summer. Fuzzy principal component analysis (FPCA) and the modified Costello graphical method were used to illustrate that age classes showed differences in behavioural feeding habits and use of feeding habitat. Despite benthic prey constituting the most important prey in abundance terms in all age classes, our findings suggest that ontogenetic shift among age classes can be related to several factors: (1) terrestrial invertebrates and fishes were more frequently consumed by older trout, (2) resource partitioning among age classes also occurred at the level of prey size and (3) differences among age classes in habitat utilization for feeding were evident. Levins index increases with trout size. However, a noteworthy result of this study is that no differences were found in the evenness, Shannon and Levins indices among age classes. Finally, the dietary analyses showed high values of diet overlap, but the differences in the use of feeding habitat and behavioural feeding habits are important adaptive features that may reduce the intra-specific competition in the population. © 2012 Copyright 2012 Unione Zoologica Italiana.