Diet variability and foraging strategies in brown trout (Salmo trutta): an analysis from subpopulations to individuals

Field studies were conducted to examine intra- and inter-individual diet variation in subpopulations of brown trout (Salmo trutta) at different spatial scales (between sites, between habitats (riffle and pool) within a site, and between individuals within a habitat) and different temporal scales (within subpopulations and within individuals over time) at four sites in the Glenfinish River, County Cork, Ireland. Electrofishing and stomach flushing techniques were used whereby fish larger than 85 mm were uniquely coded, allowing for repeated capture and diet analysis of individuals. A considerable degree of variation within and between subpopulations and individual diets was apparent. On the basis of novel and recent graphical models of feeding strategies, the trend was for a generalized strategy amongst trout subpopulations occupying riffles throughout most seasons, whilst specialization tended to be more frequent amongst trout occupying pools during summer and autumn. Using similarity indices and dendrograms, we illustrate that individual fish showed both feeding strategies within one habitat over time.