The effects of prior residence on behavior and growth rates in juvenile Atlantic salmon (Salmo salar)

Abstract

It is well documented that prior residence confers advantages in territorial disputes, but its impact on other aspects of behavior and fitness is less understood. We tested how prior residence influences the subsequent feeding behavior and growth performance of dispersing Atlantic salmon fry (Salmo salar) using experimental manipulations of residence in a seminatural stream tank. In replicated trials, groups of seven 'primary' fish were released into the stream tank 3 days ahead of seven 'secondary' fish. Standardized behavioral observations were made on each fish over the following 14 days, after which all fish were removed and measured. Primaries and secondaries were initially the same size and body condition and exhibited the same degree of site fidelity. However, primaries darted higher into the water column to intercept prey items, fed at a higher rate, and subsequently grew faster. Larger fish (in terms of body length) tended to be more dominant, and dominants grew faster than subordinates. However, there was no difference in dominance between primaries and secondaries. These results suggest that the well-documented advantage of early-emerging salmon fry over late-emerging fry cannot be completely attributed to intrinsic differences and that the advantage is partly mediated via a prior residence effect. Furthermore, prior residents gain foraging advantages without necessarily becoming more dominant.