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

It is well documented that prior residence confers advantages in territoria l disputes, but its impact on other aspects of behavior and fitness is less understood. We tested how prior residence influences the subsequent feedin g behavior and growth performance of dispersing Atlantic salmon fry (Salmo salar) using experimental manipulations of residence in a seminatural strea m tank. In replicated trials, groups of seven "primary" fish were released into the stream tank 3 days ahead of seven "secondary" fish. Standardized b ehavioral observations were made on each fish ot er the following 14 days, after which all fish were removed and measured. Primaries and secondaries w ere initially the same size and body condition and exhibited the same degre e of site fidelity However, primaries darted higher into the water column t o 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 domi nants grew faster than subordinates. However there was no difference in dom inance between primaries and secondaries. These results suggest that the we ll-documented advantage of early-emerging salmon fry over late-emerging fry cannot be completely attributed to intrinsic differences and that the adva ntage is partly mediated via a prior residence effect. Furthermore, prior r esidents gain foraging advantages without necessarily becoming more dominan t.