Risk-taking behavior in weight-compensating coho salmon, Oncorhynchus kisutch

The effects of food restriction on predation risk-taking behavior were studied in juvenile coho salmon, Oncorhyndtus kisutch, during the period before seawater migration in the spring. A radiographic technique enabled the study of individual food intake in a safe and risky food patch before and after exposure to a piscivorous predator. The study revealed a significant increase in food intake and specific growth rate in the weeks following deprivation, resulting in compensatory growth and a recovery of the weight loss caused by dietary restriction. The increase in food intake resulted from a change in risk-taking behavior. Following a period of diet restriction, the fish habituated falter after predator exposure, and the proportion of fish in the risky patch was significantly higher than before deprivation. Deprived fish took greater shares of the group meal compared with control fish, and the pattern of the individual share of the group meal after food restriction indicated a change in the social hierarchy. This study indicates that risk-taking behavior is state dependent and changes temporarily to compensate for a period of food restric- tion. The results are discussed in terms of trade-ofls between food and risk in a period leading up to an ontogenetic habitat shift. Key words: coho salmon, Oncorkynckus kisutch, predation, risk taking, Salmonidae, social hierarchy. (Behav Ecol 9:26-32 (1998)) I t has become increasingly clear that individuals are able to make behavioral trade-offs between food intake and risk of predation in a state-dependent fashion. Foraging at an in- creasing rate may be costly in terms of an increase in the risk