SOCIAL-BEHAVIOR OF JUVENILE CHUM SALMON, ONCORHYNCHUS-KETA, UNDER RISK OF PREDATION - THE INFLUENCE OF FOOD DISTRIBUTION

Social interactions can influence both foraging reward and vulnerabili ty to predators. We examined social interactions in groups of juvenile chum salmon, Oncorhynchus keta, receiving food that was either spatia lly dispersed, with many food items appearing synchronously, or spatia lly clumped, with individual food items appearing asynchronously. Thes e experiments were conducted both in the presence and absence of preda tors. When food was dispersed and predators were absent, juvenile chum formed schools and all individuals had access to food, despite freque nt agonistic interactions. When predators were present, schooling and feeding continued, but agonistic interactions ceased. In contrast, whe n food was clumped, dominant fish utilized aggression to monopolize fo od regardless of whether predators were present or absent, resulting i n decreased group cohesion. These results illustrate that food distrib ution and social interaction may play a role in determining how fish b alance predation risk against foraging reward.