INFLUENCES OF FOOD DISTRIBUTION ON FISH FORAGING BEHAVIOR

Juvenile walleye pollock, Theragra chalcogramma, use group foraging, m ediated by local enhancement, when searching for prey that are clumped in time and space. Local enhancement occurs when fish are attracted t o the site where another fish has discovered food. Experiments were co nducted to determine whether fish forage as individuals when food is w idely dispersed in time and space. When acclimatized to dispersed food , juvenile walleye pollock foraged as individuals and did not respond to the food discovery of others. Some fish appeared to aggressively de fend areas of their tank, a behaviour not seen in fish foraging for cl umped food. In a second experiment, examining the role of prior experi ence in fish foraging, fish were first acclimatized to clumped food an d then suddenly switched to dispersed food. Fish continued to use grou p foraging, mediated by local enhancement, with no change over 20 food discovery events. These results indicate that social aspects of fish foraging strategies are flexible, but are also influenced by prior exp erience with resource distribution.