EFFECTS OF LOCATION OF FOOD DELIVERY AND SOCIAL-STATUS ON FORAGING-SITE SELECTION BY JUVENILE ATLANTIC SALMON

Experiments were conducted to investigate the response of juvenile Atlantic salmon, Salmo salar, to changes in the location at which food entered a stream tank. Experience with the location of food input into the system significantly influenced foraging-site selection by the dominant fish. Dominant fish changed location of their foraging site in response to a change in the location of food input, and occupied, aggressively defending, sites just downstream of the location of food introduction. In contrast, subordinate fish occupied foraging sites at the downstream end of the stream tank, regardless of location of food input. As a result of both site selection and social status, dominant fish captured significantly more prey than subordinates. Our results support the contention that salmonids choose foraging sites to maximize foraging opportunities. Our results also provide a possible explanation for the use of 'atypical' foraging sites by individual fish within their home range over the course of a single day, as observed in a number of salmonid species in the field.