The Alaska Fisheries Science Center website is now part of the NOAA Fisheries website.
Some information may not be up to date. Join us at our new location,
Please contact with any questions.

link to AFSC home page
Mobile users can use the Site Map to access the principal pages

link to AFSC home page link to NMFS home page link to NOAA home page

Fisheries Behavioral Ecology - Abstracts

Ryer, C.H. and B.L. Olla. 1998. Shifting the balance between foraging and predator avoidance: the importance of food distribution for a schooling pelagic forager. Environmental Biology of Fishes 52:467-475.


It is widely held that when predator avoidance conflicts with other activities, such as feeding, avoidance of predators often takes precedence. In this study, we examine how predation risk and food distribution interact to influence the schooling behavior and swimming speed of foraging juvenile walleye pollock, Theragra chalcogramma. Fish were acclimated to either spatially and temporally clumped, or spatially and temporally dispersed food for 3 weeks. Fish were then monitored while feeding in the absence and presence of predatory sablefish, Anoplopoma fimbria. Fish foraging for clumped food swam rapidly in a loose school when predators were absent, but swam more slowly and adopted more cohesive schooling in the presence of predators, trading-off foraging opportunity for decreased vulnerability to predators. Fish foraging for dispersed food swam about slowly and did not engage in cohesive schooling in either the absence or presence of predators. These fish accepted greater predation risk in order to continue foraging, suggesting that the cost of schooling, in terms of decreased foraging opportunity, was greater when food was dispersed than when it was clumped. This lower responsiveness to predators among fish receiving dispersed food demonstrates that predator avoidance does not always take precedence over other activities, but rather, that a balance is maintained between predator avoidance and feeding, which shifts as food distribution changes.


Last updated 31 March, 2009

            | Home | Site Map | Contact Us | FOIA | Privacy | Disclaimer | | Accessibility | Print |           doc logo