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Shifting the balance between foraging and predator avoidance: the importance of food distribution for a schooling pelagic forager

Authors
  • Ryer, Clifford H.1
  • Olla, Bori L.1
  • 1 National Marine Fisheries Service, Hatfield Marine Science Center, Alaska Fisheries Science Center, Newport, OR, 97365, U.S.A. , Newport
Type
Published Article
Journal
Environmental Biology of Fishes
Publisher
Springer-Verlag
Publication Date
Aug 01, 1998
Volume
52
Issue
4
Pages
467–475
Identifiers
DOI: 10.1023/A:1007433014921
Source
Springer Nature
Keywords
License
Yellow

Abstract

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.

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