A comparison of the functional ecology of visual vs. nonvisual foraging in two planktivorous marine fishes

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Ryer, Clifford H, Lawton, Angela, Lopez, Ricardo J, Olla, Bori L
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2002
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Theragra chalcogramma
• Online Access: http://dx.doi.org/10.1139/f02-097; http://www.nrcresearchpress.com/doi/pdf/10.1139/f02-097

Some visually foraging planktivorous fish will facultatively engage in nonvisual foraging when opportunities arise or necessity dictates. Yet, little is known about the ecology of nonvisual foraging. We examined the roles of prey size, fish size, and prey density on the nonvisual foraging of walleye pollock, Theragra chalcogramma (40–100 mm total length), and sablefish, Anoplopoma fimbria (66–89 mm), in the laboratory. Both species were size selective, disproportionately consuming large prey just as they do during visual foraging. Large prey were encountered more often, presumably because they were more easily detected by the fish's lateral-line system. When foraging visually, larger fish consumed more prey, but during nonvisual foraging, there was no foraging advantage to greater fish size. Unlike visual detection distances, lateral-line detection distances may not increase appreciably with fish size. Lastly, prey density influenced nonvisual prey consumption. Walleye pollock were characterized by a type I functional response, whereas sablefish were characterized by a type II functional response. Models of planktivore foraging typically assume negligible foraging by particulate feeders below their visual foraging thresholds. On the basis of this study and field data, we suggest that foraging models for particulate feeders, such as juvenile walleye pollock and sablefish, should account for nonvisual size-selective foraging.