Behavioral responses to light gradients,olfactory cues,and prey in larvae of two North Pacific gadids (<Emphasis Type="Italic">Gadus macrocephalus</Emphasis> and <Emphasis Type="Italic">Theragra chalcogramma</Emphasis>) |
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Authors: | Amanda R Colton Thomas P Hurst |
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Institution: | (1) Fisheries Behavioral Ecology Program, Alaska Fisheries Science Center, NOAA-NMFS, Hatfield Marine Science Center, Newport, OR 97365, USA;(2) Present address: Center for Environmental Science, Chesapeake Biological Laboratory, University of Maryland, 1 Williams St., P.O. Box 38, Solomons, MD 20688, USA; |
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Abstract: | The growth and survival of larvae can be significantly enhanced through close association with patches of high prey concentration.
However, the taxis and kinesis responses used by larvae to locate and maintain residence in micro-patches remains poorly understood.
In this study, the behavioral responses of Pacific cod (Gadus macrocephalus) and walleye pollock (Theragra chalcogramma) larvae (45–100 dph) to light, prey scent, and prey were examined. Both species displayed an ontogenetic shift in response
to a horizontal light gradient, with small larvae (11–13 mm SL) exhibiting a positive phototaxis and large larvae (23–32 mm
SL) exhibiting a negative phototaxis. Whether this reversal is related to ontogenetically appropriate foraging cues or some
other aspect of the environment remains to be determined. Neither species displayed significant behavioral responsiveness
to the introduction of olfactory prey cues at either size. The aggregating (taxis) response of large larvae to introduction
of live prey was stronger than that of small larvae, possibly due to increased reaction distances and encounter rates. In
addition, both species exhibited a kinesis response of reducing the frequency of swimming bouts in response to introduction
of live prey. These results suggest that the scale of prey patchiness and the physical factors that determine patch encounter
rates are a significant determinant of larval growth and survival in the early feeding stages of marine fishes. |
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