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Journal Article

Habitat Profitability and Choice in a Sit-And-Wait Predator: Juvenile Salmon Prefer Slower Currents on Darker Nights

Neil B. Metcalfe, Sveinn K. Valdimarsson and Neil H. C. Fraser
Journal of Animal Ecology
Vol. 66, No. 6 (Nov., 1997), pp. 866-875
DOI: 10.2307/6002
Stable URL: http://www.jstor.org/stable/6002
Page Count: 10

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Topics: Fish, Velocity, Salmon, Luminous intensity, Foraging, Juveniles, Streams, Fish feeding, Light water, Animal ecology
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Habitat Profitability and Choice in a Sit-And-Wait Predator: Juvenile Salmon Prefer Slower Currents on Darker Nights
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Abstract

1. The profitability of a foraging site for a sit-and-wait predator depends on the range at which food items can be detected, as well as their arrival rate. A simple model for drift-feeding fish shows that potential profitability is dependent on the interaction between current velocity and light level, so that the water velocity at which intake is maximized is predicted to decrease with decreasing light intensity due to changes in detection range. 2. Experimental tests with juvenile Atlantic salmon showed that there was no difference in foraging efficiency between fish held in high and low velocity water until light intensities dropped below 0.1 lx (similar to full moon with a clear sky); however, below this point fish were more efficient at intercepting food in slower flowing water. 3. When given a choice of foraging location, juvenile salmon exhibited the predicted shift towards slower velocity microhabitats as light level was reduced; the most profitable feeding habitat for the fish was therefore dependent on the night-time conditions (overcast vs. full moon). The results may explain why foraging juvenile salmonids have been observed to undertake diel habitat shifts, and indicate that habitat suitability assessments made only under daylight conditions may be inappropriate.

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