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Instream cover and shade mediate avian predation on trout in semi-natural streams

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https://ir.library.oregonstate.edu/concern/articles/r494vm85v

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Abstract
  • Piscivory by birds can be significant, particularly on fish in small streams and during seasonal low flow when available cover from predators can be limited. Yet, how varying amounts of cover may change the extent of predation mortality from avian predators on fish is not clear. We evaluated size-selective survival of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in replicated semi-natural stream sections. These sections provided high (0.01 m² of cover per m² of stream) or low (0.002 m² of cover per m² of stream) levels of instream cover available to trout and were closed to emigration. Each fish was individually tagged, allowing us to track retention of individuals during the course of the 36-day experiment, which we attributed to survival from predators, because fish had no other way to leave the streams. Although other avian predators may have been active in our system and not detected, the only predator observed was the belted kingfisher Megaceryle alcyon, which is known to prey heavily on fish. In both treatments, trout >20.4 cm were not preyed upon indicating an increased ability to prey upon on smaller individuals. Increased availability of cover improved survival of trout by 12% in high relative to low cover stream sections. Trout also survived better in stream sections with greater shade, a factor we could not control in our system. Collectively, these findings indicate that instream cover and shade from avian predators can play an important role in driving survival of fish in small streams or during periods of low flow.
  • Keywords: body size, trout survival, piscivory, low flow, refuge, experiment
  • Keywords: body size, trout survival, piscivory, low flow, refuge, experiment
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  • Penaluna, B. E., Dunham, J. B., & Noakes, D. K. G. (2016). Instream cover and shade mediate avian predation on trout in semi-natural streams. Ecology of Freshwater Fish, 25(3), 405-411. doi:10.1111/eff.12221
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  • 25
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  • 3
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  • BEP was funded by an Environmental Protection Agency STAR grant, a J Frances Allen scholarship from American Fisheries Society, a grant from the U.S. Geological Survey to Oregon State University, the Watersheds Research Cooperative and various scholarships through the Graduate School and the Department of Fisheries and Wildlife at Oregon State University.
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