Journal
ECOLOGY OF FRESHWATER FISH
Volume 25, Issue 3, Pages 405-411Publisher
WILEY-BLACKWELL
DOI: 10.1111/eff.12221
Keywords
trout survival; refuge; piscivory; body size; low flow; experiment
Categories
Funding
- Environmental Protection Agency STAR grant
- J Frances Allen scholarship from American Fisheries Society
- U.S. Geological Survey
- Watersheds Research Cooperative
- Graduate School at Oregon State University
- Department of Fisheries and Wildlife at Oregon State University
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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 (0.01m(2) of cover per m(2) of stream) or low (0.002m(2) of cover per m(2) 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 >20.4cm 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.
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