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

Ecology of Freshwater Fish
By: , and 

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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.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Instream cover and shade mediate avian predation on trout in semi-natural streams
Series title Ecology of Freshwater Fish
DOI 10.1111/eff.12221
Volume 25
Issue 3
Year Published 2015
Language English
Publisher Wiley
Contributing office(s) Forest and Rangeland Ecosystem Science Center
Description 7 p.
First page 405
Last page 411
Time Range Start 2009-06-29
Time Range End 2009-08-03
Country United States
State Oregon
Online Only (Y/N) N
Additional Online Files (Y/N) N