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RESEARCH ARTICLE
Contents Vol 57(5)

Apparent predation of juvenile coho salmon (Oncorhynchus kisutch) by prickly sculpins (Cottus asper) is an artefact of trapping methodology

Londi M. Tomaro
+ Author Affiliations
- Author Affiliations

A Lewis and Clark College, 1017 SW Gaines Street, Portland, Oregon 97239, USA.

B Email: ltomaro@easystreet.com

Marine and Freshwater Research 57(5) 513-518 https://doi.org/10.1071/MF05186
Submitted: 19 September 2005  Accepted: 9 May 2006   Published: 13 July 2006

Abstract

Freshwater sculpins often inhabit the same waterways as juvenile salmonids and may impact the survival of juvenile salmonids through predation on early life-history stages. In the present study, the stomach contents of 2302 individual Cottus asper, a freshwater sculpin, collected from Auke Lake, Alaska, were examined during the boreal summer of 2000 to determine if C. asper are important natural predators of juvenile coho salmon (Oncorhynchus kisutch), and to explore possible trap bias of gear used in preliminary diet studies. The diet of sculpins collected in confining traps was compared with the diet of sculpins collected in nets. Significant predation on pre-smolt coho salmon by trapped sculpins, but none by netted sculpins, was observed. This result provides strong evidence of trap bias in the observed diet of C. asper. The remainder of the diet of trapped sculpins also differed significantly from that of netted sculpins. Significantly more trapped sculpins had eaten plant material and fish, whereas significantly more netted sculpins had consumed molluscs. Finally, sculpin diet was correlated with sculpin size, which may influence predation on other salmonid life-stages. These results expand our understanding of prickly sculpin diet and show that they are not important predators of juvenile coho salmon. These findings also demonstrate the importance of assessing the potential bias of collection gear and sampling techniques.

Extra keywords: diet assessment, gear bias, gear selection, observed diet, trap bias, trap effects.


Acknowledgments

This study was made possible largely by the generosity of Doug Jones and Judy Lum of the Alaska Department of Fish and Game, Juneau Office, as well as that of Jeep Rice and Jerry Taylor of the NOAA Fisheries Auke Bay Biological Laboratories, all of whom provided equipment and assistance in planning and implementing sculpin collections. B. Bechtold, P. Bierzychudek, K. Clifton, T. Friesen, R. Heintz, and B. Nelson provided invaluable editorial input on earlier drafts of this manuscript and S. Yamada furnished a friendly review. Two anonymous reviewers provided helpful comments. Many thanks to those who assisted with field collections and stomach sampling: B. Bechtold, J. Lum, A. Nusom, A. Tomaro, J. Tomaro, and M. Tran.


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