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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 7, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(6):930-936; doi:10.1093/icesjms/fsn076
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© 2008 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Bias in size composition of chum salmon (Oncorhynchus keta) caught by a gillnet with a geometric series of mesh sizes, and its correction using gear intercalibration

Masa-aki Fukuwaka1, Tomonori Azumaya1, Nancy D. Davis2 and Toru Nagasawa1

1 Hokkaido National Fisheries Research Institute, Fisheries Research Agency, 116 Katsurakoi, Kushiro 085-0802, Japan
2 School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA

Correspondence to M. Fukuwaka: tel: +81 154 921715; fax: +81 154 919355; e-mail: fukuwaka{at}fra.affrc.go.jp

Fukuwaka, M., Azumaya, T., Davis, N. D., and Nagasawa, T. 2008. Bias in size composition of chum salmon (Oncorhynchus keta) caught by a gillnet with a geometric series of mesh sizes, and its correction using gear intercalibration. – ICES Journal of Marine Science, 65: 930–936.

Some research gillnets with size combinations based on a geometric series have been used for research surveys underpinning the stock assessment of fresh-water and marine fish. We assessed a bias in size composition of chum salmon caught using a research gillnet consisting of ten different mesh sizes based on a geometric series of factor 1.14. In all, 11 fishing operations were conducted for gear intercalibration between the research gillnet and a midwater trawl in the central Bering Sea. The best-fit selectivity model to pooled catch data included different fishing intensities among gillnet meshes. The pooled catch efficiency and the maximum catch efficiency of the gillnet increased with fish size. Estimated size composition of chum salmon was more similar to trawl catches than to research gillnet catches. Bias in size composition of research gillnet catches may be caused by the difference in encounter probability among mesh sizes, variability in fish swimming speed based on fish size, mesh visibility influencing fish behaviour, and diel vertical migration of chum salmon. When conducting multimesh gillnet surveys for stock assessment, researchers should correct a bias in size composition by performing gear intercalibrations.

Keywords: chum salmon, gear selectivity, geometric mesh size, research gillnet, size composition

Received 6 August 2007; accepted 13 April 2008; advance access publication 7 May 2008.


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