Bias-Corrected Size Trends in Chum Salmon in the Central Bering Sea and North Pacific Ocean

We estimated bias-corrected mean fork lengths of gillnet-caught chum salmon using a size selectivity estimate of the gillnet to test how the bias correction affects the estimated temporal pattern of chum salmon body size, during 1971–1994 and 1994–2007. Results showed bias-corrected mean fork lengths were smaller than uncorrected means. Therefore, when examining ontogenetic changes in fish size (e.g. the growth trajectory) using data collected by research gillnets, the uncorrected mean fork length can overestimate the true value. Comparison of temporal trends in bias-corrected mean fish lengths to uncorrected means showed similar results because both illustrated a decrease in chum salmon fork length in 1971–1994, and a stable fish size after 1994. Uncorrected mean values of chum salmon fork length for fish caught using research gillnets can be used as a proxy for fish size to examine temporal trends. We conclude that interpreting temporal trends using either uncorrected or bias-corrected data will support the same general conclusions regarding long-term changes in chum salmon body size. All correspondence should be addressed to M. Fukuwaka. e-mail: [email protected] Bias-Corrected Size Trends in Chum Salmon in the Central Bering Sea and North Pacific Ocean Masa-aki Fukuwaka1, Nancy D. Davis2, Tomonori Azumaya1, and Toru Nagasawa1 1Hokkaido National Fisheries Research Institute, Fisheries Research Agency, 116 Katsurakoi, Kushiro 085-0802, Japan 2School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA