Length-based approaches to estimating natural mortality using tagging and fisheries data: The example of the eastern Aleutian Islands, Alaska golden king crab (Lithodes aequispinus)

Abstract

We evaluated natural mortality (M yr−1) estimation reliability for eastern Aleutian Islands male golden king crab (Lithodes aequispinus), an exploited stock, by comparing an integrated length-based assessment model approach and a likelihood method using tag release-recapture data. We used 1997, 2003, and 2006 tag release-recapture data to estimate the size transition matrix, M, fishing mortality, total selectivity, and retained selectivity and compared M likelihood profiles between both methods. Furthermore, we conducted simulations with varying initial survival and tag reporting rates to show that M estimation reliability declines as these rates decline. Restricted time-at-large, full initial survival, and complete reporting assumptions produce an M estimate closer to that of the integrated length-based assessment method. Because the reliability of the M estimate is sensitive to changes in these assumptions, future efforts should focus on maximizing the number of tagged crab (and hence recaptures), evaluating initial tag-induced mortality, and optimizing tagged crab recapture reporting rates. The reliance of fishery-dependent data and high tag reporting rates highlights the importance for maintaining a positive cooperation with fishers for efforts towards sustainable management.