Total and natural mortality of red king crab (Paralithodes camtschaticus) in Norwegian waters: catch–curve analysis and indirect estimation methods

Abstract

Abstract The red king crab (Paralithodes camtschaticus) is native to the Bering Sea, but was deliberately introduced to the Barents Sea during the 1960s. Since then, the red king crab has spread to Norwegian waters, and crab densities have increased sufficiently to support a coastal fishery. Information about total and natural mortality, which is important to ensure adequate management, is lacking. Estimates of annual total mortality (Z) were calculated using length-converted catch curves in three periods of different levels of exploitation. Separate analyses were run on trap and trawl data as well as on original and catch per unit effort-corrected data. Natural mortality was estimated using a linear regression of total mortality and exploitation level and by using indirect methods based on life history parameters. There was a significant increase in Z throughout the consecutive periods in both sexes. In males, the increase coincided with the increase in exploitation level. The increase in female mortality, which was not explained by exploitation level, is probably an effect of the increase in male mortality. Natural mortality (M), estimated using indirect methods, averaged 0.23 for both sexes. The estimated M using linear regression was 0.37/0.44, which may be an overestimate.