Indirect estimates of natural mortality rate for arrowtooth flounder (Atheresthes stomias) and darkblotched rockfish (Sebastes crameri)

Indirect estimates of instantaneous natural mortality rate (M) are widely used in stock assessment and fisheries management. They are essentially a form of meta-analysis, in which prior information on M and key life history parameters from a variety of stocks is used to estimate M for the stock in question. In this study we report indirect estimates of M for arrowtooth flounder (Atheresthes stomias) and darkblotched rockfish (Sebastes crameri) obtained by the methods described in Gunderson (1997), and a modification of Pauly's method (1980), and compare them with estimates previously derived by Hoenig's (1983) method. Pauly's original method was based on the correlation of M with von Bertalanffy growth parameters (K and L) and temperature. The modification we used was indicated by a number of reviews of Pauly's data (Charnov, 1993; Pascual and Iribarne, 1993; Jensen, 1996) and relies only on the correlation between M and K. The high correlation between these variables has been observed in a number of taxa and is the basis for the M-K "invariant" used widely in life history theory (Beverton, 1992; Charnov, 1993). Data on darkblotched rockfish were collected in 1986 and 1987 during research surveys conducted off the Oregon coast (43 degree 10'-45 degree 50') aboard commercial groundfish and shrimp trawlers. Data on arrowtooth flounder were collected from research trawls made during September 1993 on Portlock Bank near the eastern end of Kodiak Island, Alaska.