Estimation of Partial Recruitment and Yield per Recruit for an Otter Trawl Fishery for Deepwater Redfish

Abstract

The Canadian deepwater redfish (Sebastes mentella) fishery in the Atlantic ocean tends to be concentrated in a limited depth range to maximize catch rates and optimize size composition of the catches that vary with depth. Thus, the assumption of Beverton and Holt's yield-per-recruit analysis that all fish are equally subject to fishing mortality beyond a certain size seems inappropriate for this fishery. The alternative method of Thompson and Bell is more flexible but requires estimated age-specific, partial recruitment factors as an input. In this study, selectivity factors empirically determined for various bottom trawl mesh sizes and information from research vessel surveys on the composition of deepwater redfish catches in different depth zones were analysed to estimate partial recruitment factors for subsequent yield calculations. Partial recruitment factors were estimated for the commercial otter trawl fishery on deepwater redfish in Divisions 2J and 3K of the Northwest Atlantic Fisheries Organization (NAFO) area. From these, yield-per-recruit analysis was done by the method of Thompson and Bell and the results were compared with those obtained by the method of Beverton and Holt. The two methods gave estimates of F max that were significantly different but both methods arrived at a similar conclusion as to the most appropriate mesh size to use for maximizing yield per recruit.