Survival of Discarded Sublegal Atlantic Cod in the Northwest Atlantic Demersal Longline Fishery

Abstract

The survival of sublegal Atlantic cod Gadus morhua discarded in the U.S. Northwest Atlantic demersal longline fishery was examined for the effects that handling technique, sea surface temperature, and capture depth have on it. Longline-caught Atlantic cod were either removed from the hook by hand (unsnubbed) or by allowing the hydraulic hauler to pull the fish against the parallel steel cylinders placed vertically on the gunwale, causing the hook to pull through the jaw (snubbed). Jigged-caught fish served as an indicator of mortality occurring because of the experimental design in the survival experiments. Once caught, live fish were placed in underwater cages, and short-term survival was assessed after holding the fish for 3 d (approximately 72 h). Survival was analyzed with respect to three water depths and four sea surface temperature (SST) strata. Atlantic cod survival in these strata ranged from 31% to 100%. Depth and SST affected survival more than the dehooking technique; survival was higher in shallow depths and at lower temperatures. Unsnubbed fish had higher survival rates than snubbed fish.