The potential for both bycatch and unobserved mortality of crabs that encounter bottom trawls but are not captured have long been a concern to directed crab harvesters and managers of crab and groundfish fisheries. The current suite of management measures to control and reduce crab bycatch in Alaska groundfish fisheries includes closure areas and species-specific crab bycatch limits. However, bycatch is only one source of mortality from directed groundfish fisheries; of greater concern is the unaccounted for mortality from direct trawl gear interactions as they occur at or near the seafloor.
Addressing and mitigating the issue of unobserved mortality has been done through experiments designed to assess the mortality probabilities for crabs that pass under the various components (sweeps, wings, and central footrope) of trawl gear and aimed at modifying bottom trawl gear to lessen such probabilities. Cooperative research undertaken by scientists with the Alaska Fisheries Science Center and members of the groundfish fleet (through Groundfish Forum), with the majority of funding provided through the North Pacific Research Board (NPRB), has resulted in the groundfish fleet voluntarily modifying their bottom trawl gear to use 24-inch bobbins (versus previously used 16-inch) bobbins as a way of reducing snow and Tanner crab mortality. More information on this work can be found on the NPRB website at: