Discarding and Total Fishing Mortality Trends in the U.S. Pacific West Coast Groundfish Demersal Trawl Fishery

Discarded catch is a major concern in mixed-stock fisheries and enumeration of discard has been a challenge in marine fishery management.  We provide estimates of discarded and total catch in the U.S. Pacific west coast groundfish demersal trawl fishery from 2002 through 2009, under trip limit management.  Discarded-catch data from the West Coast Groundfish Observer Program (WCGOP) were expanded to the fleet-level using a ratio estimator.  Total estimated discard in the fishery declined by 54% across the study period and represented 33% of the annual average groundfish catch.  Fishing effort (landings and tow hours) with a high proportion of discard was observed at the beginning of the study period, and then fishing effort subsequently increased but overall discard decreased.  The largest components of discard (by weight) were Pacific hake (Merluccius productus), arrowtooth flounder (Atheresthes stomias), skates (Rajidae sp.) and spiny dogfish (Squalus acanthias).  For species managed under rebuilding plans, total catch estimates fluctuated but the discarded proportion of catch increased (39%).  For non-rebuilding groundfish species, the discarded proportion of catch decreased (21%).  This study provides the first reference of total mortality trends in the west coast demersal trawl fishery and will serve as a baseline for future comparisons as the fishery shifts from trip limit management to an Individual Transferable Quota (ITQ) program in 2011.