Discarding and fishing mortality trends in the U.S. west coast groundfish demersal trawl fishery

Quantifying discarded catch is needed to guide effective fishery management and recognize the unintended impacts of fishing; ultimately to promote a more sustainable fishery. To understand fishing mortality prior to the establishment of an IFQ management system, we provide estimates of discarded and total catch (sum of discard and landings) in the U.S. west coast groundfish demersal trawl fishery from 2002 to 2009. West Coast Groundfish Observer Program (WCGOP) data were expanded to fleet-level discard estimates using a ratio estimator. Total estimated discard in the fishery declined by 52% across the study period. On average, 29% of the annual groundfish catch was discarded at-sea. A high proportion of catch was discarded during 2002, but subsequently overall discard decreased even though fishing effort (landings and trawl tow hours) increased in the fishery from 2004 to 2009. The largest components of discard (by weight) were Pacific hake (Merluccius productus), arrowtooth flounder (Atheresthes stomias), skates (Rajidae sp.) and spiny dogfish (Squalus acanthias). In 2009 relative to 2002, the discarded fraction of catch for rebuilding species, which constrain the fishery, had increased by 39%. In contrast, the discarded fraction of catch for target species had decreased by 24%. In addition, much of the fishing effort shifted to deeper waters. Our results represent a baseline for future comparisons as the fishery shifted from trip limit management to an Individual Fishing Quota (IFQ) program in 2011.