Analysis of Salmon Bycatch in Trawl Fisheries to Aid in Developing Management Measures

Ecosystem fisheries management as practiced by the North Pacific Fishery Management Council (NPFMC) involves many facets including measures to avoid exceeding prohibited species catch (PSC) limits.  Likewise, another ecosystem principle ensures that catch limits remain below overfishing levels (typically set equal to maximum-sustainable yield levels) based on single-species assessment models for each stock or stock complex.  This means that the management system is based explicitly on multispecies considerations.  Salmon has been a prohibited species since the days of foreign and joint-venture trawl fishing in the Eastern Bering Sea and management has evolved as after two decades of an extensive scientific observer data collection program.  These data, supplemented with summer surveys and cooperative research programs provide unique insights on the temporal and spatial structure of salmon stocks during their oceanic stage.  In particular, patterns of bycatch appear to be affected by season, location, and temperatures.  However, year-effects appear to be the largest factor indicating that inter-annual variability in environmental conditions and/or run sizes likely play an important role in bycatch.  For new more optimal management measures (such as closure areas), the available data are limited due to the occurrence of past closures.  Other challenges include accounting for the extent that salmon taken as bycatch are immature and may not have returned to spawn for a number of years and estimating the extent that salmon bycatch originated from western Alaskan river systems.  Additionally, measures to reduce bycatch of one species may result in higher bycatch of others adding further complications.