Williams, Gregg H.2015-08-04199227359414http://hdl.handle.net/1773/33342Thesis(M.M.A.)--University of Washington, 1992Most fisheries, marine or freshwater, commercial or recreational, catch other species in addition to the desired, or target, species. The catch of these additional species is termed incidental catch, or bycatch. Fishery bycatch is made up of a variety of animals, from cetaceans to seabirds to unmarketable fishes. Economic and fishery management considerations may cause the fisherman to keep the bycatch species for its commercial value, or, conversely, may require the bycatch be returned to the sea. In some fisheries, bycatch is retained because of its value in relation to the rest of the catch. For example, the target species may comprise only a small part of the catch, placing a reliance on the bycatch to provide a significant contribution to the overall revenue generated. In tropical fisheries for shrimp, the catch of shrimp is usually 10 percent or less of the total, whereas the bycatch of finfish and other species, which are large in size and commercially valuable, are the principle component of the catch (Gulland 1983). In many fisheries, bycatch is discarded due to economic or management reasons. The lack of a market or suitable ex-vessel price may force discarding the bycatch. Such was the case with the bycatch of white sturgeon (Acipenser transmontanus) in the gillnet and trap fishery for Columbia River salmon prior to commercial exploitation in the early 1880s (Bricklemeyer et al. 1989). In trawl fisheries, several species are caught in addition to the target species, but only those with commercial value during open seasons may be retained. Consequendy, most of the bycatch of other species is discarded. Saila (1983) estimated the discards of all species in the world’s commercial marine fisheries to range from 12 to 20 billion pounds (0.5 to almost 1 million metric tons) of sea life.vi, 156 leavesen-USCopyright is held by the individual authors.Theses--Marine affairsThesis