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Analysis and history of the Oregon otter-trawl fishery

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  • The objective of the thesis is to present data upon which the management of the Oregon otter-trawl fishery can be based. In addition, a history of the Oregon trawl fishery is presented. A summary of gear development by many of the vessels in the Oregon fleet is presented in table form. The principal species studied are the English sole (Paraphrys vetulus), petrale sole (Eopsetta jordani), and Dover sole (Microstomus pacificus). For these three species the time of spawning, length at maturity, and relation of length to weight are determined. In addition, the number of eggs produced by English and Dover sole at various sizes is calculated. In 1948 and 1949 a total of 5,643 bottom fish were tagged from otter trawlers operating from Astoria. Almost all of these fish were English, petrale, and Dover sole, and all but a few were released in the area between Willapa bay and 2 Tillamook Head. Returns from the tagging give no indication of significant migrations north and south along the coast, but a small amount of exploratory winter fishing resulted in recovery of tagged :Dover sole in waters deeper than 200 fathoms. These Dover sole had been tagged during the summer in much shallower water. The growth of sole of the three species studied is computed from the tag returns. General comparisons of rates of tag return are made with other tagging experiments of a similar nature along the Pacific Coast. Otoliths of English, petrale, and Dover sole are used to calculate growth rates and compute age-frequency curves. It is concluded that otoliths are not completely satisfactory for determining the age of these species. An analysis of the condition of the stocks of English sole, petrale sole, Dover sole, and rockfish is made using the landing records for the period 1942-47, inclusive. The English sole were not completely exploited in 1947. During this period, the petrale sole declined in abundance at least 50 per cent. The Dover sole declined some in abundance, and the condition of the rockfish stocks is obscured because of the several species that enter this category. English, petrale, and Dover sole were measured at the time commercial landings were made and these data are analyzed for the years 1948-51, inclusive. In 1950 the catches of Ore,:,on otter trawlers at sea were sampled to get a measure of the amount of discard of both scrap fish and undersized English, petrale, and Dover sole. Approximately 17 per cent of the Dover sole, 33 per cent of the petrale sole, and 27 per cent of the English sole were discarded at sea because they were too small. Approximately one-half of the total catch at sea by weight was discarded. An analysis is made of the relationship of the mink-raising industry to the otter-trawl fishery. The species composition of the milk food is determined from market samples. An estimate is made of the total amount of fish fed to mink in Oregon in 1949 based on information obtained from questionnaires. The effect of the fishery for mink food on the stocks of fish of the various species is discussed.
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