Graduate Thesis Or Dissertation

 

Factors affecting coho salmon production in Oregon Public Deposited

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  • Eight scale characters of known hatchery and wild coho salmon (Oncorhynchus kisutch) were compared, and a linear discriminant function was used to determine if hatchery and wild adult coho salmon could be correctly identified by their scales. Eighty-two percent of the hatchery and 89% of the wild fish were correctly identified. Based on analysis of scales from adult salmon of unknown origin (hatchery or wild) and the estimated catch of hatchery coho (marked) taken by the Oregon sport fishery, concluded that 74.9% of the fish caught in the ocean from mid-June to mid-September 1977 had been released as smelts from hatcheries. Percentages of hatchery fish in the catch ranged from 85% near the mouth of the Columbia River to 61% at Winchester Bay on the southern Oregon coast. Fisheries on the south and central Oregon coast may have fished on higher percentages of wild coho salmon later in the season, probably because wild fish from coastal streams remained off of these ports while most fish destined for Columbia River hatcheries had already migrated northward. Scales from coho salmon were used to determine if location on the body from which they were taken would affect the values of five scale characters. Scales obtained from within a relatively small area above the lateral line between the dorsal and adipose fins differed widely in total radius, in radius of the freshwater zone, and in number of circuli in the freshwater zone. Scales taken farther above the lateral line had significantly lower values for all five characters observed. I conclude that substantial error can be introduced into interpretation of scale data if care is not taken to insure that scales from each fish come from precisely the same area of the body. A well chosen scrape sample yielded a result as satisfactory as that of a "preferred" or "key" scale. To investigate the relationship between streamflow and abundance of coho salmon, I correlated flow from several Oregon coastal rivers with catch of coho salmon from these rivers and with catch from the Oregon commercial troll fishery. I found a highly significant relationship between total streamflows during the freshwater residency of the fish for five Oregon coastal rivers combined and pounds of adult coho salmon caught by the Oregon commercial troll fishery from 1942 to 1962. There is also a significant relationship between total combined annual (January-December) flows for these rivers and a catch 2 years later. Conversely, I found a poor relationship between the lowest 60 consecutive days of summer flow and 2 two years later. I also found significant relationships between annual flows and catch in Tillamook Bay from 1934 to 1946. Only on the Siletz River from 1927 to 1940 do find a significant relationship between summer flows and catch. Higher flows during the freshwater stages of coho salmon probably provide more habitat and better conditions for growth as well as lessen susceptibility of fry and smelts to predation. I concluded that the relationships I found should probably not be used now to predict abundance of wild coho salmon because of (l) the unknown interaction between wild and hatchery fish, and (2) the preponderance of hatchery fish in the catch.
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