Thesis (M.S.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Christopher S. Guy. Includes bibliographical references (leaves 66-74).

Thesis (M.S.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Thomas E. McMahon. Includes bibliographical references (leaves 58-63).

Thesis (M.S.)--Humboldt State University, 2006. / Includes bibliographical references (leaves 45-50). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--University of Alabama at Birmingham, 2007. / Description based on contents viewed June 26, 2007; title from title screen. Includes bibliographical references (p. 21).

Changes in population size are governed by the birthrate, the sex ratio and the death rate. In pink salmon the average egg-production per female is about 1700 and variations from this average are insufficient to account for observed changes in adult populations. The sex ratio is approximately 50-50. Survival during the freshwater phases of the life cycle has been found to vary from approximately 1% to 24%,the average survival being significantly different in different streams. Variation is relatively greater in streams in which average survival is low. Natural survival in the ocean is considered, to average about 5% of the number of young fish reaching the sea. In the central region of the British Columbia coast the annual catch averages about 60% of the adult fish, this percentage being relatively constant for both small and large runs. Pink salmon maturing in "even" and "odd" years represent separate populations. These populations vary in size independently but may maintain a relatively constant ratio for a series of generations. This ratio varies from near equality to extreme disparity. Marked changes in the level of abundance may occur suddenly. Three types of mortality are recognized: (a) mortality which becomes relatively heavier as populations increase in density (compensatory) (b) mortality which becomes relatively heavier as populations decrease in density (depensatory) (c) mortality which is independent of density (extrapensatory). (a) is especially identified with the period of spawning and incubation;(b) is considered to occur mainly during the period of fry migration and to be due to predation;(c) may occur at any stage but is probably most variable during the period between entrance of the adults into fresh water and emergence of the fry. Population changes initiated by extrapensatory factors, among which stream-flow conditions are considered to be important, are exaggerated by depensatdry factors (notably predation on fry) but tend to be resisted by the compensatory influences which operate during the period of spawning and incubation. Stabilization of a level of abundance depends on a balance between these processes. In general, freshwater mortality is more variable than ocean mortality and plays a greater part in inducing population changes. It is suggested that the average freshwater survival of an un-fished population would approximate 2.4% and that this efficiency must be raised to about 6% to permit a sustained catch of 60% of the adult population. A lower freshwater output is likely to result in a reduction in size of the stock. Large runs in both even and odd years are not fundamentally incompatible. The possibility, of promoting a low-level stock to a persisting higher level of abundance is indicated. Chum salmon are subject to the same types of mortality as pink salmon but the results are modified by the higher average egg-production (ca.2700) and the variable length of the life cycle. The species tends to occupy streams in which physical conditions are less stable. Compensatory influences are frequently obscured by these conditions, resulting in irregular fluctuations in abundance. In the application of remedial measures similar principles apply to both species. / Science, Faculty of / Zoology, Department of / Graduate

The accumulation of butter sole within Skidegate inlet provides an important winter trawl fishery for northern British Columbia. The availability, prior to spawning, has been determined from catch statistics offered willingly by fishermen and industry. The availability fluctuates during the season but the real peak period, after the accumulated stock has been removed, occurs during the last week that fishing was permitted. Distortions which could have been produced by boats of different fishing efficiencies and, also, by boats which fished for only part of the season are compensated for. The minimum estimate of fishing intensity, as determined from tagging experiments, is 30.8%. The abundance of the stock, calculated from the fishing intensity, sex ratios, and length-weight data, is approximately 3,130,000 fish. The differential appearance of the sexes upon the grounds has been determined. The male fish appear upon the grounds first and are later followed by the females. Tag returns provide information concerning movement between the various grounds within the inlet and also dispersion from the inlet into Hecate strait after spawning has occurred. / Science, Faculty of / Zoology, Department of / Graduate

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