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Fish Bulletin No. 62. Catch per-Unit-of-Effort in California Waters of the Sardine (Sardinops caerulea) 1932–1942


As is recognized by all fisheries students, the total catch of any species does not usually measure the size of the population available to the fishermen. The size of the total catch depends on the relation between the numbers of fish in the available population and the amount of effort expended. To measure changes in this relationship, the catch per-unit-of-effort has been devised by fisheries workers. Variations in this measure may result either from variations in the size of the total population, from differences in availability of all or a portion of the population to the fishermen, or from changes in the amount of effort expended. For an interpretation of the influence of these factors other sources of information must be drawn upon. The catch per-unit-of-effort is an essential tool, however, in the solution of the vexing problems of fisheries management.

For the sardine several measures of the catch per-unit-of-effort have been calculated. The first to be published was by Hart (1933) and applied to the Canadian fishery off British Columbia. For the time interval studied, 1925–1932, Hart found no significant changes in the return to the fishermen for the amount of effort expended.

In California several preliminary investigations yielded no dependable results, due to the fact that the supply of sardines off the California coast exceeded the demands of the industry to such an extent that catch limits were imposed on individual boats. Any changes in the return per-unit-of-effort merely reflected, therefore, increasing demands of the industry, which resulted in higher catch limits. By the early 1930's, however, the California sardine industry had expanded to the point where it showed evidence of utilizing a large part of the available supply. Clark (1939), therefore, made a study of the return per lunar month for the Monterey and San Pedro fisheries. That investigation showed significant fluctuations with a maximum availability of the sardine population in 1934–35 and then a decline to a lower level in the succeeding seasons. In that investigation no attempt was made to correct for time lost to the fishermen due to unfavorable weather or to adjust for the effect of "limits" imposed on the fishing boats by the processing plants. Under good fishing conditions the fishermen can catch more fish than can be handled by the plants. To prevent gluts the processors limit the number of tons which a boat may catch on succeeding nights. Early in the history of the fishery limits were nearly always in effect. In the later years they were less important but still operating to some extent.

Sette and Palmer next made a study of the San Francisco fishery which supplied the floating reduction plants operating out of that port. This study involved a preliminary analysis of the influence of weather on the catch and used an average weekly catch as the unit-of-effort. The results were in general agreement with the findings of Clark for the ports of Monterey and San Pedro.

For a more thorough understanding of the relationship between the California sardine catch and the amount of effort expended, it was necessary to bring these studies up to date. In addition it was thought advisable to make an analysis of the external influences affecting the catch for which measurements were available. Also, for other studies involving variations in the sizes of fish available to the fishermen, a unit-of-effort covering a short time interval was desired. This study was undertaken, therefore, and so planned that it yielded the average weekly catch in thousands of pounds for the San Francisco, Monterey and San Pedro sardine fisheries. As far as possible this weekly catch was adjusted so as to be freed from the influence of weather, hours of darkness and of limits. The time interval covered is 1932–33 to 1941–42.

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