UC San Diego Library – Scripps Digital Collection

This study of the variation in certain commercially important clupeoid fishes of western North America is one of a series by which it is designed to determine the relation which the varying characters of fishes bear toward the physical features of their environment. Although other characters and other environmental factors are receiving attention in these investigations, chief stress is now being laid on the correlation between the average number of vertebrae and the temperature of the water. The average surface temperature of the coast waters of San Francisco Bay (Golden Gate), Monterey Bay (Pacific Grove) and San Diego (off Coronado Beach) is indicated for the whole year by the three curves on Plate I. The marked difference in temperature between the ocean water of southern California and central California is illustrated by the curves for the San Diego region and for Monterey Bay, which is really a very open gulf. The usual maximum temperature for Monterey is lower than the ordinary minimum off San Diego. These is not an even gradation of temperature between these two localities, Point Conception marking the boundary between the cold waters of the central coast and the warmer waters of southern California. In each region, moreover, there is much local variation in temperature conditions, due not only to differences in protection and depth, but also, probably, to the differential upwelling of deep, cold water (McEwen, 1912, 1916). The curve for San Diego is taken from McEwen's 1916 paper; that for Monterey is smoothed from unpublished data supplied by Director Walter K. Fisher of the Hopkins Marine Station at Pacific Grove. The temperature curve at the entrance to San Francisco Bay, constructed by slightly smoothing Davidson's (1886) monthly averages, is intermediate between the San Diego and the Monterey Bay curves. The higher temperatures at San Francisco as compared with the Monterey records are due to the greater warming of the waters in the shallows of San Francisco harbor. As the fishes here treated are of great importance from the standpoint of the commercial fisheries, this paper is published in the present form largely as a contribution to the fishery-biology of these species. An attempt to determine definitely the racial status of the various populations of each form would, however, be beyond the scope of the present paper. Our data, however, are brought to bear on such problems. This is done to suggest conclusions, and to make our data available to the fishery investigators. We have applied to our data on the herring and the anchovy a method of analysis which we have found useful in studying the seasonal variation in the number of segments in freshwater fishes (Hubbs, 1922, 1924). By this method the correlation between individual variations and environmental factors is determined. Measure is obtained, also, of the degree to which the average number of segments fluctuates on a purely individual, as contrasted with a racial basis. The results so secured are of value in interpreting the significance of observed differences in the average number of segments for samples from different localities.