Undersea topography and distribution of dolphins of the genus Delphinus in the Southern California Bight

Aerial surveys totalling 21,902 km were analyzed in the Southern California Bight. Although the genus Delphinus is easily recognizable from aircraft, the different species are not detectable in these flights. Delphinus occur more frequently in areas of high relief than in areas of low relief. The depth of the water does not appear to influence distribution of Delphinus. The availability of prey species over areas of different relief may be a major factor influencing these distribution patterns. Although the relative frequencies of occurrence of Delphinus within depth and relief classes do not change from one half of the year to the next, the aggregation sizes differ significantly. From May through October, when anchovies are the major component of the diet and are more available as indicated by the live catch fishery records, Delphinus aggregations have a median size of 250. From November to April the median aggregation size is 40.