Scripps Institution of Oceanography

Spotted and spinner porpoise occur in coastal and offshore tropical waters of the eastern and central Pacific, as well as elsewhere in world tropical waters. They are important in the tropical yellowfin tuna fishery as indicators and aggregators of tuna. In the eastern Pacific, the range of both is a triangle with the base the coastline from Cabo San Lucas, Mexico to Columbia, and the apex extending seaward to about 10°N latitude, 145°W longitude. Variation owing to ontogeny, sexual dimorphism, individual variation, and geographical differentiation in coloration, external size and shape, and skeleton are described in qualitative and quantitative terms, and three geographical races of the spotted porpoise, Stenella attenuata (Gray, 1846), and four of the spinner porpoise, S. longirostris (Schlegel, 1841), (nomenclature is provisional) are defined.