Pantropical Spotted Dolphin
Order Cetacea : Family Delphinidae : Stenella attenuata (Gray)

Description. A small dolphin with a relatively short, black beak, blackish back, grayish sides, and white underparts; eyes usually encircled with black rings joined by a black stripe across base of rostrum; dorsal fin, flipper, and flukes black; the pale sides and abdomen often covered with small blackish spots; posterior to the dorsal fin the blackish upperparts and the flippers often covered with grayish white dots. Teeth small (diameter at alveolus 2.5-3.0 mm) and 38-42 in each toothrow. Total length, 1.5-2.0 m. Similar to S. frontalis but upperparts blackish, general size smaller, beak narrower, and the teeth smaller and more numerous.

Distribution in Texas. Occurs in the tropical and subtropical oceans of the world. Known in Texas from three individuals that were beached near Yarborough Pass on Padre Island during Hurricane Fern in September, 1971, and two separate individual strandings near Port Aransas in 1989 and 1990.

Habits. These dolphins are usually seen in groups of five to 30, although large herds of 1,000 or more are occasionally observed. Unlike many other dolphins, groups of pantropical spotted dolphins do not appear to be segregated by sex and age. These dolphins feed at or near the surface on fish, including mackerel and flying fish, squid, and shrimp.

In the eastern tropical Pacific, the following reproductive data are known. The gestation period lasts 11.5 months and lactation lasts about 11 months. At birth the calves average 80 cm in length and at 1 year are 1.4 m long. Males attain sexual maturity at about 6 years of age while females reach maturity at 5 years. The calving interval is 26 months. No data on reproductive habits are available for the Gulf of Mexico.

In the Pacific, these dolphins are killed incidentally in the course of seining for tuna. In 1970, about 400,000 were killed by U.S. vessels alone but that figure was reduced to 15,000-20,000 by 1978. Currently, incidental catch is limited by U.S. law to 20,500 per year but is usually lower than that due to declining tuna seining efforts and the recent adoption of a porpoise mortality reduction program; this international agreement by all major tuna seining countries has a goal of reducing total incidental catch to less than 5,000 dolphins per year by 1999. In the Atlantic and Gulf of Mexico, the problem of incidental catch is limited and was never as great as in the Pacific.

Remarks. This dolphin was previously known as Stenella frontalis (Cuvier).

Illustration credit: Pieter A. Folkens.