Spinner Dolphin
Order Cetacea : Family Delphinidae : Stenella longirostris (Gray)

Description. These are small dolphins that average less than 1.8 m in length and 75 kg in weight. Maximum size is about 2.1 m and 95 kg. These dolphins are very slender and have a long, slender beak that is black above and white below. Coloration is dark gray dorsally fading to lighter gray on the sides and the belly is white. A dark stripe extends from the flipper to the eye. Average total teeth, 224, is greater than for any other Texas cetacean.

Distribution in Texas. Worldwide in tropical and warm temperate waters. Known in Texas from strandings along Padre Island National Seashore.

Habits. Spinner dolphins derive their name from a habit of leaping from the water and warping their bodies into graceful curves, or spinning lengthwise before splashing back. The motives for this behavior are not known but such actions are often in themselves enough to distinguish this species.

They usually occur in groups of 30 to several hundred but may number into the thousands. Spinner dolphins feed on mesopelagic fishes, squid, and shrimp.

Adult females give birth to a single calf at 2-year intervals. Parturition usually occurs in early summer but can occur in any season. Their period of gestation is 11 months and calves are about 75 cm long at birth.

Spinner dolphins have mass stranded twice in the Gulf of Mexico. One stranding of 36 animals occurred on Dog Island, Florida, in 1961, and the other was near Sarasota, Florida, in 1976. The latter stranding involved 50-150 spinners that beached themselves at several points during an extremely low tide. The dolphins came ashore with much "squealing and crying" but this later subsided and the animals were quite passive on the beach. Several of the animals were returned, apparently successfully, to the sea; however, others merely stranded again and at least 10 died.

In the eastern tropical Pacific this species is often caught and drowned in large numbers by the tuna fishing industry. Over the last 20 years the total population in those waters has declined about 80%, from 2 million to 400,000, due to incidental catch. Gulf of Mexico populations do not receive this pressure, but data for population estimates are unavailable and population trends are not known in Gulf waters.

Illustration credit: Pieter A. Folkens.