The rough-toothed dolphin is robust, with a conical head lacking demarcation between the melon and the beak. It has a somewhat reptilian appearance. This species has large flippers (seemingly oversized for the animal), and a prominent sickle-shaped dorsal fin. The body is dark gray, with a prominent narrow dorsal cape that dips slightly below the dorsal fin. The belly, lips, and much of the lower jaw are white, often with a pinkish cast. White scratches and spots, apparently caused in part by bites of cookie-cutter sharks and other rough-toothed dolphins, often cover much of the body. The jaws contain 20-27 teeth in each row with subtle, but detectable, vertical ridges. These ridges give rise to the species’ English common name. Adults are up to about 2.8 m long. They are known to reach weights of up to 150 kg. Length at birth is unknown.
Can be Confused With
Rough-toothed dolphins are generally easy to identify when seen at close range; however, they may be mistaken for bottlenose dolphins if seen at a distance. The narrow cape and cone-shaped head will be the best clues to identification of rough-toothed dolphins in such situations.
The rough-toothed dolphin is a tropical to subtropical species that generally inhabits deep oceanic waters, rarely ranging north of 40°N or south of 35°S. However, in some areas (such as off the coast of Brazil), rough-toothed dolphins may occur in shallow coastal waters. Distribution of the rough-toothed dolphin is known to include the Pacific coast of Central and South America and Baja California; the eastern tropical Pacific; the Hawaiian Islands, the coast of Japan and the China Sea, Indonesia, Micronesia, and New Zealand; the Bay of Bengal, coast of India, Gulf of Oman, and Gulf of Aden, the Seychelles and Natal coast of Africa; the west coasts of Africa, Spain, and France, the Mediterranean Sea; the English Channel; the Atlantic coast of the United States as far north as Cape Hatteras; and the Caribbean, Gulf of Mexico, and Atlantic coast of South America.
Ecology and Behavior
Rough-toothed dolphins‘ habitat are oceanic and are seen most commonly in groups of 10-20, although herds of over 100 have been reported. They may appear lethargic and rarely bowride. At other times, they move at high speed with the chin and head above the surface, in a distinctive skimming behavior described as ‘surfing’. In the eastern tropical Pacific, they tend to associate with floating objects and sometimes with other cetaceans.
Sexual maturity is reached at approximately 10 years for females and approximately 14 years for males. The rough-toothed dolphin is thought to live up to 32 years.
Feeding and Prey
Rough-toothed dolphins seize prey and feed on cephalopods and fish, including such large fish as mahi mahi (also called dorado or dolphinfish). Recently, it has been suggested that these dolphins may be adapted to be specialist feeders on mahi mahi.
The IUCN lists the rough toothed dolphin as “Data Deficient”, as too little is known about the species to assess its conservation status. This species is not listed as threatened or endangered by the United States government. No fisheries are known to specialize on this species, but rough-toothed dolphins are one of several species killed in direct fisheries in Japan, Sri Lanka, Indonesia, the Caribbean, Papua New Guinea, the Solomon Islands, and West Africa. They are sometimes taken as bycatch in purse seine fisheries for tuna in the eastern tropical Pacific, and in gillnet fisheries in Sri Lanka, Brazil, and the offshore North Pacific. Their offshore distribution in most areas should reduce their potential problems of habitat loss and alteration.
The United States National Marine Fisheries Service has estimated the population of two stocks in United States waters. The northern Gulf of Mexico population is estimated at 852 (CV=0.31) based on data from 1991-1995 surveys, and the Hawaiian stock is estimated to be 123 (CV=0.63) based on surveys conducted in 1993, 1995, and 1998.
Jefferson, T.A. 2002. Rough-toothed dolphin Steno bredanensis. pp. 1055-1059 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.
Lodi, L., and B. Hetzel. 1999. Rough-toothed dolphin, Steno bredanensis, feeding behaviors in Ilha Grande Bay, Brazil. Biociencias 7:29-42.
Miyazaki, N. and W.F. Perrin. 1994. Rough-toothed dolphin Steno bredanensis (Lesson, 1828). pp. 1-21 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Volume 5: The first book of dolphins. Academic Press.
Pitman, R.L. and C. Stinchcomb. 2002. Rough-toothed dolphins (Steno bredanensis) as predators of mahimahi (Coryphaena hippurus). Pacific Science 56:447-450.
Watkins, W.A., P. Tyack, K.E. Moore and G. Notarbartolo di Sciara. 1987. Steno bredanensis in the Mediterranean Sea. Marine Mammal Science 3:78-82.