Steno bredanensus
Creators: name: Russell A. Mittermeier
name: Don E. Wilson
Publisher: name: Lynx Edicions
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Cetacea
Delphinidae
Steno
Steno bredanensus

description: 22.
Rough-toothed Dolphin
Steno bredanensus
French: Dauphin sténo / German: Rauzahndelfin / Spanish: Delfin de dientes rugosos
Other common names: Slopehead
Taxonomy. Delphinus bredanensis G. Cuvier in Lesson, 1828,
Paimpol, Coast of France.
This species is monotypic.
Distribution. Tropical and subtropical deep, oceanic waters in all major oceans from c.40° N and c.35° S; scarcely recorded in the Mediterranean Sea.
Descriptive notes. Total length up to 265-280 cm (males) and up to 255 cm (females); weight up to 155 kg. Neonates are ¢.100 cm in length and weigh c.15 kg.
Male Rough-toothed Dolphins are slightly larger than females. The Rough-toothed Dolphin is robust, with conically shaped head distinguished by lack of crease or clear demarcation between beak and melon. Instead, melon gently slopes into beak. They have large (17-19% total body length), slender flippers, with rounded tips, and moderately sized, falcate dorsal fin. There may be slight post-anal protrusion in some older males. Most of body is dark gray, with a darker, narrow dorsal cape that dips onto flanks below dorsal fin. Belly, throat, and lower jaw are pinkish-white. Border between white and dark-gray areas is graded and not clearly defined. Lips tend to be white. Mature Rough-toothed Dolphins often possess scars from cookie-cutter sharks (/sistius spp.) and other species of sharks. Young individuals are paler and have more muted color pattern than adults. There are 19-28 pairs of robust, conical teeth in each jaw. Teeth are covered in finely wrinkled ridges, reflected in the common name.
Habitat. Prefers deep, offshore waters beyond continental shelves but also found in shallow coastal waters within semi-enclosed regions such as in the Gulf of Thailand, Red Sea, Gulf of Mexico, Gulf of California, and Caribbean. The Rough-toothed Dolphin appears to be vagrant in the Mediterranean Sea. Its overall distribution is not well known, and it does not appear to be particularly abundant anywhere. Around the Hawaiian Islands, the Rough-toothed Dolphin is most often observed in waters more than 1500 m deep and in areas with upwelling. In French Polynesia, they are common in waters 1000-2000 m deep and within 1-:8-5-5 km of barrier reef habitat. Deepest recorded dives of Rough-toothed Dolphins are ¢.70 m, but they appear to be morphologically capable of deeper dives. Average dives last 15 minutes.
Food and Feeding. The Rough-toothed Dolphin feeds on cephalopods and fish, including large species such as mahi mahi (Coryphaena hippurus). They may hunt cooperatively to take down these larger fish. Echolocation clicks tend to consist of short pulses at low frequencies, which are likely ideal for deeper foraging.
Breeding. There is no specific information for this species, but male Rough-toothed Dolphins are thought to reach sexual maturity at c.14 years and females at c.10 years, and longevity is thought to be 32-36 years.
Activity patterns. The Rough-toothed Dolphin is a moderately paced swimmer and makes low-angled, arced leaps. Movements and dives of groups are often synchronized while traveling when group formation tends to be tight. Rough-toothed Dolphins may occasionally bow-ride alongside fast vessels and are aerially active; they occasionally breach.
Movements, Home range and Social organization. Group sizes of 10-20 Rough-toothed Dolphins are most common, but groups of up to 50 individuals have been reported in the eastern tropical Pacific Ocean and the central Atlantic Ocean. Aerial surveys have observed groups of more than 300 individuals, although these larger groups may be aggregations of subgroups. Preliminary work on social structure of the Rough-toothed Dolphin suggests more stable association patterns than are typical of most species of delphinids. In the eastern tropical Pacific Ocean, Rough-toothed Dolphins associate with pilot whales (Globicephala spp.) and Fraser’s Dolphins (Lagenodelphis hoser). Site fidelity seems to be high in Hawaiian waters. The longest reported linear distance traveled was 480 km among the Hawaiian Islands. Little data have been collected on migrations and movement patterns of the Rough-toothed Dolphin, especially from more offshore populations, so data from the Hawaiian populations may not be representative.
Status and Conservation. CITES Appendix II. Classified as Least Concern on The IUCN Red List. There are ¢.145,900 Rough-toothed Dolphins in the eastern tropical Pacific Ocean, 2746 individuals in the northern Gulfof Mexico, and 19,904 individuals around Hawaii. Population trends are currently unknown, but total abundance is likely more than 150,000 individuals. The Rough-toothed Dolphin is widespread, and there are no known major threats or reports of population declines. Rough-toothed Dolphins are not direct targets of any fisheries. They may be taken occasionally in Japanese drive fisheries (in 1976-1981, only 23 Rough-toothed Dolphins were taken in fisheries from Okinawa) and in drives off the Solomon Islands and Papua New Guinea. They are harpooned opportunistically offJapan, St. Vincent and the Grenadines, and West Africa. Off Taiwan, they are occasionally caught in gillnets, driftnets, and pelagic long lines. Rough-toothed Dolphins are only rarely caught incidentally in tuna purse seines in the eastern tropical Pacific Ocean. Only 21 individuals were taken in these fisheries in 1971-1975. They are also incidentally caught in gillnet and driftnet fisheries from Sri Lanka, Brazil, and likely in other tropical island areas. Organochlorine contamination may be an issue off Guangdong, China, where high tissue concentrations of PCBs have been reported in the Rough-toothed Dolphin.
Bibliography. Baird, Webster et al. (2008), Hammond et al. (2008p), Huang Jiansheng et al. (2007), Jefferson (2009b), Jefferson et al. (2008), de Lima et al. (2012), Miyazaki & Perrin (1994), Monteiro-Neto et al. (2000), Pitman & Stinchcomb (2002), Wang & Yang Shihchu (2007), Watkins et al. (1987), Weir (2006).
description: Published as part of Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, pp. 410-526 in Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona :Lynx Edicions on pages 512-513, DOI: 10.5281/zenodo.6610922