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Steno bredanensisrough-toothed dolphin

By jennifer greenwood

Geographic Range

Rough-toothed dolphins, Steno bredanensis have a broad geographic range which ecompasses tropical and subtropical oceans. They have been frequently sighted along various coastal areas such as Kaua’i, Ni’ihau, and O’ahu of the Hawaiian Islands, the Mediterranean Sea, the Sicily Channel, Tahiti, Moorea, and the Windward Islands. (Gannier and West, 2005; Kuczaj II and Yeater, 2007; Ritter, 2007; Shirihai and Jarrett, 2006; Watkins, et al., 1987)

Habitat

Although rough-toothed dolphins reside in both shallow and deep ocean waters, they prefer deep waters greater than 1500 m in depth. They have been found at depths of up to 2000 m. Their location is often driven by the amount of nutrients in a given area. Rough-tooth dolphins are most commonly spotted in temperate waters. They prefer sea surface temperatures of 25 ̊C during the warm season but have been discovered during the cold season in waters ranging from 17 to 24 ̊C. Rough-toothed dolphins are rarely seen ranging north of 40 degrees latitude or south of 35 degrees latitude. (Baird, et al., 2008; Gannier and West, 2005; Jefferson, et al., 1993; Kuczaj II and Yeater, 2007; Ritter, 2007; West, 2002)

  • Range depth
    5 to 2000 m
    16.40 to 6561.68 ft

Physical Description

The average adult rough-toothed dolphin reaches a length of 2 to 2.65 m and a mass of 90 to 160 kg. This species is the only dolphin species that possesses a long beak. The elongated beak is dual colored; the upper jaw is blue and gray while the lower is pale pink and white. Their colorings may vary geographically. The body of rough-toothed dolphins is dark grey with white or light colored spots on their sides. The belly, lips, and parts of the lower jaw are white. Rough-toothed dolphins have a distinctive color pattern, consisting of a dark narrow cape which passes over the eyes and arches high on the sides of the body. Some of these animals show white and yellowish scars, due to encounters with large squid, cookie-cutter sharks, other rough-toothed dolphins, and interactions with boats. Males and females are similar in appearance. However, some males can grow larger and possess a more pronounced post-anal hump and prevalent scars. Rough-toothed dolphins are commonly misidentified as bottlenose dolphins, spinner dolphins, and spotted dolphins, but closer examination of the beak, head shape, and jaw color can help distinguish these species. ("Rough-toothed Dolphin", 1998; Carwardine, 1995; Jefferson, 2002; Jefferson, et al., 1993; Kays and Wilson, 2009; Rouch and Poss, 1998; Shirihai and Jarrett, 2006; Watkins, et al., 1987)

  • Sexual Dimorphism
  • male larger
  • Range mass
    90 to 160 kg
    198.24 to 352.42 lb
  • Range length
    2.00 to 2.65 m
    6.56 to 8.69 ft

Reproduction

Little information is available regarding the mating systems of rough-toothed dolphins in the wild. (Dohl, et al., 1974; Lodi, 1992; West, 2002)

The reproductive habits of rough-toothed dolphins are not well known, though captive studies provide some information. At birth, rough-toothed dolphins measure 1 to 1.3 m in length. Calves attempt to nurse within an hour of birth, but are initially unsuccessful, unable to connect to their mother’s mammary slits. Within the first 3 days, calves can successfully nurse, which takes place underwater and occurs throughout the day. Calves nurse, rest, and play on a daily basis. Play time generally follows nursing and includes exploration to the surface while staying in close proximity to the mother. Calves rest around midday for about 60 minutes. At 2 months of age, calves begin to eat fish and decrease nursing time. ("Rough-toothed Dolphin", 1998; Dohl, et al., 1974; Jefferson, 2002; Lodi, 1992; Ritter, 2007; West, 2002)

Rough-toothed dolphins exhibit sexual dimorphism, and mature males are longer than mature females. In both sexes, the most rapid growth occurs in the first 5 years. Females reach sexual maturity at 9 to 10 years of age at a length of 212 to 217 cm and a weight of 101 to 108 kg. Males reach sexual maturity at 5 to 10 years of age at a length of about 216 cm and a weight of 92 to 102 kg. (Dohl, et al., 1974; Jefferson, 2002; Ritter, 2007; West, 2002)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • viviparous
  • Range weaning age
    2 (low) months
  • Range age at sexual or reproductive maturity (female)
    9 to 10 years
  • Range age at sexual or reproductive maturity (male)
    5 to 10 years

In captivity, female rough-toothed dolphins protect their calves by swimming in close proximity to their young and positioning themselves between the calf and other dolphins. The length of the mother-calf relationship is unknown. A female rough-toothed dolphin, presumed to be the mother, was observed supporting a dead calf at water's surface for several days. During this time, she was escorted and protected by a number of male rough-toothed dolphins. This may demonstrate a prolonged mother-calf association in rough-toothed dolphins. Such behavior has been observed in the tight social groups of other marine mammals. ("Rough-toothed Dolphin", 1998; Dohl, et al., 1974; Kuczaj II and Yeater, 2007; Lodi, 1992; Ritter, 2007; West, 2002)

  • Parental Investment
  • precocial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
  • pre-weaning/fledging
    • provisioning
      • female
  • pre-independence
    • provisioning
      • female

Lifespan/Longevity

Rough-toothed dolphins off the coast of Japan can live to be 32 to 36 years of age, though it is presumed that members of this species may live considerably longer. The oldest individual was estimated to be 48 years old and was found stranded from the Florida coast. The longest lived individual in captivity, however, was only 12 years of age. (Jefferson, 2002; West, 2002)

Behavior

Rough-toothed dolphins are most commonly seen in groups of 10 to 30 individuals, though pods of up to 160 dolphins have been spotted containing eight smaller groups. They have also been spotted with pilot whales, bottlenose dolphins, spotted dolphins and spinner dolphins. Rough-toothed dolphins are great divers and can stay submerged for as long as 15 min. They are also fast swimmers and often swim just under the surface with their dorsal fins clearly visible. They enjoy "surfing" or bow-riding, but not as readily as other tropical dolphins. ("Rough-toothed Dolphin", 1998; Carwardine, 1995; Dohl, et al., 1974; Jefferson, et al., 1993; Lodi, 1992; Ritter, 2007)

Female rough-toothed dolphins protect their calves by swimming in close proximity to their young and positioning themselves between the calf and any other dolphin. This behavior can be characterized as epimeletic behavior, or behavior to attract support or attention from individuals in the group, species, or genus, and is commonly observed in rough-toothed dolphins. This species is also thought to demonstrate reciprocal altruism, as they swim below injured dolphins, supporting them at the surface so they can breathe. Rough-toothed dolphins have also been observed supporting deceased dolphins at the water's surface for several hours up to several days. ("Rough-toothed Dolphin", 1998; Carwardine, 1995; Dohl, et al., 1974; Jefferson, et al., 1993; Lodi, 1992; Ritter, 2007)

The most commonly observed behaviors of rough-toothed dolphins are travelling, social physical contact with pod members, feeding, resting, object play, sexual activity, and milling. In a study by Kuczaj and Yeater (2007) in their natural habitat, travelling comprised 26.6% of total time the dolphins were observed. In the same study, travel with a boat accounted for 17.5% of time. Social behaviors accounted for 11% of behaviors, which include pod members engaging in physical contact and surface swimming behaviors oriented toward one another. Feeding comprised 14.9% of their activity budget. Feeding behaviors involved tossing fish, diving for fish, and forming feeding circles. Rest occupied 9.7% of their time and was characterized as drifting in one constant direction. Milling (9%) is defined as the absence of physical contact between pod members, and swimming in a stationary location at the surface. Object play (interactions with foreign objects) represented 7.1% of observed behaviors and sexual behavior encompassed just 3.8% of observed behaviors. (Kuczaj II and Yeater, 2007)

Home Range

A stranded and then rehabilitated rough-toothed dolphin was reported to travel over several hundred kilometers to 1,500 kilometers in a five month period. Members of this species do not defend a territory. (Baird, et al., 2008; Jefferson, 2002)

Communication and Perception

Rough-toothed dolphins communicate with other dolphins through echolocation clicks, whistles, burst pulse signals, and synchronous swimming patterns. Echolocation clicks help provide a sense of location, directionality, and with identifying objects. Burst pulse signals, which can be heard by the human ear, can be social or reinforce echolocation functions. Whistles are used socially among dolphins. Rough-toothed dolphins often travel in a close school with either synchronous or asynchronous swimming patterns. In the group of synchronous dolphins, a single dolphin produces higher frequency echolocation calls than the rest of the group. Rough-toothed dolphins are also found traveling alone, and these dolphins produce lower frequency echolocation calls. (Gotz, et al., 2006; Oswald, et al., 2007)

Food Habits

The diet of carnivorous rough-toothed dolphins includes silverside, saury, needlefish, mahimahi, and squid. Their preference, however, is mahimahi. Rough-toothed dolphins are excellent divers and are known to dive to great depths in search of cephalopods and large fish. They chase their prey and toss it around with their beaks. As their common name suggests, they have rough teeth, which allow them to tear apart their prey. Rough-toothed dolphins forage in groups of 3 to 5 for predator efficiency, and they share their meals. Members of this species are also known to forage on "bait balls" of schooling fish. ("Rough-toothed Dolphin", 1998; Baird, et al., 2008; Pitman and Stinchcomb, 2002; Shirihai and Jarrett, 2006)

  • Animal Foods
  • fish
  • mollusks

Predation

Currently, there are no known predators of rough-toothed dolphins other than humans. Although they have been found with scars from bites of cookie-cutter sharks, there is no record of this species being consumed by a shark. Rough-tooth dolphins are, however, incidentally caught in fishing nets. Some humans eat this species of dolphin. (Jefferson, 2002; Monteiro-Neto, et al., 2000)

Ecosystem Roles

Rough-toothed dolphins help regulate adult populations of mahimahi. They also host a variety of parasites. Larvae and adult Anisakis have been found in their stomach, causing ulcers, internal bleeding, and gastritis. These nematodes may be transmitted by the sharing of food among dolphins and this parasite species' dependence upon various intermediate hosts. Several helminth parasites can also infect the intestines of rough-toothed dolphins, including the cestode Tetrabothrius forsteri. Several trematodes also parasitize rough-nosed dolphins, including Campula palliate in the liver and bile duct, Pholeter gastrophilus in the forestomach, and Synthesium tursionis in the intestines. (Carvalho, et al., 2010; Forrester and Robertson, 1975; Monteiro-Neto, et al., 2000; Pitman and Stinchcomb, 2002)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Steno bredanensis individuals are caught and consumed by humans in the West Indies, West Africa, Japan, and the Solomon Islands. (West, 2002)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of rough-toothed dolphins on humans.

Conservation Status

Although listed as a species of list concern on the ICUN Red List, Steno bredanensis is experiencing an increase in mortality rate. Fisheries along the coast of Ceara, Brazil incidentally catch rough-toothed dolphins in gill nets. Individuals caught in gill nets are thrown overboard or used as bait for sharks. Small numbers of rough-toothed dolphins are targeted as food for humans by direct and drive fisheries, located in the West Indies, West Africa, Japan, and the Solomon Islands. Habitat destruction due to anthropogenic disturbances also threaten populations of this species. (Mann, et al., 2010; Monteiro-Neto, et al., 2000; West, 2002)

Severe to profound hearing loss was found in 5 out of 14 rough-toothed dolphins stranded or entangled in fishing gear from 2004-2009. Hearing loss in marine mammals is contributed to five factors: congenital genetic factors, intense chronic noise from boats, old age, intense noises such as explosions, and ototoxic drug treatments that are administered during rehabilitation from dolphin strands. Hearing loss in 2 out of the 5 rough-toothed dolphins affected was contributed to genetic factors because they were young dolphins. (Mann, et al., 2010; Monteiro-Neto, et al., 2000; West, 2002)

Other Comments

In captivity, mating has occured between a rough-toothed dolphin and a bottlenose dolphin resulting in a rare Steno and bottlenose, Tursiops hybrid. The hybrid resembled a bottlenose calf and was 60 cm long at birth. The calf's respiration rate at birth was 4 breaths per minute and stabilized to one breath every two minutes by the third month. (Dohl, et al., 1974; Lodi, 1992; West, 2002)

Contributors

jennifer greenwood (author), Radford University, Karen Powers (editor), Radford University, Gail McCormick (editor), Animal Diversity Web Staff.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

food

A substance that provides both nutrients and energy to a living thing.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

1998. "Rough-toothed Dolphin" (On-line). Hebridean Whale and Dolphin Trust. Accessed March 20, 2001 at http://www.gn.apc.org/whales/dolphin8.htm.

Baird, R., D. Webster, S. Mahaffy, D. McSweeney, G. Schorr, A. Ligon. 2008. Site fidelity and association patterns in a deep-water dolphin: rough-toothed dolphins (Steno bredanensis) in the Hawaiian Archipelago. Marine Mammal Science, 24, 3: 535-553.

Carvalho, V., C. Bevilaqua, A. Iniguez, H. Mathews-Cascon, F. Ribeiro, L. Pessoa, A. Meirelles, J. Borges, J. Marigo, L. Soares, F. Silva. 2010. Metazoan parasites of cetaceans off the northeastern coast of Brazil. Veterinary Parasitology, 173: 116-122.

Carwardine, M. 1995. Whales, Dolphins and Porpoises. London: Dorling Kindersley Books.

Dohl, T., K. Norris, I. Kang. 1974. A Porpoise Hybrid: Tursiops X Steno. Journal of Mammalogy, 55, 1: 217-221.

Forrester, D., D. Robertson. 1975. Helminths of rough-toothed dolphins, Steno bredanensis lesson 1828, from Florida waters. The Journal of Parasitology, 61, 5: 922.

Galindo, J., A. Serrano, L. Vazquez-Castan, C. Gonzalez-Gandara, M. Lopez-Ortega. 2009. Cetacean diversity, distribution, and abundance in northern Veracruz, Mexico. Aquatic Mammals, 35, 1: 12-18.

Gannier, A., K. West. 2005. Distribution of the rough-toothed dolphin (Steno bredanensis) around the Windward Islands. Pacific Science, 59, 1: 17-24.

Gotz, T., U. VerfuB, H. Schnitzler. 2006. 'Eavesdropping' in wild rough-toothed dolphins (Steno bredanensis)?. Biology Letters, 2: 5-7.

Jefferson, T. 2002. Rough-toothed dolphin Steno bredanensis. Pp. 1055-1059 in W Perrin, J Thewissen, B Wursig, eds. Encyclopedia of Marine Mammals, Vol. None, 1st Edition. San Diego: Academic Press.

Jefferson, T., S. Leatherwood, M. Webber. 1993. Marine Mammals of the World. Rome: Food and Agriculture Organization of the United Nations.

Kays, R., D. Wilson. 2009. Mammals of North America. Princeton, New Jersey: Princeton University Press.

Kuczaj II, S., D. Yeater. 2007. Observations of rough-toothed dolphins (Steno bredanensis) off the coast of Utila, Honduras. Journal of the Marine Biological Association of United Kingdom, 87: 141-148.

Lodi, L. 1992. Epimeletic behavior of free-ranging rough-toothed dolphins, Steno bredanensis, from Brazil. Marine Mammal Science, 8, 3: 284-287.

Manire, C., H. Rhinehart. 2000. Use of human recombinant erythropoietin for the treatment of nonregenerative anemia in a rough-toothed dolphin (Steno bredanensis). Journal of Zoo and Wildlife Medicine, 31: 157-163.

Mann, D., M. Hill-Cook, C. Manire, D. Greenhow, E. Montie, J. Powell, R. Wells, G. Bauer, P. Cunningham-Smith, R. Lingenfelser, R. DiGiovanni, A. Stone, M. Brodsky, R. Stevens, G. Kieffer, P. Hoetjes. 2010. Hearing loss in stranded odontocete dolphins and whales. PLoS ONE, 5 (11) e 13824: 1-5.

Monteiro-Neto, C., T. Teixeira Alves-Junior, F. Capibaribe Avila, A. Alves Campos, A. Fernandes Costa, C. Pereira Negrao Silva, M. Andrade Furtado-Neto. 2000. Impact of fisheries on the tucuxi (Sotalia fluviatilis) and rough-toothed dolphin (Steno bredanensis) populations off Ceara state, northeastern Brazil. Aquatic Mammals, 26, 1: 49-56.

Oswald, J., S. Rankin, J. Barlow, M. Lammers. 2007. A tool for real-time acoustic species identification of delphinid whistles. Acoustical Society of America, 122, no. 1: 587-595.

Pitman, R., C. Stinchcomb. 2002. Rough-toothed dolphins (Steno bredanensis) as predators of mahimahi (Coryphaena hippurus). Pacific Science, 56, 4: 447-450.

Ritter, F. 2007. Behavioral responses of rough-toothed dolphins to a dead newborn calf. Marine Mammal Science, 23, 2: 429-433.

Rouch, T., S. Poss. 1998. "Species at Risk in the Gulf of Mexico Ecosystem, Steno bredanensis" (On-line). Accessed March 20, 2001 at http://lionfish.ims.usm.edu/~musweb/stenbred.htm.

Shirihai, H., B. Jarrett. 2006. Whales, Dolphins, and other Marine Mammals of the World. Princeton, New Jersey: Princeton University Press.

Watkins, W., P. Tyack, K. Moore, G. Notarbartolo-di-Sciara. 1987. Steno bredanensis in the Mediterranean Sea. Marine Mammal Science, 3: 78-82.

West, K. 2002. Ecology and biology of the rough-toothed dolphin (Steno bredanensis). University of Hawaii Library: University of Hawaii and L'Universite' de la Polynesie Francaise.

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