Rough Toothed Dolphin

Maximum longevity: 32 years (wild) Observations: Maximum longevity could be underestimated.

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.

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore , Molluscivore )

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.

Known Predators:

• humans Homo sapiens

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.

Range mass: 90 to 160 kg.

Range length: 2.00 to 2.65 m.

Sexual Dimorphism: male larger

Other Physical Features: endothermic ; bilateral symmetry

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.

Range lifespan
Status: wild: 32 to 48 years.

Range lifespan
Status: captivity: 12 (high) years.

Average lifespan
Status: wild: 32.0 years.

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.

Range depth: 5 to 2000 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: pelagic ; reef ; coastal

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.

Biogeographic Regions: nearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); oceanic islands (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

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.

Commensal/Parasitic Species:

• Cestode Tetrabothrius forsteri
• Nematode g. Anisakis
• Trematode Campula palliate
• Trematode Pholeter gastrophilus
• Trematode Synthesium tursionis

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

Positive Impacts: food

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

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.

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.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

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.

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.

Communication Channels: tactile ; acoustic

Perception Channels: tactile ; acoustic ; ultrasound ; echolocation ; chemical

Little information is available regarding the mating systems of rough-toothed dolphins in the wild.

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 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.

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.

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

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.

Parental Investment: precocial ; female parental care ; pre-hatching/birth (Provisioning: Female); pre-weaning/fledging (Provisioning: Female); pre-independence (Provisioning: Female)

Although widespread, the rough-toothed dolphin is not frequently encountered, and thus few studies have been conducted on its ecology and biology (2). Like many other dolphins, it is a sociable animal, commonly moving in groups of 10 to 20 individuals, although larger groups have also been observed, such as one consisting of up to 300 dolphins in Hawaii. In these groups, the rough-toothed dolphin has been seen with other dolphin species, as well as often associating with flotsam, the rubbish and debris found floating in the ocean (2). Often described as a sluggish or lethargic creature, the rough-toothed dolphin often swims with its chin and head above the water's surface, skimming along with a distinctive splash (2) (4). It is not the most acrobatic of dolphins, but will occasionally leap and ride the bow waves of boats (2). It feeds on a range of fish and cephalopods, with its robust, rough teeth suggesting that some particularly large fish may be eaten. Algae have also been found in the stomachs of rough-toothed dolphins, although this may have been eaten accidentally (2). It is known to dive to 70 metres to capture its prey and remain underwater for 15 minutes, although evidence suggests that this dolphin is actually capable of undertaking much deeper dives. With males reaching sexual maturity at 14 years, and females at 10 years, the rough-toothed dolphin is known to live for up to 32 to 36 years (2).

The rough-toothed dolphin is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any trade in this species should be carefully monitored (3). This dolphin is also held in captivity in a number of countries where, incidentally, they have been found to be bold and inventive animals (2). Studies of the rough-toothed dolphin in captivity may allow knowledge of this species' biology to be furthered (5).

With a head that slopes smoothly down into a long beak, and large flippers that are set fairly far back on the body (2), this rather primitive-looking dolphin is sometimes said to be somewhat reptilian in appearance (4). Named for the subtle ridges and wrinkles on the teeth (4), the body of the rough-toothed dolphin is patterned black, white and grey. It has a white underside, mid-grey sides, and a black to dark grey back. A darker region on the back, called a cape, runs narrowly from the top of the head to behind the tall, curved-back dorsal fin, where it widens (2). The body often bears the scars of bites from cookie-cutter sharks, leaving behind white patches, splotches and spots (2). Young rough-toothed dolphins often lack these white marks, and are more subdued in colour (2).

This dolphin inhabits tropical and warm temperate waters (2), usually measuring over 25 degrees Celsius (5), where it is generally found in deep, offshore waters (2).

The rough-toothed dolphin is found in all three major oceans of the world (the Atlantic, Pacific and Indian) (2), typically between 40 degrees north and 35 degrees south (4).

Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

The greatest threat to the rough-toothed dolphin is likely to be incidental capture in fishing nets (2). While this dolphin is directly hunted in several areas for its meat (5), including Japan, Sri Lanka, Indonesia, the Solomon Islands and Papua New Guinea (2), relatively small numbers are taken (6), and as it inhabits offshore waters, it is unlikely to be affected by habitat degradation and pollution to the same extent that coastal-dwelling dolphins are (2).

Red and Mediterranean Sea.

Accidental?

The rough-toothed dolphin is relatively robust, with a conical head and no demarcation between the melon and the snout. It has a somewhat reptilean appearance. This species has large flippers (seemingly oversized for the animal) that are set far back on the side, and a prominent falcate dorsal fin. The body is dark grey, with a prominent narrow dorsal cape that dips slightly down onto the side 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 mostly caused by bites of cookie-cutter sharks and probably other rough-toothed dolphins, often cover much of the body. The 20 to 27 teeth in each row have subtle, but detectable, vertical wrinkles or ridges. These lridges give rise to the species' English common name. 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 are the best clues for identifying rough-toothed dolphins.

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.

Rough-toothed dolphins have been seen most commonly in groups of 10 to 20, although herds of over 100 have been reported. They are often lethargic and individuals bowride occasionally. They often move at high speed with the chin and head above the surface, in a distinctive skimming. behaviour described as "surfing". In the eastern tropical Pacific, they tend to associate with floating objects and sometimes with other cetaceans.Rough-toothed dolphins feed on cephalopods and fish, including large fish such as mahi mahi (also called dorado or dolphinfish).

Rough-toothed dolphins are sometimes taken incidentally in purse seines in the eastern tropical Pacific, and in small numbers in directed fisheries in Japan, the Lesser Antilles, and Sri Lanka. A few have been captured live for public display. IUCN: Insufficiently known.

The rough-toothed dolphin (Steno bredanensis) is a species of dolphin that can be found in deep warm and tropical waters around the world.

The species was first described by Georges Cuvier in 1823. The genus name Steno, of which this species is the only member, comes from the Greek for 'narrow', referring to the animal's beak — which is a diagnostic characteristic of the species. The specific name honours van Breda, who studied Cuvier's writings. There are no recognised subspecies.

circum-global between 40°N and 35°S

In Atlantic: Virginia, Georgia, Florida, the Gulf of Mexico, the West Indies, and off northeastern coast of South America

tropical to subtropical, oceanic

Least Concern (LC)