Atlantic humpbacked dolphins live in tropical coastal waters off western Africa, from central Morocco southward to southern Angola.
Biogeographic Regions: ethiopian ; atlantic ocean (Native )
The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
Atlantic humpbacked dolphins belong to the family Delphinidae. They are gray in color with some lighter speckled markings along the ventral surface. These dolphins are characterized by, and named for, their uniquely elevated and rounded dorsal fin, which is referred to as a "hump-back." Atlantic humpbacked dolphins have a very large melon, rounded flippers, and a long pronounced beak. Adults weigh between 100 and 150 kg and are generally between 2 and 2.5 meters in length. Like most cetaceans, they have homodont dentition (i.e., no differentiation along the tooth row). A distinguishing feature of this species is the number of vertebrae, which is less than that of its sister species, Indo-Pacific humpbacked dolphins. This, along with the number of teeth (26 to 31 pairs), and the species' geographic range, help taxonomists distinguish between Atlantic humpbacked dolphins and Indo-Pacific humpbacked dolphins. Atlantic humpbacked dolphins have a basal metabolic rate of 1200 cm^3 oxygen/hour.
Range mass: 100 to 150 kg.
Range length: 2.0 to 2.5 m.
Range wingspan: 0 (low) mm.
Average basal metabolic rate: 1200 cm3.O2/g/hr.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Sousa teuzii is found mostly in shallow coastal waters, rivers, and estuaries. Although typically found in shallow water, it also occurs in deeper reefs where it apparently seeks refuge from predation by killer whales. When in deeper water, this species swims mostly along the ocean floor. Sousa teuzii typically stays near the shoreline within one or two kilometers of land; it is restricted to warm tropical waters.
Range depth: 20 to 65 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: reef ; rivers and streams; coastal
Other Habitat Features: estuarine
Habitat and Ecology
There is little information on the diet of Atlantic humpback dolphins. They appear to feed on nearshore schooling fishes such as mullet (Mugil spp.) and, contrary to some descriptions, are not thought to eat vegetable matter (see Van Waerebeek et al. 2004). Stomach contents have included grunts (Pristipoma jubelini) and bongo fish (Ethmalosa fimbriata) (Van Waerebeek et al. 2004).
The diet of Sousa teuszii consists mainly of fish, including mullet and sardines. Other important prey items include squid and crustaceans.
Animal Foods: fish; mollusks; aquatic crustaceans
Primary Diet: carnivore (Piscivore )
As piscivores, Atlantic humpbacked dolphins likely impact the coastal fish populations of western Africa. In Mauritania, this species maintains an interesting mutualistic relationship with local fisherman. Atlantic humpbacked dolphins respond to signals sent by the fisherman to come into shore. This helps concentrate fish near the shore and allows fisherman to meet economic demands, while decreasing dolphin by-catch. There is no information available regarding parasites of this species.
- humans, (Homo sapiens)
Atlantic humpbacked dolphins are preyed upon during all stages of life by killer whales. In order to decrease risk of predation, they often seek cover in reefs and find refuge near shore.
- killer whales, (Orcinus orca)
Life History and Behavior
Atlantic humpbacked dolphins use echolocation to find food and communicate with conspecifics, but have relatively poor eyesight. However, its enlarged melon and high brain to body mass ratio suggest that it is well equipped for communication and perception of its immediate environment. In order to avoid predation from killer whales, Atlantic humpbacked dolphins seek shelter in coral reefs.
Communication Channels: acoustic
Perception Channels: visual ; tactile ; acoustic ; echolocation ; chemical
The average lifespan of Atlantic humpbacked dolphins has not been documented, but based on data from other dolphins, is expected to be around 15 to 20 years.
Status: wild: 15 to 20 hours.
Sousa tueszii is polygynous, as a single male mates with multiple females. Calving has been reported from December to February, but may extend into other months. The exact age of sexual maturity is unknown, but most individuals reproduce between the ages of 4 and 8. The closely related Sousa chinensis breeds year round, although calves are typically born during the summer. In other dolphin species, such as Tursiops truncatus (bottlenose dolphins), mating season occurs from March through April, and calves are born between February and May. Gestation lasts for approximately 12 months and young remain close to their mother until they are about 4 or 5 years old. In Tursiops truncatus, most individuals reach sexual maturity between 5 and 12 years of age for females, and between 9 and 13 years of age for males.
Mating System: polygynous
Little information exists regarding the reproductive behavior of Sousa tueszii. Calving has been reported from December to February, but may extend into other months. The exact age of sexual maturity is unknown, but most individuals reproduce between the ages of 4 and 8. Sousa tueszii has an average of one offspring per cycle, which weighs between 9 and 11 kg. Weaning has been reported in individuals as young as 24 months but usually is completed by 48 months. In the closely related Sousa chinensis, males often court females by somersaulting, chasing them in circles, and waving their flippers. In other dolphin species, such as Tursiops truncatus, males aggressively engage females during mating season and use a social hierarchy system based on size to determine which individuals mate.
Breeding interval: Sousa tueszii breeds once yearly.
Breeding season: Sousa tueszii breeds during April or May.
Average number of offspring: 1.
Average gestation period: 12 months.
Range weaning age: 24 (low) months.
Average weaning age: 48 months.
Range time to independence: 4 to 5 years.
Range age at sexual or reproductive maturity (female): 4 to 7 years.
Range age at sexual or reproductive maturity (male): 4 to 7 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
There is no information available regarding parental care in Sousa teuszii. In other dolphin species, such as Tursiops truncatus and the closely related Sousa chinensus, gestation lasts for approximately 12 months. In these species, calves become completely independent when they are approximately 4 to 5 years old. Until the calf reaches sexual maturity, it remains close to the mother.
Parental Investment: pre-hatching/birth (Provisioning: Female, Protecting: Female)
Sousa teuszii is classified as vulnerable on the IUCN's Red List of Threatened Species. Major threats include hunting/whaling, entanglement in fishing nets, habitat destruction, and pollution. This species is listed under Appendix I of CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) and appears to be especially vulnerable to population decrease due to its small and fragmented range and its narrow ecological niche.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: vulnerable
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1996Data Deficient
- 1994Insufficiently Known(Groombridge 1994)
Rough “estimates” for the Saloum River delta, Senegal, were 100 animals, and there were thought to be at least several hundred in Guinea Bissau several decades ago (Ross et al. 1994, Reyes 1991). A small group of at least 20 dolphins resides in the Rio Grande de Buba (a fjord-like sea arm rather than a river) and upstream to the confluence of the Rio Sahol (Van Waerebeek et al. 2004). Although the species often has been reported as common (Reyes 1991, Culik 2004), there are no other numerical data on abundance. Considering the relatively small numbers observed, and even taking account of the many areas of the species’ range where there has been little or no assessment, the total population probably numbers only a few thousand.
Some Atlantic Humpback Dolphins are probably taken directly for food by local people (Van Waerebeek et al. 2004). The fishing communities of Joal and Fadiouth in Senegal have a tradition of hunting cetaceans, and others in the Petite Côte were known to hunt dolphins until at least 1996 (Van Waerebeek et al. 2004). Past and present levels of these captures, and their potential impacts on subpopulations, remain unknown (Reyes 1991). The most recently documented interaction in Senegal was in November 1996, when three dolphins were found together, each with a piece of netting tied around the tailstock on a beach of Sangomar Island in the Saloum delta (Van Waerebeek et al. 2004).
Habitat destruction, boat strikes, and environmental contamination are additional potential threats, although generally little is known about them. In Senegal there has been a permanent reduction of mangrove areas to facilitate the extension of rice culture and exploitation of forests, especially in the Fathala area. Habitat destruction and degradation may be significant factors affecting the species’ status given its nearshore distribution and the high human population densities, associated with agricultural and industrial development, in some areas. These problems will contribute to fragmentation of the dolphin population. Offshore oil exploration and development are underway in at least Gabon and Angola. Excessive fishing of neritic fish stocks in parts of West Africa also may have reduced food availability for these dolphins (Van Waerebeek et al. 2004).
These dolphins are a high priority for research and conservation because of their restricted and apparently fragmented range, narrow ecological niche, apparently low numbers, and continuing threats (IWC 2003, Reeves et al. 2003, Van Waerebeek et al. 2004).
Relevance to Humans and Ecosystems
Although there are no known adverse effects of Sousa teuszii on humans, it is thought that this species competes with local fisherman for fish off the west coast of Africa.
Atlantic humpbacked dolphins benefit fisherman in Mauritania by schooling fish into shore. Local villages intentionally hunt this species for food.
Positive Impacts: food
IUCN Red List Category
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