Lagenodelphis hosei

Fraser's Dolphin

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Fraser's Dolphin

 

Description

The preference of Fraser's dolphin for deep waters is due to the prey on which it feeds; fish, squid and crustacean species that inhabit the deeper waters of the oceans. Feeding on such food requires Fraser's dolphin to dive down to depths of at least 250 to 500 metres to hunt. It is thought that Fraser's dolphin itself may be occasional prey for killer whales, false killer whales and large sharks, and circular wounds caused by the peculiar cookie-cutter shark (Isistius brasiliensis) have been found on this species (2) (3). Fraser's dolphins are highly sociable mammals that swim around in tightly-bonded schools of 100 to 1,000 individuals (2) (6), often together with schools of melon-headed whales (Peponocephala electra), other dolphin species (2) (3), or in some areas, such as the Sulu Sea, with short-finned pilot whales (Globicephala macrorhynchus) (7). A school of Fraser's dolphins moves quickly, on very rare occasions riding the bow waves of boats, and with members of the school frequently porpoising; the term used to describe a dolphin leaping clear of the water when surfacing to breathe (2) (3). Mating in Fraser's dolphin is believed to be promiscuous, and mature females give birth approximately every two years to a metre-long calf, after a gestation period of 12.5 months. Males reach sexual maturity at an age of seven to ten years, while females are able to reproduce at five to eight years of age (2).
 

Geography

The exact distribution of this species is poorly known. Fraser's dolphin has a pantropical distribution, largely between 30°N and 30°S in all three major oceans (Jefferson and Leatherwood 1994; Dolar 2002). Strandings in temperate areas (Victoria in Australia, Brittany and Uruguay) may represent extralimital forays connected with temporary oceanographic anomalies such as the world-wide El Niño phenomenon in 1983-84, during which a mass stranding occurred in France (Perrin et al. 1994). Bones et al. (1998) reported on a stranding on the coast of Scotland.

Ecosystem

The species is widespread and abundant (with current population estimates around 300,000) and there have been no reported population declines or major threats identified.Habitat and Ecology

It is an oceanic species that prefers deep offshore waters, but it can be seen near shore in some areas where deep water approaches the coast (such as the Philippines, Taiwan, and some islands of the Caribbean and the Indo-Malay archipelago) (Perrin et al. 1994).

In the eastern tropical Pacific, it occurs more often in Equatorial - southern subtropical surface water and other waters typified by upwelling and generally more variable conditions (Au and Perryman 1985). Off South Africa, records are associated with the warm Agulhas Current that moves south in the summer (Perrin et al. 1994).

Fraser's dolphins feed on midwater fish (especially myctophids), squid, and crustaceans (Dolar et al. 2003). Physiological studies indicate that Fraser’s are capable of quite deep diving (and it is thought that they do most of their feeding deep in the water column – in waters up to 600 m deep), but they have been observed to feed near the surface as well (Watkins et al. 1994).

Conservation

The species is widespread and abundant (with current population estimates around 300,000) and there have been no reported population declines or major threats identified.

 

Threats

Major Threats

Small numbers of Fraser's dolphins are taken regularly or opportunistically by harpoon in the Lesser Antilles, Sri Lanka, Indonesia (Kahn 2004), the Philippines, Taiwan and probably elsewhere in the Indo-Pacific (Jefferson and Leatherwood 1994). A few have been taken in drive fisheries in Taiwan and Japan (Perrin et al. 1994). Dolar et al. (1994) investigated directed fisheries for marine mammals in central and southern Visayas, northern Mindanao and Palawan, Philippines. Some of the hunters take only dolphins, for bait or human consumption and the species taken include Fraser's dolphins. Around 800 cetaceans are taken annually by hunters at the seven sites, mostly during the inter-monsoonal period of February-May. 

Some Fraser’s dolphins are killed incidentally in the tuna purse-seine fishery in the eastern tropical Pacific (Gerrodette and Wade 1991): 26 were estimated taken during the period 1971 - 75. A few are also taken in gill nets in Sri Lanka, the Philippines, and likely in other tropical gillnet fisheries as well. Some are killed by anti-shark nets in South Africa (Perrin et al. 1994; Cockcroft 1990). Other incidental catches in purse seines (Philippines), gillnets, driftnets (Taiwan), and trap nets (Japan) are also known (Jefferson and Leatherwood 1994).
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