Fraser's Dolphin (Lagenodelphis hosei)

 

 

 Taxonomy

In 1895, Charles E. Hose found a skull on a beach in Sarawak, Borneo. He donated it to the British Museum. The skull remained unstudied until 1956 when Francis Fraser examined it and concluded that it was similar to species in both the Lagenorhynchus and Delphinus genera but not the same as either. A new genus was created by simply merging these two names together. The specific name is given in Hose's honour. It wasn't until 1971 that the whole body of a Fraser's Dolphin, as it was by then becoming known, was discovered. At that time washed-up specimens were found on Cocos Island in the eastern Pacific, in South Australia and in South Africa.


Description

Fraser's dolphins are about 1 metre (3 ft 3 in) long and 20 kg weight at birth, growing to 2.75 metres (9 ft 0 in) and 200 kg at adulthood. They have a stocky build, a small fin in relation to the size of the body, conspicuously small flippers. The dorsal fin and beak are also insubstantial. The upper side is a gray-blue to gray-brown. A dirty cream colored line runs along the flanks from the beak, above the eye, to the anus. There is a dark stripe under this line. The belly and throat are usually white, sometimes tinged pink. The lack of a prominent beak is a distinguishing characteristic of the dolphin. From a distance however it may be confused with the Striped Dolphin which has a similar coloration and is found in the same regions. Fraser's dolphins swim quickly in large tightly packed groups of about 100 to 1000 in number. Often porpoising, the group chop up the water tremendously. The sight of seeing a large group fleeing from a fishing vessels has been reported as "very dramatic". It is also marked by having the smallest genitalia of any open sea dolphin. The species feeds on pelagic fish, squid and shrimp found some distance below the surface of the water (200 metres (660 ft) to 500 metres (1,600 ft)). Virtually no sunlight penetrates this depth, so feeding is carried out using echolocation alone.

Biology and Ecology

The preference of Fraserís 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 Fraserís dolphin to dive down to depths of at least 250 to 500 metres to hunt. It is thought that Fraserís 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.

Fraserís dolphins are highly sociable mammals that swim around in tightly-bonded schools of 100 to 1,000 individuals, often together with schools of melon-headed whales (Peponocephala electra), other dolphin species, or in some areas, such as the Sulu Sea, with short-finned pilot whales (Globicephala macrorhynchus). A school of Fraserís 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. 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 Fraserís are capable of quite deep diving (and it is thought that they do most of their feeding deep in the water column Ė in waters up to 600 m deep), but they have been observed to feed near the surface as well (Watkins et al. 1994).
Systems: Marine Mating in Fraserís 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.
 

Population and distribution

Though only accounted for relatively recently, the number of reported sightings has become substantialóindicating that the species may not be as rare as thought as recently as the 1980s. However the species is still not nearly as well understood as its more coastal cousins. No global population estimates exist. The Dolphin is normally sighted in deep tropical waters; between 30į S and 20į N. The Eastern Pacific is the most reliable site for viewings. Groups of stranded dolphins have been found as far a field as France and Uruguay. However these are regarded as anomalous and possibly due to unusual oceanographic conditions, such as El NiŮo. The species is also relatively common in the Gulf of Mexico but less so in the rest of the Atlantic Ocean. Inhabits deep, oceanic waters except in places where deep water approaches the coast, such as in the Philippines and Indonesia. The exact distribution of this species is poorly known. Fraser's dolphin has a Pantropical distribution, largely between 30įN and 30įS 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 NiŮo 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.
Countries: Native:
Angola (Angola); Argentina; Aruba; Australia; Brazil; Brunei Darussalam; Cape Verde; China; Colombia; Comoros; Cook Islands; Costa Rica; Dominica; Ecuador; French Polynesia; Ghana; Indonesia; Japan; Kenya; Kiribati; Madagascar; Malaysia; Maldives; Mayotte; Micronesia, Federated States of; Nauru; Oman; Palau; Panama; Papua New Guinea; Philippines; Puerto Rico; Saint Vincent and the Grenadines; Samoa; Senegal; Solomon Islands; South Africa; Sri Lanka; Thailand; United States; Uruguay; Venezuela, Bolivarian Republic of; Vietnam
Vagrant:
France; United Kingdom

Population:

There are estimated to be about 289,300 (CV=34%) Fraserís dolphins in the eastern tropical Pacific (Wade and Gerrodette 1993; Perrin et al. 1994), and 16,836 (CV=11%) in Hawaiian waters (Carretta et al. 2006). In the eastern Sulu Sea, Dolar et al. (2006) estimated a total abundance of 13,518 (CV=27%) Fraserís dolphins. About 726 (CV=70%) were estimated present in the northern Gulf of Mexico (Waring et al. 2006).
Population Trend: Unknown

Major Threat(s):

 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 Fraserís 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).

Conservation Actions:

The species is listed in Appendix II of CITES
The Southeast Asian subpopulations are listed in Appendix II of CMS. Subpopulation structure and the impact of direct and incidental takes require further investigation.

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