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BiologyThe 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).