Hector's dolphin  (Cephalorhynchus hectori)

Hector's dolphin, one of the rarest and smallest of marine dolphins (6), has a short, stocky torpedo-shaped body, which becomes narrow towards the tail. The beak is short and the rounded snout lacks a melon. The sides and back are light grey, there is a darker stripe along the middle, and the underside is whitish (4). The large tail flukes, flippers and characteristically rounded dorsal fin are all black (5). A black marking extends from the snout back around the eye reaching to the flipper (5). Males and females are generally similar in appearance, but females tend to be slightly longer than males (5). Calves have the same markings as adults but pale lines can be seen on darker areas, and the underside has a yellowish tint (5). The common name of this dolphin refers to the New Zealand zoologist Sir James Hector (5), who first collected the species in 1869 (4).

Endemic to New Zealand waters, this species is found on the west and east coasts of South Island, and only in a very small area off the west coast of North Island (5). Following surveys carried out in 1984 - 1985 the total population was estimated at 3-4,000 individuals, only around 2,000 of which were mature (2).

Inhabits coastal waters such as river mouths and shallow bays (7). They very rarely venture further out than 9 km from the coast (4). They prefer shallow waters and may enter estuaries and swim slightly upriver (6)

This dolphin tends to occur in groups of between two to eight individuals. These groups often join together forming larger aggregations and then split up (5). Feeding also occurs in groups and the species takes a variety of fish, squid and some crustaceans (5). Females reach maturity at around 7 to 9 years of age, and males between 6 and 9 years. Courtship behaviour involves close contact, leaping, chasing and belly displays. Calves tend to be born in late spring to early summer and the mother will not conceive again until the calf is fully independent (5). Playing with seaweed, bubble blowing and other 'games' are thought to be important social behaviours (5). Certain sounds produced by this dolphin are also thought to be important in a social context; particularly the complex clicks that are produced in large groups (5).

This species was once hunted for bait, but this has now stopped (5). Due to the coastal habitat of Hector's dolphin, the species is vulnerable to a large number of different threats such as chemical pollution, vessel traffic and habitat modification (2). Currently the most important threat to the survival of this species is bycatch by the fishing industry, particularly entanglements in gillnets that is now reported to occur throughout the range (2).

The New Zealand Marine Mammals Protection Act has made the deliberate killing or injury of marine mammals illegal (2). Under this act, the New Zealand Department of Conservation has designated a 1170 km² area as a Marine Mammal Sanctuary (5), which will provide protection for the species. Bycatch, although not illegal is possible to regulate (2), and it is clear that measures must be taken to eliminate this threat if this diminutive dolphin is to survive (6).

The Whale and Dolphin Conservation Society (WDCS)
http://www.wdcs.org

Carwardine, M., Hoyt, E., Fordyce, R.E., and Gill, P. (1998) Whales and Dolphins. Harper Collins Publishers, London

Authenticated (25/11/02) by WDCS, The Whale and Dolphin Conservation Society
http://www.wdcs.org