Cephalorhynchus hectori
Hector's dolphin

Cephalorhynchus hectori, Hector's dolphin, is the only dolphin found solely within New Zealand waters. New Zealand is made up of both a North and a South island. Hector's dolphins may be found on both the West and East coast of the Southern island, but they are restricted to a small area on the west coast of the Northern island. (Slooten et al., 1994)

Hector's Dolphins appear to prefer shallow muddy waters. They inhabit a wide range of water temperatures, 6.3-22 degrees C. They also thrive in a variety of water turbidity ranges, less than 10cm to greater than 15m. (Nowak, 1991; Slooten et al., 1994.)

Hector's dolphins are stocky and without a beak. They have disproportionately large flukes and their most noticeable characteristic is their rounded dorsal fin with its convex trailing edge. The flippers have rounded tips.

They are the smallest of the delphinids and sexually mature adults range in size from 119-145cm in length. At maturity, females are on average 10cm longer than males.

The body of Hector's dolphin is predominantly grey, with an off-white ventral surface that extends from the underside of the snout to just behind the anus. From the belly, an off-white finger-like projection points in the direction of the tail and meets a black v-shaped mark that also points toward the tail. The dorsal fin, flukes and flippers are black, and there are black markings on both sides of the head that lead from the snout to the flipper. This marking widens over the eye and runs to the corner of the mouth. The forehead is grey, but the side of the head is black. The head also has a distinct crescent-shaped black marking running transversely over its surface behind the blowhole. Calves have the same color pattern as adults but have a yellowish tinge to the white areas and vertical pale bands interrupting their dark areas.

Hector's dolphins are sexually dimorphic in the coloration around the genital slit. Males have an oval dark grey patch, and females have either a finger-like grey mark along side it, or remain completely off-white.

The jaw contains 24-31 teeth. (Macdonald, 1984; Nowak, 1991; Slooten et al., 1994.)

Hector's dolphins are usually found in groups of 2-8 individuals. Occasionally over 20 have been seen together, while there is also one record of a group of 200-300. Groups often merge and then split up again, and the intermingling of groups results in increased frequency of sexual behavior.

These delphinids inhabit well-defined geographical areas and form closed populations, although within their population, individuals (especially males) associate with a relatively large number of other individuals.

A wide variety of behaviors have been observed including different postures, body contacts, bubble blowing, leaping, tail-slapping, spy-hopping, surfing and playing with pieces of seaweed and other objects. These dolphins are rarely aggressive.

Horizontal leaps are made when dolphins are swimming at speed, bowriding, or following boats. Vertical leaps are associated with social interaction and noisy leaps may also have social importance, or they may be an attempt to dislodge parasitic whale lice. Bubble blowing, playing with seaweed and surfing are forms of social mingling. Courtship behavior also involves leaps, close body contact, chases and belly displays.

Hector's dolphins are known to have a strong attraction for small boats that travel slowly.

Different kinds of sounds are made by Hector's dolphins, including clicks at slow rates, short bursts of clicks, and cries. Complex clicks occured in large groups and had social significance. (Macdonald, 1984; Nowak, 1991; Slooten, 1994.)

Hector's dolphins appear to feed in small groups at the bottom of coastal waters mostly, but also throughout the water column. They indulge in a variety of species including surface-schooling fish, like yellow-eyed mullet; arrow squid; and benthic fish including red cod and stargazer. Crustaceans are also found in their stomachs.

Hector's dolphins are seen following inshore trawlers behind the cod-end of the net. (Nowak, 1991; Slooten et al., 1994.)

None.

Formerly, Hector's dolphin's were killed for bait for rock lobster traps, but that has ceased recently. (Slooten et al., 1994.)

Predation by Notorhynchus cepedianus, the sevengill shark; as well as Prionace glauca, the blue shark, have a large effect on mortality rates of Hector's dolphins.

Due to the coastal distribution of this species, it is vulnerable to the accumulations of pollutants such as heavy metals and pesticide residues. Chemicals such as DDT and PCBs have been found in Hector's dolphin tissues and are know to interfere with reproduction.

Accidental gillnet entanglement appears to be a major threat to the species, and as a response to this, New Zealand's Department of Conservation created a 1170km^(2) Marine Mammal Sanctuary under section 22 of the Marine Mammals Protection Act. (Honacki et al., 1982; Joint Nature Conservation Committee, 1993; Slooten et al., 1994.)

Hector's dolphin was named in honor of Sir James Hector, a former curator of the National Museum of New Zealand.

Hector's dolphin commonly carries ectoparasitic whale lice (Scutocyamus) on its skin. Several parasitic helminths and nematodes have been characterized as living in internal organs such as lung and intestine. (Slooten et al., 1994)