Hector's dolphin

Physical Description

A rare and small cetacean, this dolphin is identified by a solidly built body with a gently sloping snout and a unique rounded (mickey mouse ear shaped) dorsal fin. Hector's dolphin takes its name from New Zealand zoologist Sir James Hector, who first collected the species in 1869.

Size

Adults measure between 1.2-1.4 m and weighs up to 50 kg.

Colour

The sides and back of this dolphin are light grey, with white "flames" reaching up along the sides of its body. The underside is whitish, while the face, flippers, the dorsal fin and tail are all black. There is a crescent-shaped black mark between eyes and blowhole.

Watch video footage of Hector's dolphins

Ecology and Habitat

A dolphin that plays with seaweed and blows bubbles

The species is found in inshore waters, including river mouths, estuaries and shallow bays, commonly within about 5 nautical miles of the shore. In winter the distribution reaches further offshore, out to 15 nautical miles.

Social Structure

This dolphin tends to occur in groups of up to five individuals, which may aggregate temporarily. Young are reported to play with seaweed, blow bubbles and are involved with other 'games' which are considered to be important social behaviours. Hector's dolphin emits sounds that are thought to be used for communication, notably the complex clicks produced in large groups.

Life Cycle

Females reach maturity at around 7 to 9 years of age, and males between 6 and 9 years.

Breeding

Courtship is a fairly elaborate process, involving chasing and belly displays. Usually, calves are born in late spring to early summer and the mother will not give birth again until the calf is fully independent.

Diet

Feeding is a group activity, and prey includes fish and squid.

Population and Distribution

Four genetically distinct sub-populations

Previous population and distribution

The species appears to have been historically much more abundant and widespread, including sub-populations off the east coast of New Zealand's North Island.

Current population and distribution

There are four genetically distinct populations of Hector's dolphin: off the west coast of North Island, and the west, east and south coasts of South Island. A current estimate puts the population at around 7,400 individuals.

What are the main threats to the Hector's dolphin?

This species was once hunted for bait, but this has now stopped. 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.

Currently the main threat to the survival of this species is bycatch in net fisheries, particularly entanglements in gillnets that have been reported to occur throughout the species range.

Because Hector's dolphin exists in several discrete populations, this increases the risk of local extinctions from bycatch or a single pollution or disease episode.

Fisheries bycatch

There is a possibility that populations have declined to about a third to half of their size since 1970 because of gill net entanglement, with bycatch of this species occurring throughout its current range.

Pollution

Human-made chemicals such as PCBs, DDTs and dioxins accumulate in Hector's dolphins which could potentially affect reproductive rates.

Habitat loss

Habitat modification is another potential threat for the future. Although marine areas in New Zealand are relatively immune to degradation, coastal development such as the construction of ports and aquaculture are developing rapidly in some areas. Several deaths caused by ship strikes have been reported.

Boat disturbance

Recreational boat users interact with hector's dolphins throughout their range. Dolphin-watching tours are located at the center of the Banks Peninsula Marine Mammal Sanctuary, and new operations are beginning in the Lyttleton and Timaru areas of Canterbury. Possible impacts of recreational boating and tourism on Hector's dolphins are currently under study.