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Hector's Dolphin

Description
Common Name:
Hector's dolphin (South Island) and Maui's dolphin (North Island)

Latin Name:
Cephalorhynchus hectori (South Island) and Cephalorhynchus hectori maui (North Island)

Scientists from the Department of Conservation (DOC) and Auckland University have found the North Island Hector's dolphins differ from their more numerous South Island cousins in body form, skeletal features and DNA. The North Island dolphins are now classified as a separate subspecies and have been given the new official name Cephalorhynchus hectori maui.

Other Names:
Little pied dolphin, New Zealand dolphin, White-front dolphin

Primary Classification:
Odontocete (Toothed whale, dolphin or porpoise)

Sub Classification:Delphinidae

Description:
Like all Cephalorhynchus dolphins, Hector's dolphins do not have a distinct beak. They are also one of the smallest cetaceans, only growing to 1.5m or less.
From a distance they can look almost black but it actually has quite striking and complex markings. They have a white belly, armpits and throat, black dorsal fin and tail, and light grey sides and back.
They also have a dorsal fin that is very easy to identify because it is very rounded and leans backwards rather than straight up.

Field ID:Very small size, no prominent beak, rounded dorsal fin which leans backwards.

Length (metres):When they are born Hector's dolphins are between 60 and 75cm long. They grow to between 1.2 and 1.5 metres (4 - 5ft).

Weight:
Hector's dolphins weigh approximately 9kg (20lb) when they are born. When they are fully grown they weigh between 35 and 60kg (75 - 130lb).

Diet:Fish, squid and sometimes crustaceans.

Behaviour:
Hector's dolphins are not always as sociable as other dolphins when around boats although they will bowride, swim in the wake of passing boats and alongside slow-moving vessels. Sometimes they can be seen breaching, lobtailing and spyhopping. They are more active when groups (2-8 animals) get together.

Hector's dolphin is only found in the coastal waters of New Zealand, and in general is not well known. It is, however, unlike other memebers of its genus, fairly common and observed relatively often. Some have used the name "little pied dolphin" to refer to this species. It may be found in the New Zealand coastal waters between 35° 15' S and 46° 35' S, mostly between 41° and 46°. It is notably not found in Fiordland, on the southwestern tip of South Island, probably because the water's depth is greater than 300 meters near the shore. In general it is rare on the southeastern coast.

As with other members of Cephalorhynchus, individuals of this species are small, barely 1.5 meters. The species is easily recognized by the dark colored and rounded dorsal fin, which resembles the adipose fin of Salmon. There are black markins on the head and tail, while the body is silvery gray. The forehead coloration is unique, with a dark, curved line forming a crescent defining a light-colored area which is finely streaked with black sweeps down toward the beak. The beak is poorly developed. The ventral coloration, unseen except for beached individuals, is unique. Like other members of the genus, there are 27-32 pairs of small, sharp teeth in each jaw. Its speed at sea is known to be around 7-11 kilometers per hour, with bursts of 18 kilometers per hour. The small size and fast, low, and silent method of surfacing makes specimens difficult to see except in calm conditions.

Groups of this species are around two to four individuals, with larger groups reported. Unlike other members of the genus, this species is not terrbily shy and will often approach boats. When one individual was captured, twelve others surrounded the boat, lying motionless on the surface. In one case, an individual stayed in the net while another individual, possibly the former's mate, was trapped. It only left when the trapped animal was released. Hector's dolphin tends to move much faster around the boat than the dusky dolphin, and does not stay at the bow.

Population Size:Hector's dolphins are endangered and are one of the rarest cetaceans.

Threats:Human disturbance, chemical pollution, noise pollution, entanglement in fishing nets, prey depletion (lack of food)

 

Fisheries impacts:
Hector's dolphins have been recorded drowned in both gill nets and trawl nets but the vast majority of the reports are from gill nets. Around Banks Peninsula gill nets were estimated to drown over 230 dolphins between 1984 and 1987 (Dawson and Slooten, 1993). Both commercial and recreational fishers have failed to report Hector's dolphin deaths in gill nets, a legal requirement of the Marine Mammal Protection Act. It wasn't till a scientific observer programme was undertaken of gill net and trawl vessels off the Canterbury coast that the true level of dolphin deaths was confirmed. As the previous Minister of Conservation, Nick Smith, said "What makes me particularly angry is that fishermen have for years failed to report fatalities and denied there was a problem".

In the 1997-8 a Department of Conservation observer programme on commercial vessels recorded the deaths of six Hector's dolphins. Observers covered only 89 of 351 fishing days. "I remain cynical that fishermen claim there were no deaths during the 262 days when observers were not present," former Conservation Minister Nick Smith said. It is clear that neither commercial nor recreational gill netters are reporting deaths of Hector's dolphin.

Hector's dolphin is the world's smallest and possibly the rarest marine dolphin with a population of 3000 - 4000. They occur only in New Zealand's inshore waters and are rarely found more than 8 km from the coast. Hector's dolphin was gazetted late last year by the Minister of Conservation as a threatened species under section 2(3) of the Marine Mammals Protection Act 1978.

The dolphin is classified as a vulnerable threatened species in the most recent IUCN-World Conservation Union listings of globally threatened animal species (1996) . This listing is based on its small population size and the large number of dolphins drowned in gill nets since at least 1980. The Cetacean Specialist Group of the Species Survival Commission of IUCN, the world scientific experts on cetacean conservation, have assessed Hector's dolphin as a threatened species of vulnerable status using the agreed threatened species criteria.

The dolphins mainly occur around the South Island but an additional population lives on the West Coast of the North Island between the Kaipara Heads and near New Plymouth. The main populations are found between Motunau and Timaru on the East Coast of the South Island, on the West Coast of the South Island, and in Foveaux Strait -Te Waewae Bay area in Southland.

Genetic work carried out by Auckland University indicates there are at least three relatively distinct populations of Hector's dolphins (Pichler et al 1998) - East Coast South Island, West Coast South Island, and West Coast North Island. This means that each population must be managed separately when considering human impacts. The West Coast of the North Island population has been reduced to around 100 individuals between Taranaki Bight and the Manukau Harbour. Current research indicates that the west coast populations have been declining due to gill nets deaths (Martien et al, 1999). A survey by the Ministry of Fisheries of commercial gill netters confirmed they catch Hector's dolphin, as well as other dolphins and seals. A workshop in May agreed that for the North Island population to recover, less than one dolphin per five years would have to drown in gill nets.

The Minister of Fisheries has agreed to an increase in the rig and elephant fish catch on the East Coast of the South Island. Both species are caught by gill nets. The proposed limit of seven animals is arbitrary and was agreed without consultation with the Minister of Conservation as required by section 15 of the Fisheries Act 1996.
The fishing industry is arguing that the use of pingers (noise generating devices) on nets can reduce dolphin deaths. To work pingers must not fail (they are battery powered), the right frequency must be used, the dolphins must not habituate to them and many pingers must be used per net. It is unclear whether they will work and it could take 6 years of independent observation to confirm this during which up to 100 dolphins could drown if used on the East Coast of the South Island.

This would require a dedicated observer programme. A recent International Whaling Commission (IWC) Sub-committee meeting on cetaceans raised concern at "pingers being deployed without any apparent attempt to either test their efficacy nor to monitor their effects". They noted that "harbour porpoises and short-beaked common dolphins are the only cetacean species for which properly designed studies .. have been conducted to evaluate pinger effectiveness. Nevertheless, some bycatch has occurred in nets with active pingers during experiments and sea trials".
The IWC Committee was also concerned that dolphins could become habituated to the pingers so that, while there may be an initial drop in deaths, the rate may increase over time as dolphins get used to the pingers. This seems to have occurred with harbour porpoises where the main trial has taken place.
Previous work has indicated that the dolphin population at Banks Peninsula can only withstand around 1 individuals a year being killed by gill nets from both recreational and commercial fishers (Dawson and Slooten, 1993). For the smaller West Coast North Island population no gill nets deaths can be accepted.

References:
National Audubon Society: Guide to Marine Mammals of the World.

Encyclopedia of Marine Mammals.

Whales, Dolphins and Porpoises, Mark Carwardine 1995.

Gallery to hectors Dolphins