Dolphins and Porpoises (Families Delphinidae and Phocoenidae)
Alan Baker and Suze Baird
Dolphins and porpoises represent two families in the suborder Odontoceti, the toothed whales. The Delphinidae, or true dolphins, are usually distinguished by their beaks, the melon (fatty organ in the forehead), prominent dorsal fin, and conical, undifferentiated teeth. They range in size from the 1.5 m Hector's dolphin to 9 m killer whales. The subfamily classification of delphinids is disputed by systematists, but of the 17 dolphin genera, 12 have been observed in New Zealand waters, and these represent 15 of the 35 recognised dolphin species. One species, Hector's dolphin (including the subspecies Maui's dolphin) is the only cetacean endemic to New Zealand. The family Phocoenidae, or porpoises, closely resemble dolphins, but lack a prominent beak and have laterally compressed teeth. This family contains three genera and six species and is represented by one species in the New Zealand region, the spectacled porpoise.
Dolphin species that occur commonly around New Zealand belong to the Cephalorhynchus, Tursiops, Delphinus, Lagenorhynchus, Globicephala, and Orca genera. These dolphin species prefer coastal or shelf temperate waters and may be seen in groups of mixed species. Many use sheltered bays and estuaries as nursery areas. They have gestation periods ranging from 10 months to a year and lactation lasting one to two years. Most feed on cephalopods and mesopelagic fishes.
The endemic Hector's and Maui's dolphins are found very close inshore. These dolphins do not migrate, but show a slight shift offshore during winter. They reach sexual maturity at six to nine years and live to about twenty years. Hector's dolphins mate and calve during spring-late summer and have low fecundity, breeding only once every two to four years. Their diet consists of small fish, squid, and some benthic species, such as flatfish and cod.
The bottlenose dolphin is a cosmopolitan species occurring in tropical and temperate seas, with morphologically different inshore and offshore forms. In New Zealand waters, bottlenose dolphins are found throughout the coastal zone in small numbers, with larger groups of tens or hundreds further offshore. These dolphins enjoy a wide variety of prey and often forage co-operatively, though they are rarely seen in large pods. They mature at about six years and females give birth every three years, after a gestation of about twelve months.
Common dolphins inhabit the Atlantic and Pacific oceans, are abundant in New Zealand waters and are often seen in large schools, sometimes of hundreds of animals. The acrobatic dusky dolphins are restricted to the southern hemisphere, and the New Zealand population is geographically and genetically distinct from other southern hemisphere populations. Dusky dolphins feed mainly on small fish and squid, and diurnal and seasonal inshore-offshore movement has been reported for the well-studied Kaikoura population. Little is known about their reproduction, but calves are generally born in midwinter. The hourglass dolphin has a more southern, circumpolar distribution and prefers waters of less than 10°C. Little is known about this species, though summer surveys suggest there are about 140,000 hourglass dolphins present south of the Antarctic Convergence in January.
Pilot whales, killer whales, and false killer whales sometimes strand en masse. Long-finned pilot whales are very gregarious and often occur in groups of up to 50 animals, and occasionally, hundreds. They are migratory and feed in offshore deeper water on fish and squid. The estimated Antarctic population is 200,000 animals. Females calve every three to six years, in spring to autumn, and have a gestation period of up to sixteen months. Very occasionally, false killer whales and the more northerly-distributed short-finned pilot whales visit New Zealand waters, perhaps following food sources.
In contrast, the cosmopolitan killer whale is common around the New Zealand and Antarctic coastlines where it is the apex predator feeding on fish, squid, penguins, seabirds, seals, and other dolphins. Females mature at about five years of age and breed every five to eight years, with calving occurring in New Zealand waters in autumn. Gestation lasts up to 18 months. Stable family groups of 5-20 animals are often resident in certain areas.
The southern right-whale dolphin is a cool-water dolphin. It has a circumpolar distribution, with the Antarctic Convergence as its southern limit. These dolphins are occasionally seen off the South Island's east coast and, more commonly, south of New Zealand. This species often travels in large groups of several hundred animals. Little is known about its reproduction.
Less common occurrences in New Zealand waters are reported for five other dolphin species which usually inhabit warmer tropical waters. The spectacled porpoise, Phocoena dioptrica, is the only true porpoise in the New Zealand region with rare occurrences sighted in subantarctic waters. Little is known about this porpoise. A typical group size is thought to include two or three animals, and the few dietary data from animals in other parts of their pan-subantarctic range suggest they eat small fish and crustaceans.
Within the Delphinidae, only Hector's and Maui's dolphins are endemic to New Zealand waters and they are ranked, respectively, by the Department of Conservation as "nationally endangered" and "nationally critical". The Hector's dolphin numbers about 5400 on the west coast of the South Island and 1900 on the east coast, and the total population of the Maui's dolphin numbers less than 150 individuals. Populations of bottlenose dolphins and killer whales are also thought to be relatively small, as is reflected in their conservation status. The populations of other species of dolphins have not been extensively studied and no data are available on abundance or population trends.
Hector's dolphins are found in two genetically distinct populations off the east coast (particularly around Banks Peninsula) and west coast of the South Island. A third isolated population exists on the Southland coast. The Maui's dolphin inhabits harbours and associated shallow waters on the northern west coast of the North Island. Key areas for bottlenose, common, and dusky dolphins are the Marlborough Sounds, Kaikoura, Otago Peninsula, and Fiordland. Bottlenose and common dolphins are also found in the Bay of Islands, Hauraki Gulf, and the Bay of Plenty. These areas may be specific to certain dolphin populations. Dusky dolphins also occur at the Chatham Islands and around the subantarctic Auckland Islands and Campbell Island.
Summary of Threats
In New Zealand waters, dolphins are at risk from entanglement and capture in both static and mobile fishing gear such as set nets, purse-seine nets, trawl nets, and longlines. Exposure to toxins are of concern for some northern hemisphere populations of species such as long-finned pilot whales and bottlenose dolphins, but it is unlikely that these sources of mortality pose a risk in New Zealand waters. Species that prefer inshore waters may potentially be affected by boat activity, pollution, and development of marine farms. Natural threats include predation from other delphinids, such as killer whale predation on dusky dolphins.
Some dolphin species (common, pilot whales) prefer waters along the continental shelf break, the slope, and in areas of sharp topographic relief. Bottlenose dolphins are more usually associated with shorelines, as are Hector's and Maui's dolphins, which like murky water. Many species use harbours and sheltered bays.
State of Information
Hector's and Maui's dolphins are intensively studied and continue to be closely monitored because of their insecure conservation status. For most species, information is required on the biology, ecology, reproduction, distribution, and abundance.
Significance for Maori
Hector’s dolphins are revered as a taonga by Maori. Tutumairekurai is the most common of the Maori names for Hector’s dolphin, meaning ocean dweller. Some Maori believed that the spirits of the dead would become tutumairekurai. Papakanua, tupoupou, hopuhopu and upokohue were names also used.
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Shirihai, H. 2002. The Complete Guide to Antarctic Wildlife: Birds and marine mammals of the Antarctic Continent and the Southern Ocean. Princeton University Press, Princeton, New Jersey. 510pp.
Table 11: Dolphins and Porpoises (Families Delphinidae and Phocoenidae) in New Zealand
|Taxon||Common name||Status in New Zealand region||IUCN status||DoC status|
|Cephalorhynchus hectori||South Island Hector's dolphin||Endemic||Endangered||Nationally endangered|
|Cephalorhynchus hectori maui||Maui's (North Island Hector's) dolphin||Endemic||Critically endangered||Nationally critical|
|Delphinus delphis||Common dolphin||Breeder||Unlisted||Not threatened|
|Grampus griseus||Risso's dolphin||Vagrant||Data deficient||Vagrant|
|Lagenorhynchus cruciger||Hourglass dolphin||Vagrant||Unlisted||Vagrant|
|Lagenorhynchus obscurus||Dusky dolphin||Breeder||Data deficient||Not threatened|
|Lissodelphis peronii||Southern right whale dolphin||Breeder||Data deficient||Not threatened|
|Orcinus orca||Killer whale||Breeder||Lower risk-conservation dependent||Nationally critical|
|Peponocephala electra||Melon-headed whale||Vagrant||Unlisted||Vagrant|
|Pseudorca crassidens||False killer whale||Breeder||Unlisted||Not threatened|
|Stenella attenuata||Pan-tropical spotted dolphin||Vagrant||Lower risk-conservation dependent||Vagrant|
|Stenella coeruleoalba||Striped dolphin||Vagrant||Lower risk-conservation dependent||Vagrant|
|Steno bredanensis||Rough-toothed dolphin||Vagrant||Data deficient||Vagrant|
|Tursiops truncatus||Bottlenose dolphin||Breeder||Insufficiently known||Range restricted|
|Globicephala macrorhynchus||Short-finned pilot whale||Migrant||Lower risk-conservation dependent||Migrant|
|Globicephala melas edwardii||Long-finned pilot whale||Breeder||Unlisted||Not threatened|
|Phocoena dioptrica||Spectacled porpoise||Vagrant||Data deficient||Vagrant|