HECTOR'S DOLPHINS

Hector's dolphin (Cephalorhynchus hectori) is the best-known of the four dolphins in the genus Cephalorhynchus and is found only in New Zealand. At approximately 1.4 m in length, it is one of the smallest cetaceans, and New Zealand's only endemic cetacean.
Hector’s dolphin was named after Sir James Hector (1834–1907). He was the curator of the Colonial Museum in Wellington (now the Museum of New Zealand Te Papa Tongarewa). He examined the first specimen found of the dolphin. The species was scientifically described by Belgian zoologist Pierre-Joseph van Beneden in 1881.
There are two subspecies: Cephalorhynchus hectori hectori, the more numerous subspecies, found around the South Island, and Maui's dolphin (Cephalorhynchus hectori maui), found off the northwest coast of the North Island.^[2] Maui's dolphin is one of the eight most endangered groups of cetaceans. A 2010/2011 survey by the New Zealand Department of Conservation survey estimated that only 55 adults remained.^[3]
Māori names for Hector's and Maui's dolphin include tutumairekurai, tupoupou and popoto.

Physical description

Hector's dolphin has a unique rounded dorsal fin.

Hector’s dolphin is the smallest of the dolphins. Mature adults have a total length of 1.2–1.6 m (3 ft 11 in–5 ft 3 in) and weigh 40–60 kg (88–132 lb).^[4] The species is sexually dimorphic, with females being slightly longer and heavier than males. The body shape is stocky, with no discernible beak. The most distinctive feature is the rounded dorsal fin, with a convex trailing edge and undercut rear margin.
The overall appearance is pale grey, but closer inspection reveals a complex and elegant combination of colours. The back and sides are predominantly light grey, while the dorsal fin, flippers, and flukes are black. The eyes are surrounded by a black mask, which extends forward to the tip of the rostrum and back to the base of the flipper. A subtly shaded, crescent-shaped black band crosses the head just behind the blowhole. The throat and belly are creamy white, separated by dark-grey bands meeting between the flippers. A white stripe extends from the belly onto each flank below the dorsal fin.
At birth, Hector’s dolphin calves have a total length of 60–80 cm (24–31 in) and weigh 8–10 kg (18–22 lb).^[5] Their coloration is the same as adults, although the grey has a darker hue. Four to six vertical pale stripes, caused by fetal folds affecting the pigmentation, are present on the calf’s body until an age of about six months.

Population and distribution

 
 Hector's dolphins are endemic to the coastal regions of New Zealand. The species has a patchy distribution around the entire South Island, although there are only very occasional sightings in the deep waters of Fiordland. The centres of distribution are on the west coast between Kahurangi Point (41˚S) and Jacksons Bay (44˚S)^[6] and on the east coast around Banks Peninsula (43˚S-44˚S).^[7] Maui’s dolphin is found only on the west coast of New Zealand’s North Island between 36˚S and 37.50˚S, with the majority of animals in the central portion of this range between the Manukau and Raglan Harbours.^[8] Small populations exist along Otago coasts such as Karitane and the vicinity of Otago Harbour.
Since 2004 the accepted number of South Island Hector's had been 7,270. However extensive aerial surveys of the east coast during the 2012/13 summer and 2013 winter has led to a major revision of this figure with more Hector's in this region alone than the previous total Hector's numbers. The recognised number for east coast South Island has gone from 1,800 to approximately 9,000. The summer survey range was between 6,300 and 13,100. The winter survey range was 5,200 to 10,600.^[9]
The species has a preference for coastal waters shallower than 100 m (330 ft).^[10][11] This means they are most commonly seen close to shore, although in shallow regions, they have been sighted up to 34 km (21 mi) from the coast. In some areas, the seasonal difference in distribution is pronounced, with Hector's dolphins being sighted further offshore and in deeper water in winter, presumably in response to movements of their prey species.

Skeleton in the collection of Museo di storia naturale e del territorio dell'Università di Pisa

Ecology and life history

Caught and stranded Hector’s dolphins have provided information on their life history and reproductive parameters. The maximum observed age is 19 years for females and 20 years for males.^[4] However, a long-term photo-ID project at Banks Peninsula has shown that individuals reach at least 23 years of age. Males attain sexual maturity between five and nine years of age, and females have their first calf between seven and nine years old.^[4] The calving interval is two to four years.
These life-history characteristics mean that Hector’s dolphins, like many other small cetaceans, have a low potential for population growth. Maximum population growth rate has been estimated to be 1.8-4.9% per year, although the lower end of this range is probably more realistic.^[12]

Foraging and predation

Hector's dolphins at Porpoise Bay, in the Catlins

Hector's dolphins find their food close to shore, generally in groups of two to eight dolphins. They feed at the ocean surface and sea floor, with their diets including ahuru, yellow-eyed mullet, kahawai, arrow squid, herring, and red cod.^[13]
Hector’s dolphins are believed to be generalist feeders, with prey selection based on size rather than species. Stomach contents of dissected dolphins have included surface-schooling fish, midwater fish and squid, and a wide variety of benthic species.^[14] The largest prey item recovered from a Hector’s dolphin stomach was an undigested red cod weighing 500 g with a standard length of 35 cm.
Natural predators of Hector’s dolphins include sharks and probably killer whales (orca). Remains of Hector's have been found in sevengill and blue shark stomachs.^[15]

Conservation

Hector’s dolphin is covered by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU).^[16]

Gillnet threat

Bycatch in the bottom-set gillnets has been responsible for the majority of human-induced mortality of Hector’s dolphins. Gillnets are made from lightweight monofilament that is undetectable to the dolphins. Hector's dolphins swim into the nets, get caught, and subsequently drown. Some dolphins are able to escape from gillnets, as they are spotted displaying scars consistent with entanglement.^[17]
The nationwide estimate for bycatch in commercial gillnets is 110-150 dolphins per year^[18] which is far in excess of the level which is considered to be sustainable.^[19] Hector’s dolphins face a range of other impacts, including trawl bycatch,^[20] tourism,^[21][22] pollution^[14] habitat modification and the land originating protozoan disease toxoplasmosis.^[23]
Conservation management for Hector’s dolphin has focussed on reducing gillnet bycatch. The first marine protected area (MPA) for Hector's dolphin was designated in 1988 at Banks Peninsula, where commercial gillnetting was effectively prohibited out to 4 nmi (7.4 km; 4.6 mi) offshore and recreational gillnetting was subject to seasonal restrictions. A second MPA was designated on the west coast of the North Island in 2003. Despite this protection, the Hector’s dolphin population was predicted to continue declining due to bycatch outside the MPAs.^[8]
On 15 November 2007, the World Wide Fund for Nature launched an online petition asking Helen Clark, New Zealand's Prime Minister at the time, to introduce emergency measures to protect the Hector's and Maui dolphins.^[24] New measures were introduced by the Ministry of Fisheries in 2008, effectively banning gillnetting within 4 n.mi. of the majority of the South Island’s east and south coasts, regulating gillnetting on the South Island’s west coast out to 2 n.mi. (3.7 km) offshore and extending the gillnet ban on the North Island’s west coast to 7 nmi (13 km; 8.1 mi) offshore. There are also restrictions on trawling in some of these areas. For further details on these regulations, see the Ministry of Fisheries website.^[25] Five marine mammal sanctuaries were designated in 2008 to manage non-fishing related threats to Hector’s and Maui’s dolphin.^[26] Their regulations include restrictions on mining and seismic acoustic surveys. Further restrictions were introduced into Taranaki waters in 2012 and 2013 to protect Maui's dolphins^[27] though the presence of Maui's in these waters is not proven.