|Size compared to an average human|
Van Beneden, 1881
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.
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. Maui's dolphin is one of the eight most endangered groups of cetaceans. A 2010/2011 survey by the New Zealand Department of Conservation estimated that only 55 adults remained.
Hector’s dolphin was named after Sir James Hector (1834–1907), who 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.
Māori names for Hector's and Maui's dolphin include tutumairekurai, tupoupou and popoto.
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). 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). 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 fragmented distribution around the entire South Island, although there are only very occasional sightings in the deep waters of Fiordland. The largest populations live on the east and west coast of the South Island. Maui’s dolphin lives on the west coast of the North Island between Maunganui Bluff and Whanganui.
The latest published estimate of South Island Hector's dolphins is 7,270 and the latest estimate of Maui's dolphin is 55 individuals (1 year and older). Additional population surveys have been carried out off the east coast in 2012 and 2013. The results of these surveys have not yet been published in a peer-reviewed scientific journal.
The species' range includes shallow waters up to 100 m (330 ft) depth, with very few sightings in deeper waters. The 100 m depth contour is a better predictor of offshore distribution, depending on water depth they are found up to 20 nautical miles or more from the coast. In some areas, the seasonal difference in distribution is pronounced, with Hector's dolphins being sighted closer offshore and in shallower water in summer, and more spread out in winter. This is thought to be related to movements of their prey species.
Ecology and life history
Data from field studies, stranded individuals and dolphins caught in fishing nets have provided information on their life history and reproductive parameters. Photo-ID research at Banks Peninsula, and other locations around the South and North Island since 1984 has shown that individuals reach around 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. 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.
Foraging and predation
Hector's dolphins live in groups of two to eight individuals. They feed at the ocean surface and sea floor, with their diets including ahuru, yellow-eyed mullet, kahawai, arrow squid, herring, and red cod.
Hector’s dolphins are generalist feeders, with prey selection based on size rather than species. Typically, they feed on smaller prey which tend to measure under 10 cm. in length. Stomach contents of dissected dolphins have included surface-schooling fish, midwater fish and squid, and a wide variety of benthic species. 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.
Dolphin deaths in bottom-set gillnets and trawl fisheries have been responsible for substantial population declines in the last four decades. Gillnets are made from lightweight monofilament that is difficult for dolphins to detect, especially when they are distracted (e.g. chasing fish) or moving around without using echolocation. Hector's and Maui's dolphins swim into the nets, get caught and drown - or more accurately, suffocate (breathing is active in dolphins). Hector's dolphins are actively attracted to trawling vessels and can frequently be seen following trawlers and diving down to the net. Occasional mistakes can lead to injury or death.
The nationwide estimate for bycatch in commercial gillnets is 110-150 dolphins per year which is far in excess of the sustainable level of human impact. Deaths in fishing nets are the most serious threat (responsible for more than 95% of the human-caused deaths in Maui's dolphins), with currently lower level threats including tourism, disease and marine mining.
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. Populations continued to decline due to bycatch outside the MPAs.
Additional protection was introduced in 2008, banning gillnetting within 4 n.mi. of the majority of the South Island’s east and south coasts, out to 2 n.mi. (3.7 km) offshore off the South Island’s west coast 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. Five marine mammal sanctuaries were designated in 2008 to manage non-fishing related threats to Hector’s and Maui’s dolphin. 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.
The Scientific Committee of the International Whaling Commission has recommended extending protection for Maui's dolphin further south to Whanganui and further offshore to 20 n.mi. from the coastline. The IUCN has recommended protecting Hector's and Maui's dolphins from gillnet and trawl fisheries, from the shoreline to the 100 m depth contour.
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- Davies, N., Bian, R., Starr, P., Lallemand, P., Gilbert, D. and McKenzie, J. (2008). Risk analysis of Maui’s dolphin and Hector’s dolphin subpopulations to commercial setnet fishing using a temporal-spatial age-structured model. Ministry of Fisheries, Wellington, New Zealand. Retrieved February 2013.
- Slooten, E. and Dawson, S.M. 2008. Sustainable levels of human impact for Hector’s dolphin. The Open Conservation Biology Journal 2: 37-43.
- Bejder, L., Dawson, S.M. and Harraway, J.A. 1999. Responses by Hector's dolphins to boats and swimmers in Porpoise Bay, New Zealand. Marine Mammal Science 15: 738-750.
- Stone, G. S. and Yoshinaga, A. 2000. Hector's dolphin (Cephalorhynchus hectori) calf mortalities may indicate new risks from boat traffic and habituation. Pacific Conservation Biology 6: 162-170.
- "Hector's Dolphins". Ministry of Fisheries. 2008-10-01. Retrieved 2010-02-16.
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- Smith, Nick; Guy, Nathan. "Additional protections and survey results good news for dolphins". beehive.govt.nz. New Zealand Government.
- National Audubon Society: Guide to Marine Mammals of the World ISBN 0-375-41141-0
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- Facts about Hector's dolphins Department of Conservation - Several Images & listed as 'critically endangered' - Retrieved 2007-05-08.
- Hector's Dolphins, New Zealand Ministry of Fisheries - Retrieved 2007-02-09.
- Hector's Dolphin - Factsheet, Royal Forest and Bird Protection Society of New Zealand Inc — Retrieved 2007-02-09.
|Wikimedia Commons has media related to Cephalorhynchus hectori.|
- Specimen MNZ MM001915, collected Kaikoura, New Zealand, no date data
- NZ Dept. of Conservation - Hector's dolphin information
- NABU International www.hectorsdolphins.com