Hector's Dolphin: Wikis

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Hector's dolphin
Hector's dolphin at Kaikoura, New Zealand
Size comparison against an average human
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Eutheria
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus: Cephalorhynchus
Species: C. hectori
Binomial name
Cephalorhynchus hectori
Van Beneden, 1881
Hector's dolphin range

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 about 1.4 m in length, it is one of the smallest cetaceans.

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). He examined the first specimen found of the dolphin. The species was scientifically described by Belgian zoologist Pierre-Joseph van Beneden in 1881.

Maui's dolphin (Cephalorhynchus hectori maui) is a subspecies of Hector's dolphin found off the northwest coast of New Zealand's North Island[2]. It is the most endangered subspecies of marine mammal (other cetaceans with a similarly perilous conservation status inhabit rivers and estuaries only). There are approximately 110 Maui's dolphins remaining.

Māori names for Hector's and Maui's dolphin include Tutumairekurai, Tupoupou and Popoto.

... thirty years ago there were over 26,000 Hector's and Maui's dolphins. Today, due to human activity, there is a struggling population of around 7,270 Hector's dolphins - and Maui's are the rarest marine dolphins in the world with around 110 left - WWF Apr. 2007 [3]

Contents

Physical description

Hector's dolphins have a unique rounded dorsal fin.

Hector’s dolphin is the smallest of the delphinids. Mature adults have a total length of 1.2-1.6 m and weigh 40-60 kg[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 and weigh 8-10 kg[5]. Their coloration is the same as adults, although the grey has a darker hue. Four to six vertical pale stripes, caused by foetal folds affecting the pigmentation, are present on the calf’s body until an age of about 6 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 40˚S, with the majority of animals in the central portion of this range between the Manukau and Raglan Harbours[8].

Abundance has been estimated from a series of five line-transect surveys between 1998 and 2004. The abundance estimate for South Island Hector’s dolphin is 7270 (CV = 16%)[5,6], and for Maui’s dolphin is 111 (CV = 44%)[7]. Current population size is estimated to be 27% of the abundance in 1970 before significant human impacts occurred[9].

Hector's dolphins at Porpoise Bay, in the Catlins.

The species has a preference for shallow, coastal waters less than 100 m deep[10][11]. This means they are most commonly seen close to shore, although in shallow regions they have been sighted up to 34 km from the coast. In some areas, there is a pronounced seasonal difference in distribution, with dolphins being sighted further offshore and in deeper water in winter, presumably in response to movements of their prey species.

Ecology and life history

Bycaught and stranded Hector’s dolphins have provided information on the life history and reproductive parameters of the species. 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 old. 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].

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, mid water fish and squid and a wide variety of benthic species[3]. 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 orca.

Conservation

Bycatch in bottom-set gillnets has been responsible for the majority of human induced mortality of Hector’s dolphins. The nationwide estimate for bycatch in commercial gillnets is 110-150 dolphins per year[13] which is far in excess of the level which is considered to be sustainable[14]. Hector’s dolphins face a range of other impacts including trawl bycatch[15], tourism[16][17], pollution[3] and habitat modification.

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 n.mi. (7.4 km) 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.[18] 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 n.mi. (13 km) offshore. There are also restrictions on trawling in some of these areas. For further details on these regulations see the Ministry of Fisheries website[19]. Five marine mammal sanctuaries were designated in 2008 to manage non-fishing related threats to Hector’s and Maui’s dolphin[20]. Their regulations include restrictions on mining and seismic acoustic surveys.

References

  1. ^ Reeves, R.R., Dawson, S.M., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. (2008). Cephalorhynchus hectori. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 24 March 2009. Database entry includes a brief justification of why this species is of endangered.
  2. ^ Baker, A.N., Smith, A.H. and F.B. Pichler. 2002. Geographical variation in Hector's dolphin: recognition of a new species of Cephalorhynchus hectori. Journal of the Royal Society of New Zealand 32: 713-727.
  3. ^ Jenny Riches. "Hector's and Maui's survival in Kiwi's hands, says WWF". http://www.wwf.org.nz/news/2007/07-04-03-maui.cfm. Retrieved May 11 2007.  
  4. ^ Slooten, E. and Dawson, S.M. 1994. Hector’s dolphin Cephalorhynchus hectori. Pp. 311-333 in: Handbook of Marine Mammals. Volume V (Delphinidae and Phocoenidae) (S.H. Ridgway and R. Harrison eds). Academic Press. New York.
  5. ^ Slooten, E. 1991. Age, growth and reproduction in Hector’s dolphins. Canadian Journal of Zoology 69: 1689-1700.
  6. ^ Slooten, E., Dawson, S.M. and Rayment, W.J. 2004. Aerial surveys for coastal dolphins: abundance of Hector’s dolphins off the South Island West Coast, New Zealand. Marine Mammal Science 20:477-490.
  7. ^ Dawson, S.M., Slooten, E., DuFresne, S.D., Wade, P. and Clement, D.M. 2004. Small-boat surveys for coastal dolphins: Line-transect surveys of Hector’s dolphins (Cephalorhynchus hectori). Fishery Bulletin 102: 441-451.
  8. ^ Slooten, E., Dawson, S.M., Rayment, W. and Childerhouse, S. 2006. A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species? Biological Conservation 128: 576-581.
  9. ^ Slooten, E. 2007. Conservation management in the face of uncertainty: effectiveness of four options for managing Hector’s dolphin bycatch. Endangered Species Research 3: 169-179.
  10. ^ Bräger, S., Harraway, J. and Manly, B.F.J. 2003. Habitat selection in a coastal dolphin species (Cephalorhynchus hectori). Marine Biology 143: 233-244.
  11. ^ Rayment, W., Dawson, S. and Slooten, E. In press. Seasonal changes in distribution of Hector’s dolphins at Banks Peninsula, New Zealand: implications for protected area design. Aquatic Conservation: Marine and Freshwater Ecosystems. DOI: 10.1002/aqc.1049.
  12. ^ Slooten, E. and Lad, F. 1991. Population biology and conservation of Hector’s dolphins. Canadian Journal of Zoology 69: 1701-1707.
  13. ^ 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. 113 p. http://www.fish.govt.nz/NR/rdonlyres/B034115D-247A-42E5-B08F-F5D267046C59/0/HectorNIWAriskanalysis.pdf
  14. ^ Slooten, E. and Dawson, S.M. 2008. Sustainable levels of human impact for Hector’s dolphin. The Open Conservation Biology Journal 2: 37-43.
  15. ^ Starr, P. and Langley, A. 2000. Inshore Fishery Observer Programme for Hector’s dolphins in Pegasus Bay, Canterbury Bight, 1997/1998. Published client report on contract 3020, funded by Conservation Services Levy. Department of Conservation, Wellington. 28p.
  16. ^ 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.
  17. ^ 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.
  18. ^ Tell New Zealand to protect endangered dolphins, World Wildlife Fund Passport Panda website, retrieved 11:10 a.m. Saturday, 15 March 2008.
  19. ^ http://www.fish.govt.nz/en-nz/Environmental/Hectors+Dolphins/default.htm?WBCMODE=PresentationUnpublished++%23MainContentAnchor%23MainContentAnchor
  20. ^ http://www.doc.govt.nz/conservation/marine-and-coastal/marine-protected-areas/marine-mammal-sanctuaries/

Further reading

External links

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