Hector's dolphin (scientific name: Cephalorhynchus hectori) is one of the rarest marine dolphins in the world. Native and restricted to only coastal regions of New Zealand, this species has a very small population which continues to decline. Although New Zealand has made illegal any catching of marine mammals, this species remains endangered, and in some regions (North Island subpopulation) critically endangered. Hector's dolphin is member of the family Delphinidae, part of the order of cetaceans.
The common name, Hector's dolphin, refers to the New Zealand zoologist Sir James Hector, who first collected the species in 1869.
Kingdom: Animalia (Animals)
Hector's dolphin is one of the rarest and smallest of marine dolphins. These mammals are stocky (torpedo like) and lack a beak. They have disproportionately large flukes and their most noticeable characteristic is their rounded dorsal fin with its convex trailing edge. Also,the flippers have rounded tips. Their length ranges in size from 119 to 145 centimetres.
Males and females are generally similar in appearance, but females tend to be slightly longer (about ten cm longer) than males.
This dolphin is primarily grey, but has both black and white markings. They are sexually dimorphic in the coloration around the genital slit. Males have an oval dark grey patch, and females have either a finger-like grey mark along side it, or remain completely off-white. The head also has a distinct crescent-shaped black marking running transversely over its surface behind the blowhole. Calves have the same markings as adults, but pale lines can be seen on darker areas, and the underside has a yellowish tint.
Females reach maturity at around seven to nine years of age, and males between six and nine years. Courtship behaviour involves close contact, leaping, chasing and belly displays.
Calves tend to be born in late spring to early summer, and the mother will not conceive again until 2-4 years have passed when the calf is fully independent Little is known about the gestation period or length of lactation.
This dolphin species tends to aggregate in groups two to eight individuals. These groups often join together forming larger groupings, and then split.
Playing with seaweed, bubble blowing and other games are thought to be important social behaviors. Certain sounds produced by this dolphin are also thought to be significant in a social context; particularly the complex clicks that are produced in large groups.
Cephalorhynchus hectori is the only dolphin found solely within New Zealand waters. Hector's dolphins may be found on both the west and east coast of South Island, but they are restricted to a small area on the west coast of the Northern island.
This dolphin Inhabits coastal waters such as river mouths and shallow bays, and very rarely ventures further than 9 km from the coast. They prefer shallow, muddy waters and may enter estuaries and swim slightly upriver. They have also been known to inhabit a wide range of water temperatures (anywhere from 6.3 to 22.0 degrees C), and turbidities (less than 10 cm to greater than 15 m).
Predation by the Seven gill shark (scientific name: Notorhynchus cepedianus), and the blue shark (scientific name: Prionace glauca) have a significant effect on mortality rates of Hector's dolphins.
Hector's dolphins appear to feed in small groups generally at the bottom of coastal waters, but also throughout the water column. They consume a variety of species including surface-schooling fish, such as yellow-eyed mullet; arrow squid; and benthic (bottom dwelling) fish including red cod and stargazer. Crustaceans have also been found in their stomach contents.
The New Zealand Marine Mammals Protection Act has made the deliberate killing or injury of marine mammals illegal. This act provides protection for Hector's dolphin. Bycatch, although not illegal is difficult to regulate, and it is clear that measures must be taken to eliminate this threat if this diminutive dolphin is to survive.
The species as a whole is listed as Eendangered, however, the North Island subpopulation is listed as critically endangered.
Because of this dolphin's coastal habitat, this species is vulnerable to chemical water pollution (DDT, PCBs, and certain other herbicides and pesticides), vessel traffic, and habitat modification. Currently, the most important threat to the survival of this species is bycatch by the fishing industry, particularly entanglements in gillnets. In this sense, excessive bycatch is a type of overfishing. The chemicals from pollution, however, also seriously threat the species, and have been found in Hector's dolphin tissues and are know to interfere with reproduction.
Also, predation by the Seven gill shark (scientific name: Notorhynchus cepedianus), and the Blue shark (scientific name:Prionace glauca) have a major effect on mortality rates of the Hector's dolphin.
Refefences and Further Reading
- Encyclopedia of Life. 2010. Cephalorhynchus hectori (P.-J. van Bénéden, 1881) Hector's dolphin
- IUCN. Hector's Dolphin
- UNEP-WCMC database (February, 2002) http://quin.unep-wcmc.org/
- Macdonald, D. (2001) The New Encyclopedia of Mammals. Oxford University Press, Oxford.
- Cetacea.org (February, 2002) www.cetacea.orghectdol.htm
- Animal Diversity Web (February, 2002)
- Whale and Dolphin Conservation Society (WDCS) (February, 2002)
- Carwardine, M., Hoyt, E., Fordyce, R.E., and Gill, P. (1998) Whales and Dolphins. Harper Collins Publishers, London.
- 1993. World checklist of threatened mammals. Peterborough, UK: Joint Nature Conservation Committee.
- Gordon DP, Beaumont J, MacDiarmid A, Robertson DA, Ahyong ST. 2010. Marine Biodiversity of Aotearoa New Zealand. PLoS ONE 5(8): e10905. doi:10.1371/journal.pone.0010905
- Gordon, D. (Ed.) (2009). New Zealand Inventory of Biodiversity. Volume One: Kingdom Animalia. 584 pp
- Honacki, J., K. Kinman, J. Koeppl. 1982. Mammal Species of the World. Chicago, Illinois: Allen Press Inc..
- IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
- Macdonald, D., p. Evans, B. Wursig. 1984. All The World's Animals. New York, New York: Torstar Books Inc..
- Mead, James G., and Robert L. Brownell, Jr. / Wilson, Don E., and DeeAnn M. Reeder, eds. 2005. Order Cetacea. Mammal Species of the World: A Taxonomic and Geographic Reference, 3rd ed., vol. 1. 723-743
- Nowak, R. 1991. Walker's Mammals of the World. Baltimore, Maryland: Johns Hopkins University Press.
- Perrin, W. (2010). Cephalorhynchus hectori (P. J. Van Beneden, 1881). In: Perrin, W.F. World Cetacea Database. Accessed through: Perrin, W.F. World Cetacea Database (accessed 2011-02-05)
- Rice, Dale W. 1998. Marine Mammals of the World: Systematics and Distribution. Special Publications of the Society for Marine Mammals, no. 4. ix + 231
- Slooten, E., S. Dawson. 1994. Hector's Dolphin. Pp. 311-331 in S. Ridgway, R. Harrison, eds. Handbook of Marine Mammals. London, UK: Academic Press Ltd..
- UNESCO-IOC Register of Marine Organisms
- Wilson, Don E., and DeeAnn M. Reeder, eds. 1993. Mammal Species of the World: A Taxonomic and Geographic Reference, 2nd ed., 3rd printing. xviii + 1207
- Wilson, Don E., and F. Russell Cole. 2000. Common Names of Mammals of the World. xiv + 204