Maui's dolphin

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Maui's dolphin
Two Maui's dolphins.jpg
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus: Cephalorhynchus
Species: C. hectori
Subspecies: C. h. maui
Trinomial name
Cephalorhynchus hectori maui
Baker et al., 2002

Maui's dolphin or popoto (Cephalorhynchus hectori maui) is the world's rarest and smallest known subspecies of dolphin.[1] They are a subspecies of the Hector's dolphin. Maui's dolphin are only found off the west coast of New Zealand's North Island. Hector's and Maui's are New Zealand's only endemic cetaceans.[2] In 2012 it was estimated there were 55 Maui's dolphins older than one year old in the world.[3] Maui's dolphins are generally found close to shore in groups or pods of several dolphin. They are often seen in water shallower than 20 metres deep, but may also range further offshore.

In 2012, the majority of a government-appointed panel of experts estimated that 4.95 Maui's were killed each year due to set-netting and trawling. In May 2014, the World Wildlife Fund in New Zealand launched "The Last 55" campaign, calling for a full ban over what it believed is their entire range.[4][5] The International Whaling Commission supports more fishing restrictions but some in the New Zealand government are opposed to the proposals.[6][7][8] In June 2014, the government decided to open up 3000 km2 of the West Coast North Island Marine Mammal Sanctuary - the main habitat of the Maui's dolphin - for oil drilling. This amounts to one quarter of the total sanctuary area.[9]

Etymology[edit]

The word "Maui" from the Maui's dolphin's name comes from te Ika-a-Māui, the Māori word for New Zealand's North Island. However, the Māori word for the dolphin itself is popoto.[10]

Genetics[edit]

In 2002, Maui's dolphins were classified as a sub-species of Hector's dolphin. Previously, they had been known as the North Island Hector's Dolphin. Dr Alan Baker found that genetic and skeletal differences in the Maui's dolphins made them distinct from others in the Hector's species.[11] These significant differences over a small geographical distance have not been found in any other studies of marine mammals.[12] There have so far been 26 different mitochondrial DNA identification haplotypes in the Hector's species, the Maui's ‘G' haplotype being one of them.[13]

In 2002, it was not known that Hector's dolphins were capable of swimming from the South Island to the North Island and co-existing with Maui's dolphins. Instead it was understood that the deep waters of the Strait had been an effective barrier between South Island Hector's and its North Island Maui's subspecies for between 15,000 and 16,000 years.[13] It was therefore surprising to researchers that the 2012 Auckland University/Department of Conservation boat survey tissue sampling of Maui's in core range, which included historical samples, revealed three Hector's dolphins identified in this range area (two of them alive) along with another five Hector's being disclosed or sampled between Wellington and Oakura between 1967 and 2012.[14]

There is no evidence so far that the Hector's and Maui's interbreed,[14][15] but, given their close genetic composition, it is likely that they could. Interbreeding may increase the numbers of dolphins in the Maui's range and reduce the risk of inbreeding depression. But such interbreeding could eventually result in a hybridisation of the Maui's back into the Hector's species and lead to a reclassification of Maui's as again the North Island Hector's. Hybridisation in this manner threatens the Otago black stilt[16] and the Chatham Islands' Forbes parakeet[17] and has eliminated the South Island brown teal as a subspecies.[18] Researchers have also identified potential interbreeding as threatening the Maui's with hybrid breakdown and outbreeding depression.[14]

Physical description[edit]

Range of Maui's dolphin (blue) in New Zealand's North Island, with the area covered by the net ban marked in red.

Having distinctive grey, white and black markings and a short snout, they are most easily recognized by their round dorsal fin. Maui's dolphins are generally found close to shore in groups or pods of several dolphins. They have a solidly built body with a gently sloping snout and a unique rounded dorsal fin. (Maui's and Hector's are the only dolphins with a well-rounded black dorsal fin.) Females grow to 1.7 meters long and weigh up to 50 kg. Males are slightly smaller and lighter. The dolphins are known to live up to 20 years.

Population, distribution and presence of Hector's[edit]

Maui's dolphins are classed by the Department of Conservation in the New Zealand Threat Classification System as "Nationally Critical".[19]

Maui's are only found off the west coast of the central North Island of New Zealand. Since 2001 the known range of the Maui's has been between the Kaipara Harbour south to Raglan Harbour.[20] Most sightings of the dolphins are made in their core range about 30 km north and south of the Waikato River mouth.[21] There are old records of dolphin sightings off the east coast of the North Island between Wellington and the Bay of Plenty, which indicates a more widespread and larger previous Maui's or Hector's populations.[12] Historical presence has been confirmed by DNA analysis, dating back to Wellington Harbour in 1873.[20]

A DOC survey report in 2012 estimated 55 adult Maui's remained.[3] This is a marked decrease from a 2004 survey that found the population to be around 100 dolphins.[22] A survey of Maui's dolphins in 1985 estimated their numbers to be at 134.[11] The data from the 2012 report is not directly comparable with earlier aerial surveys because of the different methods used and that the 2012 survey effort had concentrated on the area within one kilometre from shore, but the reports highlight that the population is very small and are indicative of a recent decline.[20]

Whether there are some Maui's migrating southwards, or only Hector's migrating northwards into Taranaki waters, is a matter of debate. A dolphin, either a Hector’s or Maui’s, was caught in Taranaki waters in a set net off Cape Egmont on 2 January 2012. A dolphin, DNA tested as a Hector's, was found washed up on the Opunake beach on 26 April 2012.[23]

Cephalorhynchus dolphin sighting information released by DOC in September 2013 includes listing three public sightings of Hector’s type dolphins along the coastline immediately north of Wellington in late 2011. There were four other sightings between Whanganui and Waitara in early 2012.[24] Another sighting was recorded along the Poverty Bay coast of the North Island at this time as well.

Sightings of this type of dolphin along the coast north of Wellington are infrequent, with the DOC database reporting only seven since 1970.

A 2013 research paper [15] concluded the migration of Hector’s northwards from the South Island occurs but is not frequent. It cited confirmed Hector’s DNA from strandings in 2005 at Peka Peka and in 1967 at Waikanae, along the Horowhenua coastline.

The authors found the DNA evidence of whether the Hector’s were migrating from the east or west coasts of the South Island inconclusive. They suggested there was “the potential for a small and elusive resident population of Hector’s dolphins along the southern part of the North Island, outside the current range of the Maui’s dolphin, or along the northern part of the South Island between the East and West Coast populations of Hector’s dolphins..."

During the 2012/2013 summer DOC conducted five aircraft and six boat searches, between New Plymouth and Hawera, without seeing any Maui's or Hector's.[25]

Between July 2012 and May 2013, 419 MPI observer sea days were totalled on five fishing vessels in this area. More than 10,800 km were covered, with 255,700m of nets deployed between two and seven nautical miles from shore, without seeing any Maui's or Hector's dolphins. By 23 March 2014 observers had been at sea for 757 days.[26]

Ecology and behaviour[edit]

Vocalizations and echolocation[edit]

Maui's dolphins use echolocation to navigate, communicate and find their food. High-frequency ultrasonic clicks reflect back to the dolphin any objects found in the water.[27]

Foraging and predation[edit]

Maui's dolphins feed on small fish, squid and ocean floor dwelling species like flatfish and cod.[28] Maui's dolphins spend much of their time making dives to find fish on the sea floor. They also find fish and squid in mid water and at times feed near the surface.[27]

Social behaviour and reproduction[edit]

Female Maui's dolphins are not sexually mature until they are 7 - 9 years of age. They then produce one calf every 2 - 4 years.[29]

They have been observed playing (e.g. with seaweed), chasing other dolphins, blowing bubbles, and play fighting.[23]

Very little is known about the Maui's dolphin reproductive physiology.

Threats[edit]

Since records began in 1921 there have been 45 cases of deceased Maui dolphins recorded, though at least six have turned out to be Hector's.[30] According to the Department of Conservation's Incident Database, 31 of these dolphins either did not have their cause of death assessed or it was unknown. Six deaths were linked to possible or known net entanglement, 6 deaths to natural causes, and 2 deaths to human interaction.[31]

Fishing[edit]

Dolphins can get entangled in nets and drown.[32] The DOC Incident Database contains no reports of a Maui's mortality in a trawl net.[20]

Some groups in the fishing industry are against increased bans on set nets into waters further offshore and inside harbours, and say there are other factors responsible for the decline in population, including disease, pollution, mining and natural predation.[33]

Since the first major restrictions on commercial fishing to protect Maui's were imposed in 2003, 12 Cephalorhynchus hectori mortalities have been listed along the West Coast of the North Island. Of these, three have been confirmed as Hector's and the deaths of all bar one were from natural causes. The single death attributed to fishing occurred in January 2012.[31] The most recent dolphin death reported was from old age, with no indications of fishing injury and she was found on a beach near Dargaville on 13 September 2013. An analysis of microsattelite DNA shows the dolphin was a Maui's.

This DOC Incident Database information is contrary to a NABU paper submitted to the Scientific Committee of the International Whaling Commission in June 2013, which referenced back to the Database that the number of fatal Maui's entanglements in fishing nets has increased, from an average of 1 per year, to 1.33 per year, since 2008.[34]

Disease[edit]

In 2006, Brucella were found in a dead Maui's dolphin and DOC says this bacterial infection could have serious ramifications for the small Maui's population. Brucellosis is a disease of terrestrial mammals that can cause late pregnancy abortion, and has been seen in a range of cetacean species elsewhere,[35] though not so far in Hector's or Maui's.

In 2012, post mortems on Hector's and Maui's showed that most were infected with the protozoa Toxoplasma. Two of the three Maui's were killed by toxoplasmosis. Toxoplasmosis is known to reduce fertility in livestock, with cats playing a key role in its transmission. It is not known how toxoplasmosis spread to Maui's and Hector's dolphins, nor is there any funding available for research into this.[20] though Auckland City Council has decided to assist Massey University research by providing cat fecal samples.[36]

Fishing restrictions[edit]

In 2003 a ban on using commercial set nets was added to an existing ban on recreational set netting from Maunganui Bluff (north of Auckland) to Pariokariwa Point (north Taranaki), out to four nautical miles from shore.[37] In 2008 the restriction on set netting was extended out to seven nautical miles from shore along the same coastal area.

In 2008 the existing ban on trawling one nautical mile from this coast was extended to two nautical miles and extended to four nautical miles between Manukau Harbour and Port Waikato.

Set netting is prohibited inside the entrances of the Kaipara, Manukau and Raglan Harbours and Port Waikato. Current presence of Maui's further within these harbours is disputed, though they do visit the harbour mouths.

After what MPI believed at the time in January 2012 was the capture of a Maui's dolphin off Taranaki (though now says it was 'about as likely as not' to have been a Hector's) in June 2012 the New Zealand government announced an interim set net ban extension south around the Taranaki coast to Hawera and out to two nautical miles from shore,[38][39] and set netting only with government observers on board between two and seven nautical miles from land.

In November 2013 the Minister of Conservation Nick Smith, in finalising the Maui's dolphin Threat Management Plan, confirmed[40] an increase of the Taranaki set net ban of two nautical miles, further out to seven nautical miles between Pariokariwa Point and Waiwhakaiho River near New Plymouth. He said this was due to five public sightings of Hector type dolphins off Waitara since 2006.[41] Smith also announced codes of practice for seismic surveys would be implemented, regulations for inshore boat racing and the establishment of a Maui's dolphin Research Advisory Group.

References[edit]

  1. ^ "Dolphin's death reignites calls for set net ban". New Zealand Herald. 1 February 2012. Retrieved 2012-02-27. 
  2. ^ "Maui's dolphin - deep trouble". New Zealand Geographic. Retrieved 18 June 2013. 
  3. ^ a b New Zealand Department of Conservation. "Maui's dolphin abundance estimate: DOC's work". Retrieved 2012-03-13. 
  4. ^ "Maui's dolphin danger: 'We're running out of time'". New Zealand Herald. 19 May 2014. 
  5. ^ "Dolphin numbers perilously low". stuff.co.nz. 19 May 2014. 
  6. ^ Morton, Jamie (10 June 2014). "NZ 'needs to do the right thing' to save Maui's dolphin". New Zealand Herald. 
  7. ^ "New Zealand rejects calls to further protect Maui's dolphin". Agence France-Presse (Australian Broadcasting Corporation). 12 June 2014. 
  8. ^ "WWF responds to Minister’s ‘challenge’ on Maui’s dolphins". scoop.co.nz. 11 June 2014. 
  9. ^ "Oil and gas risk to Maui's dolphin 'small' - Minister". New Zealand Herald. 18 June 2014. Retrieved 2014-06-18. 
  10. ^ "Maui's dolphins- An Overview". WWF. Retrieved 14 November 2012. 
  11. ^ a b "Maui's dolphin". WWF. Retrieved 9/3/2012. 
  12. ^ a b "Cephalorhynchus hectori ssp. maui". International Union for Conservation of Nature and Natural Resources. Retrieved 2/4/2012. 
  13. ^ a b Hamner, Rebecca M.; Pichler, Heimeier,Constantine, Baker (August 2012). "Genetic differentiation and limited gene flow among fragmented populations of New Zealand endemic Hector's and Maui's dolphins". Conservation Genetics 13 (4): 987–1002. doi:10.1007/s10592-012-0347-9. 
  14. ^ a b c Hamner, R.M. "Estimating the abundance and effective population size of Maui's dolphins using microsatellite genotypes in 2010–11, with retrospective matching to 2001–07.". New Zealand Department of Conservation. Retrieved December 2012. 
  15. ^ a b Hamner, Rebecca; et al (2013). "Long-range movement by Hector’s dolphins provides potential genetic enhancement for critically endangered Maui’s dolphin". MARINE MAMMAL SCIENCE. doi:10.1111/mms.12026. 
  16. ^ Wallis, G. "Genetic status of New Zealand black stilt (Himantopus novaezelandiae ) and impact of hybridisation". New Zealand Department of Conservation. 
  17. ^ Greene, T.C. "Forbes' parakeet (Cyanoramphus forbesi) population on Mangere Island, Chatham Islands". New Zealand Department of Conservation. Retrieved December 2012. 
  18. ^ Gemmel, N.J. "Taxonomic status of the brown teal (Anas chlorotis) in Fiordland". New Zealand Department of Conservation. Retrieved December 2012. 
  19. ^ Hitchmough, Rod; Bull, Leigh; Cromarty, Pam (compilers) (2007). New Zealand Threat Classification System lists - 2005. Wellington: Science & Technical Publishing, Department of Conservation. p. 32. ISBN 0-478-14128-9. .
  20. ^ a b c d e "Review of the Maui's Dolphin Threat Management Plan". New Zealand Department of Conservation and Ministry for Primary Industries. Retrieved December 2012. 
  21. ^ "Rare encounter with Mauis dolphins". stuff.co.nz. Retrieved 2012-03-14. 
  22. ^ Slooten, Elisabeth; et al (April 2006). "A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species?". Biological Conversation 128 (4): 576–581. doi:10.1016/j.biocon.2005.10.013. 
  23. ^ a b Interim set net measures to protect Maui's dolphins, final advice paper. New Zealand Ministry for Primary Industries. 10 June 2012. 
  24. ^ "Maui's dolphin sightings database spreadsheet". NZ Department of Conservation. 
  25. ^ "Consultation on a proposed variation to the West Coast North Island Marine Mammal Sanctuary to prohibit commercial and recreational set net fishing between two and seven nautical miles offshore between Pariokariwa Point and the Waiwhakaiho River, Taranaki.". NZ Department of Conservation. 
  26. ^ "Consultation on a proposed variation to the West Coast North Island Marine Mammal Sanctuary to prohibit commercial and recreational set net fishing between two and seven nautical miles offshore between Pariokariwa Point and the Waiwhakaiho River, Taranaki.". NZ Department of Conservation. 
  27. ^ a b "Maui's dolphin - Ecology". WWF. Retrieved 10/3/2012. 
  28. ^ "Dolphins and Porpoises (Families Delphinidae and Phocoenidae)". Treasures of the sea. Retrieved 2012-03-15. 
  29. ^ "Facts about Maui's dolphin". Department of Conservation. Retrieved 9/3/2012. 
  30. ^ Hamner, Rebecca (2013). "Long-range movement by Hector’s dolphins provides potential genetic enhancement for critically endangered Maui’s dolphin". Marine Mammal Science (Society for Marine Mammalogy). 
  31. ^ a b "Hector's and Maui's incidents 1921 - 2008". Department of Conservation. Retrieved 30 July 2013. 
  32. ^ http://www.fish.govt.nz/en-nz/Environmental/Hectors+Dolphins/default.htm
  33. ^ "Threats to Maui's dolphins". Department of Conservation. 
  34. ^ "Science-based management of New Zealand's Maui's dolphins, Dr Barbara Maas, NABU International - Foundation for Nature, SC/65a/SM06". 
  35. ^ "Threats not caused by people - disease". New Zealand Department of Conservation. Retrieved December 2012. 
  36. ^ "March 2014 Minutes of the Environment, Climate Change and Natural Heritage Committee". Auckland City Council. 
  37. ^ "Interim Set Net Measures to manage the risk of Maui's dolphin Mortality". Ministry of Fisheries. Retrieved 12 July 2012. 
  38. ^ "Set net ban extension to protect Maui's Dolphin". stuff.co.nz. Retrieved 12 July 2012. 
  39. ^ Cumming, Geoff (3 November 2012). "Maui's dolphin swimming in sea of trouble". New Zealand Herald. 
  40. ^ "Additional Protection and Survey Results Good News for Dolphins". NZ Government. 
  41. ^ "Additional protection proposed for Maui’s dolphin". Minister of Conservation. 

External links[edit]