Cross-breeding raises hopes for rare dolphin

The population of the North Island Maui's dolphin has dwindled to only 150. Photo / DoC

The smallest and most critically endangered dolphin in the world may have been thrown a lifeline by its South Island relative.

Until now it was believed that the North Island Maui's dolphin has occupied separate stretches of coastline to the South Island Hector's dolphin.

But a recent population count revealed two Hector's dolphins among pods of Maui's dolphins on the North Island's west coast.

The finding has given hope to conservationists that the two closely related sub-species will breed, giving much-needed genetic diversity to the Maui's dolphin.

The Department of Conservation's Maui's Dolphin Recovery Group leader, Phil Brown, said: "We know that Maui's dolphins have a limited pool of genetic diversity, so any new input is very welcome."

The Maui's dolphin population has dwindled to 150, and it is listed as critically endangered - meaning it is likely to be extinct soon.

Mr Brown said Maui's and Hector's dolphins had been genetically separate for more than 15,000 years.

"Even if occasional breeding with Hector's occurs, it won't change the makeup of the entire population."

It was initially not known whether the two dolphins had retained some Hector's genes, or whether they were straying outside their usual range - Hector's are usually found near Haast, Banks Peninsula or Farewell Spit in the South Island.

But genetic tests undertaken by the University of Auckland and Oregon State University confirmed they were Hector's dolphins.

DoC said further research was required to see whether the two dolphins survived in their new habitat, and also whether they were able to breed with Maui's dolphins.

Auckland University dolphin expert Rochelle Constantine presented the findings at the New Zealand Ecological Society conference in Dunedin.

The main threats to Maui's dolphins, which swam slowly and close to shore, were net fishing, pollution, natural predators - orcas and sharks - and disease.

TWO OF A KIND

MAUI'S

Size: Females grow to 1.7m; males are smaller.
Weight: Females up to 50kg.
Markings: Grey, white and black, with short snout and black, rounded dorsal fin.
Population: 150 ("critically endangered").
Region: West Coast of North Island.
Reproduction: One calf every 2-4 years.
Life expectancy: Up to 20 years.

SOUTH ISLAND HECTOR'S
Size: Females grow to 1.5m; males are smaller.
Weight: Females between 40-60kg.
Markings: Grey, white and black, with short snout and black, rounded dorsal fin.
Population: 7270 ("nationally vulnerable").
Region: South Island.
Reproduction: One calf every 2-3 years.
Life expectancy: Up to 20 years.