7 Apr 2016

Three decades on the tail of Hector’s dolphins

From Our Changing World, 9:46 pm on 7 April 2016
Dolphin in mid air

A Hector's dolphin jumps out of the water - Steve Dawson thinks the splash when it lands is the dolphin equivalent of excited shouting. Photo: Steve Dawson / NZ Whale & Dolphin Trust

After 32 years and thousands of hours in the company of the world’s smallest dolphins, cetacean experts Professors Liz Slooten and Steve Dawson haven’t lost their boundless enthusiasm and drive to learn more about Hector’s dolphins.

Two to three mornings a week when the summer weather is calm enough, the University of Otago researchers head out onto Akaroa Harbour.

Partners in life as well as work, Profs Slooten and Dawson are a familiar sight zigzagging away from the small township of Akaroa, following the same route they do every trip.

Prof Dawson describes Hector’s dolphins as “incredibly boat-positive and very curious”.

“They’re wonderful little animals really,” he says. “Especially when they’re in a bigger group we can just turn [the engine] off and they’ll seem to centre their activities around the boat … it makes what we do much, much easier.”

Prof Slooten says that on a good summer’s day they might see 80 to 100 Hector’s dolphins in Akaroa Harbour, and that even on an average day they’ll probably encounter a few dozen.

Photo IDs

Two people on a small boat and a dolphin fin in the water nearby

Liz Slooten drives the boat and keeps an eye out for dolphins with notches in their fins, while Steve Dawson takes photos from the boat's bow Photo: RNZ / Alison Ballance

When they encounter a group of dolphins Prof Dawson gets out his camera, with its telephoto lens, and they spend time with the group, looking out for dolphins that have natural markings or ‘tags’.

“If there are any dolphins in the group with nicks out of the fin or colouration markings he’ll photograph those,” says Prof Slooten.

Back at base these photos are added to an ever-growing photo ID library, and compared to previous photos to see if these are familiar dolphins or new animals.

Prof Dawson says the natural markings are the best kind of tag he could hope for, and about 10 percent of the population is recognisable from these natural marks.

The photo catalogue includes about 300 dolphins that are still alive. As the study has been running for longer than a dolphin life span (Hector’s dolphins only live to 25) many of the original dolphins have now died. This number includes about 50 mature females that have been seen with at least one calf.

Counting every dolphin

Two people on a small boat

Professors Steve Dawson and Liz Slooten on their research boat in Akaroa Harbour Photo: RNZ / Alison Ballance

The pair’s career-long fascination with Hector’s dolphins, which they argue should be called New Zealand dolphins, began in 1984 when they surveyed 8300km of coastline in a 3.8m inflatable boat.  The six-month survey resulted in the first reliable data on the distribution of Hector’s dolphins and led to the creation of the New Zealand Whale and Dolphin Trust.

They have identified four genetically distinct populations of Hector’s dolphins: Maui’s dolphins are found on the west coast of the North Island, and the other three populations occur on the west, east and south coasts of the South Island.

Saving the dolphins

While Maui’s dolphin is currently estimated to number just 55 or so animals, the other populations together number just over 7000. Maui’s dolphins are listed as critically endangered, and the other populations as endangered.

Hector’s dolphins reproduce very slowly, with a female producing one calf on average every three years. This results in a low population growth rate of just 2 percent a year, and means the species is very vulnerable to any unnatural deaths, such as dolphins drowning in gill nets.

Prof Slooten says the population had been doing a “nosedive’ in the 1980s.

“When we started this study it wasn’t unusual to find dead dolphins floating around or on beaches, that had been caught in gill nets or trawl nets. So really it was carnage in the '80s and '90s,” says Prof Slooten.

A tattered Hector's dolphin fin

A male dolphin known as Fingers, from the ragged glove-like appearance of his dorsal fin, has been seen since 2005. Photo: Steve Dawson / NZ Whale & Dolphin Trust

They were appalled at the high number of dolphins they were seeing that had drowned in fishing nets and their strong science-based advocacy resulted in the creation of New Zealand’s first marine mammal sanctuary in Akaroa Harbour, in 1988. The sanctuary extends four nautical miles offshore but research has showed the dolphins range out to 20 nautical miles offshore in winter.

“We’ve now got this protection that’s ensured the population is no longer doing a nosedive, so now it’s somewhere between stable or very slowly decreasing, but we need to push the protection further offshore to allow the population to grow.”

‘Dolphins Down Under’

Prof Slooten says most people are stunned by the small size of the Hector’s dolphins, which are just 1.2-1.4 metres long. They are the most coastal of the four species of dolphins that are common in New Zealand waters and are recognisable by their rounded dorsal fin.

The Hector’s dolphin population in Akaroa Harbour is the basis of a booming ecotourism industry and each year thousands of people join trips on dolphin watching and dolphin swimming boats.

If you’d like to find out more about Hector’s dolphins, and Profs Slooten and Dawson's research project, their book ‘Dolphins Down Under - understanding the New Zealand dolphin’ (Otago University Press 2013) is a fascinating read. The book includes information on everything from dolphin acoustics to social behaviour.