Hector's dolphins are 'turning up' in Māui's dolphin populations

Thursday, 4 August 2022

Scientists monitoring dolphin movement and behaviour in Aotearoa have found Hector’s dolphins within Māui’s dolphin populations.

Māui’s dolphins (Cephalorhynchus hectori maui) and Hector’s dolphins (Cephalorhynchus hectori) are closely related and are two subspecies of the same dolphin species, according to the Department of Conservation (DOC).

Māui's dolphins are found only along the west coast of the North Island, and it is estimated there are only about 54 individuals remaining. The Hector’s dolphin population is estimated to be about 15,000, and they are classed as nationally vulnerable.

Classed as taonga by Māori, the Hector’s dolphin is one of the world’s rarest, and smallest, dolphins and is found primarily in the coastal waters off the South Island.

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DOC science adviser for marine species Anton van Helden said finding Hector’s dolphins within the Māui's dolphin population was “a big insight”.

“So far, there’s no sign of inter-breeding between Māui and Hector’s, even though they are a subspecies and in all likelihood, they should be able to.

“But we do have animals and new animals that turn up in that Māui population from the Hector's dolphin population at the moment. We don’t have enough information to say exactly where those animals are coming from, and when we start to understand that, we can see what implications it has in terms of their management.

“We’re always trying to find out more about the animals because they're really important. They're important to us, they’re iconic, they’re endemic to New Zealand, and they’re not found anywhere else in the world,” van Helden said.

Using the very latest research technologies, scientists have been hoping to find out if the Hector’s dolphin population in the Marlborough Sounds is genetically unique from other groups across the top of the South Island.

Although extensive studies have been carried out on other populations around Te Waipounamu, very little is known about those that reside in the Marlborough Sounds.

Van Helden said scientists were trying to get an understanding of the genetic relationships and the “connectivity” of adjacent Hector’s dolphin populations across the top of the south.

Epigenetic clocks had enabled the team to take biopsies of live dolphins and study them over the long term, rather than relying on samples collected from animals that had died.

“The typical way we have assessed and understood the ages, and how long an animal can live, at what point in their life cycle they may become reproductively active – we’ve done that from dead animals washed ashore and looked at the ages of teeth,” van Helden said.

This involves “sectioning teeth in much the same way you might look at rings in a tree”, he said.

“But now we've got new techniques that have been developed, and it’s very exciting because we’re just under way, and it allows us to start to look at the ages of animals simply by using tiny little biopsy samples.”

Van Helden said new research tools also allowed scientists to see what the dolphins were feeding on, which in turn could give the team an insight into the animals’ movements.

“The research on their diets is pretty new. It’s [about] understanding their isotopic range, which will essentially tell us where they’re feeding and what sorts of species they’re feeding on.

“This will help us through time as we navigate trying to understand the implication of things like climate change on the distribution of animals, and their associated diets,” van Helden said.

It was hoped the data collected would allow the team to see if the populations across the top of the south remained separate, or whether animals interacted and moved between groups.​

“We have very little information about animals from Golden Bay and Tasman Bay, and whether they are related to either the animals on the top of the West Coast, Marlborough Sounds, or the animals in Cloudy Bay at the top of the East Coast.

“Some of the questions to still ascertain are whether or not those Hector’s dolphins in the Marlborough Sounds are genetically different, or just an extension of the Cloudy Bay population and whether or not they’re in the Sounds all the time, or whether they move between those two populations.”

Van Helden said the more information his team had about the animals and how they lived, the better equipped they would be in managing and protecting them from potential threats, including toxoplasmosis, an infectious parasite that was predominantly spread through cats’ urine and could be catastrophic to dolphin populations.

“We know that dolphins all around the country are susceptible to catching this and dying from this disease, and that seems to be pretty significant,” van Helden said.

He said a previous attempt to conduct an aerial survey to determine the population size of Hector’s dolphins in the Marlborough Sounds was thwarted by issues with the aircraft.

“Due to restrictions of the plane they were using at the time to do that survey, while the rest of the South Island was done using that particular approach, they weren't able to do that over the Sounds.

“So, one of the new techniques we’re hoping to use to get a sense of population size in the Marlborough Sounds is to work with Maui63, who have developed a large, fixed-wing drone that uses artificial intelligence to be able to spot dolphins.

“It will be able to run transects – lines going backwards and forwards with the drone and counting the numbers of animals in an area and then repeating it.

“By doing that we can capture and recapture the assessment and get a population size,” van Helden said.