Scientists reignite spat over plan to save Māui dolphins

11:34 am on 3 June 2020

Marine scientists are again butting heads over a plan to protect endangered Māui and Hector's dolphins.

Maui dolphin.

Māui dolphins. Photo: Earthrace Conservation / Liz Slooten

A threat management plan for the dolphins was the subject of debate when it was released last year, labelling cat poo a greater risk to the dolphins than fishing nets.

Professor Liz Slooten using an underwater pole-cam to study dolphins.

Professor Liz Slooten using an underwater pole cam to study dolphins. Photo: Supplied / Steve Dawson

Now, a marine expert has published work tearing apart the methods underpinning the plan, prompting the man behind it to againdefend his work.

Liz Slooten sold her house in the 1990s to buy a catamaran so she could survey Māui and Hector's dolphins.

More than 30 years on, the Otago marine biologist and her research partner professor Steve Dawson have published a countering to the science used to put together a proposal aimed at protecting these rapidly disappearing mammals.

Prof Slooten said the plan was based on assumptions about where fishing happened and much of that was unknown.

"Only since 2008 and only for about 60 percent of the fishing boats have we got GPS locations. If we've only got locations for 60 percent of the fishing effort then we're going to have to assume that that's representative of the whole fishery," Prof Slooten said.

"It's a problem of not having enough raw input data to put into the model and therefore having to make way more assumptions than you'd normally have to make. They've kind of put 10 percent of their efforts into gathering good data [and] 90 percent into modelling really bad data," she said.

"Statisticians call that polishing turds."

Liz Slooten and Steve Dawson in 1984 preparing to conduct a dolphin survey.

Liz Slooten and Steve Dawson in 1984 preparing to conduct a dolphin survey. Photo: Supplied / Steve Dawson

The year-old proposal was met with fierce debate when it was first released, with its claims that toxoplasmosis - spread by cat poo - posed six times as much risk to these dolphins as fishing nets.

It includes options for expanding the marine mammal sanctuaries, based on the perceived threats these dolphins face

But the man who led the risk assessment for the Ministry for Primary Industries, marine scientist Jim Roberts, said Prof Slooten's claims were packed with misinformation.

"It's kind of ludicrous to say that you're making up for a lack of data with models. Models are fit to data and she's a professor of conservation science and should know that," Dr Roberts said.

"Essentially, if you have very low sample size it will reflect that in the estimate that comes back out in terms of the uncertainty around those estimates."

He has written a 14-page rebuttal to the professors' paper, defending his working.

He concluded: "A balanced and well-thought-out review of the risk assessment would have been welcomed. However, the critique was based on multiple errors of fact and misrepresentations of the risk assessment and its inputs. This is concerning because most readers probably won't have the time or resources to fact-check their critique. It is also a missed opportunity to improve the risk assessment of threats to Hector's and Māui dolphins, more generally."

Liz Slooten in a Volkswagen Combi, in the 1980s that Steve Dawson converted into a camper van so the pair could conduct research in the field.

Liz Slooten in the 1980s in a Volkswagen Combi that Steve Dawson converted into a camper van so the pair could conduct research in the field. Photo: Supplied / Steve Dawson

Prof Slooten reiterated her disbelief in the toxoplasmosis claim and went after methods used to calculate things like breeding rate.

She said the assumptions made were like giving someone a map with only half the roads on it.

"This poor government are trying to make a decision based on a dolphin map and a fishing map that are just not very good maps. And MPI have been told this repeatedly by individual scientists by their own expert panel, and they just won't listen."

Dr Roberts was at Niwa when the work was carried out. He is now an independent consultant to MPI and the Department of Conservation.

He said in the sample of 36 dead Hector's and Māui dolphins, toxoplasmosis was responsible for a third of their deaths.

"And this isn't 'died with toxo', what actually happened is toxo infection had necrotised whole suite of their organs, so it very definitively had killed them. If something is necrotising the organs of a quarter of your sample of animals, this seems to be an ongoing problem and it's widespread around New Zealand."

'Uncertainty about toxoplasmosis'

Conservation Minister Eugenie Sage admitted there was much to learn about the risks these mammals face.

Conservation Minister Eugenie Sage unveiled the Predator Free 2050 Strategy at Otari Wilton's Bush this morning.

Eugenie Sage. Photo: Rachel Thomas

"There is considerable uncertainty about toxoplasmosis but it has been found in beach cast dolphins, so we need to know more about the impact that feral cats and cats are having with toxoplasmosis. But we know with much more certainty that it is fishing impacts."

She said that was why the threat management plan focused on expanding marine mammal sanctuaries, while officials learned more about the risk of toxoplasmosis.

Sage said work was still being done to finalise the plan and "I hope we can make an announcement soon".

In a statement, Seafood NZ chief executive Jeremy Helson said: "We dispute Liz Slooten's take on the science and note it has not been peer reviewed."

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