Source: Radio New Zealand
Supplied / Claire Garrigue
More than half a century after the last whale was caught and killed in New Zealand, humpbacks are showing promising signs of recovery.
An international study involving researchers from the University of Auckland shows humpback breeding is getting more competitive, which suggests the population is growing.
University of Auckland marine biologist Dr Emma Carroll had been working with researchers in New Caledonia to track the local humpback whales.
Comparing data collected over decades, Dr Carroll described a stark difference in breeding habits between the first part of the study, conducted in the 2000’s, and the second part, in the 2010’s.
“For the first part of the study, when the population was really small, young males and old males had the same number of babies or paternities,” she explained.
“But in the second half of the study, as the population is recovering from whaling, we see that older males are actually more dominant.”
What Carroll described was called a “reproductive skew”.
Many species had a reproductive skew that favoured older, larger males, and these “super-males” had the most children.
But when their population was decimated in the 60s and 70s, humpback whales lost the luxury to be picky.
To maintain genetic diversity, Carroll said the whales moved away from their reproductive skew.
Supplied / Claire Bonneville
“We think that when the population is low, the fact that young males and older males have the similar chances of having offspring, that is actually quite good for the population,” she said.
“Because it means that every male can contribute, which means lots more genetic diversity can be continued or carried through the population.”
As the decades rolled on, female whales had more options, and the males were getting more competitive.
“Then we see as the population gets bigger, there’s this kind of preference towards older males. And it just shows us that whaling and the reduction in the population size has led to changes in these behaviours through time.”
New Zealand’s relationship with whaling had a long and complicated history.
In a 1996 report by RNZ’s Spectrum, Marlborough whaler Joe Heberley described the moment his profession reached a tipping point.
“As time wore on, we knew that whaling was going to become history, and it was a sad day, you know,” Heberley said at the time.
“We knew that the Japanese and Russians had got in and slaughtered the pod of whales that were feeding the New Zealand coast. We knew that by the numbers that we had spotted coming through Cook Strait, that something had happened.”
Supplied / Claire Garrigue
By 1964, New Zealand’s whaling industry had made its last catch, and sentiment began to shift.
New Zealand voted in favour of an international moratorium that banned commercial whaling from 1986.
Greenpeace oceans campaigner Juan Parada is proud of that transformation, but feared New Zealand had lost its conservational edge in the decades since.
“It’s clear that New Zealand had a big turnaround, from being a whaling nation we became vocal defenders of whales, and that’s something to be really proud of,” he said.
“Our point of shame really is to be the last country that is bottom trawling in the South Pacific high seas.”
Parada said New Zealand’s reluctance to give up bottom trawling presented a massive threat to whales.
“When bottom trawlers drag their heavy nets on these delicate habitats, the entire ecosystem is wiped out,” he said.
“I definitely think that bottom trawling is the worst thing that we’re doing. It would be really easy to stop, really, and that would make a huge difference for the ocean.”
Carroll said only a couple of generations had passed since whaling was outlawed, and she hoped to track the whales’ changing behaviour in the decades to come.
“The fact that we’re seeing this shift now, that means if we continue to monitor this population, which is relatively small and easy to monitor, it means we can see this change in behaviour through time,” she said.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand