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NZ’s whales almost killed off – Expert Reaction

Posted in Science Alert: Experts Respond on March 17th, 2016.

Relentless whaling decimated New Zealand’s southern right whale population to just a fraction of pre-whaling numbers by the start of last century, finds a new study.

An international team of researchers combined historical records from whaling logbooks with modern genetic data to determine that around 30,000 southern right whales swam in New Zealand’s waters before 19th century whalers arrived.

By 1925, whaling had reduced this population to just an estimated 110 individual whales.

“We find that the population declined rapidly following early 19th century whaling, and came close to extinction in the early 20th century, with less than 20 mature females estimated as surviving the bottleneck,” write the authors.

Recovery of the whales has been slow; the researchers estimate that the current number of southern right whales in New Zealand waters is only 12 percent of the pre-whaling population.

The study is published in the Royal Society journal Open Science, and was led by Prof Scott Baker from Oregon State University who is also Adjunct Professor of Molecular Ecology at the University of Auckland.

The SMC collected the following expert commentary.

Dr Rochelle Constantine, Marine Mammal Scientist, School of Biological Sciences, University of Auckland, comments:

“We came very close to losing the southern right whale from New Zealand waters, with at best, only a few hundred remaining after an intense and devastating period of commercial whaling followed by a brief hunt by Soviet whalers just as the population was beginning to make a comeback. The fact that they spend their winter months in the waters of the remote sub-Antarctic Auckland Island was perhaps the main reason why they have slowly been recovering from the estimated 15-20 mature females that remained.

“There are very few threats to them at the sub-Antarctics which allowed them to breed and calve in a largely undisturbed environment.

“Southern right whales are increasingly being seen around the New Zealand mainland, most frequently in Southland but every few years we see whales up in the Northland region. We know from their DNA and photo-identification that these whales are often also seen in the sub-Antarctics so they are slowly expanding their range again which is encouraging.

“They are vulnerable to vessels strike and too much attention when near the mainland coast – a few years ago we had a mother-calf pair and the calf was hit by a small boat that left propeller cuts across its back. These whales will often come close to shore and will approach boats so it’s easy to harass them or injure them. We advise people the give them room so they can safely swim throughout all of our waters and hopefully recover to their pre-exploitation numbers estimated to be ~29,000 – 47,000 whales.”

Dr Will Rayment, Department of Marine Science, University of Otago, comments:

“This analysis highlights the devastating impact that humans had on whale populations throughout the world. Southern right whales would have once been a very common sight in New Zealand’s coastal waters, but suffered a precipitous decline due to two decades of intense hunting in the 19th century.

“The study reveals just how close the population came to being wiped out altogether.

“We should be very thankful that a tiny remnant population remained and has slowly been increasing in numbers since the ban on commercial whaling. But we should also be mindful that as the population recovers, southern right whales will increasingly be impacted by human activities. Elsewhere in the world, right whale populations suffer modern day impacts from a range of sources, including fishing, shipping and pollution of their environment.

“We need to heed these lessons if southern right whales are to recover to anything near their former abundance in New Zealand waters.”

Dr David Thompson, Ecologist, NIWA, comments:

“The research by Jennifer Jackson and colleagues is both sophisticated and timely. For the first time, we have a robust estimate of pre-whaling abundance of southern right whales in the New Zealand region specifically, as opposed to across the whole southern hemisphere more generally, with which to compare to the recovery of the species.

“Southern right whales came perilously close to regional extinction and the New Zealand population remained  extremely small for decades. Although Jackson’s work shows that the current New Zealand population is only about 12 percent of pre-exploitation levels, they also suggest that in 50 years’ time this value could be as high as 95 percent.

“Given that whales are now fully protected in New Zealand, I would like to think this prediction proves accurate and that I’m not too old to see southern right whales spending their winter in Wellington harbour in the not too distant future.”

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