By Sarah-Jane O'Connor 16/03/2016

It took less than 150 years to decimate a population of the southern right whales around New Zealand and the species has yet to recover beyond a fraction of the pre-whaling size, genetic and historic data shows.

Researchers at Oregon State University – including Scott Baker who is an adjunct professor at the University of Auckland – combined historic information on hunting and sightings with genetic data to estimate the abundance of southern right whales before whaling.

whaleTheir results, published today in Royal Society Open Science, suggests a pre-whaling population in New Zealand waters of 28,800 to 47,100 was knocked back to about 15 – 20 mature females between 1914 and 1926, or a total population of less than 150 whales.

A 2009 estimate put the current population at about 2200, recovering at about 7% a year.

Right whales, Eubalaena spp., were particularly impacted by whaling because they were an easy catch. The slow swimmers have a high fidelity to certain bays for calving, so they made an easy and predictable target, and when dead they float, making for easy collection.

Southern right whales, Eubalaena australis, spend winters feeding in oceans around South Africa, Argentina, South Australia and in New Zealand’s Subantarctic oceans. Before European whalers arrived, southern right whales – called Tohoroā by Māori – were common around New Zealand waters.

But they were the target of whalers from about 1791 and between 1827 and 1980 an estimated 35,000 to 41,000 southern right whales were killed in New Zealand waters. By the early 20th Century, the whales had virtually disappeared from New Zealand seas.

The authors said a conservative estimate put the current population at about 12% of the pre-whaling abundance with slow annual growth meaning the numbers would not recover for at least another 50 years.

University of Otago’s Dr Will Rayment, from the marine science department, said the study highlighted 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.”

He said it showed just how close the population came to being wiped out entirely and that it was lucky a tiny remnant population remained, which had been slowly growing since commercial whaling was banned.

“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,” he said.

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

University of Auckland marine mammal scientist Dr Rochelle Constantine said the devastating period of commercial – followed by a brief, illegal hunt by Soviet whalers in the 1960s – brought New Zealand very close to losing southern right whales from its waters.

“The fact that they spend their winter months in the waters of the remote Subantarctic 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 Subantarctics 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 Subantarctics so they are slowly expanding their range again which is encouraging.”

Dr Constantine said the whales were vulnerable to vessels hitting them and too much attention as they started coming back to the mainland coasts. She advised people to give them space so they could travel safely through our waters and hopefully recover back to the pre-hunting numbers.