The feeding zone stretched over 2000km east to west, and about 1000km north to south. Key feeding areas were near the Subtropical Front, a boundary between warm, salty subtropical waters and cooler Antarctic waters.
Globally, the population of southern right whales dwindled to as few as 400 individuals early last century because of whaling – but now, there are thought to be about 15,000.
Dr Emma Carroll, associate professor at the University of Auckland and senior author of the study, said the feeding zone they identified wasn’t just important for whales – other animals like seabirds, sharks, and seals relied on it too.
Now, scientists are calling for the region to be protected under the High Seas Treaty.
Also known as the Biodiversity Beyond National Jurisdiction Agreement, this treaty would let nations propose areas where fishing and other activities were limited, and would come into force once more nations had signed up.
According to the alliance’s website, 139 countries have signed the High Seas Treaty, but only 52 of a required 60 have ratified it. New Zealand is among those yet to do so.
Two whales just ‘surfing the ocean currents’, study shows
As well as tracking those 25 whales that identified as treating New Zealand waters as their home, the study also tracked 15 that bred and had their young in the waters around Australia.
Another interesting outcome of the study, Carroll said, was discovering two of the whales in the Australian group that “looked like they [were] surfing the ocean currents”.
“The whales feed around what are called eddies, which is like a circular, rotating mass of water. Imagine the water going round your plughole, but without the plug hole.”
The scientists were able to study how much the whales were swimming, and how much they relied on currents to move about.
“It looks like these whales weren’t actively swimming, they were just riding the currents round in circles.”
These eddies also aggregated prey, Carroll said. “I just have this mental image of them basically just sitting there with their mouths open, while the prey comes to them.”
They also found the Australian whales had more diverse foraging grounds than their New Zealand neighbours, leading the scientists to wonder whether they would be better at adapting to the inevitable shifts in prey locations because of climate change.
“If there’s a bad year around Antarctica, they can go further east and have a buffer,” Carroll said. “Having a diverse range of places to go to eat is good for any animal, particularly under climate change.”
Why weren’t New Zealand whales doing the same? “It could be a remnant of whaling,” Carroll said. “We think there’s an element of learning from each other about where to go to feed. If you lose animals that know about a good place to feed, you lose that knowledge from the population.”
- RNZ
