Humpbacks really gorge themselves on krill in the Southern Ocean, because they eat much less when they are migrating to their GBR breeding grounds. They get much fatter than they are when people see them on the Ozzy Eastcoast. Photo by David Donnelly, under permit
As you read this, thousands of fat humpback whales are converging on the Australian East Coast from across the Antarctica.
Fattened up and sadly parted from the krill on which they had gorged themselves all summer, a large chunk of the Australian East Coast population is still in the Southern Ocean south of NZ. On the move since the days grew shorter and the ice started coming back and doing about 900kms a month, they are still on the first leg north from their Antarctic feeding grounds in the Ross Sea.
Not far ahead of them, more whales are crossing the Tasman Sea from New Zealand to Tasmania or Eden in NSW.
Others are coming straight up from the ice-edge to Tasmania, while still more are coming over from feeding grounds against the ice south of Western Australia.
The migration patterns are complicated. Not like the Gold Coast light rail – there’s more than one route.
Not long ago, scientists thought the whole east coast humpback population spent summer in the Antarctic’s Ross Sea, but through satellite and genetic tagging and song mapping they have found out that the Gold Coast’s favourite marine mammal has feeding grounds much further west than they originally thought.
“We are discerning new things about the population all the time,” Melbourne-based whale researcher Dr Natalie Schmitt said.
Dr Schmitt, who just finished her PhD on “Australian Humpback Whale Population and Structure” with the Australian Marine Mammal Centre, said as the East Coast population grows their structure and migration is more varied and staggered.
She spent a summer in the Ross Sea researching the humpbacks and couldn’t get over how fat they were down there.
The shape the whales are in when they are breaching for the tourists on the Gold Coast is very different to the big porky condition the marine over-eaters get into down there.
“Like chalk and cheese. They are just enormous.”
She was also fascinated by how much they were attracted to the research ship she was on in the Ross Sea.
The researcher had started by using little boats to get close to the whales to take skin biopsies, but the whales were so interested in the ship she found she didn’t need to.
“They were really attracted to the ship. Play around… Roll around the ship… So we ended up taking our biopsy samples off the ship’s hull.”
From the genetic tagging she did there, Dr Schmitt made a significant discovery that the East Coast humpbacks aren’t the only whales that use the Ross Sea and Belleny Islands feeding grounds as previously thought. They share it with whales from the South Pacific Population especially New Caledonia. She also said there was very strong evidence that the South Pacific herd sometimes joined in with the East Coast population to hug the Australian coast, so she’s hoping for funding to find out.
In summer the Southern Ocean that circles Antarctica is a wild changeable place… High pressure systems with total stillness and acid blue skies… The bedlam of 100 knot blizzards, mountainous seas and shifting ice… Endlessly light… Penguins… Pods of killer whales like puppy dogs, porpoising quickly in a hurry to get somewhere… Graceful minke whales rolling over to look at the plane flying above them… Huge flocks of snow petrels and albatross shepherding the big orange icebreaker Aurora Australis… Rare sightings of super groups when up to 40 whales of different species can be seen in all directions… And humpack whales feeding like there’s no tomorrow…
CSIRO statistician Dr Natalie Kelly has worked with the Australian Antarctic Division for seven years and has spent four summers at the Australian Antarctic base – Casey Station.
Her research involves aerial surveys of minke whales from a spotter plane. She said saw a humpback down there every few days.
Humpbacks go to the Antarctic purely to eat for four months, she said, because they don’t always have the opportunity when they are on their eight month round trip to the Great Barrier Reef to calf.
“The go beserk.
“Go bananas.
“Feed as much as they can, just over a ton of krill a day.”
“Eat!
“That’s it. That’s all they do, except for staying out of the way of the big killer whales.”
“It’s classic baleen feeding. Come in, turn on their side, take a big gulp of water and krill and push the water out through the baleen,” Dr Kelly said.
The East Coast humpback population is going up by 10 percent a year so they are “not food limited”.
Humpbacks tend to feed where dense balls of krill mass up against the ice. They eat mostly near the surface but new research done on the South American population near the Antarctic Peninsular revealed they’ll dive up to 200m compared to minkes’ 300m for krill, but only if they need to. And they don’t go as far into the ice as minkes.
She called humpbacks the “can can dancers of the whales.”
Dr Kelly said when the “humpies” are migrating they’ll only eat when a big ball of fish or krill is put in front of them, so the opportunities are sporadic.
However, there’s very good evidence that some of the East Coast humpback population aren’t making the migration south to the Antarctic every year.
Instead of migrating, they sometimes stay where there is enough food to sustain them, south and east of Tasmania and around NZ, Dr Schmitt said.
“We know they feed off Eden in NSW. They don’t need to go down to the feeding grounds if they don’t have to,” she said.
They are a lot more “fickle” than previously thought, with their choices mostly depending on ocean currents and food.
There were several cases lately of detours from the norm. For example a humpback was sighted on March 23 near Kiama north of Jervis Bay which is extremely early in the migration cycle. It’s not known if he summered on the east coast or migrated from the Antarctic early.
Cetacean researcher David Donnelly said he saw a photo recently of an East Coast humpback taken in an Antarctic feeding ground south of Western Australia, much further west than East Coast humpbacks have been previously documented.
The whale scientist had seen the humpback named Bladerunner several times before. The female was easily identifiable with very distinctive scars from devastating injuries inflicted by a ship’s propeller about 10 years ago.
“She’s very shy of boats for obvious reasons,” he said.
“There’s no question it was her.”
More is being revealed all the time about humpbacks, but there is so much that humans don’t know about these animals.
As Dr Schmitt said, “The plot thickens.”