Drone pictures reveal the toll of raising young calves on whale mothers

New drone pictures reveal that a southern right whale mother named Scooter dramatically shrank in width – by 43 centimetres in just two months – as she fattened her calf.

Other mothers experienced a similar loss in condition, becoming so skinny their spinal cords began to show.

Murdoch University researchers, sponsored by WWF-Australia, are using drones for the first time to do a health check on southern right whales, which are making a comeback after nearly being hunted to extinction.

WWF-Australia whale researcher Chris Johnson said the dramatic loss of condition that whale mothers undergo means they are especially vulnerable to emerging threats.

"These include getting tangled in marine debris, disturbance from oil and gas development, and global ocean warming which could reduce their food supply in Antarctica," he said.

"That's why this project is so important. If the condition of the whales changes in the future it could be a sign that human activities are having an impact.

"Nurturing a calf is already tough enough for the mothers without humans adding to the pressure," Mr Johnson said.

Southern right whales journey thousands of kilometres from their Antarctic feeding grounds to Head of Bight, South Australia to give birth. They stay for about three months to fatten their calves before returning to Antarctica.

For about four months they do not eat and rely solely on their fat stores.

Scooter measured 2.85 metres across on July 3 and only 2.42 metres across on September 4.

Another mother, Bella, went from 2.49 metres across to 2.17 metres, losing 31 centimetres of width in the same period of time.

In those two months, Bella's calf grew from 5.84 metres long to 7.67 metres long. Southern right whale mothers must quickly fatten their calves so they are strong enough for the long journey back to Antarctica.

Murdoch University researcher Dr Fredrik Christiansen said the toll on southern right whale mothers meant they could only give birth every three to four years.

"When they arrive they have significant fat reserves, they are wide all along their body. When they leave they look like giant tadpoles. They have a head which is still big and robust, but the rest of the body is skinny and you can even see the spinal cord showing up," Dr Christiansen said.

"There is still so much unknown about whales. My long-term goal is to understand how human impacts, both lethal and sub lethal, affect behaviour, health, and ultimately the recovery of whale populations," he said.

Murdoch University's Professor Lars Bejder said there was much to learn.

"Southern right whales are recovering but nowhere near to the same extent as humpback whales. And we don't really know why and that's one of the big questions we're hoping to answer," he said.

Murdoch University collaborates with Curtin University and the Great Australian Bight Right Whale Study which has recorded individual life histories for many of the whales at Head of Bight, dating as far back as 1991.