A mother’s love – the whales that go months without food to raise their calves
A RECENT STUDY has found female southern right whales undergo dramatic physical changes after calving – losing significant body mass to ensure the survival of their calves.
The study – undertaken by Murdoch University’s Cetacean Research Unit (MUCRU) and sponsored by WWF – was conducted using drones at the Head of Bight in South Australia, an important nursery where the endangered species aggregates from late May to October each year to give birth and raise their calves.
It’s part of a larger project aiming to investigate how behavioural disturbance – from sources such as climate change and shipping traffic – can accumulate over time and affect the health and body condition of the whales and in turn, how that can affect reproduction and population size.
“If we figure out that link then we can look at the conditions of animals in different years and predict the consequences of both environmental and human factors at a population level,” said Dr Fredrik Christiansen, a research fellow with MUCRU.
Video courtesy WWF / MUCRU
And the findings were significant – researchers found female southern right whales abstained from eating for the first four months of their calves’ life, relying solely on fat stores to not only survive themselves, but feed their calf – with some losing as much as 43cm in width over the three-month period.
“Although we knew the females were not feeding during breeding season, quantifying the cost of reproduction for these animals – it’s really been an eye-opener,” Fredrik said.
“That they can invest so much energy into calf growth and do all this based on body reserves alone – that’s pretty amazing.”
The cost of raising calves
Each year, the endangered whales migrate to Australia’s southern coast from Antarctic feeding grounds to breed and calve, with over 80 mother and calf pairs resting in the Head of Bight’s protected waters this year.
Fredrik says when the females first arrive after months of building up fat stores, they are significantly larger than the males, but after calving, their lower-abdomen dwindles, often to the point that their spinal cord begins to show.
“It’s their reproduction strategy – they’re called capital breeders,” Fredrik explained.
“When their calves are born they are about 5m, while the female is 14m – they’re very thin and then throughout the season they get longer and much fatter – really robust.”
“It’s really nice – you see them going from this small scared creature to this brave creature going and checking out other whales.”
Bella lost 31 centimetres in width in 63 days. Pictured on July 3 (top) and September 4 (bottom). (Image: Fredrik Christiansen)
With such a high reproductive cost, the findings suggest females in poorer body condition may have to reduce their energy investment in their calves to avoid jeopardizing their own health and survival.
A well-known population
In 1991, the Great Australian Bight Right Whale Study began – which is currently being led by Curtin University – gathering important information on the biggest aggregation of the baleen whales in Australia.
“The long-term monitoring program is really important as it informs us about the size and trends of the population,” Fredrik said.
“It’s a well-studied area, so we know a bit of its history – how old they are, how many calves they’ve had, when they had their last calf etc.”
Southern right whales were almost hunted to extinction in the 19th century, however since hunting ceased, Fredrik says the main threats to the whales today come in the form of human disturbance.
“We’re lucky along the south coast of Australia that there isn’t a lot of shipping traffic – other populations outside of Australia are not doing so well,” Fredrik explained.
Due to the huge cost of reproduction, female whales only calve at three to four year intervals, and Fredrik hopes that they will be able to raise funds to return to the area for the next three years to monitor the females that did not calve this year.
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