Climate squeezing Australia’s southern right whales
The southern right whale has long been heralded as a conservation success story.
The species was brought back from the brink of extinction after being hunted relentlessly by commercial whalers in the 19th and 20th centuries; The global population has slowly recovered, rising from 300 to 15,000 today.
But researchers are now finding evidence that population growth is slowing.
A study conducted by Flinders University and Curtin University has found a significant decline in the reproductive success of whales calving off the coast of South Australia at the Head of the Great Australian Bight over the past decade.
Lead author of the study, academic and Director of Current Environment Claire Charlton, explained that based on 30 years of observation of threatened marine mammals when they return to breeding, it was discovered that whales take longer breaks between births.
“If they are calving every four years instead of every three years, this could have a significant impact on their population over time,” he told AAP.
As in similar studies of South American and Southern African populations, shrinking sea ice cover triggered by climate change, marine heatwaves, changing ocean conditions and declining prey stocks were found to coincide with Australian whales giving birth less frequently.
Dr Charlton said the latest study, funded by the Minderoo Foundation, filled a gap in research and confirmed that whales frequenting Australian waters followed similar patterns to animals breeding off Argentina and Africa.
“This means that there is truly a species-wide southern hemisphere effect occurring.”
Southern right whales are a migratory species that move from their southern ocean foraging grounds to the same coastal breeding grounds between May and October each year.
During the feeding months, whales prey predominantly on krill, a small crustacean that depends on Antarctic sea ice to survive and reproduce.
More greenhouse gases in the atmosphere from burning fossil fuels are warming the ocean, causing the ice around Antarctica to melt; Sea ice coverage has been consistently below average since 2015.
“If there is less ice, less krill is produced,” Dr Charlton said.
“So there is less food for the whales, and if they have less food then they will probably be less fatty and healthier.
“And this can affect their body condition and ability to reproduce.”
Other studies have shown that the species is increasingly feeding in mid-latitude waters; This suggests they may be consuming less krill and more copepods.
This prey resource is also thought to be under threat from marine heatwaves linked to climate change.
Ship strikes, noisy underwater environments, entanglements in fishing equipment and coastal development are also thought to put pressure on marine mammals.
Dr Charlton said southern right whales were easy to study and provided a window into the health of the southern ocean.
The animals approach the shore and have unique fingerprint-like patterns on their heads that allow them to be easily identified.
“These are a direct link between what’s happening in Antarctica and what we can see in our backyards,” Dr Charlton said.
Studying whales can provide information about how krill and other species that depend on Antarctic sea ice are faring.
