Australia's population of Southern right whales has experienced substantial growth since the late 1970s when they began to recover from whaling, but a new study reveals troubling signs in their numbers visiting Australia's coastline - potentially marking a turning point in the population's recovery.
Published in the journal Global Change Biology , the study raises concerns about the recovery of the species, which was driven to near extinction by historical whaling.
"From the 1800s, Southern right whales were the preferred quarry of whalers and by the time whaling of this species was banned, only a few hundred animals remained worldwide," said lead author, Anne Grundlehner, who is a postgraduate researcher at the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS).
"Despite a substantial increase in Southern right whale numbers in Australia since the 1970s, their population recovery seems to have recently stalled at a level far below the pre-whaling levels."
Southern Right Whales are migratory baleen whales. Each year they visit shallow coastal waters of Australia, New Zealand, South America and South Africa. Sheltered waters in these regions provide a safe haven for females to give birth and nurse their calves.
"The southwest coast of Australia hosts one of the world's few Southern right whale populations that appeared to recover well after whaling. We knew their numbers were increasing since the 1970s but given recent signs of slowing birth rates in Southern right whale populations elsewhere, it was important to re-assess how their recovery was progressing in Australia," Grundlehner said.
"We analysed 49 years of aerial survey data from 1976 to 2024 stretching across more than 2,000 kilometres of coastline, available from long-term monitoring efforts initiated by the late John Bannister. And we were very concerned to find not only slowed growth in births in this population, but an actual halt and what looks like the onset of a decline.
"We found that annual births began to stagnate around 2016 and observed declining trends in the number of animals visiting the coast. While the number of mothers and their calves that visit the coast has only shown a minimal decline to date, the number of other individuals that visit has dropped by 66% between 2011 and 2024," she said.
IMAS researcher and co-author, Associate Professor Stuart Corney said that the population is still far below pre-whaling levels.
"Because this species is considered endangered in Australian waters, understanding the causes behind the stalling population growth will be critical to inform appropriate conservation actions.
"We don't yet understand the exact causes for their population growth stalling, but the Southern Ocean ecosystem must have substantially changed in response to the large-scale removal of whales in the past."
Grundlehner said "the reality is that despite the removal of whaling pressure, the present ecosystem may not be able to support the thriving population of Southern right whales we saw in the past.
"Meanwhile, climate change and other human impacts are putting pressure on marine ecosystems, which could also be playing a role."
The study was conducted in collaboration with researchers from IMAS and the Australian Antarctic Program Partnership (AAPP) at the University of Tasmania, and the Australian Antarctic Division (AAD). Aerial surveys were led by the Western Australian Museum in collaboration with Murdoch University and AAD. Surveys were funded by various Australian Government agencies and environmental programs, including the Australian Marine Mammal Centre and in recent years, the National Environmental Science Program (NESP) through the Marine Biodiversity Hub and Marine and Coastal Hub.
Cover image: Southern right whale mother
and calf off WA. Photo: Joshua Smith
