Although Australia’s population of southern right whales (Eubalaena australis) experienced substantial growth since the late 1970s when whaling saw it driven to near extinction, a new study published recently in the journal Global Change Biology has raised concerns the recovery of the species has stalled.
Lead author Anne Grundlehner, marine ecologist and data scientist, and a postgraduate researcher at the University of Tasmania’s Institute for Marine and Antarctic Studies, said southern right whales were the preferred quarry of whalers because of their meat and high oil content. By the time whaling of the species was banned, it was estimated only a few hundred animals remained worldwide.
“Despite a substantial increase in their numbers in Australia since the 1970s, the population recovery of southern rights seems to have stalled at a level far below the pre-whaling levels,” Grundlehner said.
Southern right whales are migratory baleen whales that visit the shallow coastal waters of Australia, New Zealand, South America and South Africa each year. The 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 had increased since the 1970s, but given recent signs of slowing birth rates in their populations elsewhere, it was important to re-assess how their recovery was progressing in Australia,” she explained.
Researchers analysed 49 years of aerial survey data from 1976 to 2024 that stretched across more than 2000 kilometres of coastline. The data was available from long-term monitoring efforts initiated by the late John Bannister, a leading expert on whales who authored several books about the species. Grundlehner said the team was concerned to find not only slowed growth in births in the 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 dropped by 66 per cent between 2011 and 2024,” she said.
Co-author Stuart Corney, Associate Professor and senior lecturer in oceans and cryosphere at IMAS, said the population was still far below pre-whaling levels, but because the species was considered endangered in Australian waters, understanding the causes behind the stalling population growth was 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,” he said.
Despite the removal of whaling pressure, Grundlehner said the present ecosystem may not be able to support the thriving population of southern right whales that was seen in the past, and that climate change and other human impacts could also be playing a role in putting pressure on marine ecosystems.
The study was conducted in collaboration with researchers from IMAS, the UTAS Australian Antarctic Program Partnership, and the Australian Antarctic Division.
Anne Layton-Bennett
