In a boost for the conservation of one of the world's most elusive and least-understood whale species, researchers analysing more than 18 years of underwater acoustic recordings collected off northwest Australia have discovered that Omura's whales are most likely to be found in warm, food-rich waters.
The findings provide new insights into the habitat of one of the world's most mysterious whale species, which is listed as Data Deficient on the International Union for Conservation of Nature Red List, meaning there is currently insufficient information to accurately assess its risk of extinction.
Researchers from Curtin University's Centre for Marine Science and Technology in the School of Earth and Planetary Sciences analysed nearly two decades of underwater acoustic recordings collected across 35 sites spanning about 1800 kilometres of ocean off northwest Australia between 2005 and 2023.
The team detected Omura's whale calls throughout the year but found the whales were more likely to be present from September to May when waters were warmer.
Lead author Curtin PhD student Ciara Browne said the findings shed light on the environmental conditions favoured by a species that is rarely seen in the wild.
"Omura's whales are notoriously difficult to study because visual sightings are rare, so listening for their calls provides an important way of understanding where they occur," Ms Browne said.
"We found they were more likely to be acoustically present in warmer waters where ocean conditions create rich feeding opportunities.
"The whales were detected year-round, but their distribution shifted with the seasons, with a greater likelihood of presence during the warmer months."
The researchers found the whales were associated with sea surface temperatures above 27.5°C, stronger winds and higher levels of chlorophyll-a, an indicator of microscopic marine life that forms the base of the ocean food web.
The study also found the whales' presence increased about a month after periods of higher chlorophyll-a, suggesting they may respond to increases in productivity and prey availability that follow changes in ocean conditions.
Co-author Professor Christine Erbe, Director of the Centre for Marine Science and Technology, said understanding where Omura's whales occur was an important first step towards protecting them.
"Omura's whales were only recognised as a distinct species in 2003 and because we know so little about them, identifying the habitats and ocean conditions they favour is vital for future conservation efforts," Professor Erbe said.
"Our findings provide an important baseline for understanding how Omura's whales use Australian waters and how they may respond to environmental change.
"This knowledge can help inform marine planning and improve our understanding of potential impacts from activities such as shipping, offshore industry and other sources of underwater noise.
"The research can also help improve our understanding of the impacts of future climate change on whale behaviour."
Western Australian Marine Science Institution (WAMSI) CEO Dr Luke Twomey said the research provided valuable evidence to support marine planning and management.
"Understanding where marine species occur, and the habitats and environmental conditions they rely on, provides decision makers with the evidence they need to make informed decisions about the future of Western Australia's marine environment," Dr Twomey said.
"Long-term datasets such as these are particularly valuable because they help reveal patterns that would otherwise remain hidden, improving our understanding of marine ecosystems and supporting planning where environmental values and human activities intersect."
The study, 'Warm, productive waters shape the habitat of vocalizing Omura's whales in northwest Australia' (https://onlinelibrary.wiley.com/doi/10.1111/mms.70279) was published in Marine Mammal Science and follows three other recent studies on the Omura's whale, led by Ms Browne.
