Distribution and Seasonality of the Omura’s Whale (Balaenoptera omurai) in Australia Based on Passive Acoustic Recordings
Centre for Marine Science and Technology, Curtin University, Perth, WA 6102, Australia
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Author to whom correspondence should be addressed.
Animals 2024, 14(20), 2944; https://doi.org/10.3390/ani14202944
Submission received: 4 September 2024
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Revised: 26 September 2024
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Accepted: 10 October 2024
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Published: 12 October 2024
Simple Summary
The Omura’s whale was first described in 2003 and is currently listed as ‘Data Deficient’ on the IUCN Red List. Distributed globally in tropical waters, there remains an absence of knowledge on the species’ behaviour and ecology, especially in Australian waters. This study utilised historic acoustic data to provide the first wide-scale investigation into Omura’s whale distribution and seasonality around Australia, including any potential migratory movements they undertake. We identified the species’ acoustic presence on the east coast of Australia for the first time and its seasonal presence on the west coast. Unlike most baleen whales which migrate between the poles and the equator annually with separated feeding and breeding grounds, the Omura’s whale inhabits certain regions around Australia for all months of the year. Currently, the Omura’s whale is not listed in any management or conservation policies in Australia so the description of when and where they are inhabiting will provide the first steps in developing these policies for the species in Australia, which is particularly important given that the identified distribution of the species crosses over with a lot of offshore industry operations.
Abstract
The Omura’s whale (Balaenoptera omurai) is one of the most recently described species of baleen whale. Initially known only from stranding and whaling specimens, it has now been identified in all ocean basins excluding the central and eastern Pacific. Unlike most baleen whales that migrate between the poles and the equator seasonally, the Omura’s whale is known to inhabit tropical to sub-tropical waters year-round. In Australian waters, there remain fewer than 30 confirmed visual sightings over the past decade. However, based on acoustic records, the Omura’s whale has been detected off areas of the northwest coast of Australia year-round. This study utilises passive acoustic recordings from 41 locations around Australia from 2005 to 2023 to assess the distribution and seasonality of the Omura’s whale. The seasonal presence of Omura’s whale vocalisations varied by location, with higher presence at lower latitudes. Vocalisations were detected year-round in the Joseph Bonaparte Gulf in the Timor Sea, and near Browse Island and Scott Reef, in the Kimberley region. In the Pilbara region, acoustic presence mostly peaked from February to April and no acoustic presence was consistently observed from July to September across all sites. The most southerly occurrence of Omura’s whale vocalisations was recorded off the North West Cape in the Gascoyne region. Vocalisations similar but not identical to those of the Omura’s whale were detected in the Great Barrier Reef. The identified seasonal distribution provides valuable information to assess environmental and anthropogenic pressures on the Omura’s whale and to aid in creating management and conservation policies for the species in Australia.
Keywords:
distribution; seasonality; Omura’s whale; passive acoustics
