Risks & Threats
Entanglement and ingestion of marine debris
The Australian Government’s 2009 Threat Abatement Plan on Impacts of Marine Debris on Vertebrate Marine Life identifies six cetacean species as at risk. These are all mysticetes and include the four gulp-feeding oceanic rorquals that make up the rest of the genus Balaenoptera along with minke whales. Dwarf minke whales are considered vulnerable to entanglement in fishing gear and ingestion of marine debris. In August 2001, a stranded Bryde’s whale in Trinity Inlet, Cairns, was found to have several metres of plastic materials impacted in its gut. This incident highlights the vulnerability of rorqual whales to ingestion of marine debris.
The Great Barrier Reef Vulnerability Assessment describes a range of potential impacts to whales from rising sea surface temperatures and ocean acidification, which may impact on prey availability and migratory patterns. The feeding grounds of the Great Barrier Reef population of dwarf minke whales are still unknown, however it is possible that they migrate to the high latitudes of the sub-Antarctic and Antarctic to feed during the summer. The GBR Vulnerability Assessment notes that changes in Antarctic and temperate ecosystems associated with climate change may have profound impacts on whales by fundamentally altering these ecosystems.
At present there appears to be no commercial whaling for dwarf minke whales and the Japanese ‘scientific’ whaling program has not specifically targeted them since 1993. If full commercial whaling were to resume in the Southern Ocean it is likely that dwarf minke whales would be at risk.
We have observed scars on dwarf minke whales that appear to have been caused by traditional harpoons, suggesting that these whales have visited South Pacific island nations that engage in traditional hunting (see our life history page for more information).
There are substantial gaps in our knowledge of the biology, behaviour and life-history of dwarf minke whales that need to be addressed in order to determine the extent of human-related threats, both within and outside the Great Barrier Reef Marine Park.
Dwarf minke whales, currently regarded as an undescribed subspecies of Balaenoptera acutorostrata, are listed as a migratory species protected under the EPBC Act but with no population estimates available because of “insufficient data” (Australian Action Plan conservation status “no category assigned, because of insufficient information”) (Bannister et al., 1996). The IUCN redlist categorisation of Least Concern refers to all subspecies of B. acutorostrata and is based on estimates from parts of the range in the northern hemisphere. A separate category is not assigned to dwarf minke whales.
The Minke Whale Project considers the following research questions to be of a high priority for the conservation and management of dwarf minke whales:
- What is the size of the GBR dwarf minke whale population?
- What are the whales’ migratory patterns?
- What are the longer-term effects of SWW interactions on individual dwarf minke whales’ behaviour?
- What is the significance of the whales’ aggregation in the GBR?
The Minke Whale Project will continue to work in collaboration with the tourism industry, management agencies, conservation groups and other stakeholders in monitoring the sustainability of the GBR swim-with-whales activity and aims to address these ‘big picture’ questions through expanded research efforts and collaborations.