South Australian marine ecosystems are facing a critical tipping point as dolphin mortalities reached a 12-year high in 2025. Data from the South Australian Museum and government reports indicate that at least 70 dolphin carcasses were recovered last year, with an additional 20 reported through the first five months of 2026. Experts attribute this spike to a combination of a devastating Karenia cristata algal bloom and a persistent marine heatwave that has disrupted local food chains.
The Link Between Algal Blooms and Dolphin Emaciation
The primary driver behind the recent surge in dolphin deaths appears to be a severe shortage of prey. According to Dr. Catherine Kemper, a former curator of mammals at the South Australian Museum, many dolphins found in Gulf St Vincent were severely emaciated. Research shows that populations of southern calamari—a staple food source for common dolphins—dropped to 80% below baseline levels in Gulf St Vincent and Spencer Gulf during the height of the bloom.
While dolphins do not possess gills and are not directly poisoned by the algae in the same manner as fish, the indirect impact on their food supply is clear. A spokesperson for the South Australian Department for Environment and Water confirmed that weight loss in recovered animals suggests the bloom triggered a ripple effect through the marine food web. This pattern of chronic weight loss has been observed across multiple species, including seals, turtles, little penguins, and various bird populations.
Did you know?
The 2025 mortality rate for dolphins in South Australia is the highest recorded since 2013, a year characterized by a significant outbreak of morbillivirus among cetaceans.
Comparing Historical Mortality Data
Dr. Kemper, alongside dolphin researcher Dr. Mike Bossley, recently presented findings at the Australian Mammal Society and Australasian Bat Society conference. Their analysis compared museum data spanning from 2001 to 2024 against recent government-commissioned postmortems. The comparison highlights a shift in mortality drivers:
- 2013 Outbreak: Primarily driven by morbillivirus, a disease-based event.
- 2025–2026 Spike: Primarily driven by environmental stressors, including food scarcity and marine heatwaves.
Dr. Bossley notes that while dolphins regularly face threats from boat strikes, fishing gear entanglement, and shark predation, the high frequency of emaciated carcasses in 2025 points toward a reduction in food availability rather than isolated accidents.
Future Challenges for Marine Mammal Monitoring
The ability to track these trends is currently compromised by administrative changes. Dr. Kemper highlighted that the 2023 dissolution of the South Australian Museum’s long-standing marine mammal postmortem program has hindered scientific analysis. Both she and Dr. Bossley are calling for the reinstatement of systematic postmortems to better understand the long-term impacts of climate-driven events like marine heatwaves on local wildlife.
Citizen science remains vital. Reports from the public continue to assist government staff in monitoring marine health. If you encounter injured or deceased marine life in South Australia, contact the Department for Environment and Water to ensure the data is recorded.
Frequently Asked Questions
Are dolphins dying directly from the algal bloom?
No. According to the South Australian Department for Environment and Water, dolphins are likely dying due to the indirect effects of the bloom, which has decimated their prey populations, leading to severe emaciation.
Why were 2025 mortality numbers so high?
The spike is attributed to the combination of the Karenia cristata algal bloom and a marine heatwave that began in September 2024, both of which severely disrupted the marine food chain.
What is being done to track these deaths?
Researchers are using historical museum data and ongoing reports from citizen scientists, though experts are calling for a return to formal, systematic postmortem programs to improve the accuracy of environmental impact assessments.
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