The number of dolphin deaths in South Australia spiked dramatically in 2025 after a devastating algal bloom decimated their food sources, according to long-term data. At least 70 carcasses of common and bottlenose dolphins were found across SA last year, with 20 more reported in 2026, including the beloved Port River dolphin known as Zoom. Many of these animals were severely emaciated, particularly in Gulf St Vincent, which was heavily affected by the bloom.
Algal Bloom and Food Shortage Linked to Dolphin Deaths
Dr. Catherine Kemper, a former curator at the South Australian Museum, noted that dolphin mortalities in the gulf in 2025 were the highest since 2013, when a morbillivirus outbreak struck. She strongly suspects that for common dolphins, the underlying cause was a food shortage. Their primary prey, southern calamari, saw populations plummet by 80% below baseline levels in Gulf St Vincent during the bloom of Karenia cristata algae, which began in March 2025.
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Marine Heatwave Compounds the Crisis
A concurrent marine heatwave has affected southern Australia since September 2024, further stressing marine ecosystems. Citizen scientists and government staff recorded dead dolphins alongside hundreds of other marine species. While postmortems did not directly indicate algal toxins, the emaciation of many animals points to the bloom's impact on their food web.
| Year | Dolphin Deaths Reported | Key Cause |
|---|---|---|
| 2025 | 70+ | Algal bloom (food shortage) |
| 2026 (partial) | 20+ | Algal bloom (ongoing) |
| 2013 | Dozens | Morbillivirus disease |
Key Takeaways from the Dolphin Deaths Spike
- At least 70 dolphin carcasses were found in South Australia in 2025, the highest in 12 years.
- The algal bloom decimated southern calamari populations by 80%, a key food source for dolphins.
- Emaciation was common among affected dolphins, linking deaths to food shortage rather than direct toxins.
- A concurrent marine heatwave has worsened conditions since 2024.
FAQ
What caused the spike in dolphin deaths in South Australia?
The spike is primarily linked to a devastating algal bloom of Karenia cristata that began in March 2025, which decimated the dolphins' food sources, particularly southern calamari.
How many dolphins died in 2025?
At least 70 dolphin carcasses were recorded in South Australia in 2025, with an additional 20 reported in early 2026.
Were the dolphin deaths caused by algal toxins?
Postmortems did not show direct effects of algal toxins, but many dolphins were emaciated, suggesting the bloom caused a food shortage rather than poisoning.
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