Dolphin deaths in South Australia spike after algal bloom decimates food sources
Dolphin Deaths in South Australia Spike After Algal Bloom
Dolphin deaths in South Australia spike - Long-term monitoring data has revealed that South Australia experienced its highest dolphin mortality rate in over a decade during 2025. The surge in dead marine mammals washing ashore coincided with a devastating algal bloom that severely impacted the region's marine ecosystem. According to comprehensive records, at least seventy carcasses of both common and bottlenose dolphins were discovered across South Australian coastlines throughout the previous year. The situation continued into 2026, with an additional twenty cases reported, including the recent passing of Zoom, a beloved dolphin from the Port River area.
Many of the deceased animals were discovered in Gulf St Vincent, a substantial marine zone situated west of Adelaide that bore the brunt of the environmental crisis. These dolphins were found in severely emaciated condition, suggesting widespread nutritional stress throughout the population.
Investigating the Root Causes of Increased Mortality
Dr. Catherine Kemper, who formerly served as curator of mammals at the South Australian Museum, provided crucial insights into the situation. She noted that dolphin deaths in the gulf during 2025 represented the highest figures since 2013, when dozens of animals succumbed to morbillivirus, a disease affecting cetaceans. Kemper explained the connection between the bloom and food availability.
We suspect strongly that for common dolphins the underlying cause was a food shortage, because one of their major prey is southern calamari, and southern calamari populations were just decimated in Gulf St Vincent during the algal bloom.
Citizen scientists and government personnel have been documenting dead dolphins since the Karenia cristata algae bloom commenced in March 2025. This environmental event has also claimed hundreds of other marine species. Compounding the situation, a marine heatwave has been affecting southern Australia since September 2024, potentially adding additional stress to already vulnerable populations.
Research Analysis and Scientific Findings
Working alongside dolphin researcher Dr. Mike Bossley, Dr. Kemper conducted a thorough analysis combining citizen reports with museum records spanning from 2001 to 2024, as well as dolphin postmortems commissioned by the state government. They presented their comprehensive findings at the Australian Mammal Society and Australasian Bat Society conference on Thursday.
While published postmortems did not show direct effects from algal toxins, many of the deceased animals exhibited severe emaciation. Kemper suggested this could be connected to how the bloom impacted their primary food sources. Government research indicated that southern calamari populations in both Gulf St Vincent and Spencer Gulf dropped to eighty percent below baseline levels.
Dr. Bossley emphasized that dolphins naturally wash up for various reasons throughout their lives. He noted that boat strikes, fishing gear entanglement, and shark attacks all contribute to mortality rates. However, the condition of many 2025 carcasses pointed toward prey scarcity.
Dolphins get hit by boats, get tangled up in fishing gear, get attacked by sharks, but many in 2025 were very skinny, suggesting a lack of prey, particularly squid in the case of common dolphins.
He added that the algal bloom significantly impacted squid populations, making reduced food availability the most likely explanation for the increased death toll. The marine heatwave may have served as an additional contributing factor to the crisis.
Systemic Challenges and Future Recommendations
Dr. Kemper highlighted that the 2023 disbanding of a decades-long marine mammal postmortem program at the SA Museum had complicated efforts to fully understand the bloom's impact on cetaceans. Both she and Dr. Bossley have advocated for the reinstatement of systematic postmortem examinations.
A spokesperson for South Australia's Department for Environment and Water confirmed that disruption to marine food chains appeared to be a contributing factor to the increased dolphin deaths recorded in 2025 and during the first five months of 2026. The spokesperson clarified that while dolphins lack gills and are not directly affected by algal blooms in the same manner as fish, experts believe certain marine wildlife may have experienced impacts from both food chain disruption and algal biotoxins.
The department noted that findings of weight loss in deceased animals suggest indirect effects of the algal bloom on food sources as a potential cause of illness or death. Chronic weight loss has been documented in numerous postmortems for animals tested since the bloom's arrival, in