Algal bloom impact on key fish stocks in South Australia’s gulfs
Overview
Since March 2025, a large algal bloom caused by Karenia species has affected the waters of Gulf St Vincent, Spencer Gulf, Kangaroo Island and nearby areas. The bloom has resulted in widespread marine life deaths, impacting fish, shellfish and other sea life.
As part of the response, fisheries and fish stocks are being assessed to understand the impact of the algal bloom on commercial fish species.
Latest summary report
Download Summary report: Algal bloom impact on key fish stocks in South Australia’s gulfs – March 2026 ( ).
Main findings
- The algal bloom has had the strongest negative effects in Gulf St Vincent, where several key fish species have declined sharply.
- Spencer Gulf fisheries appear to be less affected, except for Southern Calamari.
Gulf St Vincent and Kangaroo Island
- King George Whiting: Evidence of recent declines with widespread indication of post-settlement failure.
- Southern Calamari and Southern Garfish: Severely affected with additional evidence of egg mass/juvenile declines.
- Western King Prawn: Strong evidence from scientific surveys of low catches and very little bycatch.
- Blue Swimmer Crab: Catches have been impacted but estimates from recent targeted surveys indicate that abundances have improved.
- Abalone: High mortality observed in parts of the gulf.
Spencer Gulf
- King George Whiting and Southern Garfish: Generally stable
- Southern Calamari: Evidence of catch declines across broad spatial scales.
- Western King Prawn and Blue Swimmer Crab: Catches remain within normal ranges.
- Southern Rock Lobster: Found mostly outside the affected areas – no sign of impact.
About the research
This assessment uses:
- analysis of commercial fishing data
- scientific (fishery-independent) surveys
- targeted fishing surveys with commercial operators
- bycatch and species sampling
- routine fishery stock assessment surveys for prawns, crabs, lobsters and abalone.
For all species, the assessment relies heavily on spatial and temporal analyses of commercial logbook data across all fishing sectors.
To quantify fishery impacts, monthly catch and catch rate (expressed as catch per unit effort, CPUE) from March 2025 onwards, were compared against the 3-year monthly average for each species to give an idea of 'before' and 'after' algal bloom impact.
Other reports
- Summary report: Algal bloom impact on key fish stocks in South Australia’s gulfs – January 2026 ( )
- Summary report: Algal bloom impact on key fish stocks in South Australia’s gulfs – November 2025 ( )
- Summary report: Algal bloom impact on key fish stocks in South Australia’s gulfs – October 2025 ( )
- SARDI algal bloom response: Assessment of fish stocks in Spencer Gulf and Gulf St Vincent – March 2026 ( )
- SARDI algal bloom response: Assessment of non-quota fish stocks in Spencer Gulf and Gulf St Vincent – March 2026 ( )
- Blue Crab Fishery: 2026 fishery-independent survey results – April 2026 ( )
- Gulf St Vincent Prawn Fishery: Harmful algal bloom – Fishery independent survey results November–December 2025 ( )
- Appropriate location and timing of spatial spawning closures for King George Whiting– April 2026 ( )
- Summary of key results for snapper prior to the harmful algal bloom ( )
- Algal Bloom Fishery Management Roadmap ( )
Next steps
- SARDI continues to collect and analyse data to track impacts and provide further advice to PIRSA and industry.
- Updates will be shared as new information becomes available.