Key Takeaways
- The mass mortality of fish in the Hartenbos Estuary in Mossel Bay is not due to a red-tide, but rather sewerage discharge and resultant eutrophication and ammonia toxicity.
- Recent water samples for the Hartenbos Estuary were compliant with applicable standards, according to the Mossel Bay municipality.
- A visible red-tide has been observed from Elandsbaai to the Olifants Estuary on the West Coast, with no reported mortalities of fish or shellfish.
- A bioluminescent red-tide has been reported in Walker Bay, Hermanus, with no reported fish or shellfish mortalities.
- The Department of Forestry, Fisheries and the Environment (DFFE) advises against eating shellfish collected from affected areas due to the risk of toxicity.
Introduction to the Issue
The Department of Forestry, Fisheries and the Environment (DFFE) has released a statement regarding the mass mortality of fish in the Hartenbos Estuary in Mossel Bay, attributing the cause to sewerage discharge and resultant eutrophication and ammonia toxicity, rather than a red-tide. This comes after the Mossel Bay municipality announced that recent water samples for the Hartenbos Estuary were compliant with applicable standards. The DFFE has been monitoring the situation closely, and has also reported on the presence of red-tides in other areas, including the West Coast and Walker Bay, Hermanus.
The Situation in Hartenbos Estuary
The mass mortality of fish in the Hartenbos Estuary has been a cause for concern, with the Mossel Bay municipality confirming that the emergency mechanical breaching of the estuary was necessary to address the issue. The municipality reported that critically low dissolved oxygen levels were recorded in the system, triggering an intervention in accordance with the provisions of the Approved Estuary Mouth Management Plan. A contractor was deployed onsite, and clean-up operations are ongoing. Scientific observations have confirmed that the fish kill resulted from severe oxygen depletion within the estuary, caused by an algal bloom exacerbated by low water levels, elevated temperatures, and nutrient-rich conditions.
Red-Tides on the West Coast
In addition to the issue in Hartenbos Estuary, the DFFE has reported on the presence of red-tides in other areas. A visible red-tide has been observed from Elandsbaai to the Olifants Estuary on the West Coast, with no reported mortalities of fish or shellfish. The DFFE has advised that while there have been no reported mortalities, there remains a high risk of toxicity, and it is still advised that all shellfish, irrespective of being washed out or collected from shore or subtidal, should not be eaten. The DFFE is continuing to monitor the situation closely, and is working to assess the extent of the red-tides and resultant mass mortalities on the West Coast and South Coast.
Bioluminescent Red-Tide in Walker Bay
A bioluminescent red-tide has been reported in Walker Bay, Hermanus, with no reported fish or shellfish mortalities. The phytoplankton producing this red-tide are capable of producing spectacular flashes of color at night, making it a unique and interesting phenomenon. However, the DFFE is still advising a cautionary approach, and recommending that no shellfish be collected and eaten from this area. The presence of this red-tide serves as a reminder of the importance of monitoring and managing our coastal ecosystems, and the need for continued research and understanding of these complex systems.
Conclusion and Next Steps
In conclusion, the mass mortality of fish in the Hartenbos Estuary is a serious issue that requires continued attention and monitoring. The DFFE’s findings that the cause is sewerage discharge and resultant eutrophication and ammonia toxicity, rather than a red-tide, highlight the need for effective management and mitigation strategies to prevent similar incidents in the future. The presence of red-tides in other areas, including the West Coast and Walker Bay, Hermanus, serves as a reminder of the importance of continued monitoring and research. The DFFE will continue to work to assess the extent of the red-tides and resultant mass mortalities, and to advise the public on any necessary precautions to ensure public safety and protect the environment.