Forestry, Fisheries and the Environment on mass fish mortalities in Hartenbos Estuary in Mossel Bay

The Department of Forestry, Fisheries and the Environment (DFFE) reiterates that while the mass fish mortality observed in the Hartenbos Estuary in Mossel Bay is not linked to the red tide, but it is also not due to a sewerage spillage. Through engagements with the Mossel Bay Municipality, it has been determined that this particular incident can be attributed to a combination of interacting factors, including, but not limited to:

• Elevated nutrient inputs from multiple sources, leading to eutrophication;
• Reduced freshwater inflow due to water abstraction and dam development within catchments, resulting in slower water movement and increased susceptibility to algal blooms; and
• Harmful algal bloom and high phytoplankton biomass.

These are some of the conditions that lead to eutrophication and ammonia toxicity, which the recently released National Biodiversity Assessment and earlier studies highlight as key contributors to fish mortalities in South African estuaries – especially in smaller and temporarily closed systems, such as Hartenbos. 

The DFFE cautions members of the public against handling or consuming any washed-up marine organisms. Such organisms may pose serious health risks and are not safe for consumption, regardless of the suspected cause of mortality.

Furthermore, the DFFE’s Water Quality Monitors, with other relevant local authorities and stakeholders, have since confirmed that the oxygen levels in the water have normalised and the situation is under control.  

For media queries contact: 

Zolile Nqayi 
Cell: 082 898 6483 
E-mail: znqayi@dffe.gov.za 
 

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