The Mossel Bay municipality says the fish kill resulted from severe oxygen depletion within the estuary. The Department of Forestry, Fisheries and the Environment (DFFE) says the mass mortality of fish in the Hartenbos Estuary in Mossel Bay is not due to a red-tide, but is the result of sewerage discharge and resultant eutrophication and ammonia toxicity. This comes after the Mossel Bay municipality said recent water samples for the Hartenbos Estuary were compliant with applicable standards.
DFFE on Sunday confirmed that the large numbers of dead white mussel, whelks and other shellfish that washed out at St Helena Bay and Elandsbaai on the West Coast was confined to these areas. Observations by Fisheries Control Officers (FCOs) and satellite imagery indicate visible red-tides from Elandsbaai 100 km northward, to above the Olifants Estuary on the West Coast. “There have been no mortalities of fish or shellfish reported associated with these visible new red-tides.
However, 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,” DFFE said. Satellite imagery and reports by members of the public and FCOs, also confirmed a visible red-tide in Walker Bay, Hermanus. This red tide is bioluminescent, the phytoplankton producing spectacular flashes of colour at night.
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