GARDEN ROUTE NEWS - SANParks is aware of the fish mortalities in the Touw River and is monitoring and managing the situation. Currently the deaths appear to be very localised between the mouth and Freesia Rocks. That is the message from Dr Sandra Taljaard, manager of Wilderness Garden Route Region SANParks.
She was reacting to enquiries after a reader shared concern regarding dead fish in the river with George Herald.
Section ranger Jonathan Britton said SANParks has been managing and closely monitoring matters since the first dead fish were reported. He stressed that there is no reason for panic.
No fish deaths have been observed upstream at Ebb and Flow, Island Lake, Langvlei or Rondevlei. Island Lake, Langvlei and Rondevlei are all connected to the Touw River and collectively form the Wilderness Lakes. The Touw River is classified as an Estuarine Lake which is temporarily open/closed to the sea. In the open phase the estuary is open to the sea and there is a tidal exchange of water.
Over time the long shore sand drift becomes stronger than the forces that keep the mouth open and the estuary enters the closed phase. The open and closed phase of the estuary are ecologically different and neither phase is "better" than the other, there are just different ecological processes at play that all work together.
Dr Sandra Taljaard. Photo: Eugene Gunning
Personal interaction with the estuary often drives the notion and preference of a "good open phase" and "bad closed phase".
According to him the water quality results are all within normal parameters for the estuary, no ammonia nitrogen typically found in detergents and an indicator of sewage was detected and orthophosphates, an indicator of fertilisers, were also not detected. 80% of the dead fish were spotted grunter and the phenomenon was very localised, between Freesia Rocks and the lagoon mouth.
If there were water quality issues a far larger number of dead fish and a wider range of species would have died upstream and along the entire course of the estuary, however a more intensive water and environmental analysis is being conducted as part of the broader investigation.
Similar short-lived mortality events in the Touw River also occurred in the winter of 2019 and 2020. Spotted grunter was also the dominant species.
A marine scientist takes a close inspection of a dead fish.
"We have observed lesions and growths on the dead fish collected and we are currently investigating these to try and make a definitive diagnosis to see if this is a direct cause for the deaths or if there is a secondary stress that subsequently results in a secondary infection.
Rangers patrol on a regular basis, collect dead fish and record information on the species. Numbers and samples are kept for analysis. There is something that is targeting mostly spotted grunter or the spotted grunter are more susceptible than other species.
SANParks have been investigating this together with our marine scientists, aquatic scientists, veterinary scientists, Department of Forestry Fisheries and Environment fish and marine specialists as well as local academics, and are working together to better understand the cause of the deaths.
Making a diagnosis is not always simple or obvious as disease and death are part of life in the ecology of the Touw River Estuary.
"There is no need for panic. However, residents and fisherman are advised not to collect and eat any of the dead fish. During this event fishermen are advised to practise catch and release and avoid eating fish that display any unusual looking lesions."
SANParks scientists use instruments to measure water quality in the Touw River.
The Garden Route National Park Management Plan, with links to all the scientific literature that the Management Plan is based on can be found here. This will provide an understanding of the complexities of managing an estuary in an urban context as well as insight into the decision-making principles and framework regarding the mechanical breaching of the Touw River Estuary.
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