Fish and shellfish washouts and mortalities on the west coast of South Africa
25 March 2021
Over the past week large fish and shellfish aggregations, in the shallow nearshore, as well as mortalities and washouts, have been observed in three different parts of the coast from Elands Bay to north of the Olifants River Estuary, in the Port of Cape Town and in False Bay. The stressed and stranded animals include sardine, harders, white stumpnose, cuttlefish and octopus. Surprisingly, no lobster (kreef) walkouts or kills have been reported whereas in False Bay, mostly pufferfish (blaasops) have washed up on the shore.
The phytoplankton identified at Elands Bay is not toxic and therefore unlikely responsible for the fish and shellfish mortalities there. The washouts and mortalities are more likely a result of the current icy and anoxic (zero oxygen) deep water, conditions there which are probably driving fish and shellfish into the warmer, shallow and more oxygen rich nearshore. Some of these stressed fish become too weak to avoid being stranded or washed up on the shore. A word of caution, this non-toxic confirmation is only for Elands Bay and does not preclude the red-tide to the North or South also including toxic forms of phytoplankton. This, and the possibility that some of the fish and shellfish may have been dead and rotting for longer than thought, makes it a wise choice to not feed any to family, friends, or pets.
The fish mortalities in False Bay are almost exclusively of the evil-eye pufferfish (blaasop) with counts of 300 to 400 dead fish per km of shore. There are no reports or data of any adverse water conditions or red-tide toxins that may have caused this.
The Pufferfish carry the deadly neurotoxin (Tetrodotoxin) and should not be eaten. Beach dog walkers are strongly advised to keep their pets away from them. If one’s dog does eat whole or part of a pufferfish, vomiting should be induced immediately, and a veterinary surgeon consulted.
Satellite composite map, red areas showing the highest phytoplankton densities and extent of the red tide on the West Coast.
