Cape Town – In case you have noticed a foul fishy smell at the V&A Waterfront – more so than usual – management has revealed that the reason why is due to a "system overload".
V&A Waterfront spokesperson Donald Kau said every year the marina has mullets (type of fish) breeding in the basin of the harbour, and this year the number was “quite high”.
“We also saw a large school of mackerel entering the harbour, and the high volume of fish obviously impacted on the levels of oxygen in the water, causing the fish to die.
“The dead fish is a great source of food for the Cape Fur Seals and the seagulls, hence the heightened activity of marine life in the harbour,” Kau said.
“It is also confirmed that the school of mackerel was followed by a pair of Humpback Whales, so the harbour basin literally had a "system overload".”
Kau said the marine and harbour team see this kind of activity every year and when it happens, they mitigate the reduced oxygen by opening the lock and flushing the bay with the water from the canals – which gets done up to six times a day.
“They indicated that one sometimes sees similar events at estuaries, and it is a very 'natural occurrence'. The mullets return every year to breed and their numbers are being monitored, so this annual occurrence does not seem to impact on its numbers too negatively as only the strong survive.”
Kau said the public will notice the strong smell because of the dead fish and that they have the Marine Wildlife Management team on the water scooping up the floating fish.
“We have also increased the fresh water flows into our harbour basins to increase the oxygen levels in the water which is important for its aquatic life.”
Two Oceans Aquarium provided more insight behind why the fish had died, and how the recent activity has impacted on them.
“The fish started dying, because they used up all the oxygen in the basin. The dead fish are now floating to the surface of the water as they decompose and, as a result, the ammonia levels are increasing in the water.
“Seals and sea birds have been dining out on the fish and teams from the Waterfront are working to remove the dead fish to stem the rotting fish odour due to decomposition,” the aquarium said.
Seals and sea birds have been dining out on the fish and teams from the Waterfront are working to remove the dead fish to stem the rotting fish odour due to decomposition. (You'll notice the smell when you visit us...) 🦨 pic.twitter.com/Dlj0atLTck
— Two Oceans Aquarium (@2OceansAquarium) March 29, 2021
“Because of the high ammonia levels (1mg/litre), the aquarium has had to shut off the water supply from the harbour and will be running on a closed system (no incoming water) to protect the animals in our care.”
The aquarium said that all the water in their exhibits comes out of the marina and is comprehensively filtered before being added to the displays, “but we can't filter out these concentrations”.
"Because of this there will not be any sea water available for Two Oceans Aquarium members until further notice.“
Cape Argus