But fish die-off remains a partial mystery

credit Steve Benjamin from Animal Ocean

Just when you thought you’d seen it all, Mother Nature sprung a surprise at the V&A marina where a mass fish die-off  got tongues wagging and nostrils turned away in disgust.

Dead and decaying fish was still being removed from the marina at the time of newsletter publication, with more being churned up by passing vessels. The smell rivals even the stink of corruption hovering over the Zondo Commission.

The Victoria & Alfred blamed the die-off on “system overload” – a result of too many fish circulating in too small a space.  An above average number of mullet depleted the oxygen levels, causing the fish to die. “Every year we have mullets breeding in the basin, and this year the number was quite high,” said spokesman Donald Kau. “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.”

“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”.

“The marine & harbour team sees 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 (this gets done up to six times a day). They indicated that one sometimes sees similar events at estuaries, and it is a “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.

A private contractor, Spill Tech, was brought in to help the clean up, and officials engaged the Two Oceans Aquarium to help understand what had occurred.  Staff had their hands full scrubbing the slipway and cleaning wheelie bins used to collect the smelly debris.  “We can’t determine how thick is the layer of dead fish on the bottom,” said one source involved with the clean up.  “The water does look a bit clearer this morning, but we don’t know if we are starting on the mending process or whether this is part of the ups and downs of decaying fish.”

credit Steve Benjamin from Animal Ocean

Sea Search co-founder Simon Elwen said whale fish feeding was unusual and possibly the fish had responded to the presence of whales by moving into the marina: “It might well have been that the fish responded (to the whales) and moved further way,” Elwen said. “But perhaps it is good news that there are so many sardines around; there have been a lot of small pelagic fish reported in False Bay as well, and a lot of animals including common dolphins and penguins really rely on those fish..so perhaps this will help all those animals,” Elwen said.

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