MOSSEL BAY NEWS - Yesterday there were hundreds of anchovies in the shallows at Santos Beach, Mossel Bay.
Also, anglers on the shore from Beacon Point to The Point were pulling fish out of the water, one after the other.
See a gallery of photos: Abundance of fish
It seemed as if the waters were teaming with fish.
Mossel Bay photographers Christiaan Stopforth and Michael de Nobrega posted photographs and videos on Facebook sites of the many anchovies in the shallows and people catching fish.
On enquiry from Mossel Bay Advertiser, Shawn Mey, a local fishing expert, explained that the reason for the anchovies and many other fish was the thermocline phenomenon.
A thermocline is a distinct, rapid temperature change in a layer of a large body of water, where the temperature decreases rapidly with depth, separating a warmer, mixed surface layer from colder, deeper water.
This affects the behaviour of fish.
Mey, who owns a local fishing charter company, and who has many years of experience of fishing, noted: "This is something that takes place every year, but we do not always see it specifically, locally, in Mossel Bay."
He said there were pockets of warm and cold water.
Mey said that the many anchovies were followed by fish who feed on them, mainly sharks, and it was mainly "bait" fish that the anglers caught from the shore yesterday.
Some anglers were also catching the Atlantic bonito (Sarda sarda), a large mackerel-like fish of the family Scombridae.
Mey said south-easterly winds had caused the phenomenon of the many fish. Ichthyologist Nadine Strydom, based at Nelson Mandela University in Gqeberha, corroborated Mey's view about the winds. She said: "Typically strong south-easterly winds cause this."
South-easterlies, influenced by the Agulhas Current, bring warm water to the eastern and southern coasts of South Africa.
Explaining the phenomenon of many fish more fully, Strydom said: "It's unusually warm or cold water that causes this.
"It’s sudden changes to sea temperature from wind-driven oceanographic events.
"Sometimes warm water sheets off the Agulhas current and is blown to the shore, making water warmer and more tropical species follow and then get trapped by cooler waters of the area, or localised upwelling causes very cold water to rise from depths and fish get stunned."
Today's sea temperature in Mossel Bay is 18.6 degrees Celsius and yesterday's was 17.7.
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