Flocks of seabirds, particularly gannets, hovering overhead are just as greedy, and frequently gorge themselves to the point that, unable to lift off the water, they in turn fall prey to the thousands of sharks following the shoals.
The South African sardine (Sardinops sagax), also known as the pilchard, is usually found in huge shoals in the upper layers of the ocean. Like anchovies and herrings, they are small, primitive fish belonging to the group known as clupeoids. They are short-lived and fast growing, reaching a length of about nine inches (23 centimeters) in two years.
The runs are probably caused by changing water temperatures, said Sheldon Dudley, a senior scientist at the NSB.
The sardines like water temperatures below 68 degrees Fahrenheit (20 degrees Celsius). In winterJune and July in the southern hemispherethe surface water cools along the east coast, allowing the sardines to expand their habitat and move north.
It is the comparatively narrow continental shelf along the east coast and consequent narrower strip of cold surface water during winter that make the sardines so much more visible, said Dudley.
This year's run has been particularly good; sardine stocks are high, foreign tourism numbers are up. Even better, the businesses supporting sardine tourismboat tours, dive trips, beach guides, and expeditionsare multiplying as word of the "The Greatest Shoal on Earth" spreads.
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