THE "GREATEST SHOAL ON EARTH"

Article - @KZNSharksBoard

Each year in June or July along the KwaZulu-Natal coast the word gets out and, within hours, crowds of frenzied human predators converge on the area to join sharks, gamefish, marine mammals and birds in a feeding orgy. It is a time of plenty for all as large shoals of sardines move in a band up the coast. Fresh, frozen, canned, pickled or bait - whatever way you consider them, sardines (also known as pilchards) will have featured somewhere in the lives of many South Africans. Like their close relatives, the anchovies and herrings, sardines (Sardinops sagax) live out their lives in huge shoals in the surface layers of the ocean. Although these fish are small, collectively they comprise nearly a quarter of the world's fish catch by weight, making them one of our most valuable groups of fish.

Sardines are cold-water fish and are usually associated with areas of cold ocean upwelling, where deeper, cooler, nutrient-rich water currents surge to the surface when they strike shallow coastal areas. Sardines are commonly found in enormous shoals on the west coasts of California, South America, Japan, Australia and, of course, southern Africa.

In the large sardine (pilchard) fishery along the Western Cape coast, about 200 000 tonnes are caught annually. Each night, weather and season dependent, fleets of purse-seiners set out from harbours dotted along the coastline. Once a shoal has been located, huge nets are used to encircle and draw the fish up alongside the vessel before they are pumped on board. Depending on the quality of the fish, the catch may be canned or ground into fishmeal. This fishery employs thousands of people in the Western Cape, and is the economic backbone of many coastal communities in the area. Up the east coast, the annual catch drops progressively from about 10 000 tonnes in the Eastern Cape to several hundred tonnes in KwaZulu-Natal waters.

Sardines live fast and die young. They grow rapidly to reach a length of just under 20 cm and sexual maturity in two years, but rarely live longer than three years. In compensation, they are highly fecund, each female producing many thousands of eggs in her short lifespan. The main spawning grounds are on the Agulhas banks off the southern Cape coast, where the adults gather for a prolonged breeding season through spring and early summer. The eggs are simply released into the water, fertilized and left to drift off in the open ocean. A benign ocean current carries most of the developing larvae westwards and northwards into the productive waters along the west coast. After growing into juvenile fish that are strong enough to swim against the current, they aggregate into dense shoals and slowly make their way back to their spawning grounds in the south, thereby completing their life cycle.

Sardines feed primarily on plankton, minute plants and animals that they filter from the sea using sieve-like gill rakers. In turn, the exceptional productivity of sardines fuels the populations of most of the larger marine predators. Gamefish, birds, seals and dolphins compete with man for a share of the bounty. The sight of wheeling squadrons of gannets folding their wings to plummet into the water around a school of hundreds of dolphins surging after a boiling mass of panic-stricken fish is an extraordinary spectacle. So too is the equally frenzied behaviour of man when shoals of sardines are pushed ashore during the famous 'Sardine Run'.

The Sardine Run is an annual phenomenon sparked by the entry of large shoals of sardines into the waters of southern KwaZulu-Natal during the winter months. Although the great bulk of South Africa's sardine stock is to be found in the cooler Cape waters, each winter a small proportion of the stock moves eastwards up the Wild Coast. These shoals take advantage of cool water on the continental shelf of the east coast that occurs seasonally as a narrow band between the coast and the warm, southward flowing Agulhas Current.

It is not clear what advantage the sardines gain by entering KwaZulu-Natal waters. On the contrary, in fact, local waters are less food-rich than are Cape waters, the favourable cooler conditions are only temporary and, to make matters worse for the sardines, they are accompanied by many predators which prey on them heavily. Because the fish become concentrated near the surface in a narrow inshore band of water, the shoals are quickly located by schools of marauding predators that are whipped into a frenzy by this brief period of plenty in these otherwise less productive waters. Sharks, such as the copper, dusky, blacktip and spinner, join gamefish such as shad, garrick and geelbek, and marine mammals like Cape fur seals and dolphins in hot pursuit of the shimmering mass of sardines, or each other. As the shoals are driven to the surface, birds - Cape gannets, cormorants, terns and gulls - plummet out of the sky to pillage from above. The appearance of common dolphins along the KwaZulu-Natal south coast is closely associated with the arrival of the Sardine Run and it has even been suggested that the female dolphins use the plentiful food supply to wean their calves and replenish their depleted fat stores.

The progress of the Sardine Run is closely monitored by anglers, who flock to the beaches and rocks to participate in excellent game-fishing. Commercial fishing of the sardines themselves is also undertaken using beach seine nets, which are pulled from the shore. While one group of fishers holds a rope at one end of the net, the other end is cast around the shoal of fish using a small boat. The encircled fish are then dragged ashore, where they are quickly scooped into baskets both by the fishers and many eager helpers. These fish are usually sold for human consumption or bait. Particular wind and current conditions may force the sardines very close to the beach, where they are easily caught using baskets, hand nets or even skirts! In fact, when sardines are beaching anything goes, and it is not uncommon to see grandmothers competing with teenagers for 'their' share of the feast in a social occasion that draws crowds into the surf and even larger crowds of awed and amused spectators.