THE GREAT SARDINE RUN

      One of the wildest, most dramatic natural happenings on Earth is the great sardine run along the eastern coast of South Africa in the Indian Ocean in May, June and July, the Southern Hemisphere's winter.  Several shoals of sardines, with many millions of individuals in each school of foot-long, stream-lined, silvery fish, move north with cold currents of ocean from Antarctica along the South African coastline to feed on an abundance of zooplankton and phytoplankton suspended in the water.  Those shoals are so extensive they can be seen from planes, and even from space.  

     I have seen sardine runs on television documentaries and on our computer.  And I have witnessed their shoals being attacked and eaten by hungry sharks, birds and mammals of various kinds.  

     Generally, shoals of sardines are deep in the ocean by day to avoid predators.  But at dusk they rise to the surface to feed on plankton.  Those nutrients are caught in gill rakers and transferred to the throat and stomach of each sardine.  

     Common dolphins seek sardine shoals to consume as many as they can.  They noticeably pursue those shoals north along the South African coast, which attracts the attentions of gannet birds, pelicans, gulls, sharks, fur seals, Bryde's whales and other predators associated with oceans.  

     Dolphins drive the sardine schools to the surface where they are more easily seen and caught by those intelligent mammals.  Up to five thousand dolphins could attack one shoal of fish at once, which really diminishes the sardines' numbers.  And while on the surface, the sardines are vulnerable from gannets, pelicans and gulls' dives into the ocean to snare sardines from above.  The gannets actually "fly" under water in pursuit of sardines.  The sardines are then trapped between predators in the ocean and diving birds from the air.    

     The sardines' only defense against such intense predation in the open ocean, where there is no where to run and no where to hide, is to form large, spinning balls of their many millions to confuse, even intimidate predators.  Those great, swirling masses of sardines, all swimming in the same direction, might even appear as large, individual creatures to the predators.  But many of the predators persevere and eventually penetrate those spinning, seemingly impenetrable millions of fish and begin to devour them.  Over time, those rolling balls of sardines get smaller and smaller, until, in some cases, nothing is left of them except scales drifting down through the salt water.

     Sardines are a forage fish for many kinds of creatures associated with oceans.  Some larger, ocean critters may not exist at all without the great masses of sardines to annually feed on. 
































spinning 

        

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