It's one of the great spectacles of the oceanic world -- a huge number of sardines following a coastal current around the southern coast of Africa, pursued by sharks, dolphins, seabirds, etc.
The thing is, they aren't going anywhere. Their only destination is the gullets of what eats them.
So why do they go there? Turn out it is mostly an accidental phenomenon.
Pulses of cold seawater mislead millions of sardines into swimming along the South African coast to their death
"One popular explanation holds that the sardines participating in the run belong to a distinct eastern subpopulation that evolved in the Indian Ocean, so the fish are migrating to ancestral spawning territories there by instinct. But a genomic analysis of hundreds of South African sardines reveals that those in the run hail from the Atlantic Ocean, suggesting that the spectacular migration may serve no benefit to the fish and instead traps them in hostile waters, researchers wrote this fall in Science Advances.
“We're used to adaptations benefitting an organism, but it doesn't always work that way,” says Jessica Glass, a marine biologist at the University of Alaska Fairbanks who was not involved in the study. “These animals are doing something that doesn't actually benefit them in the long term.”So if it doesn't benefit them, why do they do it?
"Sardines from the Atlantic Ocean sometimes stray too far into warm southern waters, where they may encounter brief pulses of cold, nutrient-rich water upwelling along the coast that reminds them of their home range in the Atlantic, he says. The cold-adapted fish unwittingly follow these waters northeast only to become stranded in warmer Indian Ocean waters when the upwelling ceases. Already suffering biologically from the warm conditions, the sardines are assaulted from the air and sea by countless predators."So, to put it simply, they take a wrong turn at the cold current.
Safety in numbers (sort of):
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