Fresh crates of sardines are seen for sale to members of the public at the Warner beach, south of Durban on June 20, 2021. The sardine run of southern Africa occurs from May through July when sardines move northwards along South Africa's East Coast. This phenomenon attracts masses of fishermen and locals to the shores to watch the sardines and some catch and sell them. (Photo by RAJESH JANTILAL / AFP)
This spectacular event, considered the “Greatest Shoal on Earth”, involves the movement of hundreds of millions of sardines from their cool-temperate core range into the warmer subtropical waters of the Indian Ocean, on South Africa’s east coast.
The sardine run is triggered by the upwelling of cold water on the southeast coast and as they swarm north they get sandwiched between the coast and a southward-flowing hot current that exceeds their physiological capacity.
They are then preyed upon by huge numbers of dolphins, sharks, seabirds and even whales, an event that has featured in many nature documentaries.
Watch: Sardine fever on SA’s East Coast
In a new study in the journal Science Advances, South Africa and Australian scientists tested the hypothesis that the run represents the spawning migration of a distinct east coast stock adapted to subtropical conditions.
The scientists generated genomic data for hundreds of sardines from around South Africa, including data from regions of the genome that are primarily associated with differences in water temperature along the coast.
The results showed two sardine populations in South Africa: one in the cool-temperate west coast (Atlantic Ocean)
and the other in warmer east coast waters (Indian Ocean).
Each regional population appears adapted to the temperature range it experiences in its native region.
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