Durban - Global warming could lead to the end of the famous sardine run off the east coast of South Africa, the spectacular event that brings tourists from around the world to the KZN coastline.
The “Greatest Shoal on Earth” may date back to the glacial period when what is now the subtropical Indian Ocean was a cold-water sardine nursery.
These were some of the findings of South African and Australian scientists whose study in the journal Science Advances tested the hypothesis that the sardine run represents the spawning migration of a distinct east coast stock adapted to warm subtropical conditions.
According to the scientists, the sardine run is triggered by the upwelling of cold water on the south east coast and as the silvery fish swarm north, they get sandwiched between the coast and a southward-flowing hot current that exceeds the sardines’ physiological capacity.
The shoal can be spotted by the huge numbers of predators which arrive, including dolphins, sharks, sea birds and even whales.
One of the study’s authors, Professor Luciano Behegaray of Flinders University Molecular Ecology Lab in Australia, said the scientists generated genomic data for hundreds of sardines from around South Africa, including data from regions of the genome which were 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 that it experiences in its native region.
“Surprisingly, we also discovered that sardines participating in the migration run are primarily of Atlantic origin,” said Behegaray.
Another author of the study, Professor Peter Teske of the University of Johannesburg (UJ), said: “The cold water of the brief upwelling periods attracts the west coast sardines which are not adapted to the warmer Indian Ocean habitat.
“This is a rare finding in nature, since there are no obvious fitness benefits for the migration, so why do they do it? We think the sardine migration might be a relic of spawning behaviour dating back to the glacial period. What is now subtropical Indian Ocean habitat was then an important sardine nursery with cold waters,” said Teske.
Behegaray warned: “Given the colder water origins of sardines participating in the run, projected warming could lead to the end of the sardine run.”
While the sardine run involves a huge number of fish, the scientists found that even though it could mean the loss of one of nature’s most impressive migrations which attracts tourists from around the world, it only involves a relatively small portion of the South African sardine population, so “the effects on the population as a whole are likely to be negligible”.
However, Ugu South Coast Tourism chief executive Phelisa Mangcu said yesterday that the impact of such a change on the sardine run would be devastating.
“The annual sardine run, which enjoyed two bumper seasons in 2020 and 2021, is undoubtedly one of the KZN South Coast’s biggest drawcards. From a tourism perspective, the sardine run is a major driver of our winter campaigns, attracting anglers hoping for big catches, as well as visitors from outside the area simply wanting to be a part of this world-renowned spectacle.
“The impact of climate change on this natural phenomenon would be devastating, obviously from a tourism perspective, as well as for seine netters who rely on the sardine run as a food source and income generation through sales.
“Beyond the sardine run, the KZN South Coast’s tourism economy hinges on our incredible nature-based options, including our many game and nature reserves, dive sites, gorges and valleys. Climate change will impact all of this, which is why addressing the reality of climate change simply cannot wait,” said Mangcu.
The issue required each person to change their behaviour to prioritise “biodiversity and the health of the natural world with every decision made”, she said.
The Independent on Saturday