The sardine run in southeastern Africa is a mass migration into an ecological trap

Sardines duped by water currents?

22 March 2022

The annual migration of tens to hundreds of millions of sardines off the east coast of South Africa that culminates in a feeding frenzy for predators may be an ecological trap that doesn’t benefit the species.

There has been much speculation regarding why sardines participate in the mass migration, which has been dubbed ‘the greatest shoal on Earth’.

Now, a team led by researchers from University of Cape Town has found evidence that temporary water currents may trick the sardines into participating in a migration that offers them no long-term benefits.

They identified two stocks of sardine: those from the Indian Ocean that prefer warmer waters and those from the Atlantic that prefer cooler waters. Surprisingly, they also found that only sardines from the Atlantic participate in the run.

The sardines may be deceived by brief cold upwellings that lead them to warmer waters and an armada of waiting predators, the researchers conjecture.

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References

1. Science Advances 7, eabf4514 (2021). doi: 10.1126/sciadv.abf4514