4 min read

Why Hundreds Of Frenzied Sharks Are Drawn To South Africa Annually

<p>YouTube/dan peter</p>

Seeing a shark while diving is considered a pretty rare find. Seeing dozens - perhaps hundreds - while diving is another experience altogether. One diver off the coast of South Africa found himself in the midst of a massive, swirling swarm of sharks on a recent trip:

As it turns out, while this sight is stunning, it's far from rare.

"It's spectacular but not unusual," Dr. George Burgess, Director of the Florida Program for Shark Research, told The Dodo. "Whenever you get an aggregation of fishes like what you're seeing here, there are going to be predators there - even if those predators are normally solitary, like sharks are."

This particular gathering happens once a year, every year. Called the sardine run of South Africa, the frenzy is brought on by a gathering of millions of small fish, migrating Southern African pilchard (Sardinops sagax). Naturally, many fish in one place draw hungry predators, and it's not just sharks. Sea birds, dolphins and porpoises all gather in one enormous, if chaotic, feast. Sometimes, a whale even crashes the party, like this episode in 2011:

"There are probably 10 to hundreds of sharks gathering at any given time," said Dr. Neil Hammerschlag, research scientist at the University of Miami's Rosenstiel School of Marine and Atmospheric Science. "But it's dynamic - the fish are moving around like the wind, or like a flock of birds that's always changing shape. It's ephemeral."

This isn't the only gathering like it in the world - but it is one of the largest. And while it's total biomass rivals that of East Africa's famous wildebeest migration, it's certainly not without its threats, said Burgess.

"The situation with sardines is that their biggest predator is humans," he said, noting that overfishing has the potential to cause big problems for the sardine run - and the animals that rely on it. "Many organisms count on that seasonal resource for food. A reduction in the number of the sardines would have a very deleterious effect on all of those organisms because they all depend on the sardines."

Without proper fisheries management, he noted, the entire ecosystem could be affected - and massive spawning aggregations like these could take a major hit: