In March 2021, a grisly scene materialized on the beaches of South Africa. Giant bat-winged manta rays sprawled belly up on rocks. Hulking bull sharks lay dead in the sand. Puffer fish littered shorelines like deflated footballs.
“This kind of a phenomenon is certainly not something that I’ve ever been aware of,” said Oregon State University marine ecologist Bruce Menge, who studies how currents shape coastal ecosystems but was not involved in the fish kill research, published today inThe die-off in South Africa caught the attention of Australian shark researcher Nicolas Lubitz, then a Ph.D.
For fish that prefer warmer waters, such as bull sharks, the cold was more than they could endure and its swift onset left them trapped, Lubitz says. “If it drops in 24 hours by 9°, that makes it pretty lethal.” It's hard to say with certainty that the trend is driven by climate change, in part because these upwellings are so localized that they aren’t well represented in models looking at interactions between the ocean and climate, says David Schoeman, a marine climate change ecologist at the University of the Sunshine Coast who worked on the paper.