Waters Once Dominated by Great Whites Now Ruled by a New Species of Shark
The great white shark has been knocked off its throne in the waters off South Africa to be replaced by another predator.
A Scientific Reports study based on almost two decades of observations showed that when the great white shark began to disappear, its place at the top of the food chain was taken by the sevengill shark.
These predators “closely resemble animals from the Jurassic period, and can easily be told apart from other sharks due to having seven gill slits instead of the typical five in most other sharks,” Melissa Christina Marquez wrote in a Forbes analysis of the study.
The study reported that in 2017 and 2018, great white sharks began to disappear off of Seal Island, a small island located near Cape Town, South Africa. The study could not pinpoint the cause, but in her commentary on the research, Marquez noted that orcas, also known as killer whales, had killed several great white sharks during the time period when the great white population declined.
As to why the killer whales emerged on the scene, Marquez said there is no easy answer.
The current theory is that a different type of killer whale came into the region.
“There are substantial gaps in our understanding of these orca-shark relationships, as well as the relationship sharks have with one another and their environment. It remains unknown if and when the white sharks may return to their historical numbers in this famous part of the world,” she wrote.
“While the reasons for their decline and disappearance remain unknown, it provided a truly unique opportunity for us to see what happens to an ocean ecosystem following the loss of an apex predator,” Dr. Neil Hammerschlag, a marine ecologist from Miami University and the study’s lead author, said in a statement, according to The U.K. Independent.
What is clear, the study noted, was that once the great white sharks were no longer rulers of the waters off Seal Island, sevengill sharks expanded their territory.
“We hypothesize that the anomalous emergence of sevengill sharks at Seal Island during 2017 and 2018 was the result of predation — and/or competitive — release in the absence of white sharks,” the study said.
“Sevengill sharks have no equal in the local food web besides the great white shark and orcas (Orcinus orca) that reside here,” Marquez noted for Forbes.
Sevengill sharks have been put on the International Union for Conservation of Nature’s Red List of threatened species, although the infrequency of sightings is largely the cause of that, according to The Independent.
Sevengill sharks can grow to over nine feet in length.
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