A new study has documented the decline of great white sharks from an area off South Africa. The study found that the disappearance of great whites has led to the emergence of different predators.

Seal Island in False Bay, South Africa, is well known for its great white sharks. A research team spent over 8,000 hours observing great whites from boats. They recorded 6,333 shark sightings, and 8,076 attacks on seals. These data revealed that for more than a decade, great white numbers were relatively stable, but in 2015 sightings began to drop off steeply.

“In 2017 and 2018, their numbers reached an all-time low, with great whites completely disappearing from our surveys for weeks and months at a time,” said study lead author Neil Hammerschlag. “While the reasons for their decline and disappearance remains unknown, it provided a truly unique opportunity for us to see what happens to an ocean ecosystem following the loss of an apex predator.”

“In 18+ years of working at Seal Island, we had never seen sevengill sharks in our surveys,” said co-author Chris Fallows. “Following the disappearance of white sharks in 2017, sevengill began to show up for the first time and have been increasing in number eve r since.” Sevengill sharks, a top predator from a different habitat. A living fossil, sevengill sharks closely resemble relatives from the Jurassic period, unique for having seven gills instead of the typical five in most other sharks.

The researchers documented 120 sevengill shark sightings over two years and even witnessed an one attacking a live seal. Historically, the only well-known aggregation site for sevengills in False Bay was located 18 km away from Seal Island within inshore kelp beds. The study suggested that the appearance of sevengill sharks at Seal Island was due to the disappearance of great whites, thereby allowing sevengills to exploit the area.