University of Miami Rosenstiel School of Marine & Atmospheric Science published a new study, documenting unexpected consequences following the loss of great white sharks from an area off South Africa. The study revealed that the disappearance of great whites has led to the emergence of 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.
These findings are part of a long-term collaborative study between shark researcher Neil Hammerschlag from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, and wildlife naturalist Chris Fallows from Apex Shark Expeditions.
The research focused on the waters surrounding Seal Island in False Bay, South Africa, a site well known for its “flying” great white sharks that breach out of the water when attacking Cape fur seals. Since the year 2000, the research team has spent over 8,000 hours observing great whites from boats, during which 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.
The study lead author Neil Hammerschlag said that in 2017 and 2018, the number of whites reached an all-time low. The reasons for their decline and disappearance remains unknown and it provided a truly unique opportunity to see what happens to an ocean ecosystem following the loss of an apex predator.
Researchers state that in 18+ years of working at Seal Island, they had never seen sevengill sharks in their surveys. But following the disappearance of white sharks in 2017, sevengill began to show up for the first time and have been increasing in number ever since.
This research shows new insights into the diverse ways that a marine ecosystem can be changed following the loss of an apex predator.