South Africa's capital has made an unusual plea – it wants its great white sharks back.

The decline in numbers of the legendary predator off Cape Town's coast has led to an emergence of sevengill sharks - which are increasing in number, according to MailOnline.

New research, which focused on the sharks found in the waters surrounding False Bay, revealed unexpected consequences from the decline in numbers of the great white shark.

The 18-year study has documented a fall in shark numbers around Seal Island – which became famous for images of great white sharks breaching the water to catch seals.

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Since 2017, sightings declined and were sometimes reported months apart.

But just when you thought it was safe to go back in the water, another predator has appeared.

While researches had never seen sevengill sharks in the 18 years of the study, they now appear to dominate the area.

It was suggested that this emergence was due to the decline in great whites, as the sevengill sharks no longer have the risk of predation from great whites, or the competition for food.

The sevengill shark is named for its seven gills – instead of the typical five found in most sharks – and closely resembles relatives from the Jurassic period.

The study began in 2000, as a collaboration between shark researcher Neil Hammerschlag, of the University of Miami Rosenstiel School of Marine and Atmospheric Science, and wildlife naturalist Chris Fallows, of Apex Shark Expeditions.

Since the great whites moved on, the sevengill shark has moved in. Photo / Getty Images
Since the great whites moved on, the sevengill shark has moved in. Photo / Getty Images

The data resulting from the study showed the number of great whites were stable until 2015, when they began to drop.

"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," lead author Dr Neil Hammerschlag said.

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"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."

During the years of decline, 120 sevengill shark sightings were documented and one was witnessed attacking a live seal.

The number of great white sharks around Seal Island have declined since 2015. Photo / Getty Images
The number of great white sharks around Seal Island have declined since 2015. Photo / Getty Images

Historically, the sevengill had only appeared 18km away from Seal Island, within inshore kelp beds.

The study suggested the decline in great whites could be due to overfishing or habitat loss – or that they had moved elsewhere to due to shifts in environmental conditions or prey.

A previous study found both species of shark were being prayed on by killer whales.

These findings were published in the online journal Scientific Reports.