South Africa's famous great white sharks have become a major draw for tourists in recent years, but according to a new report that human interaction may be one of the main threats to the population's future. The latest research reveals that the number of great white sharks off the South African coast is declining rapidly, with the current population potentially too low to revive.

There are 350-520 great white sharks left off the South African coast, 50 percent fewer than previously thought, according to a six year study carried out mainly in Gansbaai, a shark hotspot nearly 100 miles from Cape Town. According to the researchers, the sharks could die out as they face threats of human interference, ocean pollution, and a limited gene pool

"South Africa's white sharks faced a rapid decline in the last generation and their numbers might already be too low to ensure their survival," said Sara Andreotti, research leader and marine biologist at the University of Stellenbosch.

Scientists say there are still thousands of great white sharks off the coast of Australia, Canada, and the east coast of the United States.

Thousands of tourists travel to South Africa's Western Cape each year to catch a glimpse of the ocean's top predator from underwater cages, but human interaction has made the largest contribution to declining local shark numbers.

Shark nets used to protect swimmers and surfers killed more than 1,000 great whites off the Durban coast in the 30 years up to 2008, while trophy hunting and pollution also killed off large numbers of a species which can trace its lineage back 14 million years.

South African great white sharks also have the lowest genetic diversity of all white shark populations globally, making breeding more problematic and the likelihood of illness higher, the study showed. The report included documentation of individual sharks by their dorsal fins.

There are only 333 great whites capable of breeding in South African waters, below the 500 usually needed to prevent "inbreeding depression," the study found.

"We are already in a situation where our number of breeders is below the minimum level required for a population to survive," Andreotti told reporters.

Losing great white sharks, which have no natural predators, would have a knock-on effect on ocean ecology. Common prey, such as the Cape fur seal, could flourish in their absence and reduce fish numbers.

South Africa helped pioneer great white shark conservation and in 1991 became the first in the world to declare the predator a protected species, with other countries including the US and Australia following suit.