South Africa's great white sharks are in danger of dying out as a result of human interference, ocean pollution and a limited gene pool.
There are between 350 and 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 160km from Cape Town.
"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.
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.
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.
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 Australia and the US following suit.