At a presentation in the Two Oceans Aquarium in Cape Town, marine biologists from the Dyer Island Conservation Trust in Gansbaai, painted a bleak picture of the state of the global Great white shark population. In the Gansbaai area, they identified 532 individuals over a five year period and when these numbers are extrapolated to a regional scale the estimated population is only around 1,000, despite the fact the species has been protected in South Africa since 1991.
How did they do it?
Over a 5 year period, researchers from the Dyer Island Conservation Trust have taken around 20,000 photos of dorsal fins of the Great whites in Shark Alley, located between Dyer Island and Geyser Rock of the South African coast near Gansbaai. Shark Alley has one of the highest concentrations of Great whites globally and is well-known for shark cage diving. The researchers joint the Marine Dynamics shark boat on a daily basis not only to take pictures of shark fins, but also to raise awareness on shark conservation issues amongst the tourists embarking on this exciting activity.
The dorsal fins of dolphins and sharks are unique, a little like human fingerprints, each with small or not so small bits taken out by their peers. Each of the 20,000 fins were painstakingly compared using Darwin, a shark fin identification programme. One of the challenges was that fins, unlike fingerprints, change over time, such as the photo below showing the changing outline of Vindication’s dorsal fin. Darwin would sometimes pick up the matching shark straightaway, whereas other times Ed, one of the researchers on the team, would need to compare 100s of fin pictures before finding the matching one. Out of these 20,000 photos they identified 532 individuals. The full scientific paper is available online.
What are the greatest Shark threats?
Sharks are not residential, but migrate up and down the coast, sometimes over very large distances. Many of the sharks identified in Gansbaai would travel as far north as Madagascar. This means that many Great whites pass through Mozambican waters, were 1,000s are killed for their fins, sold to Asia for the shark fin soup industry. On a global basis, it is estimated that each year 10 million sharks are killed for this reason. Furthermore, an estimated 50 million sharks get caught up in fishing nets and lines and die as by-product of the fishing industry. These numbers are across the board of all shark species and the Great white is a percentage of those figures.
Off the coast of KwaZulu Natal there are still very old fashioned shark nets and drumlins to “protect” the surfers and bathers enjoying these warm waters. The efficacy of the nets is a highly contentious topic, but we know that the nets are designed to kill whatever gets into it, including dolphins, turtles, rays, and sharks. In the 23 km or so of nets along a 320 km coastline, the Natal Shark board retrieves around 30-40 great whites and many 100s of other sharks every year.
It is therefore no surprise that marine conservationists are extremely worried about the status of the Great white shark, an apex predator of our oceans. They are calling for better international policies to protect the shark, more education and awareness raising, and a more positive profiling of the shark in the media.