Gauging the threat

Great white shark research project

The Problem

Thinking globally before locally

For the longest time, the vast majority of talk regarding great white shark populations across the globe, was being done without formally estimating how many resided at Dyer Island, Gansbaai.

The White Shark Trust, founded in 2002 and operated by Michael Schol (now of Save Our Seas), collected data for several years with a view to publishing such a study. For various reasons, that never came to fruition.

“But who cares?”

That’s not an unreasonable question. Nor is “What’s the Dyer Island population got to do with the rest of the world?” were it not for one simple fact.

That is, great white sharks (in addition to being awesome) are highly migratory. They rarely hang around one place for too long. I’ve seen the same sharks in both Gansbaai and Mossel Bay, multiple times. Sometimes separated by months, other times years. It’s not just a national occurence, either.

Big shark

Flag is just one of the many sharks to be spotted in both Mossel Bay and Gansbaai, South Africa. Photo by Alison Towner.

Shark Nicole was the first great white shark recorded swimming to Australia and back from Gansbaai. This lack of ‘residency’ in the traditional sense, means its not unreasonable to argue that every location that white sharks frequent, is of equal relevance to the rest.

If there’s one exception to this rule, it’s most likely going to be Gansbaai.

Or as Oliver Jewell likes to call it – the McDonalds Drive-Thru for great white sharks.

The great white shark capital of the world

Gansbaai is largely recognised as the great white shark capital of the world and rightly so. Researchers, tourists and film crews have been flocking to the town for years. The occurence of white sharks in this area is not a seasonal one, nor do they require extensive searching to find.

Marine Dynamics Shark Tours and the Dyer Island Conservation Trust had been wanting to get a population study of white sharks off the ground for years.

I joined the team specifically to facilitate this, viewing countless individual fin photographs taken over the course of several years. The rest of the team comprised marine biologists Oliver Jewell, Michelle Wcisel, Alison Towner and Ryan Reisigner.

It was my role to identify individuals so we could generate a population estimate for the species.

The above film consolidates all the key details about this project into a neat(ish) ten minutes. Because watching is easier than reading.

Data analysis and Results

Using a program called Darwin, I spent somewhere between eight and ten months, matching great white shark fins to eachother.

This gave us a database of individual animals, along with the dates they were sighted.

From this, a model was then used to calculate what the total population of great white sharks in Gansbaai was.

You can read the full publication at Plos One.

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