Great white shark detectives

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29th May 2012
Submitted by heather

Despite their notoriety, great white sharks remain a mystery. So Thomas Peschak ventures out in a flimsy kayak to uncover the secrets of the fish we love to fear...

Great white shark detectives

Despite their notoriety, great white sharks remain a mystery, so researchers have had to find new ways to get closer to their subjects. Marine biologist Thomas Peschak and his colleagues venture out in flimsy sea kayaks to uncover the secrets of the fish we love to fear.

A long, shadowy form cruised close to a beach packed with swimmers and sunbathers. A steely-grey dorsal fin punctured the glassy surface. What was unmistakably a great white shark headed into water so shallow it left whirlpools of sand in its wake. Just metres from some bathers, it turned and swam along the beach away from them.

It could have been a scene from Jaws. What was the shark up to?

This was the summer of 2003 at Shark Bay, South Africa, an inshore area a few kilometres north of Dyer Island and Shark Alley. The next day, we saw three more great whites in the same area, so we began daily surveys. On some of our 10km transects, we found more than 20 different great whites, an astonishing density.

These sharks differed from those we had studied near Dyer Island the winter before. More than 95 per cent of the sharks encountered inshore were females, while the Dyer Island populations were 60/40 female to male.

These sharks were also distinctly larger (over 4m in length) and smaller (less than 2.5m), with very few individuals in between. In addition, female sharks here exhibited fresh bite wounds around their pectoral fins and gill areas. Why exactly were they gathering so close to the shore? Were these feeding, mating or birthing grounds?

Never-seen behaviour

 
We needed more direct behavioural observations to answer these questions. Our usual motorised research vessel was of little use, as it was unable to enter very shallow water. Plus, the electromagnetic discharges and vibrations emitted by the outboard engines disturbed the sharks.
 
Without the funds needed for aerial observation, we settled for a mode of transport that was manoeuverable and quiet – non-motorised sea kayaks.
 
This up-close study of sharks has revealed unusually high levels of social interactions for what was previously considered a solitary species. The sharks methodically swim up and down, parallel to the beach, their paths crossing at frequencies that are unlikely to be random.
 
When two sharks meet, they swim ever-tighter circles around one another and then often follow each other along the beach. These interactions occur at a very relaxed pace, without any signs of aggression or obvious competition. Could they be a prelude to mating?
 
It will take more time in the field to be sure. Our biggest obstacle is the short time the sharks spend inshore. After a few months, they suddenly disappear from the shallows and, while some head to Dyer Island to hunt seal pups, many vanish completely. Where do they go? To find out, we needed more sophisticated technology. Enter Ramon Bonfil of the Wildlife Conservation Society, king of satellite tagging. 
 
Crossing the Indian Ocean
 
28 February 2004: dawn is breaking over the eastern fringes of the Indian Ocean, a few kilometres off the western coast of Australia. A light breeze ripples the water surface. Suddenly, a small canister topped with an antenna bobs up and starts transmitting information gathered during three months spent largely under water. Satellites orbiting 850km above pick up the signal and send it across the world.
 
A few hours later, Ramon Bonfil arrives at his New York office and nearly chokes on his breakfast bagel. He types the following email message: “Nicole is in Australia!”
 
Nicole, now a 3.8m-long great white shark, was first sighted and identified in 1999 near Dyer Island. We observed her returning to the area every year between July and December. But her whereabouts for the first half of the year were a mystery.
 
In 2001, researchers showed that white sharks from South Africa were genetically closely linked to white sharks off Australia – suggesting that some individuals may cross the Indian Ocean.
 
This would have major implications for great white conservation. Before 2004, great whites were protected in South African and Namibian waters, but were still legally caught in most other waters for their jaws, teeth and fins. With the species not listed on CITES, the Convention on International Trade in Endangered Species, little could be done to stop this exploitation.
 
Nicole was tagged on 7 November 2003 with a PAT satellite tag programmed to remain attached to her until 28 February 2004 – when it surfaced near Australia. Her 11,000km journey represents the first recorded transoceanic migration for a great white. Then, on 20 August 2004 she returned to South Africa. In just over nine months, Nicole had swum more than 22,000km.
 
Armed with the evidence that South Africa’s protected sharks visit unprotected waters, a case was made at the 2004 CITES meeting to list the great white on CITES Appendix II. The proposal was accepted, and trade in any part of the species is now prohibited. 
 
We are now closer than ever to understanding the true nature of this predator. But we still have so many questions. That’s the thing about great whites – the more you study them, the more mysteries you uncover. Back to the kayak, then…
 
To visit Thomas Peschak's website, click here
 
 
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