A nearly 5 metre long female white shark next to the boat

A trip to Seal Island (part II)

Seal Island, launchpad in the foreground
Seal Island, launchpad in the foreground

The first couple of hours of our time at Seal Island were spent watching for natural predations by white sharks on seals. I found it quite emotionally draining, and almost gave myself whiplash swivelling my head from side to side in an effort not to miss anything. After that the boat was anchored, and a small chum slick was created from the boat in order to draw sharks closer. A tuna head on a float attached to a rope was also used to create water movement and a scent trail to draw sharks closer for observation.

Whenever a shark approached, Adrian and Alison attempted to identify it (they recognise many of the sharks that frequent the island from their markings and scars), estimated its length, determined (if possible) its gender, and any other distinguishing marks. A GoPro camera, mounted on a pole between two laser lights enables the researchers to estimate the dimensions of each shark more accurately, if it comes close enough to the boat to be filmed underwater. This is a remarkable yet simple technique that enables precise calculations because the distance between the two lights, the position of the camera, as well as the cameras’ field of vision, is known. This can also be a way of enhancing the information-gathering potential of the BRUVs currently being tested in False Bay. Tissue biopsies are taken on some of the sharks, also using a long pole.

There was much excitement (from me, at least) when we saw one of the sharks tagged by the Ocearch expedition. A small piece of red fishing line was caught on its tag; Adrian reached over and removed it when the shark surfaced next to the boat. The tag was much smaller than I’d imagined. Unfortunately the magic confluence of enough time at the surface plus satellite overhead did not occur, and when I searched the tracking website for a False Bay ping on 25 July I was disappointed. So I don’t know the name of this shark, or where she was from, but I was very happy for the sighting!

The Ocearch-tagged white shark that visited us
The Ocearch-tagged white shark that visited us
The tagged shark on the surface
The tagged shark on the surface

Another visitor who caused great excitement was an unknown (i.e. not recognised by her distinguishing marks) female shark of absolutely tremendous proportions – she was nearly five metres long. Adrian said she was the largest white shark he’d seen in False Bay. She swam around the boat several times. The sharks were surprisingly hard to see from above, even with absolutely calm conditions and bright sunlight. The water clarity was fairly good, too. Their bodies are extremely well camouflaged from view.

A nearly 5 metre long female white shark next to the boat
A nearly 5 metre long female white shark next to the boat

While we were at anchor and looking at sharks from the surface, the cage diving boats were at anchor nearby, and looking at sharks underwater from their cages. They also spend a bit of time towing a decoy (cut out of a seal, made from rubber or carpet or similar material) behind their boats in order to elicit a predatory response from passing sharks.

After an enthralling procession of beautiful animals past the boat, it was time to raise the anchor and head back to shore.

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Clare

Lapsed mathematician, creator of order, formulator of hypotheses. Lover of the ocean, being outdoors, the bush, reading, photography, travelling (especially in Africa) and road trips.

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