Sunday, 27 July 2014

White sharks at Muriwai

Encounters with sharks underwater in Tonga recently (see below) have caused me to reflect on these magnificent creatures, and the shark attack last year at Muriwai Beach, which killed film maker Adam Strange. I had taken a South Island friend swimming at Muriwai three days before the attack, and was struck by how the coroner's report, and the media generally had concluded that there was no way the death could have been prevented. Adam had been swimming in deep water between the gannet colony and Oaia Island, home to a thriving fur seal outpost.

Muriwai and Oaia Island at sunset ... (U Machold)
Fur seals are a staple of the great white shark diet. There are estimated to be at least a hundred great whites in Foveaux Strait at Stewart Island where seal colonies proliferate. In the 1990s, fur seals began to breed again in the North Island, after years of being hunted to near extinction, and Oaia Island is one of the few significant colonies here. Great whites migrate up to 3,300 km annually and it's a reasonable assumption they visit Oaia Island on the way. Water visibility at Muriwai is very low, which means sharks are invisible to us, and may cause sharks to mistake human swimmers for seals.

NIWA has tracked the migration routes of great whites using tags

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