Holiday habits of our great white sharks
Scientists say project following great whites’ movements will help to protect species
Scientists aim to help protect great white sharks by tracking where they go on holiday. Data gathered from 10 years of tracking the sharks — a protected species — will be used to discover where and when they are at the greatest risk of being inadvertently caught by fishing gear.
Scientists from Niwa and the Department of Conservation (DoC) have tagged 95 sharks since 2005, mostly from around Stewart Island and the Chatham Islands.
The sharks’ behaviour and movements have been followed as they head north from the islands.
Niwa fisheries scientist and shark specialist Dr Malcolm Francis said researchers were surprised to find most took “tropical holidays” during the winter. “The first one or two we saw do this came as a real surprise. They go between May and July and return between December and March, spending more time out of New Zealand waters than in.” By comparison, great whites living around the southern Australian coast travelled mainly up the coasts, seldom venturing into the open ocean.
The scientists had now finished tagging and the data was being analysed to see if the sharks’ paths were crossed by the distribution of commercial fishing in those areas.
“We want to see if there are any links with where sharks are known to occur, and the time of year, to see where . . . they are most vulnerable.”
There were more reports of sharks being caught as bycatch before the species was protected, he said. “We’ve had very few since.” The analysis information would be available for policy makers to make decisions on species management.
The project’s aim had been to find out how mobile the sharks were, how far they travelled and where to, and their habitat requirements.
The tagging also showed great whites travelled in “a remarkably straight line” on their migrations. They usually travelled about 100km a day, but had done up to 150km.
In the afternoons, they tended to spend time at the surface, but also regularly dived between 200m and 800m. The record depth was 1246m.
“We assume they’re feeding. We also don’t know how they navigate in a straight line, or why.’’
DoC shark scientist Clinton Duffy said the researchers found juveniles inhabited shallow coastal waters and harbours around New Zealand, feeding mainly on fish.
But once they grew to about 3m the sharks began to feed on marine mammals and headed towards seal colonies. “Biologically, white sharks are fascinating,’’ he said.