Data gathered from 10 years of tracking great white sharks
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 have
spent the past decade tagging great whites - a protected
species - and following their movements.
Since 2005, 95 sharks, mostly from around Stewart Island and
the Chatham Islands, have been tagged and their behaviour and
movements observed as they made their way north from the
islands, mostly towards Fiordland and up the West Coast.
Niwa fisheries scientist and shark specialist Dr Malcolm
Francis said only a few of the tagged sharks headed up the
east coast and, when they did, it was mostly in deeper water.
The group had now finished the tagging programme and the data
was being analysed to see whether the sharks' paths were
crossed by commercial fishing boats 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 the areas they
are most vulnerable.''
There were more reports of sharks being caught as by-catch
before the species was protected, he said.
''We've had very few since.''
There was mostly gill net and longline commercial fishing
operating off the West Coast and the majority did not have
wide observer coverage on board to report any interactions
with the sharks, he said.
The information from the analysis would be available for
policy-makers to make decisions on management of the species.
The project's aim had been to find out how mobile the sharks
were, how far they travelled and where to, and their habitat
Researchers were surprised to find most great whites took
''tropical holidays'' during the winter, Dr Francis said.
''The first one or two we saw do this came as a real
"They go between May and July and return between December and
March, spending more time out of New Zealand waters than
By comparison, great white sharks living around the southern
Australian coast travelled mainly up the coasts, seldom
venturing into the open ocean.
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 a day.
In the afternoons, they tended to spend time at the surface,
but they also made regular dives of between 200m and 800m -
the record depth was 1246m.
''We don't know why they're doing that - we assume they're
feeding. We also don't know how they navigate in a straight
line, or why.''
''It's a big puzzle and not one we are likely to work out,''
Dr Francis said.
While researchers had found out where and when the sharks
went around northern Stewart Island, they did not know what
they did close to mainland New Zealand.
Despite the controversy around the sharks' interaction with
people in recent times, he believed people were ''relatively
''Their focus is on seals and fish, not humans.''
Doc shark scientist Clinton Duffy said the researchers found
juveniles inhabited shallow coastal waters and harbours
around New Zealand, feeding mainly on fish.
Once they grew to about 3m in length, they began to feed on
marine mammals and headed towards seal colonies.
Estimating the size of the population was difficult, as new
sharks appeared each year around Stewart Island, he said.
''Biologically, white sharks are fascinating. The opportunity
to tag them and find out their migratory behaviour over the
past decade has been incredibly interesting and valuable.''