NZ great white sharks take 'tropical holiday'
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China Daily via agencies, July 8, 2011
New Zealand's great white sharks enjoy an annual "tropical holiday", swimming thousands of kilometers to warm South Pacific waters before returning home, researchers said on Thursday.
Scientists who monitored the giant predators for the past six years at Stewart Island, off New Zealand's south coast, found that they regularly set off for destinations such as Tonga, Fiji and Vanuatu in midwinter.
They then returned to Steward Island after about six months, some using their powerful navigational instincts to reach almost the exact spot where scientists had tagged them the previous year, the researchers said.
New Zealand's National Institute of Water and Atmospheric Research (NIWA) said the study provided an insight into the life cycle of great whites, the largest predatory shark, which can grow to 8 meters long.
"The pieces of the puzzle are gradually coming together," NIWA Principal Scientist Malcolm Francis said.
"We knew that most of our white sharks emigrate from New Zealand during winter and travel several thousand kilometers for a tropical holiday.
"Now we have discovered that many, perhaps most of them, make the return trip to exactly the same place in New Zealand."
Scientist studied great whites at Steward Island and the Chatham Islands, 750 km east of New Zealand, which are considered "hot spots" for the sharks because their large seal colonies are a rich food source.
Data from electronic tags showed the sharks made deep dives of 800 meters during their migrations, possibly to feed on squid and deep-water fish. One shark reached a depth of 1,200 meters on its way to Australia.
The researchers found large numbers of great whites at Stewart Island during this year's expedition in April, tagging 27 during the three-week trip, three times the previous record in 2009.
But NIWA, which conducted the research with the Department of Conservation and Auckland University, said it was still unclear whether great white numbers were stable or declining.
The species is listed as vulnerable and has been protected in New Zealand waters since 2007.
While it is known that great whites live up to 50 years, they mature slowly and produce relatively small litters of about 10 juveniles every 2 to 3 years, meaning populations take a long time to recover from any setbacks.
Francis said the ongoing study would help scientific understanding of the fearsome predators.
"We hope that we will collect a detailed and exciting dataset that tells us where each shark was and when," he said.
