Saturday, July 09, 2005

Unexpected move done by tagged great white shark

Tagged great white shark makes unexpected move – implications for conservation
New Zealand and Mexican marine scientists analysing the movements of great white sharks in the southwest Pacific say that news that one of the sharks fitted with a satellite tag in April had left New Zealand waters has implications for the species’ conservation and management.

The four-metre shark, nicknamed Tessa, was tagged at the Chatham Islands on 8 April by an international team of marine scientists led by Dr Ramón Bonfil of the New York-based Wildlife Conservation Society, Dr Malcolm Francis of the National Institute of Water and Atmospheric Research, and Clinton Duffy, a Department of Conservation scientst.

This is the first time pop-off archival satellite tags (PAT tags) have been used to track white sharks in New Zealand waters. PAT tags collect information on depth, temperature, and light levels and store this for several months. This information is then used to reconstruct the animal’s movements. At a predetermined date and time the tags detach, float to the surface and transmit summaries of the data via satellite to the scientists.

Tessa’s tag began transmitting its position to Dr Bonfil at the Bronx Zoo at 11:19 hrs GMT on 5 July. The tag was 1000km NNE of Chatham Island and 800km east of the North Island, placing Tessa in international waters close to the southern end of the Louisville Ridge, a remote chain of underwater volcanoes.

The result surprised the team, because the shark had travelled across very deep water to an area not previously known to be inhabited by white sharks, Mr Duffy said today.

“The unexpected result demonstrated the value of the research and how little is known about these animals.”

“We speculated it was possible that white sharks may move out of New Zealand’s Exclusive Economic Zone to the north, as there have been occasional captures reported from tuna longliners fishing near the Three Kings Rise, but none of us expected any of the sharks tagged at the Chathams would head in that direction.”

Dr Bonfil said the use of satellite tags “provides an incredible insight into the lives of these large, mobile sharks, which was previously unattainable”.

Data collected from the tag would provide extremely valuable information on the movements of white sharks, he said.

The tag will continue to transmit archived information for another week, after which it will be possible to reconstruct the approximate route taken by the shark, estimate its swimming speed, and determine its daily depth and temperature ranges.

Dr Francis said that by studying the movements of tagged sharks, they “hoped to understand more of the species’ habitat requirements, migrations and behaviour. Without this basic information, it is very difficult to determine how much impact humans are having on them, and to decide on the best way to conserve their population.

Although white sharks have received a bad press in the past, we now realize that they have decreased dramatically in numbers in several parts of the world and need our protection. White sharks grow slowly and do not produce many young, so they cannot sustain high catches.”
Dr Bonfil said: “we have no way of knowing what the shark is doing in that area, it might be feeding up there, or moving further on, we don’t know.

However, it reinforces the need for international cooperation on research and management of this species”. Based on his previous work in South Africa he said it was “possible the shark would return to New Zealand, possibly even to the place it was tagged at the Chatham Islands.”
The remaining PAT tags are scheduled to release on 5 September and 5 October 2005.


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