More of New Zealand's great white sharks to be tagged
An international team of marine scientists returns to the Chatham Islands next week hoping to fit satellite tags on up to 13 great white sharks. The tags will allow the scientists to track the sharks' movements for up to nine months.
3 March 2006.
The team is led by Dr Ramón Bonfil of the New York-based Wildlife Conservation Society (funded by National Geographic), Dr Malcolm Francis of the NIWA, and Clinton Duffy of the Department of Conservation.
White sharks are long-lived and slow to reproduce. They have a ferocious reputation, but their population numbers are low and have declined drastically in some parts of the world. Better information on the behaviour and distribution of white sharks will help inform management decisions about their protection.
In April last year, the same team of scientists used satellite tags on New Zealand great whites for the first time. They tagged four sharks using pop-up archival tags (PAT tags) which record information about the depth, temperature, and light levels as the animals swim through the water. The tags then detach at a pre-programmed date, float to the surface, and transmit the data via satellite. One tag detached prematurely, but the others provided unexpected results.
All three sharks travelled great distances to tropical regions. "We knew white sharks turned up in the tropics on occasions," says Dr Malcolm Francis, "but to see all of them travel there was a surprise. If anything, we thought they'd move closer to mainland New Zealand."
This year, the team plans to follow the sharks for a longer period, programming their tags to stay on for up to nine months (rather than a maximum of six). They are keen to check whether other sharks make similar long distance journeys and whether any of them return to the Chathams.
The team hopes to tag eight sharks with the PAT tags, and to tag five sharks with the more sophisticated 'SPOT' (Smart Position Or Temperature Transmitting) tags. This will be the first time SPOT tags have been used on sharks in New Zealand waters.
The SPOT tags are attached to a shark’s dorsal fin and have an aerial. They will transmit data to satellites whenever the shark’s fin breaks the surface of the water. "During their long distance journeys, the three sharks last year spent 60-70% of their time in the top few metres of water, so we're quite hopeful that we can get almost real-time information about shark movements from the SPOT tags," says Dr Francis.
To do the tagging, the team are again working with Tim Gregory-Hunt, Chatham Islands cage diving operator and skipper of Tessa B. PAT tags can be attached using a long pole. SPOT tags are more challenging because the shark has to be caught and partly hoisted out of the water onto a 'cradle' or stretcher at the side of the vessel. Water is continuously run over the shark’s gills, and a vet monitors all parts of the operation. Dr Bonfil has successfully used SPOT tags on sharks in South Africa.