Tuesday, 09 September 2008
Another tagged New Zealand great white shark has migrated to the Great Barrier Reef off Australia – one of nine sharks to be satellite tagged this year.
The three and a half metre shark, nicknamed ‘Thomas,’ was tagged with a popup archival satellite tag. The tag records information on light levels (from which approximate daily latitude and longitude can be estimated) as well as water depth and temperature so that the shark’s movements can be tracked.
After a predetermined time (six months for this shark) the tag pops off the shark, floats to the surface and transmits the data to a satellite that emails the information back.
‘Thomas’ was tagged by Department of Conservation (DOC) scientist, Clinton Duffy, off Ruapuke Island in Foveaux Strait, in February. The satellite tag popped up at Swain Reefs, off Rockhampton, late in August.
"This is only 100 kilometres from where another tag popped up last year from a shark tagged at Stewart Island after having travelled over 3000 kilometres," says Mr Duffy.
The shark tagging project, which began in 2005, is an international collaborative programme being run by the National Institute for Water & Atmospheric Research (NIWA), DOC, and Dr Ramon Bonfil from Shark Tracker/NABU (Germany).
NIWA fisheries scientist Dr Malcolm Francis says this has been a bumper year for white shark tagging.
“Until this year we’ve only been able to tag six white sharks in three seasons of field work. This year has greatly added to our tally with three more being tagged at Stewart Island and six more at Chatham Islands. Two tags have failed but we still have six more tagged sharks in the water which are due to report back between October and January, offering us an amazing insight into the secret lives of these apex predators.”
Once all the data has been transmitted from the latest shark, the project team will be able to determine the route the shark took, how deep it dived, and the water temperatures it experienced.
“Previous tagged white sharks have dived as deep as 1000 metres and encountered temperatures ranging from 3 degrees in deep water to 24 degrees in shallow tropical waters. This huge range in temperature is very unusual among fishes,” Dr Francis says.
Other tags have popped up in New Caledonia, Vanuatu, and half-way to Tonga.
“Previously we thought great whites were cold water, coastal sharks but we now know that many make trans-oceanic migrations to tropical waters. The reason for their winter tropical holiday is still unknown but we think they may be searching for newborn humpback whale calves, because all tags have surfaced in or near known humpback calving sites.”