A record 27 great white sharks have been tagged by scientists around the Titi (Muttonbird) Islands off the northeast coast of Stewart Island.
The scientists are studying the periods during which great whites inhabit 'hotspot' locations, whether the sharks are resident or transient at these locations, and the size of the population inhabiting New Zealand.
The Chatham Islands and Stewart Island are two great white shark hotspots. They aggregate in these areas during autumn–winter to feed on NZ fur seals, which form large colonies on rocky islands.
The three-week field tagging trip was undertaken by scientists from the National Institute of Water and Atmospheric Research (NIWA), Department of Conservation (DOC), and the University of Auckland during April this year.
Acoustic tags were injected into the muscle below the dorsal fins of the sharks.
"Previously we have used 'pop-up' tags. They stay on the shark for a predetermined time and record depth, location, and temperature, so they are useful for tracking shark movements to the tropics and back," explained NIWA Principal Scientist Dr Malcolm Francis. "After about a year the tag 'pops up' and transmits its data via satellite".
Each tag costs about $5,000.
"On this trip we mostly used acoustic tags as we wanted information on a small scale, which we get with acoustic tags – it's accurate to within a kilometre - and they are cheaper at $400 a tag," says Dr Francis.
The scientists hope to collect detailed data on each tagged shark's movements.
Previous research work has shown that nearly all great white sharks migrate northwards to warmer waters during winter–spring and spend several months in the tropics.
Great white sharks were protected in New Zealand waters in 2007 and cannot be targeted by fishers.
3 News
source: newshub archive
