Malcolm Francis, of the New Zealand National Institute of Water and Atmospheric Research (NIWA), says, “We used to think great white sharks were shallow-water coastal species that lived in cold areas, where there were lots of seals to eat,” he said. “Now we have changed our impression of what they do.”
What changed his mind were three four-metre-plus great whites tagged off the Chatham Islands, east of New Zealand’s main islands, which arrived in Tonga, 3000km north, for a midwinter feast of humpback whale calves.
NIWA and the Department of Conservation in New Zealand have been attaching satellite tags to great whites, to measure position, depth and water temperature. After several months, the tags pop off and float to the surface, where the data is transmitted to a satellite.
Dr Francis said that this year two Stewart Island whites had gone 4000 kilometres to Queensland’s Great Barrier. Surprisingly, they go in a straight line. “They seem to know where they are going,” he said, noting that they moved through the water at between 4kmh and 5kmh, or an impressive 120km a day.
Up to 70 per cent of the time they are near the surface but this winter one of the whites dived. “We’ve got what we think is a world record of 1000 metres for a white shark.” He believes it would have gone after a giant squid or phosphorescent fish. At that depth it would be pitch black and the white would have been guided in by the fish glow.
“They head off to the tropics, and we’re not quite sure what they are doing but we think they are showing interest in humpback whales,” Dr Francis said.
Tags were found in humpback whale calving areas. Evidence exists of whites feeding on dead whales and dead calves. Now NIWA thinks the whites follow the whales when seal numbers decline in colonies over winter.