Kaikoura dolphins provide questions

Press, 1 December 1987, Page 35

Kaikoura dolphins provide questions

The public perception of dolphins is heavily influenced by television’s “Flipper,” that Rin Tin Tin of the deep who is so friendly he would be cuddly if he weren’t so wet ’ The truer picture, though, is that of highly efficient predators, hunting for prey like wolves in a pack. Dusky dolphins, for example, are known to live in groups of up to 400 animals with apparently highly structured, co-operative feeding habits. The group will break up into smaller groups, or “pods,” when searching for food. When one pod finds a school of fish, it will herd it to the surface, where all the other pods will converge to take turns in polishing off the prey. But are the other pods sum-

moned by their colleagues, and if so, how? Or are they opportunists, taking their cue from, say, the seagulls which also gather for a free meal? And how do their feeding techniques change, depending on the seasons, the types of prey, and the behaviour of their prey? These are the kinds of questions being asked by American researchers In a long-running study of dusky dolphins off the Kaikoura coast. The dusky dolphin is a small species, growing to about 180 cm in length. It Is found only in the Southern Ocean, on both sides of southern South America and both sides of New Zealand’s South Island. In winter, they venture as far north as Hawke Bay. They are also occasionally seen off South Africa and Tasmania.

The reasons for coming to Kaikoura to study them include the abundance of high ground close to the sea — ideal for observation posts — and the availability of a well set-up base in the form of the University of Canterbury’s Edward Percival Field Station. The study has occupied Frank Cipriano, a graduate student from the University of Arizona, for the best part of three years. He is now back at Kaikoura, on his fifth trip in that time. During this summer’s programme, he is being helped by Bernd and Melanie Wurslg, on sabbatical leave from the California State University. Seven teams of Earthwatch volunteers are also helping, each team doing a two-week stretch sometime between September and late January.

Research consists largely of monitoring the movement of the animals, mostly by visual means, either from land or by boat. Some dolphins are captured, and details of age, sex, weight, size and condition noted before release. Some are fitted with tiny radio transmitters which allow them to be tracked at night or in poor weather. The team has set up base among the aerials and instruments of the weather station on the Kaikoura Peninsula, and other observation posts on the coastal hills. The dolphins are tracked with powerful, tripod-mounted binoculars, and a directional radio aerial for those fitted with transmitters. Members of the team take turns to monitor the signals at three-hourly intervals

through the night. The transmitters’ signals disappear when the dolphins are underwater, so the length and depth of dive can be assessed, which in turn gives clues to the type of food they are seeking. Frank Cipriano says that in summer the dolphins seem to stay close to shore by day and move further out in the evenings. In winter, they stay out all the time. He is interested in finding out how that relates to the different types of food species available. The only way to find out exactly what dolphins eat is to examine the stomach contents, but the team will not kill animals to find out. They are careful to minimise disturbance to the dolphins, to the extent of fitting the radio

transmitters with special magnesium nuts, which corrode within a matter of days and allow the devices to fall off (at SUS3OO apiece). Oh the rare occasions that a dead specimen is found, the stomach contents have shown that they tend to go for smaller species of fish and squid. Fishermen have occasionally voiced fears that the dolphins compete with them for commercial species, but that seems not to be the case. Mr Cipriano says their main food appears to be lantern fish, a small, non-commercial species found in deep water world wide. But they also eat some hoki, which could put them offside with fisherman as the fish becomes more in demand for surimi (fish paste) production.