Rise and rise of the killer whale?

Published on Sunday 20 July 2008 22:01

EXPERTS are monitoring sightings of killer whales swimming in Scottish waters to determine whether there has been an increase in the number of the mammals.

A two-year survey is being conducted by Aberdeen University to establish whether orca populations are increasing in Scotland's seas or if there are simply more recorded sightings.

Experts are also looking at the relationships between different killer whale groups in the North Atlantic and building up a catalogue of photographs so more individuals can be identified.

The Shetland-based survey is being carried out by Andy Foote, an Aberdeen University postgraduate researcher, and Dr Volker Deecke from the St Andrews Sea Mammals Research Unit.

They will be tracking the movements of killer whales and feeding information into a database to draw up a clearer picture of the number and habits of the mammals.

Speaking about the project, which has been funded by the Carnegie Trust, the European Commission, the Scottish Executive and Scottish Natural Heritage, Mr Foote said: "As part of the getting-to-know-you process, once an orca is identified from features on photographs, it is given a number and is named after a location.

"For instance, a seven-metre-long adult male, which often operates solo, is number 014 and is called Bigga after the whale-shaped island in the sound between mainland Shetland and neighbouring Yell."

He said that sometimes Bigga joined a five-strong pod regularly seen around Shetland that is headed by an adult male given the number 032. He added that it was the seal population and mackerel shoals that keep the mammals in food.

"They do seem primarily interested in seals and go very close to the rocks while hunting," Mr Foote said. "They must be touching the rocks at times. One we saw recently had a big new scar along its body that possibly resulted from contact with rocks. However mackerel shoals forming far out to sea are another important food source and they attract pods from a wide range of the North Atlantic."

Dr Peter Evans, director of Sea Watch Foundation, set up to monitor whales and seals in the British Isles, said the foundation had found the number of killer whales had increased in the waters around Shetland and Orkney. This, he said, was a result of an increase in food available to them – including a rise in mackerel and herring in the northern part of the North Sea.

He also said herring stocks had shifted in northern Norway, forcing the whales into Scottish waters. He added: "The third reason is that the seal population is increasing and is providing the whales with extra food in the summer."

However, Richard Fairbairns, director of Sea Life Surveys, a research project in Tobermory, Isle of Mull, said that in his area there had been an increase in sightings, not whales.

FACTBOX

THE Orca or Killer Whale is the largest species of the oceanic dolphin family. It is found in all of the world's oceans, from the cold Arctic and Antarctic regions to warm, tropical seas.

Orcas are distinctively marked, with a black back, white chest and sides, and a white patch above and behind the eye.

Males typically range from 19-26ft and weigh in excess of six tonnes. Females are smaller, generally ranging from 16-23ft and weigh between four to five tonnes. The largest Orca ever recorded was a male off the coast of Japan, measuring 32ft and weighing more than eight tonnes. On average, an Orca eats about 45kg of food a day.