Hans J Marter

25 August, 2008

SHETLAND's resident killer whales live off common seals, have an intensive social life and are the pride of islanders.

These are the preliminary findings of a three month field study carried out by a group of marine scientists from the universities of Aberdeen and St Andrews.

Their visit to the isles was part of a long term study into the population structure and identification of killer whales around Scotland's coast.

They have had numerous close sightings of groups of the cetaceans in Shetland waters, but mainly of a group of five animals and an individual male.

Speaking before leaving Shetland, Dr Andy Foote, of Aberdeen University, said the project had so far identified around 25 of the estimated 30 to 40 orcas that live in Shetland's coastal waters.

Colleague Dr Volker Deecke, of St Andrews University, added: "We have learned, first of all, that some of the animals are quite resident. We have followed a group of five animals for a six week period.

"A big part of their diet during that time was marine mammals. We didn't know when we came here whether they were fish or mammal eaters, or whether they eat both. We were able to document that they were always feeding on marine mammals.

"That ties in with the acoustic as well. The animals are extremely quiet, they don't call very often, and that is consistent with them hunting marine mammals, because marine mammals have good underwater hearing. All the predation we witnessed were harbour seals," he said.

Researcher Harriet Bolt said the killer whales’ eating habits had contributed to the decline of the local seal population.

The team found that the group structure of animals was rather "fluid", giving rise to speculation that animals were gathering purely to hunt together.

Dr Deecke, who had previously carried out orca research in the Pacific, said the local behaviour was different to what he had experienced elsewhere.

"We found that the killer whales we followed this summer were very different from killer whales in the Pacific that live in very stable groups, or at least some populations do. Some animals never leave the group, they are born into the group and they die in the group.

"Here it may be an adaptation for different hunting strategies, in that they form bigger groups when hunting certain prey. But that is speculation," he said.

The team said that local people had been “brilliant” in supporting their research by alerting them to killer whale sightings and providing a wealth of background information.

"You really get the sense that these animals are part of people's lives. Local people are proud of them, thrilled to see them, and keen to show them to other people.

"Islanders have been very supportive of our research work. It was a real pleasure working up here,” Dr Deecke said.

The team is now back on the Scottish mainland where they will spend the next few months working their way through photos, genetic material and acoustic recording before returning to Shetland next summer.

Dr Foote, however, will be back in the isles in October when he joins skipper George Anderson on board the pelagic trawler Adenia heading for the mackerel grounds.

During the last few years, Dr Foote said, he had observed groups of up to 50 killer whales feeding of mackerel off Shetland.