Gardaí and wildlife and conservation officers are investigating the discovery of more than 40 dead grey seals, the majority of them pups, on the foreshore on Beginish Island north of the Great Blasket off Co Kerry.
A further five adult seals were found shot in the head in nearby Brandon Bay. All of the seals on Beginish appear to have been shot, although a small number of the pups may have died of natural causes.
Divers with a local diving school discovered the seals on Wednesday.
The Minister for the Environment, Mr Roche, who has responsibility for the National Parks and Wildlife Service, condemned the slaughter as "cruel and barbaric". The seals were a protected species under the Wildlife Act 1976, he said, and it was an offence to hunt or kill them.
Sgt Mossie O'Donnell of Dingle Garda station said the seals had been shot - they had not been bludgeoned and they had not been disembowelled as suggested earlier in the day. "This is a despicable type of crime," Sgt O'Donnell said. "It has happened in this area before."
Conservation officers also denied the pups had been clubbed or hammered with nails. "The evidence so far is the seals were shot," the National Parks and Wildlife Service manager in the region, Mr Paddy O'Sullivan, said. Last night he said the service was preparing to mount a round-the-clock watch on the seals in west Kerry
Fewer than 600 grey seals, or a third of the country's total seal population, live on the Blasket Islands. The seals breed during August and September. They are particularly vulnerable during and after the breeding season.
There has been concern in recent years over a rapid decline in the grey seal population in the area. The bulk of the seals live on the Great Blasket and their presence is one of the reasons it is being put forward for World Heritage site status.
Conservation officers fear that the attacks on Beginish could have wiped out most of this year's pups.Mr Roche urged has anyone who had information about the killings to contact Kerry gardaí.
Ms Pauline Beades of the Irish Seal Sanctuary called on the wildlife service to protect the seals. Seals were part of the attraction of west Kerry, where Fungie the Dingle dolphin was "living proof" that eco-tourism worked, she said.