Three dead dolphins have been washed ashore on the west coast.
Officers from the Irish Seal Sanctuary travelled to northwest Mayo yesterday to examine the dolphins, which were washed up earlier at Portacloy and Blacksod Point.
Samples will be taken from the carcasses and post-mortems performed to determine the cause of death.
Mr Terry Flanagan, chairman of the Irish Seal Sanctuary, said last night he was concerned, particularly as the deaths came in the wake of recent seal deaths along the Wexford and Welsh coasts.
Mr Flanagan said there was no indication yet as to why the Mayo dolphins died.
The Irish Seal Sanctuary has renewed its call on the relevant authorities, such as the Department of the Marine and BIM, to investigate the high mortality among marine mammals in recent months.
The Wexford seal deaths took place in an area where there had been a recent oil spill, Mr Flanagan said.
