An unprecedented feeding aggregation of Killer whales spotted?in offshore waters off northwest Ireland last Friday, according to the Irish Naval Service.

Large numbers of Orca have been sighted off Ireland. [Irish Naval Service]

"On Jan 27th and 28th we observed a significant number of Killer whales approx 30 miles West of Tory Island, approx position 55 degrees 30 minutes North 009 degrees 30 minutes West." Paddy Harkin, Captain of the L.E. Niamh said.

"In one of our photographs upwards of eight Killer whales can be observed in a single photo, an estimate of 10 whales being visible at any one time is on the conservative side. On one occasion at least a dozen Killer whales were within 200 metres of the ship."

The Killer whales were among large shoals of mackerel, and there were approx 25 fishing vessels mackerel fishing in the area.

Large quantities of mackerel were being caught; one foreign fishing vessel had 4,000 tonnes onboard while several others had over 1,000 tonnes, and all fishing vessels were catching in excess of 200 tonnes per day.

According to Paddy, several of the fishing skippers reported that the Killer whales had accompanied the mackerel shoals and fishing vessels from 57 degrees north, which is to the west of the Hebrides.

The fishing skippers estimated that there were over 100 Killer whales in total, and these estimates are consistent with best estimates of the Irish Naval personnel.