Scientists have made a rare sighting of a family of orca killer whales off the west coast of Ireland. Researchers spotted seven of the huge mammals as they breached the Atlantic waters.

Ocras, the killer whales with the distinctive black and white markings, can weigh up to six tons and measure up to 26 feet in length.

The sightings were made by researchersthe onboard the Marine Institute’s Celtic Explorer vessel working on the ongoing "Cetaceans on the Frontier" survey, part of the national Sea Change strategy.

The team made the discovery on Friday near the Porcupine Seabight, a deep-water basin lying south-west of Ireland and south-east of the Porcupine Bank.

Read more: Irish Air Corps releases rare footage of 80ft whales off of Co. Cork

On their blog, Cetaceans on the Frontier, the researchers wrote: “Two enormous, black, triangular dorsal fins came looming out of the water together on our starboard side no more than 50m out,” the team stated on their blog.

“As the minutes ticked by at incredible speed our count increased from two to three to five to seven. A mix of large fins and medium to small fins were noted, indicating a family group.

“After 20 minutes or so of fantastic viewing with photo-ID images secured, the group of killer whales split off on their own track and we left them to it continuing back on our survey route.”

This was the first time the explorers had seen killer whales.

They wrote, “Some of the marine mammal observers present today have many hundreds of observation hours and thousands of at-seas miles under their belt without having encountered killer whales before today, whilst for some of the students joining us on the trip for their first time offshore, things could not have worked out better.”

Here’s footage taken from previous sighting in Donegal: