Marine experts say the world's second largest animal is becoming a more frequent visitor to the Welsh coast.
Footage of the whales was captured off the Pembrokeshire islands
Volunteers with the Sea Trust have captured footage of a school of up to 10 fin whales swimming near the Pembrokeshire islands.
They say the mammals were once a rare sight in Welsh waters but have become far more common in the past decade.
A similar school was spotted in the Irish Sea last summer but this sighting was much closer to mainland Wales.
The charity, part of the Wildlife Trust for south and west Wales, surveys and monitors marine life off Pembrokeshire.
Chairman Cliff Benson said the school was spotted as volunteers were helping a camera crew working on the BBC TV series Coast.
"We were actually doing a bit of a 'recce' last Thursday," he explained.
"They wanted us to show them some dolphins but as we were coming back in we saw these "blows" in the water - it was amazing.
"Initially it was just one, then another on the other side of the boat.
"There were at least six and there could have been as many as 10."
Adult fin whales can weigh anywhere between 30 and 80 tonnes and are the second largest animal on the planet behind the blue whale.
"Until recently they were as rare as hens' teeth," added Mr Benson.
"It's just in the last five to six years they have been recorded in much larger numbers off the coast of Ireland and also Cornwall."
He said there could be a number of factors responsible ranging from global warming to an increase in the numbers of herring in the waters following restrictions on catching the fish.
"We are just not really sure," said Mr Benson.