A drone has captured the jaw-dropping moment a fin whale, the second largest living creature on the planet, opened its enormous mouth and swallowed thousands of gallons of water off the Pembrokeshire coast in Wales. The footage, filmed by videographer Rhys Morgan, shows the whale's expandable pleats stretching to take in up to 18,000 gallons of water and krill at once. Morgan was out fishing with a friend when it happened, and he says it was complete luck that his drone caught the whale feeding and swimming alongside dolphins. Second only to the blue whale, the fin whale can grow up to 24 metres long and weigh up to 70 tonnes, making it one of the largest animals ever to have lived. For all that size, it is a fast and elusive swimmer that spends much of its life in the open ocean, surfacing only briefly before vanishing beneath the waves.

Morgan, from Houghton in Pembrokeshire, works at an oil refinery by day and says he was brought up on the water. He got into marine videography after using a friend's drone to film sea creatures near the surface, and he says moments like this make you feel very small out there. He explains that his crew tries to keep its distance from wildlife in the boat, but whales sometimes pop up right beside them when they are anchored and fishing. Dr Marianna Chimienti, a marine top predator ecologist at Bangor University, called it a rare and fortunate encounter. She says feeding at the surface is a normal part of the species' foraging strategy, but seeing it in coastal waters is spectacular, and she added that in theory these whales should have migrated by now. Little is known about fin whale migration, which is believed to differ from that of blue and humpback whales, though they tend to be more abundant in higher latitudes in warmer months and in lower latitudes in colder months, with plenty of variation.