A common dolphin calf has been killed by four bottlenose dolphins in an attack that could become more common as the oceans warm, a cetacean expert has warned.

People on a dolphin spotting trip from New Quay, Ceredigion, were left “hysterical” by the incident on Thursday at 18:10 BST in Cardigan Bay, where the calf was thrown out of the water.

Climate change means common dolphin numbers are increasing in the area, where resident bottlenose dolphins will hunt them as a form of “play”, said Matthew Westfield from the UK Cetacean Strandings Investigation Programme (CSIP).

It recovered the calf -estimated to be two years old – to perform an autopsy.

“Across the UK we are seeing more attacks where a bottlenose dolphin attacks a common dolphin juvenile,” he said.

A boat owned by Dolphin Spotting Boat Trips and carrying 12 passengers spotted what they initially thought was a porpicide – the name given to the deliberate killing of a harbour porpoise by bottlenose dolphins

The group included Ghost, a favourite with dolphin spotters.

“Ghost and another dolphin she was with all of a sudden started speeding towards this larger group of dolphins,” said passenger Holly Williams, 35.

“They started jumping out the water and we thought they were just playing.”

They saw something being flung out of the water by the dolphins and initially thought it was a salmon.

The company’s photographer Sarah Michelle Wyre, 30, said they soon realised it was a common dolphin calf.

“My daughter was hysterical,” said Ms Williams.

“She loves animals and is very sensitive.”

Dylan Coundley-Hughes, 22, is a researcher for the SeaWatch Foundation caught the attack on camera.

“These kind of attacks are so rare to see in person. We know they happen in the wild but it’s rare they’re ever seen,” he said.

Mr Westfield said the increasing number of common dolphins in the area mean more interactions with the resident population of about 250 bottle nose dolphins.

“Its not that clear why they do it,” he said.

The food the two types of dolphins eat only “slightly” overlap, he explained.

“The bottlenose is probably the most intelligent cetacean we see on the Welsh coast.

“They are an apex predator with a huge intelligence and a lot of free time because they are so good at hunting.”

He said the attacks are probably down to “something as simple as play”.

They are also brutal he said, adding: “The calf was most likely with its family pod when the bottlenose dolphins separated it off.”