Experts baffled by dolphin attacks on porpoises
"One possibility is that they see the porpoises as competitors for food, especially if there's a shortage of prey in the area"
The BBC has reported that three-out-of-four attacks by bottlenose dolphins noted in recent weeks from New Quay-based Cardigan Bay Marine Wildlife Centre (CBMWC) were fatal.
Cardigan Bay enjoys a rich marine environment and is home to bottlenose dolphins, harbour porpoise, atlantic grey seals and a variety of bird life. There are also regular visitors to the bay which include sunfish, basking sharks and even leatherback turtles.
Scientists have always known that dolphins attack porpoises, but it is the frequency of the attacks that is causing the most confusion. In May, volunteers from CMBWC rescued a porpoise that was left stranded on the beach after being chased by dolphins. Last month researchers saw three dolphins killing a porpoise, with another similar incident last week.
Speaking to BBC Radio Wales, Sarah Perry from CBMWC said that such attacks are not unknown, but it is rare to see them happening in Cardigan Bay. She said: "One possibility is that they see the porpoises as competitors for food, especially if there's a shortage of prey in the area."
"Although porpoises normally go for smaller prey, dolphins will eat anything. However there's been no other indication recently of any shortage."
The centre suggests that another reason for the attacks could be down to the low numbers of females prompting the attacks by males. Porpoises are similar in size to a dolphin calf, and male dolphins have been known to kill young dolphins in order to mate with the calf's mother.
The centre said it is unclear which dolphins have been responsible for the attacks.
Sarah Perry added: "One animal we're familiar with, Nick, a female, was seen in the area when we rescued the porpoise last month, and she was also seen nearby in last week's attack. Our records show that she's been seen before with the animals we think were responsible for the attack, so it may even be that she's teaching others."
