Two rare striped dolphins strand in Cornwall

16/06/2012 12:50:59 Death of two rare striped dolphins in Cornwall may be due to disease
June 2012. The recent death of two striped dolphins found near Fowey in Cornwall has raised concern among two local marine conservation organisations - British Divers Marine Life Rescue (BDMLR) and Cornwall Wildlife Trust's Marine Strandings Network (MSN) - who work together to study and protect cetaceans around our coast. Striped dolphins are a species rarely seen on the Cornish coast, more commonly found in southerly regions such as the Mediterranean.

They first became aware of the strandings when Dave Jarvis, Director of BDMLR, received a call from local residents in Fowey, who had found the first dolphin stranded alive on the beach at Coombe Haven. The local residents attempted to assist the dolphin by putting it back in the sea, but sadly it stranded again and died before rescuers could reach the spot.

BDMLR vet Darryl Thorpe, and volunteers Emily Jenkinson and David and Hilary Pugh-Jones, examined the animal. Darryl reports,

Broken jaw
"It had a severely broken jaw, probably due to being dashed against rocks in the rough seas. It was also malnourished and would have had to be euthanased if it hadn't already died, as it wouldn't have survived long in that state."

BDMLR alerted the Trust's Marine Strandings Network Co-ordinator, Jan Loveridge, and the female dolphin was examined, photographed and recorded by volunteers at the scene for the MSN's research into dolphin deaths. The recorder, Faye Archell, found a number of other lesions on the dolphin's body, including deep rake (teeth) marks inflicted by a bottlenose dolphin.

Whale lice
Faye explains "This has become a common, if surprising, sight in Cornwall in stranded cetaceans and just shows how aggressive bottlenose dolphins can be towards their own and other species. Other lesions in the skin were colonised by tiny long whale lice - fascinating creatures only 5mm in size that live out their lives on dolphins and whales by hanging on with their enormous hooked claws. Pox marks were also seen on the skin, suggesting the possibility of underlying disease, together with a possible rope mark on the tail fluke."

The MSN's advisor and pathologist James Barnett was called to the scene, with fellow scientist Nick Davison, who volunteered his time to assist. Despite the bad weather, they managed to retrieve the animal with the help of volunteers and took it away for a full post-mortem examination at the Animal Health and Veterinary Laboratories Agency, Polwhele, where they are based.

Second stranding
Meanwhile, the Trust's Marine Strandings Network had received another call to its Hotline from members of the public about a second animal they had seen on Polridmouth beach, about a kilometre away. Vet Katie Lewis, one of the MSN's many trained volunteers, went to search along the coast for it and found that it was another dolphin of the same species.

Broken beak
Katie says "I examined it and saw that this dolphin also had a broken beak and some possible net marks on the dorsal fin. Other than that, there were no indications as to why it died, although it wasn't in a very good nutritional state."

The plan was to also try to retrieve this dolphin for post-mortem. However, it was washed out to sea before this could happen, and was not seen again until the next afternoon, when it was recorded by volunteer Sarah Loftis. It was then not suitable for post-mortem examination. From its condition, this male dolphin appeared to have died earlier than the first, which posed something of a puzzle. For two dolphins of this relatively rare species to wash up together in the same area, at the same time and yet not be in the same condition, is highly unusual.

Puzzle
Jan Loveridge, MSN Co-ordinator says, "The explanation could be that, as both dolphins were malnourished, they may have been diseased and that can lead to them behaving abnormally. This could also increase their vulnerability to bottlenose dolphin attack, as has been suggested from previous post-mortem examinations. One could speculate that the female dolphin was staying close to its companion, which had already died, and it then stranded in the bad weather after coming too close to shore. It could have also been attacked by bottlenose dolphins."

Although we may never know the sequence of events, the post-mortem examination findings on the female dolphin may provide further clues. This information will be added to the Defra-funded Cetacean Strandings Investigation Programme's database of dolphin strandings in the UK to which Cornwall, as a hotspot for dolphin deaths, makes a substantial contribution. This research has shown that increasingly, disease is a major factor in the deaths of dolphins and porpoises, which gives those trying to conserve cetaceans great cause for concern.

BDMLR and the Trust's Marine Strandings Network are very grateful to members of the public for reporting strandings. They recommend that marine animals are not put back in the water until they have been examined by a qualified vet and stabilised, as they may not survive due to their injuries, or may simply drown.

If found, live-stranded dolphins should be reported to BDMLR on (01825) 765546 and dead strandings to the MSN Hotline on 0845 201 2626. Both numbers are covered every day of the year by volunteers. For more information about the Trust's Marine Strandings Network, or if you would like details on how to volunteer, please visit www.cwtstrandings.org