1st September 2008

It has been a busy time for marine biologists on the Isles of Scilly with two highly unusual marine mammals washing up on the western shores of St Agnes within days of one another.

Sadly, both animals were already dead but this provided a unique opportunity for local scientists to examine them.

Sowerby's beaked whale (Mesoplodon bidens)

A very rare female Sowerby's beaked whale washed in at Periglis. These are normally deep water species, feeding on squid and cuttlefish. At 3.64 metres (12 feet) long, this animal was too big to be taken for post-mortem. However, members of Cornwall Wildlife Trust's Marine Strandings Network were able to collect measurements, photographs and skin samples that will be analysed by the Institute of Zoology. This whale species is very hard to spot at sea which makes any study of live animals difficult and it is extremely rare to see one here in the south-west.

St Agnes Coastguard Mike Hicks, who found the animal, said, "It was sad to see such an impressive animal out of her natural environment but I'm pleased we were able to help gather information from her and at the end of the day it was a privilege to see something that most people never will."

Risso's dolphin (Grampus griseus)

Just as the Trust's Marine Strandings Network volunteers had returned to the mainland, Mike was alerted to another, smaller animal a quarter of a mile away from the Sowerby's whale. Mike sent photographs to the Marine Strandings Network volunteer co-ordinators to confirm the identification of the animal. The animal was identified as a baby Risso's dolphin that was young enough to still be dependent on its mother for nourishment. Mike's report sparked a huge effort involving many people and organisations to bring the animal back for post-mortem at the Veterinary Laboratories Agency in Truro.

Risso's dolphins are often seen around Cornwall, although not as frequently as bottlenose and common dolphins. What was particularly interesting about this baby was that initial observations suggested it had been killed by bottlenose dolphins.

Bottlenose dolphin attacks on harbour porpoises have been recorded in the Moray Firth, Scotland, in Wales and Cornwall. The motives for such attacks are unclear, although some scientists have suggested one theory that competition for declining food stocks may trigger the behaviour.

Infanticide (killing of offspring) is also known amongst bottlenose dolphins in Virginia in America and has been considered an influence with this species practising their aggressive skills on their smaller cousins in UK waters.

Jan Loveridge, volunteer co-ordinator for the Trust's Marine Strandings Network, said, "Despite their friendly image, bottlenose dolphins can be aggressive towards one another and on the rare occasion that we see a dead bottlenose wash ashore, it often has rake, or tooth marks inflicted by its own species. However, we have recently begun to see an increase in the numbers of young and female harbour porpoise that have clearly been attacked by bottlenose dolphins and results from the post-mortems carried out on these animals confirm this."

"The discovery of yet another species that has suffered from these attacks is of particular interest, especially as it was so young. It was very important, despite the difficulty involved, that the Risso's dolphin should undergo a post-mortem examination."

The baby dolphin was collected and transported by willing members of the public on St Agnes to a pick-up point for an inter-island vessel which took the animal to the quay side at St Mary's. There it was off-loaded by a Trustee of the Isles of Scilly Wildlife Trust, Ann Horton and her team of dedicated volunteers. They then waited until it could be loaded onto the Scillonian III for its return voyage to the mainland.

Ann Horton of the Isles of Scilly Wildlife Trust gratefully acknowledged the help that so many people had offered, "The Isles of Scilly and Cornwall Wildlife Trusts wish to extend their thanks to everyone involved in helping to get this animal to Truro for post-mortem. We are particularly grateful to the Isles of Scilly Steamship Company who made everyone's efforts worthwhile by offering free passage for the animal to Penzance."

In conclusion, Ann pointed out the need for more trained Marine Strandings Network volunteers on the Isles of Scilly. She continued, "This event highlights how important it is to have trained people to attend stranded animals on the Islands. If a freshly dead animal is to be considered as a candidate for post-mortem, speed in identification and transportation is paramount, particularly as the time involved is obviously increased by the need for four hours passage across the Atlantic. We hope the success in retrieving this important dolphin will encourage others to volunteer".