Two wildlife campaign groups say the UK Government is failing under European law to give proper protection to the harbour porpoise.

BBC Environment Correspondent Richard Wilson: Thousands are killed in fishing nets

The groups, the Wildlife Trusts and the World Wide Fund for Nature, want the government to act urgently to safeguard one of the key habitats for the species, the waters off the coast of Pembrokeshire.

Although it is the UK's most common marine mammal, the harbour porpoise has suffered a significant decline this century.

It has now vanished almost entirely from the southern North Sea and the English Channel.

It is often caught in fishing gear, and 2,200 animals are thought to die this way every year in the Celtic Sea hake fishery alone.

That is more than 6% of the estimated number of harbour porpoises in the area.

No protection yet

The species can also be affected by pollution and by disturbance from users of jet skis and other leisure power craft.

Under the 1992 European Habitats Directive the government is obliged to protect sites that are important for listed species.

The harbour porpoise is listed in the directive, but the government has not yet designated any areas to protect it.

Fishing is a serious threat

The Trusts say research has shown that the waters off Strumble Head in Pembrokeshire support the highest porpoise populations in Wales.

The Director-General of the Trusts, Dr Simon Lyster, said: "Our research has shown that harbour porpoises are present within this area throughout the year.

"The presence of adults with young calves in May and June shows that the waters are important breeding grounds.

"It is vital that the government designates these waters as a special area of conservation under the directive to allow it to be managed sympathetically."

Both the harbour porpoise and the bottlenose dolphin have been associated with south-west Wales for centuries.

One theory says that the city of Swansea was originally called "Swine Sea", after the huge numbers of porpoises, or sea swine, found in Swansea bay.