The number of dead porpoises found on the region's beaches with apparent gruesome bite marks has risen to four.

The EDP reported on Tuesday how the discovery on consecutive days last month of two porpoises with bite marks at Horsey and neighbouring Winterton had fuelled speculation that sharks or a killer whale could be feeding off our coastline.

Since then two more readers have come forward with photographs of dead porpoises with similar injuries found at Covehithe near Southwold and Overstrand near Cromer. All were washed up within the space of about a month.

National shark expert Ken Collins, who runs a shark-tagging programme at the University of Southampton, examined the image of the porpoise found at Covehithe by painter and decorator Mike Baker and confirmed it appeared it had been bitten by a shark.

He said: 'There is no obvious damage of the kind that occurs if a porpoise has been caught up in fishing gear.

'It is not clear whether it was killed by a shark or a shark was scavenging on a dead porpoise.'

Dr Collins, who had previously confirmed likely shark bite marks on the Horsey porpoise, said it would not have to be a large shark as a porpoise was only the size of an alsatian.

However, he said it was perfectly feasible for a great white shark to be found in our waters, although he admitted that the possibility would be a 'lightning strike'.

Mr Baker, 46, of Essex Road, Lowestoft, said: 'I often walk along the beach at Covehithe and when I did so back in February I had my camera with me.

'When I saw the porpoise I thought, 'wow', that has got bite marks and it looks pretty mutilated.

'I have seen a dead seal on the beach before but never a porpoise.'

The porpoise at Overstrand was found by Norwich shoe shop assistant Christina Evans, 58, who was with her partner Malcolm Reeve on the beach where they have a hut. Ms Evans, who lives at Keswick Hall, near Cringleford, said: 'We often watch seals from our beach hut, but the sight of a porpoise was unusual.'

She said they took a photograph of it at the time, in February, but only realised something unusual might be happening when they saw the story in Tuesday's EDP.

Mr Reeve, 58, a technician, said: 'I don't want to think about whether there is a shark out there because I like going swimming.'

EDP naturalist Percy Trett believes the attacks are more likely the work of a killer whale, which are found in the waters off Scotland and sometimes in the North Sea.