Rescuers are hoping to spot stricken whale from the air

Marine experts called off their five-day search for the Minke thought to be about five miles off the coast between Cardigan Bay and Aberaeron.

The RSPCA is now relying on the vigilance of members of the public but inspector Richard Abbott said the chances of the whale's survival was "virtually nil".

"I've got the feeling that the next time we hear about it, it would have beached itself dead," he said.

"It's going to die. I'm convinced of it."

Mr Abbott said the netting had obviously been lodged in the mouth of the whale - described by eyewitnesses as very thin - for some time so it had been able to dive to feed.

The whale has not been seen since last Tuesday

He said it was likely the net had embedded itself into the flesh of the whale's mouth - and was likely to become infected.

Meanwhile, a number of boats remain at Aberporth ready to launch if the whale is seen.

Gwyndaf Williams, the pilot of the twin-engine Piper Seneca chartered in an effort to locate and rescue the stricken mammal took to the air for the final time on Saturday and flew for three hours over 200 sq miles.

The crew have had numerous setbacks throughout the week because of fog caused by the hot weather.

Visibility was seriously hampered on several occasions when the crew hoped to spot the small whale.

Flying at 500m above the sea, the crew members were able to make out porpoises in the water and even small pieces of rubbish like plastic bags, but the whale was nowhere to be seen.

Dolphins and whales can suffer horrific injuries, say experts

"If it had been on the surface in the area we searched we would have seen it easily," Mr Williams said.

Attempts to reach the whale and take it to safety began a week ago, but there has not been a confirmed sighting since Tuesday.

Marine experts feared the whale animal was facing a slow death from starvation and exhaustion.

Thousands of whales, dolphins, and porpoises are washed up on beaches every year in similar conditions.

Environmentalists, led by the Wildlife Trusts, have been campaigning for changes in commercial fishing practices to prevent such tragedies, known as by-catch deaths.

The animals often follow shoals of fish caught by trawlers and get tangled in the vast nets.

Their injuries are often so severe that they bleed to death.

Adult Minke whales are usually between seven and 10m long and can weigh up to 10 tonnes when fully grown.