ARBROATH was mourning the loss of four of its sons last night as investigations began into why a fishing boat sank suddenly in near perfect conditions and what delayed the launch of a major search for eight hours.

An air and sea search for the missing crewmen in the North Sea, 100 miles north-east of Aberdeen, was called off by Aberdeen coastguard last night.

Hopes that they might have escaped from the Westhaven AH190 on board a liferaft were dashed when the Coastguard Agency confirmed that a Remotely Operated Vessel, or mini submarine, with video equipment had inspected the wreck and sighted a body in the wheelhouse.

The Westhaven's two liferafts were also spotted in the wreck, and the coastguard admitted it was ''unlikely'' that any of the four would have survived.

A spokesman for Aberdeen coastguard said: ''Bearing in mind those on board could have been in the water for 31 hours, the survivability factor has vanished.''

Meanwhile, in a separate fishing tragedy, two bodies recovered from the sea off Cornwall were identified as fishermen from the St Ives-based Gorah Lass. A search for its third crewman was abandoned for the day as darkness fell.

On Saturday night, Westhaven skipper George Pattison, 38, first mate Mark Hannah, 30, and crewmen Chris Prouse, 23, and Alan Cunningham, 28, sailed out of Arbroath harbour on what was to be their last voyage.

Mr Pattison, an experienced skipper, had bought the former Westhaven FR375 only three months earlier and the 23-year-old Buckie-built boat was in excellent condition. It recently had a new engine and passed a seaworthiness test. He had retained the name but changed the registration.

On Monday morning at 9.30, Mr Pattison radioed his brother who was fishing nearby to tell him that their nets were held fast - his last message. Two hours later a satellite picked up a beacon signal to indicate a vessel was in trouble.

The beacon was identified as coming from the Westhaven FR375 because the change of name had not been registered following the sale, although the ship's agents claim the paperwork was sent to the Marine Safety Agency in Plymouth.

A statement by coastguard headquarters said there had been speculation surrounding the registration delay by both the Marine Safety Agency and the Coastguard Agency.

''The results of the inquiries into the registration of the beacon concerned will be passed to the Marine Accident Investigation Branch, who are investigating this accident. At the time of the accident the Westhaven was fishing in very close proximity to another fishing vessel of the same name. Both fishing vessels were also once owned by the same person.''

The new Westhaven FR375, by remarkable coincidence, was fishing just 15 miles away at the same time. This added to the confusion. It meant that although efforts were made throughout the day to identify any vessel in trouble it was 7.30pm before a full scale search was launched.

Surface vessels searched throughout the night and at dawn flotsam from the vessel was found.

Yesterday afternoon the trawler was located in 140 metres of water near the Claymore and Piper fields and close by an oil pipeline. The search which had involved two helicopters, an RAF Nimrod and more than 15 vessels including three Arbroath fishing boats was called off at dusk.

Among 10 fishing boats which joined the search was the Deejay, with Mr Cunningham's brother Derek and Mr Pattison's brother, Gordon, on board.

Last night, Mr Peter Donald, manager of the vessel's agents the Arbroath Fishermen's Association, said: ''The families have asked me to implore the authorities to try to recover the bodies.''

A coastguard spokesman said discussions were under way about an attempt to recover the body.

Mr Donald condemned those who had suggested that fishermen failed to re-register the beacons when vessels changed ownership.

''The required postcard was sent to Southampton on December 30 and received on January 3. They can say what they like about fishermen but in this case the necessary paperwork was completed. If they have no information in Aberdeen about that it is not the skipper's fault and he is at the bottom of the sea as a result of this delay.''

Mr Mike Park, vice-chairman of the Scottish White Fish Producers' Association, said that they knew in this case that Mr Pattison had re-registered the beacon.

He said that although the two vessels had the same name it was their numbers which identified them. ''The names are only cosmetic,'' he said.

Arbroath MP Andrew Welsh called for a full inquiry to establish the truth of what happened.

Mr Alex Smith, a retired skipper and chairman of the Scottish White Fish Producers' Association, said the Westhaven was a ''fine boat'' and it was a mystery what might have happened. He said snagged nets would not normally pull a vessel down.