An underwater survey using robots will be carried out after a fishing vessel capsized and sank, leaving two men presumed dead.

Duncan MacDougall and Przemek Krawczyk went missing following the incident on Loch Fyne in Argyll and Bute on January 18.

The wreck of the trawler, Nancy Glen, is currently lying at a depth of more than 140m.

The families of the two men believe their bodies may still be on board, and a campaign to retrieve them has raised around £150,000.

The Marine Accident Investigation Branch (MAIB) is investigating the loss of Nancy Glen and is trying to establish why the two crew did not survive.

Issuing an update on Friday, the government agency said remotely-operated vehicles would be used to survey the wreck, after sonar searches are carried out next week.

However the MAIB said it did not plan to raise the wreck of the 40ft vessel.

An MAIB spokesman said: "The Northern Lighthouse Board vessel NLV Pharos will be conducting a multi-beam sonar survey of the wreck of Nancy Glen for the MAIB next week.

"This is planned to take place on Monday, although it is dependent on weather and sea conditions on the day.

"Pharos has hull-mounted equipment that operates from the surface to map the seabed and potential obstacles around the wreck, which is lying at a depth of over 140m.

"This data is important to allow us to plan and execute a successful underwater ROV (remotely operated vehicle) survey of Nancy Glen."

He continued: "We have issued an invitation to tender for companies specialising in underwater surveys using ROVs at these depths, and expect to conduct the ROV survey in the coming weeks.

"Currently, we do not anticipate that we will need to raise the wreck of Nancy Glen as part of our safety investigation."