Two official investigations have been launched after the 15-
The four crew abandoned the vessel. Two bodies were later found including one man who tried to swim to shore.
Another fisherman who swum to an island was found safe and flown to hospital in Stornoway.
Maritime emergency services and police have been carrying out extensive searches for the missing fourth crew member.
The Marine Accident Investigation Branch (MAIB) which is probing the sinking pledged to examine all details in an effort to establish the cause of the tragedy.
Arriving in Stornoway, MAIB inspectors Robert Cranstone and Paul Bryson (pictured above) offered their “sincere condolences to family and friends” of the crew.
Mr Cranstone said they intended to carry out a “full and thorough” examination of the events surrounding the incident.
He said: “We are at a very early stage of the investigation. This is the very, very start of our investigation.”
Police Scotland which is carrying out a separate inquiry said officers are in contact with the families.
Chief Inspector Alastair Garrow said: “Police Scotland have an enquiry team working alongside other agencies and the known circumstances will be reported to the procurator fiscal.
"There will be further investigations necessary to fully establish what has happened."
Maritime accident investigation launched into fishing boat sinking
11 April 2016