An extensive search around Blackrock Island off the Co Mayo coast has concluded without finding any trace of two missing Coast Guard crew members.

Paul Ormsby and Ciarán Smith were lost when their helicopter crashed into the island on 14 March.

The Marine Institute's Holland 1 remotely operated vehicle (ROV) had been surveying an area some 40 metres below sea level for a number of weeks.

Some exploratory dives are scheduled to take place by Garda divers when conditions are suitable but this afternoon's development effectively means the search has been scaled back, almost four weeks after Rescue 116 crashed.

Coast Guard and Civil Defence volunteers will continue to carry out targeted searches of coastal areas and monitor specific areas of interest in the coming weeks.

Fishermen and others putting to sea are also being urged to remain vigilant for any sign of debris that could help find the two missing crew members.

In a statement released on behalf of the agencies involved in the operation this evening, the Air Accident Investigation Unit, the Coast Guard and gardaí expressed their gratitude to the hundreds of volunteers from around the country that had taken part in the search effort.

Particular mention was made of the Defence Forces, RNLI crews and Civil Defence members who had contributed thousands of hours to the effort.