The Risso's dolphin has a shark-like dorsal fin
There have been more sightings of Risso's Dolphins off the Pembrokeshire coast than anywhere else in the UK, according to a new report.
Conservationists have been monitoring wildlife activity from the bridge of the Stena Line ferry as it sails between Fishguard and Rosslare.
The Sea Trust's study aims to provide a picture of dolphin, whale and porpoise numbers throughout the year.
It will help shape assembly government marine protection policies.
The report is being launched by television wildlife expert Iolo Williams and environment minister Jane Davidson at the Senedd.
The trust said it was the first of its kind in Britain featuring 12 monthly surveys of cetacean presence in UK waters.
Volunteers have been using the ferry crossing since 2004 to monitor marine activity in the Irish Sea.
Trust co-ordinator Cliff Benson said: "To perform year-round surveys of cetaceans depends on the availability and cost of hiring suitable boats.
"Added to this is the need for suitable weather and the availability of capable and experienced crews. Because of this, most of the published data on cetacean numbers is often based on snapshot surveys."
The common dolphin is also regularly spotted during ferry crossings.
"What is unique about our "Stena Europe Ferry Surveys" is they have been conducted on a monthly basis, since 2004. We have been using the bridge of the super ferry as an observation platform on its regular daily crossings."
Risso's Dolphins are among the larger members of the dolphin family and generally do not approach boats.
They are found worldwide in temperate and tropical waters, usually in deep waters rather than close to land.
Ms Davidson said: "This study is very important as it's one of the few that monitors these animals all year round to build a comprehensive picture of the populations and distribution throughout the year.
"Having such an insight will play a part in our mission to identify and manage highly protected Marine Conservation Areas under the new Marine and Coastal Access Bill.
"It will also provide evidence to inform the new marine planning system we will be developing for Welsh waters, again as a result of the Bill."
According to the report the three most commonly recorded cetaceans in the Irish Sea were Harbour Porpoise, Common Dolphin and Risso's Dolphin.
Mr Benson said it was a surprise Bottle Nose Dolphins were only seen occasionally, even though nearby Cardigan Bay is considered to have a population of over 200.
"This in itself is a significant finding," he added.