The conservationists with the Sea Trust charity, based in Pembrokeshire, recorded the "dolphin-fest" from the deck of the Stena Europe ferry en route from Fishguard to Rosslare.
Sea Trust director Cliff Benson confirmed the sighting of "a pod of eight Risso's dolphins, 40-plus common dolphins [and] four porpoises" among others as soon as the ferry headed west of Tusker Rock.
Altogether in the three-hour passage across the Irish Sea, the volunteer surveyors recorded a total of 99 common dolphins, 10 Risso's dolphins and 26 harbour porpoises. "That's not bad for a winter trip," said Benson.
He added that while there are threats to the Irish Sea's cetaceans from scallop dredging and the like, "to date our surveys show this area is teeming with life.
“This is Wales and Ireland we are talking about not Bermuda so get this amount of dolphin and porpoise activity with whales thrown in as well is incredible."
Stena has welcomed Sea Trust volunteers on board its vessels since 2004 to check on cetaceans and other marine wildlife in the waters between Ireland and the UK on a monthly basis.
And as reported previously on Afloat.ie, Seatruck Ferries has also been providing free passage to UK marine wildlife researchers to discover how many dolphins and seabirds make their home in the Irish Sea.
Meanwhile, BBC News reports that a pod of more than 100 bottlenose dolphins was recently spotted off the Isle of Man.
The Manx Whale and Dolphin Watch said it received a number of sightings from the east and west coasts of the island in the northern half of the Irish Sea, reporting a hive of activity.
"The group sizes tend to be relatively ginormous," said Tom Felce of the group. "So if they are here you can't miss them."