This tail off the Co Down coast has heralded a flurry of excitement – as experts confirmed it was only the fifth sighting of a humpback whale in the Irish Sea in 100 years.
But the excitement has risen to fever pitch after two sightings on consecutive days turned out to be of different humpbacks.
Wildlife fans have been training their binoculars on the sea off the Ards Peninsula following the two humpback sightings.
According to Ian Enlander of the Irish Whale and Dolphin Group (IWDG), the first humpback sighting on Sunday was made by Lennie Wells 10 miles west of Donaghadee – only the fifth Irish Sea sighting since records began.
"On Monday there was another sighting with photographs and that was eight miles north of the Copeland Islands," he said.
But when IWDG sightings co-ordinator Padraig Whooley compared the images, he discovered something amazing – the distinctive shapes of the undertail flukes (lobes of a whale's tail) revealed that they were not the same animal.
"He is fairly confident that these are two separate individuals," Mr Enlander said. "Getting a humpback whale in Northern Irish waters is exceptional. So getting two on consecutive days is all your Christmases rolled into one!"
This year has been a particularly good one for humpback whale sightings, with a recent run in the south west of Ireland.
And comparison of the tail flukes has added four or five new individuals to the Irish humpback catalogue in the last week alone, Mr Enlander said.
"It had taken 15 years to get the first 30," he said.
"It's not clear what the reason for all these sightings is. It could be an indication that the population is continuing to recover post-hunting, or perhaps they are opportunistically coming in on the back of a good feeding opportunity.
"Humpback whales are normally filter feeders but they will target large shoals of small fish."
Humpback whales breed in equatorial waters but migrate to feeding grounds in northern latitudes, Mr Enlander explained.
"We think the humpbacks in Ireland are coming up from west Africa," he added.
"Virtually all the whales will come north, the males travelling individually and the females moving up with their young calves. This could be an indication that there is good feeding in Irish waters this year."
Last night the IWDG was planning to carry out an aerial survey of the area to see if any of the humpbacks could be spotted again.
For more information on sightings visit at www.iwdg.ie
Acoustic studies have detected humpback whales "singing" off the west coast of Ireland and it has been suggested that they use the deep waters of the Rockall Trough as a migration corridor.
Humpbacks have been seen off the east, south and west coast of Ireland. The humpback has a broad, upright and bushy blow at 20-30 second intervals between dives which usually last up to seven minutes. 'Humpback' refers to their habit of bending their backs before diving, accentuating the hump in front of the dorsal fin.