Killer whales, giant turtles and real-life Moby Dicks: The rare sightings in Irish waters after major two-year survey

A blue whale – the largest creature on Earth – may also have been among a small number of whales it was not possible to positively identify from the distance at which they were observed.

The aerial survey conducted over two years reveals a wealth of bird and ­mammal life in Irish waters.

However, it also raises concerns around the health of some species and warns that the smallest member of Ireland's whale and dolphin family may be in trouble.

Common and bottlenose dolphins were plentiful, as were minke whales

It found a "marked decline" in the number of harbour porpoise recorded compared with studies carried out between 2015 and 2017. The cetacean, which grows to under two metres long at most, is often caught up in fishing nets and is vulnerable to pollution and marine noise.

"These results raise concerns," the report's authors said.

The survey, Observe II, is the second phase of a €4.5m project begun by the Government in 2014 to gather information on the birds and mammals found around the Irish coast and in our open seas. The data will help inform decisions on the locations of offshore wind farms and identify which areas at sea most need legal protection.

Scientists from University College Cork carried out extensive aerial surveys over almost 500,000 square kilometres of marine territory in the Irish Sea, Celtic Sea and Atlantic Ocean.

They were able to record not only the types and numbers of species, but where they are most often found and how they move in different seasons.

Almost 39,400 sightings of seabirds of 24 species were recorded and almost 2,200 sightings of 17 species of cetaceans. Common and bottlenose dolphins were plentiful, as were minke whales, while there were also good numbers of fin whales and humpbacks.

Pilot whales, which are usually present in good numbers, were much less evident than previously

Rare visitors – two killer whales, possibly from Iceland, and three sperm whales, which inspired the Herman Melville novel Moby-Dick – were also recorded.

Two other sporadic visitors, leatherback turtles, the largest turtles in the world, were also recorded.

However, pilot whales, which are usually present in good numbers, were much less evident than previously.

"The reason for such a large decrease in overall abundance in this wider geographic area is not known, and warrants further investigation," the report says.

Among the most commonly sighted seabirds were gannets, kittiwakes, ­fulmars and guillemots.

Kittiwake numbers were ­surprisingly high as the bird, a summer visitor to Ireland, has struggled in recent years but it is thought they were boosted by foraging birds from the UK coast.

There are conservation concerns for most of the seabird species in Irish waters so information about the areas and habitats of greatest importance to them is vital.

Junior minister for nature Malcolm Noonan said the survey's findings were a significant addition to understanding the marine environment.

"This will further enable the development of evidence-based approaches for the conservation of Ireland's biodiversity," he said.