New encounter could be clue to Vatersay orca pod 'enigma'
Researchers hope to finally identify a pod of nine orca seen off the Western Isles a year ago.
Experts say their struggle to match the animals' markings against databases shows there is still much to discover about orcas that appear off Scotland.
Individual orca can be identified from their saddle patches, a grey area on their backs just behind the dorsal fin. The patch is different on every orca.
Researchers hope to encounter the pod again during surveys this summer.
The Mull-based Hebridean Whale and Dolphin Trust (HWDT) scientists will try to take better quality images than those taken last June to better match them against records.
Scotland's west coast is home to a group of eight older orca known as the West Coast Community.
There is also a northern community known as the 27s, seven orca that move between Shetland, Orkney and Scotland's north mainland coast.
The 27s take their name from the identification number of the group's "matriarch".
Among other orcas seen around Scotland's north coasts are animals that move down from Iceland to feed.
The pod seen near Vatersay in the Western Isles last year included two large males and two juveniles.
Dr Lauren Hartny-Mills, the trust's science and policy manager, said attempts already made to match the pod to animals in records had been unsuccessful.
She said: "Despite our collaboration with other organisations and experts to identify the animals, the pod remains an enigma.
"It shows there is still a lot to discover about the cetaceans visiting Scottish waters."
Andrew Scullion, who runs Orca Survey Scotland, added: "I've been collating killer whale sightings from across Scotland since 2017 and it was fascinating to see these pictures of individuals I've not come across before.
"There's still much to learn about the orca frequenting Scottish waters."
Scotland's West Coast Community was made up of nine animals.
But the ninth member, Lulu, was found dead on the Isle of Tiree in 2016 after becoming entangled in fishing lines.
Tests later revealed her body contained among the highest levels of polychlorinated biphenyls, or PCBs, ever recorded.
The chemicals were banned from the 1970s but are still in the environment.
John Coe, a bull orca in the group, is believed to have had his own brush with death.
An injury to his tail is thought to have been inflicted by a shark.