The Irish Whale and Dolphin Group says it is "nothing short of remarkable" that two humpback whales - first photographed 20 years ago off the Cork coast - have been spotted together once again off west Kerry.
The sighting happened last week as an IWDG team was carrying out research off the Blasket Islands.
Humpback whales can be identified by unique markings on their tail flukes and dorsal fins.
Having encountered four humpbacks, the IWDG team noticed that two of the group were numbers #1 and #2 in the IWDG Irish Humpback Whale Catalogue.
The pair had first been photographed in September 1999 in the Kinsale gas fields, off the Cork coast.
"We can actually look at the catalogue online at sea nowadays. We noticed that the first whale we had just photographed was number one in the catalogue.
"It was the very first whale we had photographed way back in 1999, almost 20 years ago to that day.
"Even more amazingly, the whale that it was with was number two in the catalogue. We had photographed that whale 20 years ago with number one," said the IWDG's Simon Berrow.
The pair of humpbacks were also photographed together in 2004 and the IWDG says further images put them in the same area in December 2008 and December 2012.
"This really shows the value of long-term research. It also shows the value of citizen science that people are out there taking pictures, sending them to the group, so that we can start to tell the stories of individual whales.
"To think that this pair could have stayed together for 20 years in treacherous waters with busy shipping lanes, sonar blasting, ghost drifting fishing nets and plastic pollution is nothing short of remarkable.
"It must be the peaceful southern coast and an abundance of food that attracts them year after year," added Mr Berrow.