Orca found in Uist 'one of oldest males ever recorded' say scientists

Scientists believe a killer whale found dead in the Western Isles is one of the oldest male orcas ever recorded following analysis of its teeth.

The animal, discovered on a shoreline on South Uist in 2015, is thought to have been 65 years old or older.

A Scottish team of researchers studied the ringed layers that formed annually in one of its teeth.

The researchers said a clue to the orca's age was the absence of traces of radioactive fallout from atmospheric nuclear weapons tests, conducted near oceans in the mid-20th Century, in the oldest layers of the tooth.

The US, Russia and UK were among countries to carry out atmospheric nuclear weapons tests before they were banned in 1963.

The tests were carried out above ground at locations that included the Russian Arctic and the South Pacific.

The explosions released vast amounts of radioactive particles, with some of it ending up in marine environments where it contaminated wildlife.

The researchers said the absence of traces of radioactive fallout in the oldest layers of the orca's tooth suggested it was born before the weapons tests began.

Traces were found trapped in other layers as the killer whale grew.

The team said male orcas have an average life expectancy of 30, although this is largely based on studies of Pacific killer whales.

Two males, known as Aquarius and John Coe and often spotted off Scotland's west coast, are thought to be older than 50.

Females can live into their 80s or longer.

The scientists also studied a tooth taken from Lulu, a member of a group of orcas known as the West Coast Community.

Lulu was found dead on a shoreline on the Isle of Tiree, in the Inner Hebrides, in 2016.

The scientists said her tooth carried a different type of "radioactive fingerprint" - one known as the Sellafield signal.

It was produced by radiocarbon discharges into the Irish Sea from the Sellafield nuclear reprocessing facility in Cumbria and carried by currents to the west of Scotland where Lulu hunted her prey.

The researchers also examined a tooth from a sperm whale nicknamed Moby, whose skull is today on display in the National Museum of Scotland in Edinburgh.

Moby died after he stranded on mudflats along the Firth of Forth in 1997.

Analysis suggested he was at least 43 years old. Again the absence of nuclear weapons fallout in older layers of his tooth helped scientists to work out his age.

The research was led by scientists at SUERC - Centre for the Isotope Sciences in partnership with researchers from the universities of Glasgow, Edinburgh and St Andrews and National Museums Scotland.

The team's study has been published in the journal, Frontiers in Marine Science.

The teeth used in the study were provided from the collection of the Scottish Marine Animal Stranding Scheme (SMASS).

For Dr Kieran Tierney, of SUERC - Centre for the Isotope Sciences, the research had a personal resonance.

He said: "My parents took me to see Moby when he arrived in the Firth of Forth in 1997, when I was six years old.

"A few days later, we saw pictures of him dead on the shore, and I had so many questions: How could this huge, amazing animal die so suddenly? Where had he come from? What sort of life had he had?

"Those questions have always stayed with me, and they have been a fundamental part of what has driven my career at the overlap of marine science and isotope research."