SCOTLAND’S unique resident pod of killer whales will become extinct within two decades as they cannot reproduce due to high levels of illegal chemicals found in the waters along the west coast, scientists have revealed.

The community of eight orcas found off the Western Isles have been recorded since the early 1980’s but they have never managed to successfully reproduce which scientists believe is down to huge levels of deadly PCB’s in the sea.

PCBs - or polychlorinated biphenyls were banned in the late 70s amid fears about their toxicity.

But an autopsy carried out on Lulu, a killer whale which was found on Tiree in 2012, revealed she had one of the highest levels of the man-made chemical ever recorded. This is more than 100 times above the level that scientists say will have biological consequences for a species.

Now fears for the very future of the unique west coast pod have been revealed in the first ever Hebridean Marine Mammal Atlas which showcases findings by the charity’s scientists.

The atlas confirms the Hebrides is a global hotspot for whales, sharks and dolphins with 30,000 animals recorded there since 2002.

But it also documents that the UK’s only resident pod will almost certainly become extinct as a calf has never been recorded despite it consisting of four males and the same number of females.

Recent estimates suggest that Europe produced between 299,000 and 585,000 tonnes of PCBs.

But while industry has stopped using PCBs in the manufacture of everything from transformers to thermal insulation and paints to adhesives, millions of tonnes of the chemicals continue to be in circulation.

Killer whales have an 11-month lactation period during which they produce very high-fat milk for their calves and the higher the fat, the easier it is for PCBs to dissolve in it. While PCBs are no longer produced, they are extremely hardy as they were designed to resist extreme heat.

Lulu had PCBs measuring 957mg/kg and at these levels, species stop reproducing.

Dr Lauren Hartny-Mills, Science and Policy Manager at Hebridean Whale and Dolphin Trust, which compiled the atlas, said: “It would be a great shame if the pod becomes extinct as it is unique. They have sloping eye patches and sharp, pointy teeth and resemble species found in Antarctica rather than others in the UK.

“PCB’s are extremely difficult to break down and as killer whales are at the very top of the food chain, they are more vulnerable than other marine mammals.

“To put it into context, recent research has predicted that half of all killer whales on the planet are set to be wiped out by ingesting PCB’s. That is the scale of the problem”. But while there are fears over the killer whale population, a total of 23 cetacean species - a quarter of all known globally – have been recorded off the Hebrides on annual research trips and the new marine atlas showcases their findings.

Since 2002, the charity’s research ship, Silurian, has travelled more than 100,000 kilometres, the equivalent of sailing two and a half times around the world, on trips around the Hebrides - recording 30,000 animals. The recorded sightings show the region’s extraordinary biodiversity and shed new light on its whales, dolphins and porpoise – collectively called cetaceans – and basking sharks.

Dr Hartny-Mills added: “This pioneering research is transforming our understanding of the Hebrides’ remarkable cetaceans, while offering new insights about trends and changes in the marine environment.”

The charity’s discoveries include the Hebrides being a vital feeding ground for minke whales and basking sharks, and that the region is one of the most important areas for harbour porpoise in Europe.

The trust’s evidence was used to identify the boundary of Scotland’s first protected area for harbour porpoise, approved by the Scottish Government in 2016.

Researchers were also the first to suggest that bottlenose dolphins live year round off Scotland’s west coast.

Television presenter Liz Bonnin, patron of the trust, said: “It is increasingly clear that the Hebrides is a truly special place for cetaceans and basking sharks, and that we need to do far more to protect them and their environment. I had the great pleasure of sailing on Silurian and I am thrilled to be able to lend my support to such an outstanding organisation which works directly towards these goals.”

The new Hebridean Marine Mammal Atlas can be downloaded at hwdt.org/hebridean-marine-mammal-atlas.