A working dog from the Scottish Highlands has been named animal of the year by a charity for hunting down an invasive marine creature called the carpet sea squirt.

This organism, also nicknamed "sea vomit", is particularly harmful to coastal wildlife and economies.

Working at low tide with her owner, Dr Texa Sim, black Labrador Sgiath has found hundreds of colonies of the sea squirt, which - if left uncontrolled - can smother and kill native species.

Sgiath (pronounced Skee-ah) is thought to be the UK's first sea squirt-hunting dog.

Carpet sea squirt can be tricky to spot among seaweed

The International Fund for Animal Welfare (IFAW) , external is awarding Sgiath animal of the years at its 26th annual animal Action Awards ceremony on Thursday 15 October.

Sim, a marine ecologist based near Glencoe, has had Sgiath since she was a puppy and the bond between the two is strong.

"Sgiath is incredibly clever. Her problem solving and her ability to take on new challenges and learn so quickly are just phenomenal, and it's so amazing to watch."

As a pup, Sgiath was trained as a mountain rescue dog. The Labrador proved to be so good that Sim wondered if she could use her skills to help with marine conservation work.

Sgiath has been trained to recognise the scent of the carpet sea squirt. And now, the six year old joins her owner on the beaches to sniff it out.

Sim says the dog is always right when pointing out a sea squirt, which can be difficult to spot, looking like slime among seaweed and on structures like pontoons and oyster cages.

Carpet sea squirt, or sea vomit, has spread to several places around the UK

"When I first started this project, I genuinely didn't know whether it would work," said Sim.

"No one had really explored whether dogs could help tackle this problem in the marine environment. It began as a proof-of-concept project and has exceeded every expectation I had."

Dogs' scent detection skills are often used in conservation work on land, including tracking endangered species and helping investigate environmental crime. At low tide, Sgiath can, as Sim puts it "dive down under the seaweed".

"She just does a survey with her nose, essentially, she can pinpoint exactly where it is, so it's much easier," she said.

Marine experts believe that carpet sea squirt, formally named Didemnum vexillum, came from Japan. It arrived on the shores of the south of England and Wales in 2008.

It can appear in various shades - from orange to cream - and has now spread to several seaside locations across the UK.

It reproduces quickly during the warmer summer months and, with warming seas, there are fears it could spread further.

Dr Martyn Kurr, a marine biologist from Bangor University told BBC News that non-native or "biofouling" species, like the carpet sea squirt, can outcompete native wildlife for valuable nutrients.

"These species also clog up aquaculture pens, marine infrastructure, and machinery such as boat propellors," he explained.

Efforts to control and clean up these problematic marine invaders costs millions of pounds every year across Europe.

To get Sgiarth proficient in both mountain rescue and marine conservation has needed hard work and long hours from both dog and owner.

To locate and draw attention to a lost hiker on mountainous terrain, Sgiath is trained to bark and bounce around.

Sim explained that she trains Sgiath to give what's known as a "passive indication" when she finds the sea squirt.

Sgiath has been trained to stare when she finds carpet sea squirt

When we speak to Sim over Zoom from her home, her two dogs are curled up in their beds at her feet. Apparently, when Sgiath is not out finding lost people or marine creatures, she likes to be wrapped up in her dog blanket.

Sgiath, and Sim's younger Labrador Uisage, are both working dogs that are driven to do their jobs with treats and play.

Kurr, from Bangor University, said that scientists were just starting to realise that "these wonderful animals can smell changes in water that signal a marine invasion which otherwise might have gone unnoticed".

He added: "It's fantastic to see Sgiath get this much deserved award, and I'm very excited to see what other wonderful work we can do with sniffer dogs."