Visitors are to be banned from another Scottish island in an effort to limit "the terrible effect" a recent outbreak of bird flu is having on seabird colonies. 

Mousa in Shetland has joined a list of 23 small islands where public landings are being stopped until seabird chicks have fledged.

NatureScot's decision comes to protect the UK's smallest seabirds, European storm petrels. 

The island is home to around 11,000 breeding pairs of the birds, known as alamooties in Shetland, accounting for almost half of Great Britain's population.

Several hundred pairs make their homes within Mousa Broch, an iron age round tower, prompting fears visitors could transfer the virus around the island and within the broch on their footwear. 

READ MORE: Conservation agency says visitors to 23 Scots islands must be banned to stop bird flu spread

A highly pathogenic variant of avian influenza HPNI has decimated wild bird numbers across Scotland, particularly hitting great skua, gannets and guillemots.

Recent sample surveys show up to an 85 per cent decline in great skua numbers in Orkney colonies. 

According to the Department for Environment, Food and Rural Affairs there are 537 cases of bird flu among 28 species over 142 locations in Scotland. However, this is likely to be a significant underestimate of true figures. 

While storm petrels seldom mix with other seabirds, there is a high rick of them picking up the virus where visitors have walked on the island. 

Eileen Stuart, NatureScot’s deputy director of nature and climate change, said: “Restricting visits to Mousa was not an easy decision, but we are increasingly concerned about the terrible effect avian flu is having in Shetland’s seabird colonies.

“Together with the Scottish Government and the Animal and Plant Health Agency, we have looked at biosecurity measures to allow the broch to remain open to the public while the storm petrels are nesting.

"However, the logistics of getting enough clean water out to the broch and ensuring that visitors can clean and disinfect their footwear adequately has proved too challenging for this season.”

The Mousa Boat will stop running trips to the island from July 30 for the remainder of the 2022 season due to the closure of the broch.

Visiting cruises, recreational boats and sea kayakers are requested not to land on Mousa until mid-October. 

RSPB Scotland’s Shetland manager, Helen Moncrieff, said: “We greatly appreciate the decision to stop running the boat service to Mousa to give the precious seabirds on the island the best chance of survival during this devastating outbreak of avian flu. Storm petrels breed all around the island, including the Broch, and draw thousands of visitors to the reserve.

“The impact avian influenza is having on tour operators is incredibly tough, particularly after the last few years. We are grateful for the sacrifices that The Mousa Boat company, and other tour operators elsewhere in Scotland, are making to help limit the spread.”

NatureScot will review the decision in March 2023 after reseachinto how bird flu spreads on different surfaces is completed .