From St Kilda’s puffins to the gannets of Bass Rock, Scotland’s seabird colonies are among its most enduring and striking natural icons, drawing visitors from around the world.

Yet it was feared many of these species could be at risk of disappearing altogether, with previous data suggesting populations have plummeted since the mid-1980s.

Now, however, hopes are rising that the decrease may in fact be slowing down - thanks in part to the eradication of rats and American mink.

The latest biodiversity indicator published by Scottish Natural Heritage (SNH) shows that seabird numbers, which declined by more than 30 per cent from 1986 to 2011, have since remained fairly stable.

And increases have been recorded at colonies where rats have been removed, such as the Shiants and Canna, benefitting species like the puffin.

SNH identified the removal of rats and American mink, which are predators to breeding seabirds, as “a crucial step” in boosting populations and securing them for the future.

However, its experts have also stressed that more data is needed if longer term trends are to be understood and lasting change achieved.

Simon Foster, SNH’s Trends & Indicator Analyst, said: “Seabirds are long-lived, for example the oldest guillemot in Scotland (and the rest of the UK) was recaptured on the Isle of Canna last summer being at least 41 years old.

“In Wales a razorbill was recorded at 42 years old, while a Manx shearwater has been found more than 50 years old.

“Clearly we need long-term data to really understand what is happening to different species, and the fantastic work by volunteers undertaking monitoring at colonies around Scotland is invaluable in providing us with a unique picture on these changes.”

Only two species, the common gull and common tern, maintained or increased in breeding numbers over the study period.

The Arctic skua, whose breeding stronghold is the Northern Isles, has experienced the largest decline.

In fact, the UK Red listed bird - known as the “pirates of the seabird world” because they steal their food from other seabirds - has suffered a 78% drop in its population.

Their decrease has been linked to changes in the availability of sandeels, which has also affected Northern Isles populations of kittiwakes and terns.

Drops are also apparent for herring gull and great-black backed gulls across Scotland.

However, while below earlier levels, there are signs of some populations, such as the guillemot and black-legged kittiwake, stabilising, with some colonies showing increases.

Common tern and Arctic tern numbers have gone up since the last report. Terns are known to be highly variable in breeding numbers and it is too early to say if this trend is going to continue.

Scotland’s breeding seabirds are of international importance. A total of 24 species of seabird regularly breed in Scotland and they are not only vulnerable to changes in the country’s seas.

Many migrate across the Atlantic and technology is beginning to improve scientists’ understanding of their movements.

A UK wide seabird census is currently underway and the results from this will help to provide an overview on all of the species of seabirds breeding around Scotland.

Offering grounds for hope, Mr Foster said that puffins, one of the country’s most popular marine species, were among the biggest winners after the eradication of predators.

He also highlighted early signs that populations of wading birds have received a boost following the removal of mink.

“On the islands where eradications have happened, we are seeing population increases for some species,” he said.

“Primarily its the chicks and eggs they predate on but for birds that burrow, like puffins, they predate the adults as well.

“We have seen increases for puffins on the Shiants and also big increases for puffins on Canna after the removal of rats.

“American mink have also been an issue, particularly on the islands around Argyll and the west coast, but there are efforts ongoing to remove mink from these places.

“Where mink have been removed in local areas, we are seeing some improvements, not only with seabirds but with waders as well.”