There continues to be an east – west divide when it comes to the numbers of harbour seals around the coast of Scotland, according to a new report published today (11 November) by Scottish Natural Heritage (SNH).
The results of survey work from 2014 show that numbers of harbour seals are at an all-time high on the west coast of Scotland since surveys started in the late 1980s, but have continued to decline in the east.
Over the past 15 years the surveys, carried out by the Sea Mammal Research Unit (SMRU) at the University of St Andrews, have documented a decline in numbers of harbour seals on the east and north coasts and the Northern Isles.
In that time numbers have dropped by over 90% in the Firth of Tay and Eden Estuary and 75% around Orkney.
Last year only 29 seals were counted in the Firth of Tay and Eden Estuary Special Area of Conservation (SAC), set up to protect habitats and wildlife including harbour seal, compared with 88 counted in 2012 and 773 in 1992.
Drops in numbers were also recorded in other protected wildlife sites along the east coast including in the Moray Firth and Dornoch Firth.
In contrast, numbers have gone up by 60% or more in some parts of the west coast over the last six years, with some of the highest area counts recorded to date.
Harbour seals – also known as common seals – are found in cold and temperate waters throughout much of the northern hemisphere.
Scotland is home to 36% of the European population. Ongoing research by Marine Scotland is investigating the local declines on the east coast and in the northern isles.
Some factors, such as viral infection, persistent organic pollutants and interactions with fisheries have been ruled out.
Current thinking is that they are most likely due to competition with the larger and more numerous grey seals in these areas. Exposure to toxins from harmful algae is also being considered.
John Baxter, Principle Marine Adviser with Scottish Natural Heritage said: “It’s great to hear that harbour seal numbers on the west coast are doing so well but it’s of real concern that numbers on the east coast continue to drop so dramatically.
“It’s still not clear what’s causing the decline but we’re continuing to work with colleagues at Marine Scotland and SMRU to try to get a better understanding of what is going on.
“These surveys are important to help monitor seal numbers so we can work together to take action if necessary - this year we have funded further surveys of Shetland and the south-west and south-east coasts.”
Ailsa Hall, Director of the Sea Mammal Research Unit said: “Without support from SNH we would not know how the abundance and distribution of this protected species is changing over time.
“Understanding the population dynamics of this key top predator in Scottish waters, and how these dynamics differ regionally, is clearly critical in our efforts to identify the drivers of the decline.”