New data reveals 20% decline in harbour seal populations along Scotland’s west coast

New monitoring figures released today by the University of St Andrews Sea Mammal Research Unit (SMRU) show that Scotland’s west coast harbour seal numbers have dropped significantly for the first time in decades; by 20% between 2018 and 2023.

This marks a concerning turning point for the species’ survival in British waters.

The UK harbour seal population (Phoca vitulina) is genetically distinct from harbour seals elsewhere in continental Europe, so the decline of this unique population is particularly worrying in a wider geographical context.

UK harbour seals (Phoca vitulina)

This latest data, presented today at the Special Committee on Seals Science Day, reveals that numbers are now declining even on the west coast of Scotland, where previously they been stable to increasing. This region had long been considered a stronghold for the species, holding over 65% of the UK population and  offering a glimmer of hope amid widespread population declines elsewhere in the UK.

Harbour seals have experienced long-term declines across much of the UK since the early 2000s, particularly in the Northern Isles, east coast of Scotland, and, more recently, in parts of southeastern England. However, the Scottish west coast — especially areas like the Inner Hebrides and the western Highlands — had until now bucked the trend, with populations either holding steady or increasing.

Dr Debbie Russell, lead seal ecologist and Deputy Director of the SMRU said: “This is a real wake-up call. For years, we’ve viewed the west coast as a refuge for harbour seals, a place where they seemed to be doing okay. To now see declines in this region suggests that the pressures affecting these animals are becoming more widespread or severe.”

The findings are underpinned by one of the most valuable marine mammal datasets in the world — a decades-long time series maintained by SMRU, which has systematically monitored seal populations using aerial surveys, photo-ID, and tagging studies since the 1980s. This long-term perspective is crucial for detecting population trends and understanding the underlying ecological changes.

The causes of the decline remain complex. Scientists are currently investigating several potential drivers, including disease outbreak such as phocine distemper virus (PDV), environmental changes and reduces prey availability, possibly linked to climate change and competition with and predation by grey seals.

The decline on the west coast raises urgent questions about the resilience of the UK’s marine ecosystems and the need for enhanced protections for marine mammals.

Dr Carol Sparling, Director of SMRU, said: “We need to act quickly. That means continued investment in research and monitoring and the development of targeted conservation measures.”

The findings are expected to inform ongoing discussions around UK marine conservation strategies, including the management of Marine Protected Areas (MPAs) and the development of national action plans for marine biodiversity and conservation.