Steven McKenzie and Aimee Stanton
BBC Scotland News
BBC
Volunteers remove ropes from an entangled whale stranded on Raasay
There has been an “exponential” increase in marine mammal strandings in waters around Scotland, scientists have found.
The number of whales, dolphins and porpoises getting into difficulty has risen from about 100 a year to more than 300 over a 30-year period.
Researchers at the University of Glasgow said possible causes include chemical, plastic and noise pollution and accidental entanglements in fishing gear.
More than 5,140 stranded marine animals were recorded in the study between 1992 and 2022.
Strandings happen when a marine animal becomes stuck in shallow water or on a shoreline. It often results in death or injury.
The study, published in Scientific Reports, found a steep rise in strandings involving common dolphins and baleen whales – filter-feeding species that include minke and humpback whales.
The new research used data gathered by the Scottish Marine Animal Stranding Scheme (SMASS).
Harbour porpoises accounted for more than half all the strandings – 2,676 – followed by pelagic dolphins with 1,217 incidents.
A total 494 of common dolphins and 479 baleen whales had stranded over the 30-year period, according to the research.
The scientists said deep divers, such as sperm whales, and pelagic dolphins showed a steadier increase in strandings since the 1990s.
Researchers said while exact causes were difficult to pinpoint, they agreed that human activities were likely impacting on wildlife.
Scientists said “predominant threats” were declining fish stocks, noise pollution, and entanglements with lost fishing gear.
Other risks were habitat change due to warming sea temperatures, and chemical and plastic pollution.
A humpback whale was freed from fish farm gear off Skye in January
Rachel Lennon, lead author and PhD researcher at the University of Glasgow, said: “Fisheries interactions are recognised as a critical threat for marine mammals, especially for baleen whales in Scotland.
“As populations begin to recover from the impacts of historic whaling, reports of entanglement have increased.
“While determining the exact causes of strandings can be complex, identifying these emerging trends provides a vital starting point for targeting future research.”
A number of initiatives have been set up to tackle the threat of entanglements, including the Scottish Entanglement Alliance (Sea).
The coalition of conservation groups, rescue teams and fishermen has sought to find best practices to avoid entanglements, and the most effective responses to any incidents.
Getty Images
Rescuers attempting to save stranded pilot whales at Anstruther in Fife in 2012
Where do strandings happen?
Dr Andrew Brownlow, of SMASS, said: “This research shows how reports of stranded marine animals – many made by members of the public – can offer important clues about the overall health of our seas.
“These animals act as sentinels of the ocean, and rising numbers of strandings may be an early warning that something is changing in the marine environment.”
Dr Andrew Brownlow said the public played an important part in reporting strandings
Dr Brownlow added: “While some of the findings raise important concerns, the study also highlights that different regions face unique threats, each requiring tailored mitigation strategies.
“By identifying where and when species are most at risk, we can target monitoring and conservation efforts at the critical times and locations needed to best safeguard the health these ecosystems.”