The number of marine mammals stranded in Scotland has risen dramatically in the past 30 years, a study has found.
From 1992 to 2022, 5,147 cetaceans died on Scottish shores, and a new paper shows steep increases in the rate of strandings of up to 800% in some species, continuing exponentially every year.
The paper, by the University of Glasgow’s Scottish marine animal stranding scheme (Smass), follows this summer’s extraordinary sequence of rarely seen, deep-diving whale species stranding on northern European shores. Over a period of just over two weeks, 36 beaked whales and pilot whales were found in locations from western and southern Ireland to Orkney, Norfolk, the Netherlands and southern Sweden. The animals appeared to have entered shallow seas where they could not forage for their usual foods such as deep-sea squid.
The widespread locations of these events is provoking serious concern, especially among volunteer groups who work to save the stranded whales – without success, in all of the above cases.
“Clusters of beaked whales should raise suspicions,” said Dr Andrew Brownlow, the director of Smass.
It is believed that sonic disturbance can cause deep-diving whales to strand. Rachel Lennon, the lead author of the paper published in the journal Scientific Reports, said that in Scotland “sources of anthropogenic noise are abundant, including seismic survey air guns and drilling from industrial construction”.
The new paper does not cite concerns that military sonar exercises in the open ocean are a known factor in such events. Brownlow noted that a “globally unprecendented number” of 118 stranded beaked whales off Ireland and western Scotland in 2018 was traced to a single sound source off the continental shelf.
The paper appears only weeks after Smass scientists attended the strandings of four northern bottlenose whales – another beaked whale species – and a pod of 23 pilot whales on the Orkney islands. The pilot whale stranding came almost exactly a year after a record 77 of the same species stranded on the same Orkney beach. A total of 150 animals have mass stranded off Scotland this year.
Smass scientists are also concerned that the number of stranded baleen whales such as fin, minke and humpback whales has risen sharply over the survey period. This may be due to more animals moving north as waters warm due to climate breakdown. It may also be a delayed result of the cessation of whale hunting – Lennon noted that “as populations begin to recover from the impacts of historic whaling, reports of entanglement have increased”.
As surface feeders, baleen whales are prone to being caught in fishing gear, leading to protracted deaths from starvation or infection. The paper also shows an increase in the number of stranded common dolphins and harbour porpoises, which can be vulnerable to collisions with leisure craft.
The 30-year report shows that stranded whales and dolphins act as “sentinels” – visible warning signs of how human activity is affecting the marine environment.
“Clearly the oceans are changing,” Brownlow said, “and Scotland is on the edge of this flux. We now get sperm whales calving off our shores whereas we never saw females in these northern waters before. Beaked whales only used to be recorded in small numbers in the autumn. Temperature, salinity, distribution of prey, oceanic heatwaves – the pattern is moving, and we need to be better at working out where these animals are, and when.
“This is the new normal, and we must tread as softly as we can.”
