Hot on the heels of a recent mass stranding of pilot whales in Orkney, a new report indicates a worrying 125% increase in cetacean strandings across Scotland says Aoife Glass.
Of particular concern is the exponential increase in the stranding rate of baleen whales such as minke whales and humpback whales, and common dolphins.
These insights come from a new report from researchers at the Scottish Marine Animal Stranding Scheme (SMASS) at the University of Glasgow. Led by Rachel Lennon, a PhD researcher, the report analyzes 30 years of information collected from stranded animals across Scotland and the Scottish islands from 1999 to 2022.
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Cetaceans are vulnerable to changes in their marine habitat, and hard to study. They’re also an indicator of wider ocean health, offering insights into the marine ecosystems in which they live. Stranding data can provide a lot of information that would otherwise be very hard to get, and by analysing what species have stranded, where and when, SMASS hopes to be able to establish a baseline upon which future research can be built. This information can also help focus surveillance and conservation efforts where they are most needed.
Do we know why there was such an increase?
The research grouped cetacean species into broad clusters - baleen whales, short-beaked common dolphins, deep divers, harbour porpoises and pelagic dolphins - and analysed this against where the strandings took place geographically, and when they took place. The goal was to identify any trends across geographic areas, seasonal cyclicity, and over the 30-year duration of the data set.
An overall increase in cetacean stranding rates was detected, equating to 125% rate change. More significant rate increases were observed in baleen whales, which saw a stranding increase of 248%, and common dolphins at a shocking 812%. Geographic trends also emerged, with harbour porpoise strandings focussed around the East coast of Scotland, while other species were focussed more towards the West coast and Hebrides.
Why are whales stranding?
While this research is crucial for understanding the current picture of cetacean strandings in Scotland, it is very much the start of the story.
“Now that we understand what is happening with strandings, we can start to investigate why, focusing on species that show unusual or concerning trends,” explains Rachel Lennon. “For example, our study revealed an over 800% increase in common dolphin strandings over 30 years, with most cases occurring on Scotland’s west coast during winter. This was striking, since other dolphin species strand mainly in summer.”
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“Interestingly, elsewhere in the North Atlantic, winter peaks in common dolphin strandings are linked to bycatch, so we launched the Bycatch Evidence Evaluation Protocol (BEEP), originally developed by the Cornwall Wildlife Trust, to systematically assess stranded animals for bycatch signs. Our findings confirm that bycatch is occurring but had previously been under-reported.”
The picture is a complicated one when it comes to establishing the cause of a stranding, even when there may seem to be a simple explanation. Baleen whales and entanglements are a prime example.
Entanglement events occur when a whale or dolphin becomes caught in ropes or lines associated with human activity at sea, such as fisheries, and can result in a slow and painful death for the animal involved. They struggle to feed, and the action of the line pulling on their bodies or fins can cause significant injury and infection.
The research indicates an increase in the number of baleen whales involved in entanglement events around Scotland, but there could be several factors at play. This increase could be due in part to these species moving northwards in increasing numbers in response to warming waters due to a breakdown in the climate. It could also be due to recovering species numbers after the end of commercial whaling; with increasing population numbers in turn increasing the likelihood of entanglements occurring.
How can the public help?
Stranding data, such as that used by this research, relies on stranding events actually being observed and reported, which in turn relies heavily on the general public.
“Public reports of strandings are absolutely vital for monitoring, particularly in Scotland, which has around 18,000 km of coastline - far too much for any one organisation to cover alone. By engaging the public, we achieve far greater reach and can conduct effective surveillance across the country.”
The research paper makes a strong case for standardising data collection across different organisations and countries, which would allow comparison across greater areas to establish regional and even global trends in cetacean stranding.
In Scotland, and across the UK, there are systems in place for reporting both live strandings, via British Divers Marine Life Rescue (BDMLR) and dead strandings, via SMASS
Rachel Lennon is clear that researchers like her and her SMASS colleagues value highly the contributions made by the public, and invites more people to get involved. “Public involvement is essential! These reports are the primary way we collect data on cetacean strandings, making them integral to marine mammal monitoring.”
“People can contribute by using our app, BeachTrack. It allows users to log beach walks, report strandings directly, and record marine litter. This not only provides stranding reports but also helps us track search effort, which is crucial for interpreting patterns in strandings.”
“Knowing where and when people are looking gives us valuable context for understanding what we might be missing and how complete our coverage is.”
What to do if you encounter a live stranded whale or dolphin
If you encounter a live stranded marine mammal, the main advice is to call for expert assistance from British Divers Marine Life Rescue (BDMLR). Do not attempt to refloat the animal, as it may require specialist assistance.
BDMLR then suggests following their guidance while waiting for their trained Marine Mammal Medics to attend. This includes wearing protective facemasks and gloves to avoid potential transmission of viruses and bacteria, avoiding the blowhole and the tail, and keeping the skin of the animal wet by pouring water over it.
How are our changing oceans affecting cetaceans?
That our oceans are changing is beyond a doubt, but what impact that is having on its cetacean inhabitants is still not fully understood.
Warming temperatures, scarcity of prey, species migration, marine noise, plastic pollution; the threats facing whales and dolphins come from multiple directions. Researchers like Rachel Lennon and others at SMASS are working hard to understand these threats, and how they may affect different marine species, such as harbour porpoises.
“Our research shows that many harbour porpoises have multiple comorbidities, for example, lung disease and parasitic infections in the respiratory system and liver. These conditions can reduce their ability to cope with additional stressors, which may be natural (such as disease, reproduction, or foraging challenges) or human-driven (including chemical exposure, noise and plastic pollution, bycatch, and entanglement). This work is ongoing, but the goal is to reveal how these stressors interact and ultimately affect survivability and resilience.”
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Main image: Pilot whales stranding © BDMLR
