All at sea

Although such findings are always sad, the marine life discovered washed up on our beaches reveals much about the health of our seas

THE waters around Scotland’s almost 19,000km of coastline are home to an extraordinary diversity of life, both above and below the waves. With more than 20 species of cetacean (whales, dolphins and porpoises), a third of the world’s population of grey seals and a vast array of fish – including 25 species of sharks, skates and rays – it’s quite a roll call.

Few will forget an encounter with a pod of killer whales or a basking shark, while more occasional visitors to our waters include marine turtles and the giant sunfish. The extensive coastline also supports more than 40 per cent of the EU’s population of breeding seabirds.

The fact that there is so much life here is all about habitat. The waters off the west coast offer a particularly rich diversity, from towering sea cliffs and rocky shores to sheltered bays, fjord-like sea lochs and extensive stretches of sandy beach – as found at the Trust’s Sandwood property. And it doesn’t stop at the water’s edge. The seabed itself, with its mix of coarse sands, gravel and rock provides a foundation for cold-water coral reefs, burrowed mud, kelp forests and ancient maerl beds.

Such vibrant habitats provide important spawning grounds for a variety of fish, while western coastal waters not only serve as migration routes for many species of cetacean but are also vital feeding and breeding grounds.

Given their importance, the Scottish Government has established a network of Marine Protected Areas to safeguard key inshore and offshore sites. To date, they cover approximately 22 per cent of Scottish waters and include sites for nature conservation, protection of biodiversity and demonstration sites for sustainable management practices.

Health check

A healthy and productive marine environment is essential not only for the creatures that live there but also for the physical, mental and economic wellbeing of humans – particularly those living in coastal communities. Sadly, however, the pressures facing marine ecosystems are as varied as the marine life itself, while the overarching threat posed by a changing climate only serves to exert further pressure.

Although tinged with sadness, the discovery of marine life washed up on our shores can provide valuable information on the health of the marine environment. Vital details such as age, sex, body condition, diet, pollutant levels, reproductive status, and disease and parasite burdens can all be collected from carcasses. Such data enables pathologists to establish the likely cause of death, as well as assess pressures and threats, population dynamics and responses to environmental changes.

Since 1992, the collection and analysis of this data has been undertaken by the Scottish Marine Animal Stranding Scheme (SMASS). Working alongside more than 200 volunteers across Scotland – including myself and Sandwood manager, Don O’Driscoll – the SMASS team collects biometric details, tissue samples and even whole animals for necropsy.

Since SMASS first began collecting data, a variety of marine mammals have been found washed up on and around the Trust’s Sandwood estate. As well as numerous seals, discoveries have included three species of beaked whale (Cuvier’s beaked whale, northern bottlenose and Sowerby’s beaked whale), five species of dolphin (long-finned pilot whale, Risso’s dolphin, white-beaked dolphin, short-beaked common dolphin and killer whale), while carcasses of sperm whale, minke whale and harbour porpoises have also been reported.

The reasons for animals washing up on our beaches are many. Specific anthropogenic threats to cetaceans and seals include entanglement, by-catch, collisions with vessels, noise pollution and disturbance, plus chemical pollution.

Detective work

Occasionally, so-called Unusual Mortality Events (UMEs) occur that require further investigation by the Scottish Marine Animal Stranding Scheme (SMASS). In 2018, one of the largest UMEs ever recorded took place when nearly 100 beaked whales – mainly Cuvier’s beaked whales – washed up around the Atlantic coastline of the UK and Ireland between August and October.

A little-understood pelagic species, Cuvier’s beaked whales are capable of diving to depths of up to two kilometres. The concentrated time frame of the strandings plus the animals’ relative state of decomposition led SMASS to believe that death from natural causes was highly unlikely.

Cuvier’s appear to be particularly sensitive to noise disturbance, especially the kind of mid-range sonar used by the military. Such noise can disrupt diving behaviour, leading ultimately to decompression sickness and death.

Sadly, there has been a further recent spate of beaked whale strandings around the southern Irish sea. Investigations into these deaths are ongoing.

“The collection of tissue samples from stranded animals allows for the analysis of the effects of pollutants that continue to persist in the marine environment”
our beaches are many. Specific anthropogenic threats to cetaceans and seals include entanglement, by-catch, collisions with vessels, noise pollution and disturbance, plus chemical pollution.

Stored toxins

The collection of tissue samples from stranded animals allows for the analysis of the effects of pollutants that continue to persist in the marine environment. Long-lived odontocetes – toothed whales that feed high up in the food web – are at particular risk from persistent and bio-accumulative toxins such as polychlorinated biphenyls (PCBs), which build up in fat-rich tissues such as blubber. At high levels, these compounds impair immune function, disrupt reproduction and damage overall health.

These stored toxins are often mobilised when energy reserves are most needed, such as during times of environmental stress, pregnancy and lactation. This has been shown to be the case in harbour porpoises in the UK, where juveniles are exposed to a potent mixture of neurotoxins through their mother’s milk – a developmental stage where such toxins can cause the most harm.

The West Coast Community of killer whales – the only year-round resident population in UK waters – is another to suffer from the devastating effects of PCB contamination. Analysis on a 20-year-old female that died following entanglement in creel ropes and subsequently stranded on Tiree in 2016 revealed a PCB level of 957mg/kg, one of the highest levels of contamination ever recorded.

To put this into perspective, damage to health can occur at only 11mg/kg. Killer whales in the northeast Atlantic show an average of 150mg/kg. Research predicts that half of the world’s population of killer whales are at risk of dying out due to PCB contamination.

The West Coast Community prey on marine mammals rather than fish, which could explain why it exhibits such extraordinarily high PCB burdens. This population is now doomed to extinction, with only two individuals, both male, seen since 2016. The disappearance of a community that is genetically, behaviourally and phenotypically distinct from others in the north Atlantic, such as the Norway and Icelandic populations that have frequently seen around the Northern Isles in summer, will be a sad loss.

Marine litter

Of course, it’s not just about pollutant levels in our waters. In November 2019, the well-documented issue of marine litter was again brought into sharp focus when a sub-adult male sperm whale that live-stranded on Seilebost beach in Harris was found to have approximately 100kg of marine debris in its stomach. This unwelcome diet included bundles of old rope, sections of net, plastic bags, gloves, cups, packing straps and tubing.

Anger is an understandable first reaction to such a story, with considerable ire often directed towards the fishing sector. But damaged and lost gear is also undesirable for the fishing industry: as well as financial implications, snagging on so-called ‘ghost gear’ – fishing gear that has been lost, abandoned or discarded – can also be a danger to fishing vessels.

Aware of its responsibilities, the fishing industry is working on collaborative solutions. The Scottish Entanglement Alliance, a research programme involving industry representatives, researchers (including SMASS) and conservation charities, is looking to gain a better understanding of the scale and impact of entanglements.

Overall, the number of strandings has increased year-on-year over the past decade, although this is likely due to greater awareness and reporting by members of the public than any increase in mortality. What is clear is that public awareness is vital, as every piece of data improves our understanding of the challenges facing our seas – and how best to address them.

Get involved in recording valuable data around our coastline

• Report dead-stranded marine mammals to SMASS by emailing strandings@sruc.ac.uk, or calling/ texting 07979 245893 or 01463 243030. Try to provide the following details: date found; location (with grid ref if possible); photographs; species/ description; estimated length of carcass; general condition of the animal; your contact details
• Join a beach clean or remove as much litter as possible while out walking. The Beach Track app can be used to find the beaches most in need of attention. Find details of beach cleans at Sandwood, plus other volunteer work parties 
• Report live-stranded marine mammals to the SSPCA Animal Helpline on 03000 999 999, or the British Divers Marine Life Rescue on 01825 765546
• Download and use the SMASS Beach Track app to submit reports of stranded marine animals and birds, and to upload survey tracks and observations about marine litter. This contributes to a database that provides an overall picture of the health of Scotland’s beaches.

Carrie Weager is the Trust's Conservation Ranger for Sandwood Bay

• This story was originally published in the Spring 2020 issue of the John Muir Trust Journal. Become a member to receive our members' magazine twice a year
• 2020/21 is Scotland's Year of Coasts and Waters