Scientists are baffled by an ‘exponential' increase in whale and dolphin strandings in Britain – as they reveal the surprising potential causes

Daily Mail​

7 hours ago

Scientists have been baffled by an 'exponential' increase in whale and dolphin strandings in Britain.
Over the last 30 years, the number of whales, dolphins, and porpoises becoming stuck on Scottish beaches has risen from 100 per year to over 300.
In some species, such as common dolphins, rates of strandings are now up more than 800 per cent.
Researchers from the University of Glasgow 's Scottish marine animal stranding scheme (SMASS) are investigating what might be behind the rise, but say the cause is uncertain.
SMASS's report comes after a wave of unprecedented mass beaching incidents, during which 150 animals have mass stranded in Scotland so far this year.
In a new paper, published in Scientific Reports, the researchers say that chemical, plastic, and noise pollution might be part of the problem.
Likewise, a rise in animals becoming accidentally entangled in fishing gear could be driving more whales and dolphins into trouble.
Some species, such as the deep–diving beaked whales and pilot whales, may also be driven close to shore as climate change alters their prey's distribution.
Stranding occurs when marine mammals swim close to shore and find themselves trapped in shallow water, often leading to death or injury.
Between 1992 and 2022, 5,140 marine mammals were recorded becoming stranded on Scottish beaches.
More than half of those strandings included harbour porpoises, with 2,676 becoming trapped on beaches.
Pelagic dolphins, a group of ocean–dwelling dolphins, were the second most common, with 1,217 strandings.
Common dolphins made up a further 492 strandings, while baleen whales – a group of filter–feeders including minke and humpback whales – were stranded 489 times.
The steepest rises were found among common dolphins and baleen whales, with strandings rising exponentially from 2010 onwards.
Deep–diving animals like sperm whales and pelagic dolphins showed steady, but slower, rates of increase.
Lead author Dr Rachel Lennon told Daily Mail: 'The sharp rise in strandings is certainly concerning, particularly for baleen whales and common dolphins.
In 2023, a pod of 55 pilot whales were found beached on the shore of Traigh Mhor beach on the Isle of Lewis in Northwest Scotland (pictured). Scientists say that the number of mass beaching incidents could be a serious concern for whale populations
'The key question now is why this is happening. If the rise simply reflects increasing populations, then it may be less alarming.
'But if it is being driven by threats such as entanglement or other human pressures, then it represents a serious conservation concern.'
The researchers say that the exponential increase in stranding events is likely due to a combination of different factors.
'These animals are facing increasing threats in our waters, including chemical, plastic and noise pollution, bycatch, and entanglement,' says Dr Lennon.
Noise pollution is a particular cause for concern since it can disorient animals and disrupt their communications.
Dr Lennon points to one incident in 2018 when a single sound source caused the mass beaching of 118 beaked whales across Scotland and Ireland.
Some studies have also linked mass strandings to military sonar use, but Dr Lennon says this was not the case for the strandings in the current study.
Strandings may also be on the up because there are simply more animals in Scottish waters.
Following the end of whaling, populations of baleen whales like minke whales and humpback whales have been increasing.
Dr Lennon adds: 'Common dolphins, which are traditionally found further south, have shifted north into Scottish waters, likely in response to warming seas as a result of climate change.'
Likewise, the study found that juveniles make up an increasing number of sperm whales found beached.
The researchers argue that this suggests 'a potential shift in habitat use, with younger individuals being driven northwards, potentially in response to climate–induced shifts in target prey.'
Similarly, increasing participation in citizen science projects like SMASS's BeachTrack app is increasing the frequency at which beachings are recorded.
However, Dr Lennon stresses that the public plays a vital role in helping to understand, and eventually, prevent beachings.
She says: 'Reports from the public are the primary way we collect data on cetacean strandings, making them integral to marine mammal monitoring.
'Knowing where and when people are looking gives us valuable context for understanding what we might be missing and how complete our coverage is so that we can better protect these animals.'
HUMPBACK WHALE POPULATIONS AND THEIR THREATS
Humpback whales live in oceans around the world. They travel incredible distances every year and have one of the longest migrations of any mammal on the planet.
Some populations swim 5,000 miles from tropical breeding grounds to colder, plentiful feeding grounds - this is why it is difficult to estimate population size, according to the National Oceanic and Atmospheric Administration (NOAA).
Of the 14 distinct populations, 12 are estimated to number more than 2,000 humpback whales each and two are estimated to number fewer than 2,000.
Some populations (such as those off eastern and western Australia) are believed to number in excess of 20,000 animals—a remarkable recovery given that the same populations were almost eradicated by whaling almost sixty years ago.
By contrast, the smallest known population is one which inhabits the Arabian Sea year-round, and may number as few as 80 individuals.
Threats to humpback whales include decline in food like Krill due to a combination of climate change and industrial-scale fishing.
Humpback whales can become entangled by many different gear types including moorings, traps, pots, or gillnets.
Once entangled, if they are able to move the gear, the whale may drag and swim with attached gear for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury.
There is evidence to suggest that most humpback whales experience entanglement over the course of their lives, but are often able to shed the gear on their own.
Inadvertent vessel strikes can injure or kill humpback whales.
Humpback whales are vulnerable to vessel strikes throughout their range, but the risk is much higher in some coastal areas with heavy ship traffic.
Underwater noise threatens whale populations, interrupting their normal behaviour and driving them away from areas important to their survival.
Sound has been shown to increase stress hormones in their system and mask the natural sounds humpback whales require to communicate and locate prey.