Nearly 5,000 harbour porpoises, dolphins and whales have been left stranded on UK shores in the last decade, a study has revealed.

The Government said 4,896 cetaceans were reported washed up between January 1 2011 and December 31 2017.

The findings are part of a seven-year review published by the Government and led by the international conservation charity ZSL (the Zoological Society of London).

Infectious

Researchers recorded 21 different cetacean species – nearly one quarter of the total currently known to science – as well as six species of marine turtle and several species of large bodied sharks.

The highest number of strandings in a single year was also recorded in 2017, with more than 1,000 noted.

The team also investigated several large-scale mass stranding events involving multiple animals, including one in July 2011, in the Kyle of Durness, Scotland where 70 long-finned pilot whales stranded together.

They also conducted 1,030 post-mortem examinations to identify why individual animals had died.

Infectious disease and incidental entanglement in fishing gear – also known as bycatch – were two of the most common findings.

Deaths

Bycatch accounted for 23 percent of common dolphin deaths and 14 percent of harbour porpoise deaths.

Others caused directly by humans included 25 animals killed by ship-strike and a single Cuvier’s beaked whale that suffered a gastric impaction following the ingestion of marine litter in 2015.

Cetologist Rob Deaville, who led the study, said: “It’s difficult to say conclusively what’s driven this rise, but it’s potentially associated with multiple causes – including increases in local reporting effort and seasonal variation in the population density of some species.

“As both nets and propellers can cause characteristic injuries, we can readily diagnose causes of death which are directly related to human activity, such as bycatch and ship-strike.

“However, the total proportion of deaths linked to the impact of humans is actually likely to be higher over the period covered by this report.

Habitats

“For example, cases of infectious disease may be associated with exposure to chemical pollution, including legacy pollutants such as PCBs, which can have immuno-suppressive effects.”

Mr Deaville added: “Although in some respects the data paints a bleak picture, there are still positives to be drawn.

“Between 2011 and 2017 we recorded 21 cetacean species including one – the dwarf sperm whale – that had never been previously seen in the UK.

“That’s nearly a quarter of all currently known species, reflecting the range of diverse habitats around our coast.

Extraordinary

“It may be that, as the climate continues to change, the pattern of strandings around the UK may also change but we’ll have to wait to see what future reports find.

“That’s the value of monitoring programmes. We produce long-term, continuous data that picks up changes in the UK’s marine biodiversity that other approaches might miss.

“By investigating stranded cetaceans, we can also gain a real insight into the wider health of the marine environment and the frankly extraordinary wildlife that can be found around our shores.”

This Author

Rod Minchin is a reporter with PA.