Hundreds of dead crabs on the beach at Seaton Carew, Hartlepool, in 2021
Paul Grainger
A mysterious die-off of crustaceans on the north-east coast of England was probably caused by industrial pollution, according to a new study, contradicting the findings from a government report.
What is going on?
In October 2021, tens of thousands of dead and dying crabs and lobsters started washing up along the Tees estuary on the North Yorkshire coast and then further south in the fishing town of Whitby. The UK’s Department for Food, Environment and Rural Affairs (Defra) launched an investigation into the deaths in December 2021.
More dead crabs washed up on the coast in the region in February 2022. Fishing communities in Hartlepool told the BBC in June that they feared their businesses would fail due to a dramatic fall in catch numbers this year.
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What is Defra’s explanation?
In May 2022, Defra’s report found that no single, consistent causative factor behind the deaths could be identified. But it pointed to a rapid increase in the population of algae, known as an algal bloom, identified in the region using satellite imagery. The report also found that it was unlikely that chemical pollution or the bioaccumulation of pyridine – which is used as anti-corrosive treatment in marine infrastructure – had caused the deaths.
What does the new study say?
John Bothwell at the University of Durham, UK, says that he didn’t totally believe the findings of Defra’s report into the crustacean deaths. “The evidence for the deaths [collected by Defra] was circumstantial,” says Bothwell. “There’s a lot of good stuff in the agency report, but the satellite imagery shows the presence of chlorophyll – but chlorophyll can come from any kind of algae, not necessarily toxic ones.”
He reached out to the North East Fishing Collective and together they raised £30,000 to commission an independent study into the deaths. Bothwell and his colleagues collected samples of water and dead crabs from the region and tested the effects of pyridine on crabs. They also modelled the effects of dredging on contaminating water bodies with pollutants.
The findings, which have been sent to Defra but not yet published, argue that the deaths probably weren’t caused by an algal bloom and are more likely to be due to pyridine pollution.“It’s not consistent with the patterns of mortality that you normally see with algal blooms,” says Bothwell. “It doesn’t normally preferentially affect crabs.” He says algal blooms aren’t always toxic to marine life and that the toxins found in the crabs weren’t commonly associated with the blooms.
The report suggests that pyridine pollution may better explain the deaths of these crabs and lobsters. The researchers found a high concentration of pyridine in the sediment off the coast and the dead crabs also had a high concentration it in their systems. They also found that pyridine causes twitching behaviours in the crustaceans before death, which is similar to observations made about the dying animals earlier in the year.
Bothwell says it is unclear how exactly pyridine accumulates in the systems of crustaceans. He also says the high levels of the chemical don’t necessarily mean that it killed the crabs and lobsters. “Pyridine could be a marker of something else,” he says. “There could be a number of factors combining here.”
Where could pyridine pollution have come from?
The source of high levels of pyridine in the water is unclear, but Bothwell says there are industrial plants in the region that produce it, which could be responsible.
The mouth of the river Tees was dredged in September and October 2021 to maintain channel depths at nearby ports. This material was then dumped into the water and may have contained contaminants, according to Bothwell.
Last month, more dredging work began to clear space for the new Teesside Freeport, which will cover an area of around 1800 hectares.
In August 2022, the Royal Society for the Protection of Birds called on the government to stop dredging the Tees estuary until a scientific analysis had been conducted to rule it out as the reason behind crustacean deaths in the north-east.
How has Defra responded?
“A comprehensive investigation last year included extensive testing for chemicals and other pollutants such as pyridine,” says a Defra spokesperson. “It concluded a naturally occurring algal bloom was the most likely cause [of the crustacean deaths].
“We recognise the concerns in regards to dredging, but we found no evidence to suggest this was a likely cause. There have been no materials licensed for disposal at sea in the area which would fail to meet international standards,” they say.
“This is a complex scientific issue, which is why we took a thorough, evidence-based approach. We welcome research carried out by universities and will continue to work with them, including studying this report carefully,” says the spokesperson. “We are aware there have been some localised reductions in catch rates and we are continuing to monitor shellfish populations in the area.”
Defra plans to meet researchers who conducted the new study this week.
“We need to find out what’s happening so that the same thing doesn’t happen anywhere else in the UK,” says Bothwell.
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