An academic has refuted the findings of an independent panel that claimed it was very unlikely pyridine was the cause of the mass crab die-off.

Dr Gary Caldwell, a senior lecturer in applied marine biology at Newcastle University, said the Crustacean Mortality Expert Panel had displayed ‘remarkably poor’ scientific practice. A new report published on Friday concluded the most likely cause is a disease new to UK waters, however, it did not rule out that a combination of factors could have contributed to the unusual deaths.

The panel stated there was a less than 10% chance that pyridine or maintenance dredging led to the deaths of thousands of crustaceans in October 2021. And it believes there is a less than 33% chance that an algal bloom, which was originally pointed to by Defra as the most likely cause, was to blame.

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The scientists also claimed there was less than a 1% chance that the capital dredging being carried out by Teesworks that started in September 2022 is linked to any crab deaths. Defra Secretary Therese Coffey is currently considering whether further tests need to be carried out so a firm conclusion can be reached.

Dr Caldwell, who is also a Green Party member, said: “The report concludes that it is about as likely as not that a pathogen new to UK waters – a potential disease or parasite – caused the unusual crustacean mass die-offs, despite the fact that there was no direct evidence for the involvement of any pathogens, and that Cefas had previously dismissed the involvement of disease. The failure to evidence this conclusion is remarkably poor scientific practice.”

He added: “The dismissal of pyridine involvement also ignores the chemistry of the molecule, including its propensity to adsorb to sediment particles and its capacity to remain for many years in the environment if protected from oxygen. The report also overlooks the fact that we detected pyridine in surface sediment fully seven months after the mass die-offs, and that we have been prevented from taking sediment core samples to quantify pyridine levels in the deeper sediment.”

The Northern Echo: It’s hardly worth going out anymore - fisherman Paul GravesIt’s hardly worth going out anymore - fisherman Paul Graves (Image: SARAH CALDECOTT)

The academic also believes that the panel did not take into consideration the “virtual elimination” of barnacles at the Staithes long-term monitoring site, which pyridine is known to kill.

Speaking on Friday, Lancaster University academic Prof Crispin Halsall who was on the expert panel said ongoing wash-ups should “put the pyridine story to bed.” He added: “If you think about it, you would need an ongoing, very large source of pyridine throughout 2022 to be causing that and that’s clearly not the case.”

Prof Halsall said it’s highly unlikely pyridine would accumulate in significant quantities in deeper sediments and it was not the case that there was a historical reservoir of the chemical under the River Tees. Traces of pyridine have been found but not at the concentrations needed in seawater to make it toxic, according to the Lancaster University academic.

Read more: Looking back at how a dreadful toxic waste spill on Teesside was cleaned in the 70s

Dr Caldwell has previously highlighted that there were high levels of pyridine in the tissues of the dead crabs, however, Prof Halsall said this was part of the decay process when they died.

The panel believes a new pathogen is the most likely cause because it would explain the sustained period of the die-off, the 70km stretch of coastline it affected, the unusual twitching of dying crabs and the deaths being predominantly crabs rather than other species.

It’s not just scientists who have spoken out in the wake of this new report, politicians across the region have responded and taken swipes at each other in the process.

Last week, Stockton North Labour MP Alex Cunningham said: “Sadly local Tories seem to think the matter is now closed with this report and are more concerned with protecting the Tees Valley Mayor’s flagship policy. As far as I and many others are concerned the matter is very much not closed.”

On Monday, he added that the panel did not know for certain that dredging, or another factor, was not the cause. He added: “It is also important that new dredging is properly monitored to ensure it isn’t contributing to ongoing problems.”

In the wake of the report, Conservative Tees Valley Mayor Ben Houchen said he would always take decisions based on the science and the report was thorough and conclusive. In a piece in The Times on Monday he hit out at those who linked the dredging to the die-off.

He added: “It was the aim of these Labour figures and activists to undermine this vision (freeport) for their own short-term political gain. They were willing to risk a generationally transformative development in a deprived area simply to undermine a positive Conservative objective.”

Regarding dredging, the Tees Valley Combined Authority has previously said it operates to the highest standards in line with its MMO licences and guidance from Government agencies.


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Thousands of dead crustaceans began to wash up on Teesside’s beaches in October 2021. A Defra report initially said the most likely cause was a naturally occurring algal bloom, but the findings were widely disputed by independent marine and university experts as well as the fishermen, who claimed dredging on the Tees had unearthed historical toxins, including a chemical called pyridine, leading to the die off.

The row continued with campaigners calling for a halt to dredging until more tests were carried out. The government panel was set up late last year to assess all evidence relating to the worrying occurrence.