It follows a series of mass mortalities of crabs and lobsters were recorded along the Northeast and North Yorkshire coasts during autumn and winter of 2021.

Overall, the panel was unable to identify a clear and convincing single cause for the unusual crustacean mortality. It concludes that ‘a novel pathogen is considered the most likely cause of mortality (despite the lack of direct evidence of such a pathogen), because it would explain these key observations.’

Disputing the conclusion

The panel was convened following scientific evidence presented by Dr Gary Caldwell, Senior Lecturer in Applied Marine Biology, to the EFRA Select Committee.

Led by Dr Caldwell, early research in the lab revealed high levels of pyridine, a chemical with a long history of release into the River Tees, in the tissues of the dead crabs.

In this research, edible crabs (Cancer pagurus) were exposed to a range of pyridine solutions, while their behaviour, indicators of cellular stress, and survival over periods of up to three days were recorded. At the upper range of tested concentration which was comfortably within the pyridine levels found in the dead crabs, pyridine caused convulsive behaviours, paralysis and death within six hours. The onset of paralysis took longer as the pyridine concentrations were lowered, but mortalities remained high even at lower concentrations.

The research showed that pyridine is highly toxic to crabs - even below the levels recorded by the Environment Agency from the body of dead crabs.

Further modelling showed that pyridine would be quickly transported along the coastline, with areas around Hartlepool and Redcar worst affected, with the potential to kill approximately half of the crab population after only 24 hours of exposure. Levels of pyridine sufficient to kill approximately 10% of the population within three days were predicted to reach as far south as Whitby and Robin Hood’s Bay. The timeline of the transport of pyridine along the coast closely matched the timeline of mortalities reported by the fishing community and the general public.

The scientific work has been submitted for independent peer review and publication via normal academic channels, after which they will be openly accessible.

Dr Gary Caldwell, Senior Lecturer in Applied Marine Biology, 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.

“We agree with the Panel’s conclusion that the involvement of a harmful algae bloom is unlikely. However, 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 7 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 Panel also failed to recognise the virtual elimination of the barnacle population from the Staithes long term monitoring site, which is positioned midway along the modelled trajectory of the sediment plume. Pyridine is a well known and powerful antifouling agent that is used to kill barnacles.”

Scientists from Newcastle, Durham and York universities respond to the outcome of the expert panel

The team of scientists who conducted the research to determine the toxicity and potential for environmental transport of pyridine issued a joint statement following the Panel’s findings:

“We acknowledge the conclusions of the Independent Expert Panel, convened by the Office of the Chief Scientific Advisor, Prof. Gideon Henderson, into the likely causes of the mass marine mortality events along the North East and Yorkshire coast, which resulted in the collapse of the inshore lobster and crab fishery.

“Researchers from Newcastle, Durham and York universities, commissioned by the North East Fishing Collective with funding from the Fishmongers’ Company’s Fisheries Charitable Trust, argued that the die-offs were unlikely to be the consequence of a naturally occurring algal bloom. We believe that the available evidence is more consistent with the involvement of some form of pollution, possibly involving the release of the industrial chemical pyridine from dredging activity.

“Given that the weight of evidence indicates an industrial source for the die-offs, it is disappointing to see that the Independent Expert Panel have reached the conclusion that the die-offs were likely caused by an unknown pathogen, despite there being no direct evidence for this. The academic team will continue to undertake research into these events.”