An independent study has linked the deaths of thousands of crabs and lobsters and a mystery dog illness to dredging for the government’s flagship freeport on Teesside – a key to the Conservative’s post-Brexit, “levelling-up” agenda. The report has led local fishers to reject a government theory that an “algal bloom” is responsible for the huge piles of dead crustaceans that began washing up on beaches along England’s north-east coast in October. A multi-agency investigation led by the Department for Environment, Food and Rural Affairs (Defra) concluded on Friday that the mass crustacean deaths, which the fishing industry says have threatened their livelihoods and led to fears of a collapsing ecosystem, “potentially resulted from a naturally occurring harmful algal bloom”. Algal blooms are a rapid overgrowth of algae that can produce dangerous toxins in the water, sometimes marked by a coloured scum on the water. Scientists have warned that they are becoming more frequent and more toxic worldwide, and could be linked to the climate crisis. Dog walkers on the beach at Saltburn-by-the-Sea in North Yorkshire. Dog walkers on the beach at Saltburn-by-the-Sea in North Yorkshire. Photograph: Christopher Thomond/The Guardian Tim Deere-Jones, an independent marine pollution consultant and author of the report, said there was “no empirical evidence to support the theory that it’s got anything to do with an algal bloom”. Deere-Jones, who has 30 years of experience around dredging issues as a consultant, instead said the data obtained via freedom of information requests from Defra and other agencies, linked the mass mortalities to a specific chemical, pyridine, which can be released into the environment as a waste product from industrial processes. “So far, the available evidence points clearly to pyridine as a potential cause of the mortality,” he said. His analyses point to several potential sources of pyridine discharge to the estuary, which could date back decades, but has embedded deep into the seabed. “On the basis of the established fact that pyridine preferentially deposits out into estuarine sediments, rather than remains in the water column, it seems likely that the new deeper dredging being constructed has uncovered and redistributed pyridine-laced sediments to the regional marine environment,” he added. While Defra said that “any levels [of pyridine] detected in crab tissue are likely to be linked to biological processes and not necessarily from the environment”, Deere-Jones pointed out that samples from control crabs collected in Penzance had just under 6mg per kilogram of the toxic chemical, the Saltburn crabs were found to have more than 400mg per kg. “That’s not a natural level, that’s a human impact level,” he said. Looking north across the Tees estuary towards Seal Sands from South Gare. Looking north across the Tees estuary towards Seal Sands from South Gare. Photograph: Mark Pinder/The Guardian Defra, which reviewed satellite date showing an algal bloom along the coastal area in late September 2021, rejected this explanation, concluding it is “unlikely that chemical pollution, sewage or infectious aquatic animal diseases were the cause of the deaths”. Advertisement The agency also said there was no evidence linking recent reports of dead seals, the mystery dog illness causing sickness and diarrhoea following walks along the coast in January, or the dead sea birds washing up in their hundreds in October. However, the North East Fishing collective, a group of commercial fishing associations, angling societies, conservationists and stakeholders along the north-east coast of England, have labelled the explanation as “utter rubbish”. The group say they have all been “dramatically impacted by the recent events on the east coast. Our incomes have been slashed, our livelihoods under threat and our environments eroded.” Fishers from Hartlepool to Scarborough say their catch of crab and lobsters remain 80%-95% down and dead crabs and lobsters were reported last week in Saltburn and Maske, which they say is unlikely to have been caused by an algal bloom in October. Following a protest last November, the group set up a crowdfunder and commissioned Deere-Jones to investigate. They have called for further investigations into the high levels of pyridine found in crabs and an immediate stop to dredging activity in the Tees, where they say one vessel “conducted a years’ worth of dredging in 10 days”. A spokesperson for the fishers said algal blooms “do not occur naturally in our coastal waters in October. The temperatures are far too low” and demanded more evidence for the theory beyond satellite images. A Defra spokesperson said: “Our sampling established that no pyridine was present in the water or sediment samples we collected but was detected in crab tissue from both impacted areas and non-impacted areas elsewhere in the country”.