The UK’s largest nature conservation charity is urging the Government to reopen an investigation into the deaths of thousands of lobsters and crabs off the Yorkshire coast.

The Royal Society for the Protection of Birds (RSPB) said it is “deeply concerned” about the deaths and dredging of the River Tees must be halted until the cause has been determined.

The crustaceans have been washing ashore, mainly in North Yorkshire and Teesside, since October last year.

Fishermen, who claim their livelihoods are at risk because catches have been decimated, believe the deaths are linked to harmful chemicals disturbed by dredging that is being done for the Teesside Freeport.

Dead crabs and lobsters have been washing ashore since October last year

An investigation, led by the Department for Environment, Food and Rural Affairs (Defra), ruled out dredging and found a naturally occurring algal bloom is “the most likely cause”.

Marine pollution consultant Tim Deere-Jones, who was hired by local fishermen to analyse Defra’s investigation, has cast doubt over the findings. He said Defra has “no empirical evidence” to support its conclusion and the chemical pyridine is “strongly suspected” to be the cause.

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Blanaid Denman, Senior Conservation Officer for RSPB, said: “RSPB are deeply concerned by the ongoing mass die-offs of crustaceans along the northeast coast, centred around the Tees Estuary. And the potential effects on the wider marine ecosystem, including seabirds.

Local fishermen, who claim their livelihoods are at risk because catches have been decimated, believe the deaths are linked to harmful chemicals disturbed by dredging in the River Tees

“We understand that the first event, which occurred in October 2021, was investigated by Defra who found the crabs and lobsters contained exceptionally high levels of pyridine, an industrial pollutant, alongside a number of known algal toxins.

“As the source and impact of the pyridine was unclear, the investigation concluded in November that a rare toxic algal bloom was the most likely cause and the investigation was formally closed in March 2022.

“However, this was not a one-time event. While algal bloom toxicity may have been a factor in October, the die-offs have continued throughout the last nine months which clearly indicates an alternative underlying cause, requiring urgent investigation.

“RSPB strongly recommends that Defra reopens their investigation into these die-offs with immediate effect and further, adopts a responsible approach by halting dredging of the Tees until a full scientific analysis can rule it out as a contributory factor.”

In his report, Mr Deere-Jones said pyridine has been produced as a by-product by industrial activity around the River Tees for more than 100 years and there is evidence to suggest sediment containing the chemical may have been disturbed by dredging.

Pyridine was found in some of the crabs, but Defra said the chemical, which can form naturally in crustaceans after death, did not kill them and “varying amounts” have been found in crabs in other parts of the UK.

However, Mr Deere-Jones said Defra has failed to explain why levels of pyridine found in crabs in the North-East were around 80 times higher than those found in crabs in Cornwall.

Defra has said it has no plans to reopen the investigation, which was “comprehensive” and involved “extensive testing for chemicals and other pollutants, including pyridine”.

The Government said is not planning to compensate fishermen, because it was a naturally occurring event.

Nature charity urges Government to reopen investigation into crab and lobster deaths