A second government investigation, published in January 2023, stated neither an algal bloom or pyridine poisoning could explain the deaths over such a long period of time, wide area and the unusual twitching in crabs.
[3] A spokesperson for the Environment Agency said, "Samples of water, sediment, mussel and crab have been collected and are being sent to our labs for analysis to consider whether a pollution incident could have contributed to the deaths of the animals."
[4] At the time of the initial waves of deaths, the Environment Agency stated that "there is no evidence of any link to recent strandings of marine mammals and seabirds across the UK and counties along the North Sea coast.
"[13] The Department for Environment Food & Rural Affairs (Defra) said, "We are not aware of any link with the issue of crustaceans washed ashore in the area late last year [and domestic pets].
Environment Agency operations manager Sarah Jennings said, "We've used both traditional and innovative screening methods to analyse samples of water, sediment and crab looking for traces of contamination.
Defra, which started an investigation in December 2021, stated the die-off was the result of an algal bloom, however, some academics have raised the dredging issue as the shellfish had high levels of pyridine.
[17] The North East Fishing Collective (NEFC) crowdfunded a £30,000 study conducted by researchers at Newcastle, Durham, Hull and York universities, who concluded that the levels of pyridine resulted in the mass deaths.
[19][20] In early February 2022 it was reported that, "Defra and partner agencies have completed a thorough investigation of the cause of dead crabs and lobsters which were found washed up on the North East coast between October and December 2021.
Following significant testing and modelling to rule out possible causes, Defra and partner agencies consider that the deaths of the crabs and lobsters potentially resulted from a naturally occurring harmful algal bloom.
"[21][22] In June 2022 George Monbiot wrote in The Guardian, "Astonishingly, although there is no evidence that it conducted such sampling, the government concluded not only that a bloom had occurred, but that it was caused by a particular, toxic species: Karenia mikimotoi.
There is no plausible mechanism by which a Karenia bloom could cause the mass death of lobsters and crabs without also killing large numbers of fish, sea urchins and many other species."
A Freedom of Information request to the Department for Environment Food & Rural Affairs revealed some crab samples were found to have concentrations of the chemical pyridine 70 times over the expected level.
The report stated that neither an algal bloom or pyridine poisoning could "..explain the deaths over such a long period of time and wide area of coastline, the unusual twitching observed by crabs or why only crustaceans and not a greater number of species had suffered the effects."
[32] The committee heard that those who work in the fishing industry around the Tees and the County Durham and North Yorkshire coasts, were "terrified [of the] dredging going ahead", with one stating that they were experiencing an "extinction episode".