The mystery behind the deaths of thousands of crabs and lobsters along England’s north-east coast has developed a further twist, with experts saying it could be down to a new disease.
The die-offs, which began in autumn 2021 and recurred at various points in 2022, affected at least 70km (43 miles) of the coastline, with some of the crustaceans showing an unusual twitching while dying.
An initial government investigation, published in May 2021, said the phenomenon could have been caused by a naturally occurring harmful algal bloom. However, research commissioned by the North East Fishing Collective (NEFC) and carried out by researchers at the universities of York, Newcastle and Durham and Hull suggested pyridine, a common industrial chemical, was a more probable cause.
Now a report by an independent panel of experts, convened by the chief scientific adviser to the Department for the Environment, Farming and Rural Affairs, has said that while it was not possible “to identify a clear and convincing single cause for the unusual crustacean mortality” it was unlikely algal blooms were to blame, as they were unlikely to explain the twitching or deaths during winter months.
The team also add it is very unlikely that the die-offs are a result of a pyridine or another toxic pollutant.
Crispin Halsall, a professor of environmental organic chemistry at Lancaster University and an author of the report, said the team scrutinised the findings from Newcastle University and other sources carefully – although it did not collect or analyse new samples.
“The finding of the panel and my group was that we just could not find evidence for high levels of pyridine in the coastal seawater at levels, which are going to cause acute toxicity to crabs,” he said.
The report noted that a prolonged, substantial release of a toxic chemical would be necessary to result in the observed die-offs, which Halsall said was not the case, adding that the paper put “the pyridine story to bed”.
Another suggested cause, capital dredging on the Tees, was deemed exceptionally unlikely to be the reason for the die-offs.
However, the report suggested another possibility: the deaths could be down to a novel pathogen, a cause deemed “about as likely as not” – however they stress there is a lack of direct evidence of such a pathogen.
The report added it was possible that several of the stressors considered could have operated together to lead the die-off, a point reiterated by Dr Tammy Horton, a research scientist at the National Oceanography Centre and co-author.
“For example if there was a harmful algal bloom, that could have given greater stress to the environment generally, there could have been slightly lower oxygen as a result of that, and that could have triggered the mass mortality as they are less able to cope with viral load, for example, of this potential new pathogen,” she said.
The report was met with criticism by academics from the universities of York, Newcastle and Durham.
“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 probably caused by an unknown pathogen, despite there being no direct evidence for this. The academic team will continue to undertake research into these events,” they said in a statement.
Joe Redfern, the secretary of Whitby Commercial Fishing Association, said he and the NEFC were surprised and disappointed at the conclusions of the report.
“Cefas [Centre for Environment, Fisheries and Aquaculture Science] had previously screened [for] many diseases both native and international. There is only one known pathogen know to jump from species to species and that was tested for,” he said.