LONDON (AP) — British scientists said Friday they don’t think pollution killed thousands of crabs that washed up on beaches in northeast England, though they are unsure what did cause the unusual die-off.

The crustaceans were found dead or dying along more than 70 kilometers (44 miles) of coastline in late 2021, with some displaying unusual “twitching” while in the throes of death.

Environmentalists suspected toxins released by dredging to expand a port in Teesside, a heavily industrial area, might have been responsible. Research last year by academics, backed by the fishing industry, suggested the industrial pollutant pyridine, possibly from dredging at the mouth of the River Tees, as a potential cause.

But a panel of scientists and industry experts set up by the British government said it found no evidence pollutants were to blame.

The group, chaired by Gideon Henderson, chief scientific adviser to the government’s environment department, said it was “very unlikely” that pyridine or another toxic pollutant caused the die-off.

“We just could not find evidence for high levels of pyridine in the coastal sea water,” said Lancaster University environmental chemist Crispin Halsall, who worked on the report.

The group concluded it was “about as likely as not” that a pathogen new to U.K. waters – a potential disease or parasite – caused the crab deaths. The scientists said they were unable to identify what pathogen, if any, was responsible.

“We’ve come up with probably more questions than answers,” Tammy Horton, a researcher at Britain’s National Oceanography Center who worked on the study, said.

She said it was “highly unlikely” there would be any human health implications from a pathogen of crab and “seafood would be safe to eat.”