The report broke down the change in weight and value of landings of shell fish such as crab, lobster and scallop in ports around south west England and Guernsey.
It showed that the value of crab landings in the island were down more than 95% in 2025, with just under £250k wiped off compared with 2024.
Landings of lobster had dropped 94%, and scallops over 70%.
Stewart said the study, which was funded by the UK Government and local authorities in the South West, followed concern among ministers and counsellors.
“Around April and May last year the issue was really coming to a head, at that stage fisherman were mostly seeing damage to their catches and weren’t catching many octopus themselves,” he said.
“Nothing like this has been seen for 75 years, so there is no living fisherman who’d probably seen it before. So this was such a weird thing for people to see, it seemed unnatural.”
Stewart said he had not spoken to Channel Island governments during his research, but the issue needed to be taken “seriously”.
“You’re looking at fishermen really suffering economic hardship and a very uncertain future,” he said.
“We recommend further research into the actual economic and social effects because one fishing boat at sea actually support a number of jobs on the shore as well.
“And also, fishing has such a strong tie to communities, to history, to culture.”