Officers from Environment Canada's enforcement division have searched the offices of a N.B. aquaculture company seeking clues to the source of an illegal pesticide found in lobsters last year.

Hundreds of dead or weak lobsters were hauled up in traps about a year ago in Grand Manan's Seal Cove and off Deer Island.

Tests by Environment Canada found they had been exposed to cypermethrin — a fast-acting synthetic insecticide that is illegal to use in Canadian waters and is toxic to lobsters. It has been used to kill sea lice in European fish farms.

On Thursday, the federal officers raided the offices of Cooke Aquaculture Inc. in St. George, Blacks Harbour and the corporate head office in Saint John. Files were seized during the raid.

A spokesperson for Cooke said the company has co-operated with the investigation, though it has been disruptive and unpleasant for employees.

Robert Robichaud, from Environment Canada's enforcement division, said when a search is required, officers try accomplish it as quickly as possible.

"We try to do that in a way that it's less disruptive to the companies," Robichaud said. "Obviously in this case we had eight locations, therefore the numbers were used to scatter the officers so that we could achieve those goals to make sure that things happen efficiently and rapidly."

The investigation continues.