A fisherman who had for years volunteered to help untangle endangered whales from fishing lines was struck and killed by a whale off New Brunswick, Canada, on Monday shortly after helping in its rescue, a Canadian agency said.

The volunteer, Joe Howlett, was on a Department of Fisheries and Oceans “fast response” vessel and helping to cut lines from an entangled North Atlantic right whale, the department’s minister, Dominic LeBlanc, said in a statement.

Mr. Howlett, who was a member of the Campobello Whale Rescue Team, was struck just after the whale was cut free and began to swim away in the Gulf of St. Lawrence.

“They got the whale totally disentangled, and then some kind of freak thing happened and the whale made a big flip,” Mackie Green of the team told The Canadian Press. Mr. Green started the rescue team with Mr. Howlett in 2002.