The whale, an endangered blue, is believed to be about nine metres long. It was discovered Sunday floating on its back about three kilometres off Campbell's Cove.
Fisherman Russell Macphee suspects the whale got tangled in or swallowed some fishing gear.
"Just really don't know," Macphee told CBC News.
"It seemed like he got turned upside down, he can't get back. At one time it looked like he was on shore or on rock. His belly is scratched up."
The whale was first spotted by a search and rescue crew that rushed to the scene after receiving a report of an overturned boat.
Fisheries and Oceans Canada will determine what to do with the carcass.