Transport Canada says the mandatory 10-knot speed limit for large vessels will remain in the Gulf of St. Lawrence as long as right whales are in the area.

The department imposed the speed limit this summer as right whales started turning up dead throughout the Gulf.

Fifteen of the endangered species have died in the waters off the east coast of Canada and the U.S. this year.

A report released Thursday said four died from blunt force trauma from collisions with ships while two appeared to die after being entangled in fishing gear.

Whales could stay in the Gulf until December

Transport Canada is steadying the speed restriction as the Department of Fisheries and Oceans continues to monitor the right whales in the Gulf.

"We've had a couple of weeks where we haven't had as much flight time due to bad weather but we're continuing our aerial surveillance, continuing to survey with our passive acoustics," said Matthew Hardy, a division manager with the Department of Fisheries and Oceans Canada. 

The whales could stay in the region until at least December, when they begin migrating.

"There is no indication that they have moved on at this point. So we expect them to stay … potentially up until December, but we don't know at this point."

Travel through Gulf could take longer 

Meanwhile, Marine Atlantic is warning travellers that trips between Cape Breton and Newfoundland could take longer in the coming weeks.

whale, Miscou Island

Pathologists believe four of the whales found dead this summer were the result of collisions with ships. (Shane Fowler/CBC)

The corporation expects all vessels in the Cabot Strait will be ordered to slow down when right whales begin migrating.

Ferries crossing the Strait usually travel around 15 knots.

With files from Island Morning