Boaters are being urged to use caution after a humpback whale with a large gash on its back was spotted in Howe Sound on Monday.

Researcher Jackie Hildering with the Marine Education and Research Society says the wound was almost certainly caused by a strike from a boat propeller.

"These accidents are happening far too often," she told On The Coast host Gloria Macarenko.

"The average boater isn't even aware even that humpbacks are back in the waters in the numbers they are.

"It's morbid to look at but … so important that boaters realize this is happening both for their own safety and the whales' safety."

A humpback whale was seen in English Bay the morning of April 8, 2016. 0:34

Risk to whales and boaters

The population of humpback whales in B.C. oceans has been increasing but they remain a species of special concern under the Specie at Risk Act.

The massive creatures can be "oblivious" to boats on the ocean because they don't have biosonar, Hildering said.

They are also much larger and dive for a longer period of time than orcas — but are still very acrobatic.

Another shot of the injured Howe Sound whale showing its wound. (Ruana Singh)

"In a word, humpbacks are far more unpredictable... If you consider their size, this is also a very big risk to boaters as well," she said, recounting how one person was rendered a paraplegic after a crash last year.

Hildering says the society is focusing on educating boaters with the phrase "see a blow, go slow." That is, when they see a whale spraying water in the air with their blowholes, slow down.

Boaters can also look for birds on the water's surface as signs there could be whales nearby.

People are urged to report any collisions with marine mammals — or entanglements or other disturbances — to the Observe, Record and Report line at 1-800-465-4336.

Listen to the full interview with Jackie Hildering:

With files from CBC Radio One's On The Coast