Social media video of a commercial fisherman tossing an explosive into a raft of sea lions has prompted an investigation by the Department of Fisheries and Oceans.

The video was posted this week on the Facebook page of the Pacific Balance Pinniped Society, a group that's been calling for a cull of seals and sea lions on the B.C. coast.

It shows dozens of sea lions swimming beside a boat when a man lights a bear banger and throws it into the water. After it detonates, the spooked sea lions can be seen quickly diving under the surface as someone behind the camera chuckles.

On Thursday, Jonathan Wilkinson, the Minister of Fisheries, Oceans and the Canadian Coast Guard, described the behaviour in the video as "completely unacceptable."

"Our conservation and protection officers are investigating," Wilkinson said.

Bear bangers are small explosives that are generally used to ward off aggressive wildlife. The fisherman in the video, Allan Marsden, told CTV News that's part of the reason he decided to use one.

"I got bit before. I'm lucky that I'm not in a wheelchair, or worse, dragged overboard and drowned by the sea lion," he said. "There's nothing I won't do to protect the crew on this boat. Nothing."

The video prompted a strong response online, with some commenters even threatening Marsden over his behaviour. He said the people who are up in arms don't understand the kinds of problems growing sea lion populations are causing in the industry.

Reminder: it is illegal to disturb #seals, #sealions or other marine mammals. This includes the use of acoustic deterrents such as seal bombs or other explosives. If you see a disturbance to marine mammals in BC, please report it to us at 1-800-465-4336. https://t.co/kT9YQiR9rH pic.twitter.com/mKZSEmpueO — DFO Pacific (@DFO_Pacific) March 7, 2019

His boat was out to test herring for roe percentages, efforts he said are being hampered by sea lions driving the fish too deep for their nets.

"It's bad. It's very, very bad," Marsden said. "There was not one live fish in that net when we finished that tow, and for no other reason than sea lions drove the fish down."

The other reason he used the bear banger was to give his crew a chance to catch some herring to test, Marsden said. They still came up short.

Minister Wilkinson acknowledged there are concerns about sea lion numbers, but said that’s "a separate issue."

"There is a conversation going on about the number of seals and sea lions on both the east coast and the west coast, and there's a legitimate conversation to be had about the impacts of that," Wilkinson said.

"That is different from a specific example where people are harassing and doing something that is clearly illegal with respect to marine mammals."

The Vancouver Aquarium told CTV News there have been other reports of fishing operations using noise deterrents when animals interfere with their work, but warned they can have serious impacts on sea lions' hearing.

"We're looking at a very, very tremendously powerful level of noise in close proximity, which would cause physical damage to the ear and the ability of animals to hear," said Dr. Martin Haulena, the aquarium's head veterinarian.

Nick Templeman, who owns Campbell River Whale and Bear Excursions, told CTV News he found the video "disheartening," particularly the way laughter can be heard after the blast.

"My initial reaction was as bit of shock, actually, just to see it happen out there in the plain of day," said Templeman.

With files from CTV Vancouver's St. John Alexander and Allison Hurst