Federal officials are investigating after kayakers say they saw five Steller sea lions being dragged to their deaths in a fisherman's net off Vancouver Island.

Vic Neufeld and Alistair Wright of Calgary were paddling in Robson Bight when they saw the marine mammals caught in a fishing net.

"The sea lions were trying to get out. They were porpoising through the net. [The fishermen] just wouldn't open up the bag -- it was terrible," Neufeld told CTV News.

"All of a sudden there was this scream -- just a howling, deathly, drowning scream."

Steller sea lions are considered to be a species of special concern in Canada, and the Department of Fisheries and Oceans is investigating the incident.

But the captain of the Native Spirit disputes the kayakers' account. Keith Lansdowne admits that the sea lions were dragged in his net bag, but he insists they were alive when he let them go.

"I've never heard a sea lion scream. I've heard them bark," he said.

"[They were] maybe not that happy being in the net, but they were barking and swimming along as we idled down away from our setting spot. They were released unharmed."

Neither the sea lions nor their carcasses have been found. On average, wild sea lions can hold their breath for about two minutes, but they have been recorded staying submerged for between eight and 15 minutes, according to marine mammal researcher Andrew Trites.

Fisheries enforcement officers say that wildlife getting caught in fishermen's nets is a recurring problem. Just last month, a humpback whale was rescued near Tofino after becoming tangled in ropes from a crab trap.

The DFO operates a hotline at 1-800-465-4336 for people to report incidents involving marine mammals. Serious offences contravening the Fisheries Act can result in fines of up to $100,000 and as long as a year in prison; indictable offences carry a maximum $500,000 fine and two-year prison term.

With a report from CTV British Columbia's Peter Grainger