A squid fisher's video of what is believed to be type B killer whales in a river on Tasmania's north coast has baffled experts, who say the subspecies has never been officially recorded on Australia's east coast and should be chasing seals in the Antarctic ice at this time of year.

Key points: Experts believe the video shows type B killer whales off Tasmania's north coast

Experts believe the video shows type B killer whales off Tasmania's north coast A veteran killer whale watcher says "if we are correct, this will be the first record of this ecotype in Australia's eastern region"

A veteran killer whale watcher says "if we are correct, this will be the first record of this ecotype in Australia's eastern region" The video was taken by a fisher who thought he had chanced upon a school of salmon

Dean Hodgetts told the ABC he and two others had been in his speed boat chasing squid off Low Head, near George Town, on Tasmania's north coast on Sunday, when the wind picked up about 11:00am.

"We decided to come back into the [Tamar] River for a bit of shelter," he said.

"I could see sprays in the distance. I thought it might have been dolphins or salmon so we tore down there to get a bit of fishing action."

Upon arriving at the location, Mr Hodgetts said the pod of killer whales surfaced.

"[There were six to eight, all varying sizes," he said.

"There was one exceptionally large one. We could see the big white patches.

"They were cruising alongside the boat for a while moving at quite a speed, doing about 10 kilometres per hour."

Whale watchers should observe from a distance, no matter what species. ( Supplied: Out of the Blue Adventures )

Video taken by Mr Hodgetts was shared widely and made its way to David Donnelly, a marine researcher and long-time whale watcher.

"Although we are yet to receive high-resolution imagery, the Killer Whales Australia team and collaborators, the Marine Conservation Program at the Department of Primary Industries, Parks, Water and Environment Tasmania, believe the animals sighted in the Tamar River yesterday are likely to be Antarctic type B killer whales," Mr Donnelly said.

"If we are correct, this will be the first record of this ecotype in Australia's eastern region."

Animals presence in river a 'mystery'

Mr Donnelly told ABC Hobart several different ecotypes of killer whale — also known as orcas — were known to inhabit Antarctic waters.

"Type A, which is regularly seen off Tasmania's coast, type Bs [pack ice killer whale and Gerlache killer whale], which feature a large eye patch and cape with a line across the flank, and type C, which also has an eye patch and is rarely seen on Australia's east coast."

There is also the sub-Antarctic killer whale ecotype — or type D.

Mr Donnelly said there had been much "speculation" among whale watching circles since the video emerged as to "why type Bs would be there".

"We'd expect them to be working around the ice edges, working into the Ross Sea, looking for seals, not up here in the lower latitudes," he said.

The Australian Environment Department says type B killer whales typically inhabit "inshore waters, pack ice and the Antarctic Peninsula Area".

"Seals appear to be the most important prey for type B," the department's website states, adding "little is known about either local or seasonal movement patterns of Antarctic killer whales".

Mr Donnelly said the pod Mr Hodgetts saw may have been "moving into more temperate waters to reduce diotom load [algae] on their skin", however that was just one of a number of possibilities.

"We have no idea why," he laughed. "It's a mystery."

Whales of many species are frequent visitors to Tasmanian waters. ( University of Tasmania: Ben Sellers )

The news that the pod is thought to be of a ecotype not officially recorded as having be sighted off Australia's east coast before came as a pleasant shock to Mr Hodgetts, who said all onboard the boat were struck by the encounter.

"I was with my next-door neighbour and a mate's five-year-old son," he said.