The Tasmanian Government has approved the use of capsicum spray to help fish farm workers defend themselves against an increasing number of aggressive bull seals.

In half a century spent fishing Tasmania's coastline, John Hammond says he has never seen so many seals.

"You would have never heard of a seal jumping in a dinghy with an operator 10 or 15 years back. It was unheard of," he said.

"But it's happening, [it's] a fairly common occurrence these days and they get pretty nasty."

Mr Hammond says competition for food has lured the animals closer to shore.

"It's creating more pressure around the fish farms too, that's why they're going to the fish farms of course because they're running short of food I would say," he said.

Fish farmers say it has resulted in a rise in dangerous seal encounters.

Pheroze Jungalwalla from the Tasmanian Salmonoid Growers Association says the seals can be very aggressive.

He says workers above the water have been injured in seal attacks but divers are at greater risk.

"People have been bowled over, literally, by the seals trying to charge past them. Divers have been nipped, they've had their fins nipped, they've been dragged underwater," he said.

The State Government is supporting the use of capsicum spray in approved farms to be given to workers to keep on their boats.

"We were forced to find a solution for defending our staff, our staff defending themselves at close quarters, and that's why it's come about," Mr Jungalwalla said.

"So the capsicum spray can only be used by trained and certified people in very specific circumstances to protect people."

But there are doubts about whether the measure will work.

The RSPCA's Dr Paul Swiatkowski is one of those unsure about the move.

"For it to be effective you would have to be in close contact with the seal anyway," he said.

"I can't see that it would be an alternative to shooting."

John Hammond also has doubts.

"I dont know what happens with a big angry bull seal when you give him a squirt of capsicum spray. It would really turn him on I reckon," Mr Hammond said.

He says the Government should go back to the drawing board.