HALIFAX -- The federal government is shifting the snow crab fishing season, cutting the number of traps in the water and permanently reducing the speed limit in the Gulf of St. Lawrence in a desperate bid to protect North Atlantic right whales, after 18 of the critically endangered mammals died last summer and no new calves were spotted this year.

Fisheries Minister Dominic LeBlanc outlined several measures Wednesday aimed at mitigating the greatest threats to the slow-moving whales, which cruise up the eastern seaboard from their breeding grounds off Georgia every year to feed in the Gulf and the Bay of Fundy.

At least 18 of the whales -- whose population has dropped to about 450 -- were found dead off the east coast of Canada and the United States since last June. Tests showed most of the 12 found in Canadian waters had become tangled in fishing gear or had been struck by boats.

LeBlanc said the fact that aerial surveys had not found a single newborn this season underscored the need to make changes.

"We don't think it's too late," he told a news conference in Ottawa. "We think if we don't act in a very robust way, we'll set on course a very tragic outcome -- and that's why we're here today announcing these measures."

But some fishermen say their livelihoods are being put at risk by measures that could disrupt lucrative fisheries.

Robert Hache, director-general of the Acadian Crabbers Association, said a new closure of the snow crab fishery in the southern Gulf on April 28 -- possibly just days after the season opens -- will create chaos for fishermen scrambling to catch as much as they can in a shorter time.

The area being closed to fishing is one where whales tend to forage for plankton. However, Hache said, it is also particularly productive for crab fishermen.

The problems is that most crab fishermen use long lengths of rope for their traps, which can ensnare whales.

Hache said the closure may end up shifting the rope problem to another part of the Gulf, as the whales search for food in a body of water that is also a major transit route for marine traffic.

"All of the ropes that would have been in the closed area will be in another area, so you're concentrating the risk, not knowing at all what the behaviour of the whales will be," he said from Shippigan, N.B.

"This is going to create havoc in the fishery and what these measures pretend to be protecting will end up hurting the whales."

A right whale expert praised the measures, saying the mandatory changes in particular will give the lumbering animals a better shot at avoiding ship strikes and lethal entanglements.

"They are taking more drastic measures because this whale is in dire straits because of what happened in the Gulf last summer," said Moira Brown of the Canadian Whale Institute. "They are giving the whales the most room and the most chance to recover."

LeBlanc's department is also adjusting the dates of the snow crab season so it starts and ends earlier to align more closely with the whales' arrival in the region. The snow crab fishery will start as soon as possible, if icebreakers and a hovercraft can break up the ice-clogged Gulf.

Temporary closures will be enacted anywhere whales are spotted for at least 15 days, and the area won't be reopened to fishing until at least two surveillance flights show no signs of whales. As well, all snow crab gear will have to be removed from the water by June 30, two weeks earlier than usual.

There will also be lower limits for the number of traps allowed in certain areas, but those numbers have yet to be released.

Hache said the catch limit this year was set at 24,000 tonnes for the fishery, which is valued at about $100 million and involves about 400 boats from Nova Scotia, Quebec, New Brunswick and P.E.I.

Transport Minister Marc Garneau said the speed limit of 10 knots, imposed on large ships in the Gulf last year, will be reinstated in the western part of the Gulf between April 28 and Nov. 15.

Two shipping lanes with normal speed limits will be kept open north and south of Anticosti Island as long as no whales are in the area, but limits will be imposed in those lanes if that changes. Fines for violating the speed limits can range from $6,000 to $25,000.

LeBlanc promised a multimillion-dollar announcement in the coming weeks to allow snow crab fishermen to test ropeless traps, using technology that allows the remote retrieval of traps from the ocean floor. The ropes traditionally used to retrieve traps are a frequent problem for the whales.