Seal hunters and protesters are making their way to the Gulf of St Lawrence in eastern Canada for the start of the annual harp seal hunt.
Up to 325,000 harp seals can be hunted this year
During the controversial cull, hundreds of thousands of young seal pups are expected to be shot or beaten to death.
Animal rights groups argue that the hunt is barbaric and unnecessary.
But the Canadian government insists the cull is necessary to control seal numbers, and local fishermen say it gives them much-needed seasonal work.
The seal population is almost six million, nearly triple the level of the 1970s, according to the administration of Prime Minister Stephen Harper.
The government has increased the total allowable catch by 5,000, meaning that up to 325,000 harp seals can be hunted.
However, correspondents say this year the hunt will be more difficult for both sealers and protesters because of melting ice floes, which means they will have to rely on boats.
Harp seals can be legally hunted once their white coats darken at about two weeks old.
Campaigners have called on US restaurant chains to boycott Canadian seafood until the hunt stops, and they plan demonstrations around the world.
One of those opposing the cull is French film star and animal rights activist Brigitte Bardot, who on Wednesday begged Canada to stop what she called a "massacre".
Ms Bardot said she had requested an audience with Mr Harper to discuss the issue, but had been turned down.
Several Canadian politicians defended the cull earlier this week, insisting it was not cruel or offensive and it helped the local economy.
The activity reportedly earns 16.5 million Canadian dollars (£8.3m) in meat and pelt sales, benefiting thousands of local hunters.