Well, I can't say what they do out in the middle of the ocean; however, given the emissions control area requirements that have been put in place internationally, there is a 200-mile limit. All ships that are coming within 200 miles of Canadian territory have to burn low sulphur fuel. In fact, in 2015 it will be going from 1% sulphur in fuel to 0.1% sulphur content.
On December 2nd, 2014. See this statement in context.