Specifically, I don't know all the minor details, but it's to address bycatch and entanglement, bycatch being the capture and retention of species. Entanglement is entanglement in fishing gear.
Those are the two key areas they're looking at under the Marine Mammal Protection Act in the U.S. They have imposed this on their own fisheries, and they are now imposing it on their imports. Canada has quite a large number of exports.