LONDON, Dec 10 (Reuters) - Britain said on Friday it had signed a trilateral agreement with Norway and the European Union on fishing catch limits for 2022 for six jointly managed fish stocks in the North Sea. The government said the catch levels had been set in line with, or lower than, those advised by the International Council for the Exploration of the Sea in order to help protect fish stocks. "We are confident that this agreement has struck a balance that will benefit both our fishing industry and ensure our marine environment is healthy and viable long into the future," Britain"s Fisheries Minister Victoria Prentis said.