I don't know much about that part of the globe, but how about some merchants transiting out of the port? Unless all merchant shipping has been halted owing to the minefield? (maybe a corridor thru the minefield that merchant shipping uses and a SSK sitting right in the middle to ensure only merchants (not enemy subs) use it.
By the way. Great mission. Got thru it the 1st time and wasn't until I turned on the replay did I see all those mines! Yikes!. Talk about lucky sailing.