pattern your gun...with divers/sea ducks you want to put as many pellets (with good energy) in them as possible or you will lose them; a crippled skunkhead can get under water more easily than a mallard with a broken wing in a rice field or farm pond.... and yes, if their head is up keep shooting, fast!!!!
Four of us went to Alaska last year, had a great trip, but two of us had taken the time to check out our patterns with the loads of choice, and the other two used the same choke with those loads that they used to hunt puddlers...the difference in cripples was obvious.... I found my light modified choke worked well, but different guns like different chokes....