There has been Kumlien's Gull each of the last 3 years at the Town Pier in Plymouth. Each year the plumage appears to be 1 year older and so I'm assuming this is the same returning bird. Last year there was a 2nd year and a 1st year bird. I believe this is a 3rd year bird. This photo shows its primaries in flight. A "regular" Iceland Gull (rare here) would show unmarked primaries and so this pattern suggests Kumlien's.