The Shag or green cormorant (Phalacrocorax aristotelis) is a common diving piscivorous seabird of the north Atlantic Ocean. It can be distinguished from the common cormorant by its greener plumage and the pronounced tuft of feathers on its head, and also by the absence of a white throat and large white patch on its flank.
Unlike the cormorant, the shag generally breeds in sea caves and crevices in cliffs, and is rarely seen inland. It can be a serious pest of fisheries, and is frequently hunted by fishermen and others who wish to preserve fish stocks.
In the southern hemisphere the words shag and cormorant are used interchangeably for a number of species of the cormorant family.