The first image is a useful reference guide comparing the Cormorant (left) with the Shags.

The Cormorant (Phalacrocorax carbo) is a large, black waterbird whose size and colour make it very visible. With a reptilian neck, it has an almost prehistoric appearance. It is often seen standing with its wings held out to dry. 

Shags (Gulosus aristotelis) are large, dark waterbirds, a little bit smaller than Cormorants. They feed on fish, which they catch with their long, hook-tipped bills while swimming underwater. They can often be spotted perched on a rock or bank with their wings held out. In this stance, they are able to dry their feathers off which are not waterproof.