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. The Shag will generally clear the water with its jump when it dives.