The fin whale is the world’s second largest of all cetacean species after the blue whale, the largest species in the Mediterranean. The maximum total length of Mediterranean fin whales is above 20 m; probably somewhere between 21 and 23 m. It has a streamlined body and the head represents about a quarter of the total body length. Unique among cetaceans, the fin whale’s lower jaw is black on the left side and white on the right side, and is an important identification cue. The curved dorsal fin is set two-thirds of the way along the back, and is visible shortly after the blow upon surfacing; the blow is tall and columnar. Colouration is generally dark grey on the top surface, with white throat pleats, a white belly and white underside to the tail. There is a characteristic pale grey ‘blaze’ on the right side of the head and subtle chevron patterns along the back behind the blowholes. Tail flukes are broad with a distinct median notch and slightly concave trailing edge, and are rarely raised out of the water when diving. The life span of a fin whale may be 85 to 90 years.
In the western Mediterranean ship strikes constitute the main known source of anthropogenic mortality for fin whales. Shipping noise and vessel disturbance, particularly from the unregulated whale watching, is another source of concern.