The silky shark has a slim , flat body and naturally grows to a length of 2.5 m ( 8 ft 2 in ) . It can be distinguished from other large sharks by the rather small first back fin with a twist back edge , the tiny second back fin with a long free rear tip . Highly mobile and migratory , this shark is most often found over the edge of the continental shelf down to a depth of 50 m. The silky shark has a slender , streamlined body and typically grows to a length of 2.5 m. It can be distinguished from other large requiem sharks by its relatively small first dorsal fin with a curving rear margin , its tiny second dorsal fin with a long free rear tip , and its long , sickle-shaped pectoral fins .