Our analysis of production and cost begins with a period economists call the short. run. Theshort run in this microeconomic context is a planning period over which the. managers of a firm must consider one or more of their factors of production as fixed.
Sharks have two sets of paired fins on the sides of their body, in the same general position as the main wings and horizontal tail wings of a plane. The shark can position these fins at different angles, changing the path of the water moving around them.
So, whenever movie-makers want to add a little 'danger' to an ocean-based story, all they have to do was show one or more phony shark fins above the surface. But  in truth  sharks in the wild very, very rarely swim with their dorsal fins exposed above the surface. Most shark species swim fairly close to the bottom or in mid-water (the large expanse of ocean between the bottom and the surface).