Sharks have multiple fins with multiple uses:
· Pectoral fins
· Pelvic fins
· Dorsal fin(s)
· Anal fins
· Caudal fin
We’ll break down the function of each below.
These are the fins behind the shark’s head. Sharks use them to help lift and steer during swimming.
These fins are behind the pectoral fins and keep the shark stabilized during swimming… kind of like a keel on a boat! In male sharks, pelvic fins have extensions (claspers) for reproductive use.
The most famous fin which is on top of the shark’s body. Some sharks may have two dorsal fins, with the first one being bigger (unless you’re a lemon shark, whose two dorsal fins are the same size). These fins are also used for stability.
Some sharks have anal fins to provide additional stability. The anal fin is between the pelvic and caudal fins. Not all sharks have anal fins, however.
The caudal fin is what provides the thrust to the shark’s swim. This is what propels the shark forward—and its shape changes depending on the shark’s life style! The upper lobe of the caudal fin (called the upper caudal) produces the majority of the thrust, with the lower lobe (called the lower caudal) providing the lift to make up for the shark’s weight.
Fast sharks, such as makos and great whites, have lunate or crescent-shaped tails, allowing for speed over long distances.
A truncate or rounded-off tail is good for acceleration and flexibility. A tail that is “continuous,” or fluid from the body (think zebra shark) is great for maneuvering in and around crevices of a reef (and better for hunting for food). These tend to be longer, too!
Most shark tails are asymmetric, with the upper lobe being larger than the lower lobe (think bull shark, oceanic white tips). This shape usually drives a shark down as the tail moves from side to side, while the trailing edge of the lower lobe allows for some lift, as do those pectoral fins! Hammerhead sharks get extra lift from their wide, wing-like shaped heads.
That's it for this week, tune in next Monday for the next bit of this series!
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