Within the 440 different species of sharks, there is a largest diversity of fins. Each species has different types of fins that meet different biological purposes. However, with some many different kinds of fins it can get confusing understanding what each fin does and why shark species have each evolved unique fins. Here’s a simple guide to understanding what types of fins there are and what they do for the different species of sharks.
Dorsal fins are probably the most recognized of all shark fins. They are the fin that you often see cutting through the water in shark movies right before an attack, a behavior dubbed as “knifing.” Dorsal fins are located on the back of a shark. Dorsal fins act as a means to stabilize sharks so they can stay upright and prevent rolling on their backs in the water. Dorsal fins also help sharks make quick and sudden turns. Most sharks also have a secondary dorsal fin located along their back closer to their tail. However, species from the Hexanchiformes, family only have a single dorsal fin.
Dorsal fins serve other functions beyond just helping sharks be better swimmers. Some species of shark like the Port Jackson Shark and the Spiny Dogfish shark have poisoned spines on their dorsal fins that serve to protect them against predator attacks. Dorsal fins are also important in many shark mating rituals. Male sharks will show dominance and display interest by biting the female shark’s dorsal fin, while others like Reef and Bull Sharks will bite on to the dorsal fin and hold on while they copulate.
Pectoral fins are essential the “wings” of the shark. They are located on the sides of the body and typically found behind the gill slits. Pectoral fins are paired fins and create lift in the water and help sharks swim up and down in the water column. They are also useful in steering and help sharks maintain stability at high speeds. Pectoral fins are highly flexible and can be raised, lowered, curled, and buckled depending on the intentions of the shark. The size and shape of pectoral fins vary greatly among species. Some species of sharks like Angel Sharks and the Wobbegong Shark have long, flat pectoral fins that run nearly the length of their torso. These sharks are often confused with rays because of the width of their fins.
Pectoral fins also serve other functions besides just swimming. Researchers have observed that both Great White Sharks and Hammerhead Sharks will use their fins to communicate with other members of their species. Great White Sharks essentially wave messages at each other, while Hammerheads will use their pectoral fins in complex dance routines that display dominance or mating interest.
Pelvic fins, also called ventral fins, are found on the underneath side of the shark’s body. Like pectoral fins, pelvic fins are usually paired. Pelvic fins are usually the smallest fins present on a shark’s body, however they are still very important. Pelvic fins support lift and steering but also help sharks make quick decisive stops. They also stabilize the back end of the shark. This is essential since there are several species of shark that are very large like the Whale Shark that measures at 40 ft (12.2 m) in length, the Basking Shark that measures at 20-26 ft (6-8 m) in length, and the Great White Shark that grows to 20 ft (6 m) in length, it is crucial their posterior is stable.
Pelvic fins are also used in mating. Researchers have noticed that female Sand Tiger Sharks, Great White Sharks, and Nurse Sharks all use their fins to signal interest in mating. This behavior is called “cupping” because the pectoral fins will flex into a cup like shape. Female sharks will also flare their pelvic fins as a way to invite copulation. Scientists do not know how common this behavior is among the different species sharks because it is very rare to observe shark mating in the wild.
The most unusual use of pectoral fins actual comes from Bamboo sharks who will literally use them as legs to walk along the bottom of the seafloor.
Anal fins are also at the back of the shark, under the body but before the tail. Anal fins do not come in pairs like pelvic fins and often line up with the second dorsal fin. Not all sharks have anal fins. Members of the orders Hexanchiformes, Squaliformes, Squatiniformes, and Pristiophoriformes all do not have anal fins. Like pelvic fins, anal fins are used to stabilize the the back end of the shark.
Caudal fins are the tail fins of the shark. All sharks have two caudal fins, an upper and a lower. Caudal fins are used for proposal and thrust. Caudal fins come in five different shapes and size patterns depending on the species. Most open water sharks like Mackerel Sharks have evenly sized caudal fins that are crescent shaped in order to give extra speed and propulsion. Other species like Requiem Sharks have uneven caudal fins with the upper being substantially larger in an angle shape. Thresher Sharks, though a Mackerel Shark have an extreme version of this model when they upper caudal fin is half the length of their body. Bottom-dwelling sharks have longer upper caudal fins at a low angle and very small lower fin that helps them move quickly at ambush angles. Except with Angel Sharks which have the reverse. Dogfish sharks have tails with larger upper caudal fins but at different angle than the lower caudal fin. These use this configuration for faster speeds.
Sharks for the most part have the same fin configurations of any fish. However, there is a lot of variation between the different species fin sizes and uses. Once you understand the different types of shark fins, you’ll soon learn how to recognize sharks by just their fin configuration.