Shark Dorsal Fin | Function, Purpose & Structure

The shark dorsal fin is the triangular part on the back of a shark. It has a similar characteristic to most marine and freshwater vertebrates of the animal kingdom. The bony cartilage that supports the base of the dorsal fin in fish are called pterygiophores. Read on to find out more about a sharks dorsal fin.

Function Of A Dorsal Fin

Many marine species with dorsal fins are not closely related, but through convergent evolution, they have developed superficial fish-like body plans. These are ideal for their marine environment, including fish and larger marine mammals such as sharks (also whales, dolphins and porpoises) and extinct ancient marine reptiles such as various known species of ichthyosaurs. Most species with dorsal fins have only one, but some have two or three.

Sunfish use the dorsal fins and the anal fin for propulsion. In Anglerfish, the front dorsal fin has been modified to be the biological equivalent of a fishing rod or bait known as illicium or esca.

Many Catfish can lock the dorsal fin ray in an extended position to prevent predators attacking or to get into a small crevice. Some marine animals have developed dorsal fins with protective functions such as spikes or poisons. Both the Dogfish and the Port Jackson shark, for example, have spines on their dorsal fins that can secrete venom.

Billfish have very prominent dorsal fins. Like tuna, mackerel, and other scombroids, billfish are perfected by retracting their dorsal fins into a groove on their body while swimming. The color, shape, position and size of the dorsal fin will vary depending on the species of Billfish and can be an easy way to identify a particular species.

The White Marlin, for example, has a dorsal fin with a curved leading edge and is dotted with black spots. The large dorsal fin or ‘sail’ of the Sailfish is normally kept retracted for majority of the time. The Sailfish raises it’s dorsal fin when they want to herd a school of smaller fish and also after periods of extreme activity, probably to cool off.

shark fins

Shark Dorsal Fin Function

Sharks have many fins, each with their own function and purpose. The main purpose of the shark dorsal fin is to stabilize the animal when it rolls and to support it in sudden twists. Some other marine species have adapted their dorsal fins for other purposes. In fact, most sharks have two dorsal fins.

The first shark dorsal fin, also known as the ‘cranial dorsal fin’, is the fin that most of us think of when they imagine a shark roaming through the ocean. The first shark dorsal fin is the one Hollywood movies tend to describe cutting the ocean’s surface like a sharp knife. This fin is on the top of a shark’s back and is the one used to stabilise a shark’s body while in the water.

The first dorsal fin is lined with strong and flexible dorsal fibres and prevents a shark from rolling onto its back. It also helps the shark to make sharp turns when it’s swimming fast to hunt prey or escape a dangerous situation.

The second shark dorsal fin is much smaller than the first shark dorsal fin. This second shark dorsal fin is also on the shark’s back but is midway between the first dorsal fin and the tail. This second fin also helps to stabilize the shark in the water while also helping the shark swim smoothly and manoeuvre the back of its body more fluently.

Shark Fin Surface Exposures

In most shark movies, they are often portrayed with their shark dorsal fins ‘poking’ out of the water. It really does produce a dramatic image on screen – the fins look sharp and a little dangerous. However, it is one that is easy to fake. It is much cheaper to build a fake, convincing looking shark dorsal fin than use an actual shark.

You may find it hard to believe, but sharks in the wild very rarely swim with their dorsal fins exposed above the oceans’ surface. Most shark species tend to swim relatively close to the floor of the ocean or within the centre. Left to fend for themselves, most sharks don’t come close to the surface at all, as it is unknown territory.

However, sharks can be attracted to the seas’ surface by floating lures or buoys, and when studying such objects, their dorsal fin sometimes breaks the surface of the water. Sharks also sometimes venture into water so shallow that they can barely swim and, as a result, their dorsal fins sometimes penetrate the surface.

Many shark species, for example, use shallow coastal areas as breeding grounds for their young (called ‘pups‘). These shallow areas offer newborn sharks plenty of food and is often relatively safe from larger predators (often larger sharks).

It is also not that uncommon for large sharks, such as the Tiger Shark (Galeocerdo cuvier), to chase prey such as schools of fish and sea turtles in water that is shallow enough that their dorsal fins, and sometimes their entire backs, are exposed.

dorsal fin

Shark Finning & Why It Is a Huge Problem

A shark dorsal fin is also used by humans. Ever heard of shark finning? It is the cruel practice of cutting off the fins of a live shark and then throwing the rest of the creature back into the sea. Without their fins, they will die a horribly slow and painful death.

Shark Fin Soup

Shark fins are most commonly used as the main ingredient in shark fin soup in China and Hong Kong (although uncommon, it is also consumed in other countries), as well as by Chinese communities in other parts of the world.

This sticky, glue-like broth is a traditional Chinese dish that is over 1000 years old. Once a rare delicacy consumed only by the high class and Chinese aristocracy, serving it played a vital role as an indication of social status. The fibers have a pasta-like consistency, but have virtually no nice taste or nutritional value, so chicken broth or something alike is even added to enhance the flavour. Making the act of causing this suffering completely unnecessary.

In the last 20 years, the demand for shark fin soup has exploded. It is still linked to the idea of privilege and social status (a bowl can be priced up to $100), but the continuous growth of the Chinese economy have meant that hundreds of millions of inhabitants can now afford this disgusting ‘luxury’. Many consider it indispensable at big events such as birthdays, weddings, company meetings and during the Chinese New Year celebrations.

Shark Fin Chinese Medicine

The use of Shark dorsal fins are also popular in traditional Chinese medicine, although research suggests it contains a large amount of mercury and other toxins, making it barely safe for human consumption. There is also zero scientific research that proves any health benefits of consuming or using shark fin products.

An estimated 73 million sharks are killed each year by shark finning, an indiscriminate slaughter that has brought many shark species to the brink of extinction.

Many people are afraid of sharks, so do not care if they survive or not. They may not be as cute as a tiger or panda going into extinction, but from an ecological point of view, their disappearance as top predators will absolutely destroy entire ocean ecosystems.

Scientists are also fascinated by sharks, as they still have not found out how shark wounds heal so quickly and how they appear to be resistant to cancer.

It is essential to reduce demand by changing these attitudes towards shark finning and to support shark conservation. Today, there are encouraging signs that shark fin soup consumption is in decline with several airlines and hotel chains stopping selling them. In 2012, the Chinese government banned it for official occasions, although the motive was more for austerity than for conservation.

shark fin soup

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