If you’ve watched a shark swim before, you might have wondered why you only see them move forwards. Due to their body design, sharks cannot swim backwards.
Sharks are a type of cartilaginous fish, unlike the bony fishes whose skeletons are made from bone rather than cartilage. The pectoral fins of sharks are not fused to their heads, and it is these fins that limit sharks to the fact that they cannot swim backwards.
While sharks are seemingly ferocious predators of the deep, only a few truly deserve that reputation. Regulating populations of fish and other marine species, sharks rarely attack humans and typically only do so when they have confused a person with one of their typical prey species, usually seals or sea turtles.
How Sharks Swim
Sharks have a body that has evolved over millions of years to be quite streamlined, which allows the majority of species to move quite quickly through the water. Depending on the shark species and their body design, they may be cruisers, floaters, or even flappers, as some of their different movements are dubbed.
Sharks generally use their tails to move their bodies forward, by pushing water around their fins. While some sharks move their bodies in a side to side motion with their fins for balance, others such as the great white shark propel themselves through the water using their tails.
Their bodies’ design limits their ability to swim backwards, however, with pectoral fins that are unable to curve upwards. This design means they can only move forward rather than backwards.
While it might seem like this design is disadvantageous to the shark, it keeps them alive by maintaining their normal respiratory processes. As a shark moves backwards, water can enter the gills rather than being pumped out of them, which can lead to a shark basically drowning.
Instead of swimming backwards, sharks can rely on gravity to “fall” backwards, tilting in that direction and not swimming, allowing gravity to take them in a backwards motion. This still interferes with their normal respiration and is generally limited by sharks.
The Exception to the Rule
While you might have been wondering can sharks swim backwards, you probably have not thought about them walking backwards, which the so-called walking sharks have the capability of doing.
The epaulette sharks are also known as walking sharks. They can use their pectoral and pelvic fins to walk across the seafloor, over reefs, and even on land.
While these sharks can swim quite well, they cannot swim backwards. Instead, they have adapted over millions of years to be able to use their fins to help them “walk” between areas in an undulating and crawling motion, including walking backwards.
Epaulette sharks typically live in shallow coral reef systems, where they may be trapped in shallow water environments, particularly when the tide goes out. Something that might spell death to another shark is something they can use to their advantage to hunt prey such as crustaceans and small fish that have been trapped in what amounts to tide pools.
Like other sharks, they get oxygen from the water around them by using their gills. They have had to adapt to survive in areas that provide them little to no oxygen in the isolated pools of water that form at low tide.
To adapt to a low oxygen environment, these epaulette sharks can slow their heart rate and breathing, which means that they need less oxygen. Their bodies can also temporarily limit blood flow to certain areas of their brain, which further reduces their oxygen needs when they are in shallow pools of water or “walking” between tide pools.
Walking sharks live in several areas of the world, typically in the Oceanic areas such as Australia and Indonesia. They are typically most active in the early morning or evening hours, so you might have an easier time spotting them if you go to the beach or go snorkeling in the early morning or around dusk.
Walking sharks can be seen in the water, particularly around crevices in the coral reefs that they live around. When the tide is low, you might see them “walking” across the coral reefs in search of their prey, which makes for an impressive sight, especially if you get to see them walking backwards.
Sharks have evolved over the millennia to not be able to swim backwards, which would put them at risk for respiratory problems or even drowning because they largely rely on forward motion to be able to breathe.
While sharks cannot swim backwards, one category of shark can walk on land and has the ability to walk backwards, the epaulette or walking sharks. These sharks live in a restricted area of the world and have adapted to low oxygen environments within shallow pools, where they hunt their prey when the tide goes out.