Dolphins and sharks captivate us for entirely different reasons, yet this shared fascination has made them two of the most closely studied creatures in the ocean.
Despite their similar marine habitats and occasionally being mistaken for one another by the untrained eye, dolphins and sharks are fundamentally different in several ways, not least in the contrasting way we humans perceive them.
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Sharks suffer from undeserved bad PR, driven partly by the 1970’s film ‘Jaws’. Sharks may be depicted as sinister whereas dolphins are often perceived as cute. If either were to pop up whilst you were in the water, then your reaction to each might be very different.
What's the difference between sharks and dolphins?
Biologically, the most obvious contrast is that dolphins are mammals and share characteristics with humans, including being warm-blooded, giving birth to live young, and nursing their young with milk. Sharks, on the other hand, are fish.
In terms of physiology, sharks extract oxygen from water using gills located on the sides of their body behind the head, allowing them to stay submerged indefinitely.
Dolphins breathe air when at the surface of the water, through a specially adapted nostril or blowhole, located on top of their heads.
Sharks have a cartilaginous rather than a bony skeleton, which is made of a strong, flexible connective tissue called cartilage, which is also found in humans (in our ears and noses).
Whilst it is not recommended that you touch either, if you did you would find that dolphin skin feels smooth and rubbery, whilst a shark’s skin has small rough scales called denticles, which allow them to move efficiently through water by reducing drag.
Do sharks give birth to live young like dolphins?
As mammals, dolphins give birth to live young, which they feed and nurture for extended periods. Some sharks can give birth in a similar way to mammals, while other species lay eggs – some hatching within the mother’s body, while others are encased and develop inside a tough leathery egg case (sometimes known as a mermaid’s purse).
How intelligent are sharks compared to dolphins?
When it comes to behavioural and social structure, there are marked differences between dolphins who are known for their high intelligence, complex social behaviours (including cooperative hunting, play, and communication), and sharks who are often solitary and generally do not display the same level of social interaction and cooperation seen in dolphin pods. Dolphins will tend to form groups or pods - sometimes even megapods where hundreds or thousands of individuals may come together to travel or feed.
Dolphins' communication skills are very sophisticated. By emitting sound waves that bounce off objects and return to them (echolocation) a dolphin can gather information about the surrounding environment to accurately navigate and hunt. A dolphin pod will also communicate with each other using a range of vocalisations and physical behaviours. Sharks on the other hand rely primarily on their acute senses for hunting and navigation, and their communication is not thought to be as complex as that of dolphins.
Do dolphins and sharks share the same diet?
Both sharks and dolphins are apex predators, and so are crucial to marine food chains and ecosystems. Dolphins, feeding on fish, squid, and crustaceans, can employ teamwork and strategies like herding fish into tight balls for easier capture, or using tools like sponges to protect their noses while foraging on the seafloor. Sharks will prey on fish, seals, crustaceans, and even other sharks. They rely on stealth, speed, and their keen senses to detect prey.
Some species are known for their powerful jaws and multiple rows of teeth, which they use to tear apart their prey. Dolphins and sharks play a vital role in maintaining the balance of marine ecosystems, regulating prey populations to help maintain ocean diversity.
Do sharks and dolphins face the same threats?
Sadly, one similarity between sharks and dolphins is that both face numerous threats from human activities, including habitat destruction, pollution, and overfishing.
Bycatch (accidental capture in nets and fishing gear) is the biggest single killer of dolphins and sharks are also severely impacted.
Many shark species are targeted for their fins, which are highly valued in some cultures. It is very important that we reduce the threat from harmful fishing practices, better protect the habitats of these key marine species, and raise public awareness about their importance to ocean health.
A healthy ocean is vital in our fight against climate breakdown. By protecting both dolphins and sharks, we are helping to protect the planet and ourselves.
