Imagine you’re enjoying a beautiful sunny day at the beach. You and your family are having lots of fun dipping in and out of the ocean when suddenly you see an ominous dark triangular shape breaking the surface in the distance.
What could it be? Is it a shark that could be a cause for concern? Or might it be a dolphin that most people would love the chance to see swimming in the wild?
Well, worry no longer, as we’re here to help you learn the differences between a shark and a dolphin.
We’ll start by telling you how to tell their dorsal fins apart by looking at various attributes, including the shape, quantity, and the way they move.
Then, if you’re interested in learning more, we’ll dive into the other key differences between sharks and dolphins before also considering any similarities.
By the time we’re done, if you ever spot that distinctive shape at the surface, you’ll easily be able to recognize if it’s connected to a dolphin or a shark.
Dolphins and Sharks – Two Very Different Animals
Before we get to the vital subject of fin identification, let’s start with a quick bit of science to understand from the beginning that sharks and dolphins are very different animals.
Sharks are elasmobranch fish, while dolphins are aquatic mammals.
There are five families of dolphins (part of the infraorder Cetacea) and about 40 species.
The majority of dolphins by far live in the ocean (family Delphinidae), but there are also some river and brackish water species (Platanistidae – the Indian river dolphins, Iniidae – the New World river dolphins, and Pontoporiidae – the brackish dolphins).
Sharks (clade Selachimorpha) represent over 500 different species, and apart from a small number of species, most notably the bull shark that can survive in rivers, all of these are ocean dwellers.
We’ll get to what this all means later, but for now, just keep in mind that sharks and dolphins are fundamentally very different. Luckily, with a bit of insight, that makes them pretty easy to tell apart.
What’s the Difference Between a Shark Fin and a Dolphin Fin?
So, you’ve seen a fin sticking above the water’s surface. How can you tell if it belongs to a dolphin or a shark?
The fin that you’re most likely to see is the dorsal fin. These fins are highest on the animal and stick up vertically, with the primary one being roughly halfway along its back.
You may also see the tail fin, known as the caudal fin on sharks, and as flukes on dolphins.
To tell the difference between a shark and a dolphin fin, you can compare as follows.
Dorsal Fin Shape
One of the easiest ways to compare a shark vs. a dolphin’s dorsal fin is by its shape.
The dorsal fin on a shark tends to be distinctively triangular with a straighter trailing (rear) edge and a pointed tip.
On the other hand, dolphins have more of a curved hook-like shape to their dorsal fin, with a rounded tip. The fin usually arcs backward compared to the shark’s straighter shape.
Dorsal Fin Quantity
Dolphins only have one dorsal fin, whereas many sharks have two.
The shark’s primary or first dorsal is the taller one, so it is the one you’re most likely to see. However, if you see a second, much smaller dorsal fin towards the animal’s rear, you can be sure that you’re looking at a shark.
Tail Fin Orientation
If you see a tail fin vertically above the water behind the dorsal, you’re looking at a shark as a dolphin’s tail flukes are horizontal from its body.
Fin Movement or Behavior
The way that sharks and dolphins swim are very different, so by watching how the fin you’ve spotted moves, you can make an educated guess as to what you’re looking at.
A dolphin moves its horizontal tail up and down as it swims, and the dorsal fin will stay straight in the direction of travel.
A shark swims by sweeping its tail from side to side and flexing its body.
So, if you see the dorsal fin staying straight, perhaps with a bouncing movement up and down, it’s probably a dolphin. If the fin moves side to side as it swims through the water, it’s almost certainly a shark.
Dolphins often swim in arcs, coming to the surface to breathe air periodically. If you see the fin continually reappearing in a wave-like motion, it’s likely a dolphin.
It’s also common to see dolphins jump out of the water as they swim, which makes it really easy to recognize them.
Although not as frequent by any means, sharks like the great white are known to jump when hunting, and we’re sure you’d identify it quickly if one breached the surface near you!
What Other Differences Are There Between Sharks and Dolphins?
Having looked at how to tell dolphins and sharks apart by the fins you might see breaking the surface, let’s look at other differences between these sea creatures.
Two Very Different Animals – More Detail
As we’ve already mentioned, sharks are fish, while dolphins are aquatic mammals.
This means that dolphins are warm-blooded, breathe atmospheric air through a blowhole on the top of their head, and nurse their young. They also have a hard bony skeleton.
Sharks are cold-blooded fish that get their oxygen from the water around them via their gills. When baby sharks are born, they’re on their own without further care from their mother. Instead of bone, they have a skeleton made of cartilage.
In evolutionary terms, sharks have been around a lot longer than dolphins, and their ancestors date back to the Ordovician period, 450–420 million years ago.
Dolphins evolved from land mammals and first went to the ocean approximately 49 million years ago. However, it took 5–10 million years after that for them to become fully aquatic.
Most dolphins look sleeker and slimmer than sharks, and they often have characteristic long snouts. There’s one exception, perhaps, and that’s the larger Orca, which is also a type of dolphin. But even that shares the typical dolphin body layout.
The dolphin’s sleek appearance comes from its blubber, which helps keep the animal warm and streamlines the body. In comparison, sharks have a rough skin of dermal denticles, which gives the fish an extremely tough-looking exterior.
Dolphins range in size from the smallest species, the Māui dolphin (Cephalorhynchus hectori maui) at 1.7 meters long (5 ft 7 in), to the Orca (Orcinus orca), which can reach 9.5 meters (31 ft 2 in).
The 500 species of sharks have a much greater size range. The smallest is the dwarf lanternshark (Etmopterus perryi) which only measures 17 centimeters (6.7 in). However, the whale shark (Rhincodon typus) is the largest fish in the ocean and can grow as big as 18.8 m (61.7 ft)
We’ve already considered how the fins of each animal would look if you saw one popping out of the water, but what about below the surface?
When comparing fins overall, dolphins have two pectoral flippers, a single dorsal fin, and a horizontal tail fin.
The fins on a shark can vary between species. However, most species will have two pectoral fins, a pair of pelvic fins, a primary and secondary dorsal fin, a vertical caudal fin tail, and an anal fin.
As the two animals breathe in completely different ways, their breathing systems look very different. Like a whale, a dolphin has a distinctive blowhole on the top of its head. In contrast, sharks have gills on their sides, just like other fish.
Dolphins are almost always seen traveling together in pods of tens or even hundreds of individuals. In comparison, most sharks are solitary and only come together when it is time to mate.
There are some shark exceptions, like the scalloped hammerhead (Sphyrna lewini), which is seen schooling in groups of more than 100.
Dolphins are known for their incredibly high levels of intelligence. They are considered self-aware, able to experience feelings, including grief, and can play games and solve problems.
We’re certainly not calling sharks stupid (we would not dare!). However, they do not exhibit the same mammalian behaviors as dolphins.
On the other hand, it is known that sharks have brains that are similarly sized to their body mass compared to mammals, and when it comes to hunting prey, sharks can put together complex plans and even exhibit learning from each other.
Regarding speed, the fastest shark, the shortfin mako (Isurus oxyrinchus), holds a record of around 56 kph (34.8 mph).
However, dolphins are no slouches, and common dolphins (Delphinus delphis) have been clocked, reaching speeds of 60 km/h (37 mph).
It’s also believed that sharks can typically only make their high speeds in short bursts, whereas dolphins can maintain their peak for longer.
Dolphins need air to breathe and, relatively speaking, spend their time close to the surface.
In comparison, sharks can be found in every depth of the world’s oceans, including the very deepest, the Marianas Trench.
Dolphins have an array of advanced techniques at their disposal when hunting for food.
Because dolphins travel in pods, they can herd fish together into tight bait balls and work as a team to make it easy for each other to pick off a meal.
As sharks are usually solitary, they will instead use hunting techniques like striking rapidly vertically from the depths to catch their prey.
Dolphins have good eyesight, but it’s their echolocation that they mainly use to detect prey at long and short ranges.
Sharks combine a keen sense of smell and hearing with electrical sense organs, including their ampullae of Lorenzini and lateral line, to seek food beyond the visual range.
Both sharks and dolphins use internal fertilization to reproduce.
However, while some sharks give birth to live young and others lay eggs, all dolphins give birth to live calves.
Dolphins only have one calf at a time, but the numbers of baby sharks vary widely. A sand tiger shark (Carcharias taurus) will have one pup, while a pregnant whale shark has been found with over 300.
Baby dolphins stay with their mothers as they grow and are nursed for one to three years. Sharks are on their own immediately whether they hatch from eggs on the seabed or are born as live pups.
Similarities Between Dolphins and Sharks
There are a lot of differences between sharks (fish) and dolphins (aquatic mammals). However, there are also similarities.
Sharks and dolphins typically both have countershading camouflage meaning their bellies are lighter than their sides and top.
Although some sharks have specialist diets, like the filter-feeding whale shark, many are opportunistic feeders like most dolphins.
Dolphins and many sharks will happily eat fish, squid, and crustaceans and, in some cases, will be directly competing with each other for food.
Both are exceptional hunters, and many species are considered apex predators in their environment.
Is a Shark Related to a Dolphin?
“Are sharks and dolphins related” is a common question. Sharks are cartilaginous fish, whereas dolphins are aquatic mammals, so they are not generally considered related.
However, both are vertebrates (Chordata) that live exclusively in water. Ultimately, they are both in the Animalia kingdom, so the answer could depend on how loosely you wish to use the term related!
Is a Dolphin Stronger Than a Shark?
That depends on which dolphin and which shark. Many sharks, including the great white or tiger shark, will prey on dolphins.
But the dolphin family has a trump card to play in the form of the orca. This beast can even attack and kill the great white!
Do Dolphins Protect Humans From Sharks?
Incredibly there have been cases of pods of dolphins mobbing a shark and protecting a human in the ocean. Dolphins have also been seen circling surfers, protecting them from sharks showing aggressive behaviors.
The key differences between sharks and dolphins come from them being different types of animals. Sharks are cartilaginous fish, whereas dolphins are aquatic mammals.
If you see a fin breaking the surface the next time you’re at the beach, consider its shape, how many there are, and how it moves.
Remember that shark dorsal fins are generally triangular, whereas dolphins are curved with a rounded tip. You can also consider if you can see one or two dorsals, as dolphins only ever have one.
Both sharks and dolphins are incredible creatures, and while being cautious, it’s worth remembering that incidents involving people and sharks are extremely rare. While with dolphins, it’s effectively unheard of.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.