Scientists are learning more than ever about these impressive fish.
Sharks were cruising the ocean long before dinosaurs roamed the Earth, and they’re still here today.
Their basic biology is the same as it’s always been, with skin covered in tiny teeth and skeletons made not of hard bone, like other fishes, but soft cartilage, the same material as your nose and ears.
More than 500 shark species live everywhere throughout the seas; from shallow coasts to the deep sea, and a few swim up rivers and into lakes.
Scientists are still learning more about sharks all the time, finding new species and uncovering new details about their super-efficient, long, slow lives.
How long have sharks been around?
Sharks can trace their ancestry back at least 400 million years. But it’s a myth that all sharks are ancient species. Some are relatively new, including the walking sharks which evolved in the last two to nine million years.
What do sharks eat?
Most sharks are predators. They hunt for fishes and squid, as well as other sharks. Great white sharks have such high energy requirements they specialise in eating blubber-rich marine mammals, such as seals and sea lions.
Other species, like Port Jackson sharks, crunch on crabs and clams using crushing tooth plates.
A few sharks break the carnivore mould. Whale, basking, and megamouth sharks are filter feeders and sift seawater across special structures in their gills to extract tiny zooplankton.
Recently, scientists discovered that bonnethead sharks are omnivores. As much as half their diet is made up of seagrass.
How many teeth do sharks have? Why are they so common in the fossil record?
Depending on the species, sharks can have anything from several dozen, to hundreds of teeth. They continually shed worn teeth from the front of their jaws with new ones sliding forwards to replace them.
In a lifetime, a single shark can produce tens of thousands of teeth. They preserve well in the fossil record, much better than their cartilage skeletons, and they tell us a lot about ancient species and ecosystems.
A recent study of shark teeth recovered from deep-sea sediments showed that they almost went entirely extinct around 19 million years ago.
How long do sharks live?
Sharks are slow-growing and generally long-lived animals, typically taking a decade or more to reach maturity and start breeding. Hammerhead sharks can live for 30 years, and great whites for 70 years.
Greenland sharks take this slow pace of life to an extreme. Studies of radioactive isotopes laid down in their eyes when nuclear bombs were tested in the mid-20th century, revealed they can live for as long as 400 years!
Are they endangered? What threats are there to sharks?
More than one-third of all known shark species and their close relatives the skates and rays – known collectively as elasmobranchs – are threatened with extinction. They are the second most endangered group of animals after amphibians.
The main threat they face is overfishing. Millions are caught by tuna longliners that operate in the remote reaches of the high seas. A lot also get tangled in lines and nets, and caught by trawlers in fisheries closer to shore.
What’s being done to protect them? Is there anything we can do at home?
Shark conservation has been gradually improving over the last few decades.
Now regulations protect some of the most endangered species. For instance in the Atlantic, longline fisheries must now release all shortfin mako sharks they catch, hopefully some that are still alive.
International trade in many shark species is also now regulated. Marine reserves are also being set up specifically to protect sharks, such as the world’s first basking shark reserve, off the Outer Hebrides in Scotland.
At home, you can help by not buying any shark products, including obvious things like shark fin soup as well as cartilage supplements that may have come from shark skeletons.
If you eat seafood, you can support sustainable fisheries that are less likely to catch sharks as bycatch. Use the Good Fish Guide app to help look for better options.
Read more about sharks:
- Megalodons were warm-blooded, and it may have led to their demise
- Light shed on secrets of glow-in-the-dark sharks
- First ever omnivorous sharks identified