They're Older Than Dinosaurs, and Other Interesting Facts About Sharks
Michelle Milliken
When you think of a shark, the big ones may come to mind: your great whites, your tiger sharks, your bull sharks. However, there are more than 500 species, from the 40-foot-long whale shark to the dwarf lantern shark, whose length is measured in inches. Sharks can also be found from tropical waters all the way up to the Arctic. Unfortunately, one thing many of them have in common is an uncertain future. About a third of shark species are listed by IUCN, labeled as vulnerable to critically endangered. Learn more about these majestic animals and why their survival is important for the oceans… and us.
They’re Older Than Dinosaurs
Sharks have been around for some time, but just how long is staggering. Thanks to fossils, we know the first sharks appeared on the scene more than 400 million years ago. Fossilized teeth weren’t found quite so far back in the fossil record, but the oldest fossil of a shark scale dates back to the Late Ordovician Period, around 450 million years ago. Meanwhile, the earliest known dinosaurs didn’t appear until the Triassic Period, between 200 and 250 million years ago.
They Have More Than Five Senses
During all those years, sharks have had plenty of time to fine tune their senses, of which they have more than five. In addition to strong senses of smell and hearing, they also have electroreception, which allows them to detect an electrical field. This ability comes from cells around their snouts called the Ampullae of Lorenzini. Sharks can use this to sense magnetic fields, as well, which allows them to navigate using the earth’s magnetic pull.
The National Oceanic and Atmospheric Administration (NOAA) says sharks also have a distant touch sense linked with vibration. This comes from pores in their lateral line, which runs from their snouts to their tails, and which give them the ability to feel pressure changes and vibrations in the water, alerting them to prey and other predators.
Some Give Birth… And the Pups Don’t Always Have the Same Dad
Fish usually lay eggs to reproduce, but not all sharks do this. Some shark species do lay eggs, which are held within a pouch that is abandoned, but others actually develop embryos in their wombs. For these species, eggs develop and hatch in the womb, and the young are either sustained through the placenta or by living on a yolk sac. Interestingly, or horrifyingly, one pup will often eat its siblings and their yolk sacs in the womb.
These in utero siblings may also not have the same dad, as the NOAA says females will often use the sperm of more than one male.
They Have Personalities
When you think of animals with personality, fish may not be the first thing that comes to mind, but maybe they should be. Research has shown that sharks can be quite the individuals. A study conducted by scientists at Macquarie University in Australia showed that sharks have differing levels of boldness and different ways of handling stress.
Meanwhile, researchers at the University of Exeter and the Marine Biological Association of the UK also found that small spotted catsharks may be outgoing or more reclusive, regardless of how many other individuals are present or if there are changes in their environment.
Dr. David Jacoby, behavioral ecologist and study co-author, said, “These results were driven by different social preferences (i.e social/antisocial individuals) that appeared to reflect different strategies for staying safe. Well-connected individuals formed conspicuous groups, while less social individuals tended to camouflage alone, matching their skin color with the color of the gravel substrate in the bottom of the tank.”
They Congregate at a Shark Café
Many great white sharks migrate away from California as far west as the Hawaiian Islands each year. They often stop at the same random place in the middle of the two, though, far from any land. Researchers have taken to calling it the “white shark café.” It isn't entirely known why the animals decide to spend their time in the area, but recent research did find that there is very diverse ocean life there, which provides the sharks with plenty of food.
They Regenerate Body Parts
When we lose a tooth as an adult, it’s not really the best thing to experience, since it’s not like we have backups. Sharks do, though. They shed and regrow teeth throughout their entire lifetimes, sometimes going through up to 30,000 different teeth! Can you imagine the poor dental hygienist if sharks were adamant about teeth cleanings?
Sharks can regenerate damaged fins, too. A study recently published in the Journal of Marine Sciences showed how a silky shark that had lost about a fifth of its first dorsal fin to injury grew back 87% of what was missing within a year. The researchers say their findings provide insight into wound healing rates in sharks, an area of limited research.
They Can Be Hypnotized
Something as impressive as a regenerating species that outlived the dinosaurs and swims a thousand miles to go to a café may not seem like it would have a weakness, but it does. Flipping a shark upside down puts it into a state similar to hypnosis called tonic immobility. This helps researchers who study sharks implant tags into them.
One Species is Really Old
GREENLAND SHARK. PHOTO: WIKIMEDIA COMMONS / HEMMING1952
Imagine being so old you were alive for both Queens Elizabeth. If you’re a Greenland shark, it’s possible. These slow-moving sharks, found primarily in the cold waters of the Arctic Ocean and North Atlantic, are known to live a long time. The oldest member of the species found so far was estimated to be about 400 years old. These elusive animals can hang out well below a mile under the water’s surface, and all that cold must do something for them, because even if they don’t reach 400, they’re estimated to have an average life expectancy of at least 250 years.
They’re Beneficial
Sharks’ presence in the food chain makes for healthy, balanced ecosystems. When it comes to the sharks that are apex predators, their diet keeps their prey species in check, which cascades down into benefits for species that would be at risk if their predators were too plentiful. Healthy shark populations are linked with healthier coral reefs, as they prey on fish that eat smaller, algae-eating fish. This ensures these species are at appropriate levels to keep the coral healthy.
Sharks also help coastal communities boost their tourism.
They Face Threats
With nearly a third of species deemed vulnerable to critically endangered, these essential animals are obviously facing many threats. Overfishing is among the biggest issues, with up to 100 million sharks believed to be killed by humans each year. This is usually due to desire for their fins. Sharks also often find themselves the victims of bycatch. Pollution, habitat impacts, and climate change are threatening their survival, as well.
When their numbers fall, this is even more problematic than it is for some species because most sharks take longer to achieve sexual maturity and reproduce slowly, meaning population replenishment can be difficult.
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