A popular poem by the American poet John Ciardi, often taught in English classes, begins like this: “My sweet, let me tell you about the shark”. And that’s exactly what we’re going to do, on this particularly appropriate week. Without further ado, let’s talk about sharks!
Sharks first appeared around 450 million years ago, and while they looked quite different from today’s sharks, what we think of today as a “shark” has remained largely unchanged for over 100 million years. Great white sharks first appeared around 16 million years ago, and some (like the Megalodon) grew to immense sizes – up to 50 feet long or more!
What IS a Shark?
You can probably recognize most sharks as sharks when you see them, but do you really know what qualifies something as a shark? What is it that makes a shark different from other fish?
Sharks belong to a group known as cartilaginous fishes, which are unique in that their skeletons are made of cartilage rather than calcified bone like most vertebrates. This group also includes stingrays, sawfish, skates, manta rays, guitarfishes and strange-looking fish known as chimaeras.
What separates sharks from these other cartilaginous fishes? A few things. Firstly, most (but not all) sharks have a cylindrical body shape. They also have long tail (or caudal) fins and one or two back (or dorsal) fins. There are some sharks, like the angel shark, that are flattened like rays…so how can you tell if it’s a shark or a ray? The key is the gills. Rays have their gills on the underside of their bodies, while sharks have gills on the sides of their heads.
Sharks of All Shapes and Sizes
Beyond those basic criteria, there’s quite a bit of diversity and variation in the shark world. Sharks range in size from just a few inches long to nearly 40 feet in length! The basking shark and the whale shark, for example, are both among the largest fish in the world.
Despite their size, these sharks are not dangerous and actually eat some of the tiniest animals in the sea. These two sharks are “filter feeders”. They swim slowly through the seas with their giant mouths open, straining the water for tiny organisms to eat.
Some sharks are built purely for speed, like the mako shark. It can reach speeds of up to 45 miles per hour in short bursts due to its torpedo shaped, streamlined body. While most sharks like the mako must constantly swim to pass water through their gills, some can sit motionless on the sea floor, like the zebra shark and nurse shark.
Caution: Great Whites Might Bite!
Of course, no discussion of sharks would be complete without mentioning the biggest and baddest of them all: the great white shark. These huge fish can reach up to 20 feet long and weigh over 4000 pounds. They have a fearsome reputation, and these sharks have indeed been involved in attacks on humans. However, they do not intentionally hunt humans, as we lack the fat content of the sea lions and other marine mammals they typically eat.
While shark attacks do occur, they are quite rare. Other than the great white, tiger and bull sharks are the most likely to be involved in attacks on humans. Despite their reputation, most shark species are quite shy and will not attack a human unless it is provoked or bothered. The reality is that humans pose a much greater threat to sharks than the other way around.
Save the Sharks!
About 70 shark attacks on humans are reported per year. Conversely, tens of millions of sharks are harvested every year for their fins, which are used in a food dish called shark fin soup. This soup is falsely believed to have medicinal uses, leading to a sharp increase in demand in countries like China. Some shark species have declined as much as 80% in the last 50 years due to overfishing. The process of “finning” is a cruel and inhumane practice that leads to a slow and painful death for the shark involved.
While many people fear sharks, these apex predators have much more reason to fear us. They serve an important role in the marine ecosystem, and if they are not protected, the world’s oceans will suffer. These amazing creatures should not be feared, but they do deserve our respect, and our assistance in ensuring that they have a future on our planet.