This entry is part 1 of 3 in the series Shark Week

Shark Week

In July 1988, Discovery Channel launched a programming block based on sharks. The first iteration of the theme began with a piece called Caged in Fear, about abalone divers who developed a contraption to keep them safe during their harvests. Now in its 36th season, Shark Week is the longest-running cable television event in history.

The block is also trendy, often dominating summer memetics.

Originally, the intent of the network was to aid in the conservation of sharks and to clear up misconceptions about them. Networks such as Discovery or History Channel, however, have noticeably moved over the years away from educational slants toward purely entertainment vehicles. Hosts such as Andy Samberg, Shaquille O’Neal, and Dwayne Johnson have overseen a transition from a noble goal to near kitsch. Today, you’re just as likely to see mockumentaries, such as Megalodon: The Monster Shark Lives, or the likes of Michael Phelps racing great whites via CGI as you are to view something fortifying.

If you can’t necessarily fill your brain with shark-related information on Disocvery, fret not: the next 800 words or so will provide a brain-strengthening overview of the scary fish of the deep.

Sharks belong to a class called Chondrichthyes, a name that comes from the Greek words for “cartilage” and “fish.” As the name implies, these fish sport skeletons made of cartilage instead of bone. Other members of the class include rays and skates. Selachologists currently recognize 512 species of sharks, though that number could grow in the coming years, as discoveries await validation.

Despite their behemoth reputations, the size of sharks runs an awfully vast gamut. The world’s largest fish is the aptly named whale shark (remember that whales are actually mammals!), which can exceed 40 feet in length. The whale shark goes a long way to bucking the voracious, lethal stature of sharks in general, as the leviathan is a slow-moving filter feeder. On the other end of the spectrum, sharks can be tiny. The dwarf lanternshark usually doesn’t even reach seven inches in length!

Sharks inhabit all the salty waters of the world. Just a few exceptions meander into freshwater, including the bull shark and the river shark.

A whale shark - photo by Abe Khao Lak
The dwarf lanternshark - photo by Chip Clark/Smithsonian

The word “shark” features an interesting etymology. Until the 16th century, few humans had any interaction with them, which led to a lack of cohesive naming. Sailors called sharks “sea dogs.” A few species still bear this historical mark, such as the dogfish and the porbeagle. Many historians believe the modern usage of shark to convey a familial connection relates to the Dutch word schurk, which means “villain” or “scoundrel.” The terms “loan shark” or “card shark” make more sense in this evolutionary order than the reverse.

Sharks are among the oldest historical organisms on the planet. Modern sharks filled the seas while the dinosaurs roamed in the Jurassic period, though their ancestors are much more ancient, dating to the Silurian, as long as 439 million years ago.

Not only are sharks as a group ancient, but they can also become quite elderly as individuals. The Greenland shark, for example, can live to be 500 years old!

The Greenland shark - image by NOAA Okeanos Explorer Program

Perhaps the most famous pieces of a shark’s anatomy are its teeth. Most people are familiar with the triangle shape of the larger apex predators, but the chompers actually vary quite a bit, depending on the shark’s diet. Those that munch on mollusks and crustaceans have flat teeth; fish eaters feature needle-like teeth for gripping; plankton feeders still have teeth, but they are small and non-functional. The jaws of a shark are not attached to its cranium. Instead, they feature hexagonal supports, called tesserae, which are blocks of crystal blocks made of calcium salts arranged in a mosaic. Sharks constantly replace their teeth throughout their lives. The teeth are not attached to the jaw, but rather their gums. A groove in the gums moves teeth forward, as needed. Some sharks might go through 30,000 teeth before they die!

The mouth is not the only place a shark has “teeth.” Their skin is covered with flexible collagenous fibers in a helical network. Called denticles, these “teeth” provide an outer “skeleton” while also reducing turbulence during swimming. If a shark sports coloration – like the tiger shark or zebra shark – these markings come from the pigments in some of the denticles. In addition to looking dapper, these colorings can become quite efficient camouflage.

The denticles of a lemon shark, viewed through an electron microscope - photo by Pascal Deynat/Odontobase
A tiger shark - photo by Albert kok
A zebra shark - photo by Julien Bidet

The senses of sharks are quite extraordinary. Some species can detect one part of blood in one million parts of water. They also seem to smell like most creatures hear. They can tell the direction from which the blood arrived, based on the timing of it hitting their nostrils, similar to how we can tell the directionality of sound.

They also have a set of organs called ampullae of Lorenzini. These sensors can detect electromagnetic fields! Sharks employ this superpower to find prey since all living things emanate electricity. They also use it to orient themselves, based on the magnetic field of the planet. Some scientists believe they might also utilize the ampullae for navigation.

Electromagnetic field receptors (ampullae of Lorenzini) and motion-detecting canals in the head of a shark - graphic by Chris_huh

Thanks to the active imagination and fears of humans, sharks have developed the stature of people hunters. Peter Benchley, the author of Jaws and a one-time host of Shark Week, as well as Steven Spielberg, the director of the world’s first blockbuster, eventually rued their involvement in cultivating the image of sharks. Both spent significant time and energy attempting to dispel the generality of sharks as people killers.

Of course, human fatalities do occur. One study pegged the number at approximately 4.3 fatalities each year due to unprovoked shark attacks. Lightning kills around 2,000 people per year, for comparison. Further, a study by the International Shark Attack File discovered that nearly a quarter of all attacks on humans by sharks are provoked by the idiotic or ignorant. Only four species have been involved in a statistically significant number of attacks: great white, oceanic whitetip, tiger, and bull sharks. Many researchers believe nearly all unprovoked attacks come from mistaking a human for a shark’s normal prey, not from a desire to prey upon humans. Tests with juvenile sharks show them approaching humans with no attempts to bite, suggesting that sharks do not view humans as innate threats.

Sharks are, however, under attack by humans. According to a study published in Nature, shark populations have dropped by 71% since 1970. For a group that consists of many apex predators, this reduction is hard to pull off without external help. Many Pacific Islander populations revered sharks as gods, but, today, more populations view them as something to be culled. A spate of species, including the gorgeous hammerhead, are now listed as critically endangered.

A great hammerhead shark - photo by Albert kok

Humans seem to love Shark Week. Hopefully, moving forward, we can translate our love into the conservation of these powerful, ancient swimmers. 

Further Reading and Exploration

Discovery’s Shark Week – Official Website

SHARKS – Smithsonian Ocean

Sharks – World Wildlife Fund

Half a century of global decline in oceanic sharks and rays – Nature

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