50 Years Post-Jaws: Sharks' Biology Unveiled

The summer of 1975 was the summer of " Jaws ."

The first blockbuster movie sent waves of panic and awe through audiences. "Jaws" - the tale of a killer great white shark that terrorizes a coastal tourist town - captured people's imaginations and simultaneously created a widespread fear of the water.

To call Steven Spielberg's masterpiece a creature feature is trite. Because the shark isn't shown for most of the movie - mechanical difficulties meant production didn't have one ready to use until later in the filming process - suspense and fear build. The movie unlocked in viewers an innate fear of the unknown, encouraging the idea that monsters lurk beneath the ocean's surface, even in the shallows.

And because in 1975 marine scientists knew far less than we do now about sharks and their world, it was easy for the myth of the rogue shark as a murderous eating machine to take hold, along with the assumption that all sharks must be bloodthirsty, mindless killers.

But in addition to scaring many moviegoers that "it's not safe to go in the water," "Jaws" has over the years inspired generations of researchers, including me . The scientific curiosity sparked by this horror fish flick has helped reveal so much more about what lies beneath the waves than was known 50 years ago. My own research focuses on the secret lives of sharks, their evolution and development, and how people can benefit from the study of these enigmatic animals.

The business end of sharks: Their jaws and teeth

My own work has focused on perhaps the most terrifying aspect of these apex predators, the jaws and teeth. I study the development of shark teeth in embryos.

Sharks continue to make an unlimited supply of tooth replacements throughout life - it's how they keep their bite constantly sharp.

Hard-shelled prey, such as mollusks and crustaceans, from sandy substrates can be more abrasive for teeth, requiring quicker replacement. Depending on the water temperature, the conveyor belt-like renewal of an entire row of teeth can take between nine and 70 days, for example, in nurse sharks , or much longer in larger sharks. In the great white, a full-row replacement can take an estimated 250 days. That's still an advantage over humans - we never regrow damaged or worn-out adult teeth.

Interestingly, shark teeth are much like our own, developing from equivalent cells, patterned by the same genes , creating the same hard tissues, enamel and dentin . Sharks could potentially teach researchers how to master the process of tooth renewal. It would be huge for dentistry if scientists could use sharks to figure out how to engineer a new generation of teeth for human patients.

Extraordinary fish with extraordinary biology

As a group, sharks and their cartilaginous fish relatives - including skates, rays and chimaeras - are evolutionary relics that have inhabited the Earth's oceans for over 400 million years . They've been around since long before human beings and most of the other animals on our planet today hit the scene, even before dinosaurs emerged.

Sharks have a vast array of super powers that scientists have only recently discovered.

Their electroreceptive pores, located around the head and jaws, have amazing sensory capabilities, allowing sharks to detect weak electrical fields emitted from hidden prey.

Their skin is protected with an armor of tiny teeth, called dermal denticles, composed of sensitive dentin , that also allows for better drag-reducing hydrodynamics. Biologists and engineers are also using this " shark skin technology " to design hydrodynamic and aerodynamic solutions for future fuel-efficient vehicles.

Some sharks are biofluorescent , meaning they emit light in different wavelengths after absorbing natural blue light. This emitted fluorescent color pattern suggests visual communication and recognition among members of the same species is possible in the dark depths.

Sharks can migrate across huge global distances . For example, a silky shark was recorded traveling 17,000 miles (over 27,000 kilometers) over a year and a half. Hammerhead sharks can even home in on the Earth's magnetic field to help them navigate.

Greenland sharks exhibit a lengthy aging process and live for hundreds of years . Scientists estimated that one individual was 392 years old , give or take 120 years.

Still much about sharks remains mysterious. We know little about their breeding habits and locations of their nursery grounds . Conservation efforts are beginning to target the identification of shark nurseries as a way to manage and protect fragile populations.

Tagging programs and their " follow the shark" apps allow researchers to learn more about these animals' lives and where they roam - highlighting the benefit of international collaboration and public engagement for conserving threatened shark populations.

Sharks under attack

Sharks are an incredible evolutionary success story. But they're also vulnerable in the modern age of human-ocean interactions.

Sharks are an afterthought for the commercial fishing industry, but overfishing of other species can cause dramatic crashes in shark populations . Their late age of sexual maturity - as old as 15 to 20 years or more in larger species or potentially 150 years in Greenland sharks - along with slow growth, long gestation periods and complex social structures make shark populations fragile and less capable of quick recoveries.

Take the white shark (Carcharodon carcharias), for example - Jaws' own species. Trophy hunting, trade in their body parts and commercial fishery impacts caused their numbers to dwindle . As a result, they received essential protections at the international level. In turn, their numbers have rebounded, especially around the United States, leading to a shift from critically endangered to vulnerable status worldwide. However, they remain critically endangered in Europe and the Mediterranean.

"Jaws" was filmed on the island of Martha's Vineyard, in Massachusetts. After careful management and the designation of white sharks as a prohibited species in federal waters in 1997 and in Massachusetts in 2005, their populations have recovered well over recent years in response to more seals in the area and recovering fish stocks.

You might assume more sharks would mean more attacks, but that is not what we observe. Shark attacks have always been few and far between in Massachusetts and elsewhere, and they remain rare. It's only a "Jaws"-perpetuated myth that sharks have a taste for humans. Sure, they might mistake a person for prey; for instance, surfers and swimmers can mimic the appearance of seals at the surface. Sharks in murky water might opportunistically take a test bite of what seem to be prey.

But these attacks are rare enough that people can shed their "Jaws"-driven irrational fears of sharks. Almost all sharks are timid, and the likelihood of an interaction - let alone a negative one - is incredibly rare. Importantly, there more than 500 species of sharks in the world's oceans, each one a unique member of a particular ecosystem with a vital role . Sharks come in all shapes and sizes, and inhabit every ocean, both the shallow and deep-end ecosystems.

Most recorded human-shark interactions are awe-inspiring and not terrifying. Sharks don't really care about people - at most they may be curious, but not hungry for human flesh. Whether or not "Jaws" fans have grown beyond the fear of movie monster sharks, we're gonna need a bigger conservation effort to continue to protect these important ocean guardians.

Gareth J. Fraser receives funding from the National Science Foundation (NSF).