Educational Series: Sharks, Apex Predators of the Oceans, Need Our Help to Survive

By Nick Engelfried
Probably few animals evoke as much fear and even hatred as sharks, the ocean’s premier predators. Sharks have been vilified and portrayed as bloodthirsty monsters in popular culture and films like Jaws, leading to fundamental misunderstandings about their role in marine ecosystems. In reality, they are far more helpful than harmful to people and the thousands of ocean species with whom they share their habitat. On the other hand, humans–and particularly the industrial fishing industry–have had a devastating impact on sharks. This needs to change so these fascinating, important creatures can continue populating our planet’s oceans for generations to come.

There are more than 500 kinds of sharks, only a tiny fraction of which present any danger at all to people. About half of all species are a few feet long or less, with the smallest shark–the deepwater dogfish (Etmopterus perryi)–reaching a length of only about eight inches. All sharks have a few things in common, including a skeleton made of soft cartilage rather than bone. They share this particular trait with rays and skates, and together these animals make up a group called Elasmobranchii, or cartilaginous fish. Evolutionarily, elasmobranchs are among the oldest of all vertebrate animals. This means sharks and their relatives have been swimming the oceans since long before the age of the dinosaurs!

Other common features shared by sharks include their several rows of sharp teeth, which can be replaced an indefinite number of times as older ones are lost; and pointed scales known as denticles that help streamline their bodies so they can cut through the water in pursuit of prey. All sharks are predators of one type or another, with most feeding on invertebrates or fish. Only a few species ever mistake humans for a meal.

In fact, the world’s largest sharks do not eat large prey at all, instead feeding on some of the ocean’s tiniest creatures. Whale sharks (Rhincodon typus) may reach a length of 40 feet or more, but subsist on a diet of minute plankton and the occasional small fish. Like the great baleen whales after which they are named, whale sharks are filter feeders who strain water through their mouths to capture their prey. They live only in tropical habitats, and relatively little is known about them; for example, scientists have yet to observe a mother whale shark giving birth. What we can say is that whale sharks defy many of the stereotypes about sharks as a group and challenge us to re-think the assumptions we hold about them.

Our knowledge of sharks is growing all the time. Just this year, for example, researchers in New Zealand discovered that three small species from the deep ocean “twilight zone” are bioluminescent, producing light from their bodies. While bioluminescence has long been known in a variety of deep-sea fish and other creatures, it has been little studied in sharks. One of the species recently found to glow in the dark, the kitefin shark (Dalatias licha), is now the largest known bioluminescent fish and grows to about four feet long. Scientists hypothesize it and other bioluminescent sharks may produce light as a kind of camouflage. When larger predators look up from below, the reasoning goes, a kitefin’s bioluminescence would help prevent its silhouette from standing out against the relatively light waters above.

An astounding diversity of other sharks inhabit the oceans. SCUBA divers and snorkelers who frequent tropical waters will likely be familiar with the nurse shark (Ginglymostoma cirratum), a species that grows up to 10 feet long and feeds on smaller fish and invertebrates. Among the many sharks with strange behavioral adaptations are the three kinds of thresher sharks (Alopias), which use their long, whip-like tails to thrash about in a school of fish, killing or injuring prey which they later retrieve in their teeth. Then there are the dogfish, a group of more than 100 small shark species that sometimes hunt for prey in packs. The list of sharks with amazing adaptations could go on and on. Many play vital roles in the ecosystem, as top predators who regulate other marine animal populations.

Only a relatively very few sharks have been known to ever attack humans. They include the bull shark (Carcharhinus leucas), tiger shark (Galeocerdo cuvier), multiple species of hammerheads–and, of course, the great white shark (Carcharodon carcharias), the most notorious species on which many stereotypes about sharks are based. However, even these expert predators attack people very rarely. The number of recorded unprovoked attacks on humans by sharks around the world averages a little over 80 per year, an infinitesimally small number when you consider how many people swim regularly in shark habitat. On the infrequent occasions when great whites do attack people, it is likely because they have mistaken their victim for a seal or other prey animal.

Unfortunately, while sharks present very little real threat to humans, the reverse does not hold true. Almost a quarter of shark and other cartilaginous fish species are believed to be threatened with extinction because of irresponsible fishing practices, climate change, and other human-caused threats. Overall, shark and ray populations plummeted more than 70% between the years 1970 and 2018, largely due to industrial fishing. The global shark finning trade targets these beautiful animals for their body parts. Sharks caught by finners often have their appendages hacked off while they are still alive, and are then tossed back into the water to die a slow, grisly death. Yet, this is only one of the many ways humans are driving sharks toward extinction.

Many millions of sharks die each year as incidental victims of fishing operations that use indiscriminate techniques like trawling, gillnetting, and long-lining. While these methods usually target other fish species like tuna and swordfish, sharks often end up as bycatch and die entangled in nets and lines. Some countries have laws banning or regulating such destructive fishing practices, but industrial fleets are increasingly escaping these hurdles by focusing their activity on the mostly unregulated high seas. There, sharks are at the mercy of unscrupulous fishing companies.

So, what can we do to save sharks from vanishing forever? It should go without saying that being a responsible, ethical consumer is important. If you eat seafood, use sustainable purchasing guides like the Monterey Bay Aquarium’s Seafood Watch list to ensure what you buy was harvested sustainably. However, as important as such individual actions are, they are not enough to save sharks on their own. To help sharks we must transform the fishing industry through better regulation, and there are plenty of opportunities to help make this happen.

One of the most important steps countries like the U.S. can take to bring sharks back from the brink is ending the shark fin trade. Shark finning is already illegal in this country, but the sale of shark fins is not, and this loophole allows fins from sharks killed outside of U.S. waters to be consumed here. Organizations like the marine advocacy group Oceana have been pushing to pass the Shark Fin Sales Elimination Act, which would prohibit the selling of shark parts in a massive step toward ending this cruel trade for good. A great way to help sharks is to call or write to your members of Congress and urge them to support this legislation.

The decline in shark populations is due to a complex of factors, almost all linked to human activity. However, the solutions to the problem are relatively simple. We must end the trade in shark fins or other parts, and phase out the use of fishing methods that kill millions of them and other marine creatures as bycatch. Every animal lover can play a part in achieving these goals, through personal consumption choices but even more importantly by engaging in the political process. For the world’s shark species, who have been cruising the oceans for tens of millions of years, the stakes could not be higher.

Photo credit: Albert kok

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Nick Engelfried Writes About Animals, the Environment, and Conservation for the ForceChange network

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