There's SOME-FIN Special About Sanctuaries
Close your eyes and picture a shark. Any shark. What do you see? What do you hear?
Odds are, the first sound that comes to mind is dun dun, dun dun, the building strings of the Jaws theme song making the hairs on your arms stand on end. Perhaps the shark you picture is an enormous white shark coming toward you.
But the truth is, sharks are so, so much more than their scary reputation. These ancient ocean creatures began their evolutionary journey some 400 million years ago. All that time has given them plenty of opportunities to evolve into diverse animals that play key roles in ecosystems in your National Marine Sanctuary System and beyond. From tiny, five-inch pocket sharks to 40-foot whale sharks, sharks are as varied as they are amazing. And the truth is, we pose a whole lot more threat to them than they do to us.
Home Sweet Home
Sharks make their homes throughout the ocean, from the shallows to the depths. Your National Marine Sanctuary System protects these habitats so shark populations can thrive into the future.
In Florida Keys National Marine Sanctuary, mangrove roots provide a nursery habitat for all sorts of animals, including the lemon shark. Female lemon sharks give birth to live young in shallow areas like mangrove forests. For several years as they grow up, tiny baby lemon sharks find refuge among the mangrove roots. Here, they’re safe from predators like groupers and other, larger sharks.
Go a little deeper into the ocean, to coral reefs, and you’ll find sharks like blacktip reef sharks, whitetip reef sharks, and Galapagos sharks. These medium-size sharks patrol the reef throughout the day and night. In the open ocean, farther from the reef zone, you’ll find bigger sharks like blue sharks, salmon sharks, and porbeagle sharks.
But that’s not all! Even in the depths of the ocean, thousands of feet down, sharks can survive. During a 2017 expedition aboard the research vessel E/V Nautilus, researchers spotted numerous bluntnose sixgill sharks in the deep waters of Channel Islands National Marine Sanctuary. These sharks spend the day resting in depths of up to 6,000 feet (more than a mile down!) and forage for fish, invertebrates, and other sharks closer to the surface at night.
Sharks of Great Significance
An ocean without sharks would be a drastically poorer environment than the one we know and love today. That’s because sharks play an important role in food webs. Some species of sharks, like white sharks and tiger sharks, are apex predators—they’re at the top of the food web.
In places like Greater Farallones National Marine Sanctuary off the coast of California, “white sharks keep our burgeoning populations of seals and sea lions in check,” explains Mary Jane Schramm, the sanctuary’s outreach specialist. By keeping seal and sea lion populations in check, the sharks free salmon from the risk of predation. With fewer seals and sea lions hunting them, salmon can thrive and reproduce.
“White sharks keep the food web healthy,” says Schramm. Given sharks’ important role, when their numbers decrease, it can send ripples throughout the ecosystem.
Other sharks, like reef sharks, are known as “mesopredators.” They eat smaller fish and invertebrates, but also have to watch out, lest they be eaten by larger sharks and other fish. As mesopredators, these sharks work diligent-ly to keep the food web balanced and species healthy by eating weak or elderly animals.
No matter where sharks are in the food web, they play an important role—and for that reason, it’s important that we help protect these animals.
How do sharks hunt even in low light or poor visibility? They have a sixth sense—electricity.
Organs known as the ampullae of Lorenzini help sharks of all types sense electrical fields. This sensory perception helps sharks sense and lo-cate predators and prey, even if they’re buried in the sand or out of view in murky water.
Hammerhead sharks, like the great hammerheads of Florida Keys National Marine Sanctuary, are some of the best at sensing electricity. Their fa-mous broad head provides these sharks with more space for ampullae of Lorenzini. More ampullae means more elaborate sensing ability, making it even easier for hammerheads to find their prey!
More Than the Paleo Diet
Some of the most well-known sharks in your sanctuaries have a reputation for taking on large animals like seals, sea lions, and whales. But not all sharks are into big food.
Nurse sharks, which can commonly be spotted in Gray’s Reef and Flower Garden Banks national marine sanctuaries, eat crustaceans, mollusks, and stingrays off the seafloor—when they’re not napping. Flower Garden Banks National Marine Sanctuary research coordinator Emma Hickerson once came across three nurse sharks, all stuffed into the same crevice while they rested. “I wanted to ask them what movie they were watching,” she jokes.
And whale sharks, the biggest shark on Earth, actually eat the smallest prey. These common visitors to the Flower Garden Banks are filter feeders, primarily consuming plankton and small fish. In areas close to the sanctuary’s proposed expansion sites, says Hickerson, whale sharks “sometimes aggregate in the hundreds, very likely feeding on the eggs of spawning fish.” Closer to the Flower Garden Banks, small aggregations of up to 30 whale sharks can be seen sometimes. “We never expect to see a whale shark swim through when we are diving,” says Hickerson, “but on the rare occurrence when we do, we get mighty excited!”
Sharks: They Care About History, Too
Sharks are a common sight throughout your sanctuaries, and seeing one in the wild can be an awesome experience.
Monitor National Marine Sanctuary maritime archaeologist Tane Casserley encountered sharks on his first dive off North Carolina in the Graveyard of the Atlantic. “As we made it to the seafloor and oriented ourselves, I saw my first sharks swimming in and out of the schools of baitfish and through the openings of the shipwreck,” he says. He estimates that there were at least 20 sand tiger sharks, all gliding past the divers within an arm’s reach.
Though sand tiger sharks look fearsome with their jagged teeth and creepy grins, they, like so many other shark species, are generally harmless to humans. “I was so in awe of these gentle giants that I barely moved for 15 minutes,” says Casserley. “It changed my life.”
Sharks have lives outside our imagination, and they need us to rethink the way we conjure them in our minds. Whether you experience sharks while diving or snorkeling, or just admire them from afar through photos and videos, we hope they change your life, too. Their lives depend on it.