Swimming with Sharks
Starting from near Corpus Christi, Harvey the shark traveled far into the Caribbean Sea and back two years in a row, clocking more than 14,000 miles in all. Scientists at the Center for Sportfish Science and Conservation at the Harte Research Institute for Gulf of Mexico Studies attached a satellite tag to the 8-foot shortfin mako. Sending a signal every time it breaks the surface, the tag allows them to track Harvey in near real-time.
Big sharks play equally big roles in ocean ecosystems, yet scientists know little about their day-to-day lives. With many shark species declining, tracking their distribution and movement could identify critical areas to protect.
The sportfish center and recreational anglers have tagged thousands of sharks along the Texas coast since 2012 with simple numbered tags.
“To date, 94 have been recaptured,” says sportfish center director Greg Stunz. The times and places of recapture reveal patterns in the sharks’ movements. Tagged sandbar and tiger sharks each went three years before recapture. A blacktip tagged off Padre Island National Seashore traveled 580 miles before getting hooked three months later in Veracruz, Mexico. Another blacktip was recaptured three times in one year, and a great hammerhead, twice.
A satellite-tagged 11.5-foot female mako, Peggy Hughes, proved more of a homebody than Harvey, cruising near the edge of the continental shelf off Texas and Louisiana.She likely visited the Flower Garden Banks National Marine Sanctuary, an ecosystem that needs these top predators to remain healthy.
In addition to numbered and satellite tags, the center uses acoustic tags, which send signals to receivers placed in coastal inlets. These work well on species such as bull sharks, which spend a lot of time near the coast.
This summer, scientists plan to tag bull sharks in the Laguna de Terminos protected area in Campeche, Mexico.
“Tracking will help determine whether these animals are connected to those elsewhere in the Gulf,” says Nature Conservancy scientist Jorge Brenner. “Mexican fishermen catch pregnant females in the laguna, so it also may reveal whether it serves as a bull shark nursery.”
Tagging and tracking help scientists work with their peers on conservation in other countries.
“Sharks are very migratory,” Stunz says. “Tagging shows us that some of those in the Gulf spend time in up to five different territorial waters. So, we can have the best management plan in the U.S., but sharks may go beyond our range to countries where they are still harvested.”
Swimming into the wrong waters could put an end to Harvey’s impressive travels.
(Note: Harvey is named not for the infamous hurricane but for renowned sportsman Harvey Weil.)
Follow tagged sharks at ocearch.org/tracker.
Report tagged sharks at sportfishcenter.org/participate/citizen-science/report-tags.
Hammerhead Shark (pictured above)
Sphyrna sp.
Wide-set eyes, positioned on either side of their flattened head, give hammerheads 360-degree vision. Among sharks, only hammerheads have depth perception, useful for seeking prey. Hammerheads can grow up to 20 feet long and more than 1,000 pounds, although many are smaller. In the absence of male sharks, hammerhead females can reproduce asexually, but it leads to a lack of genetic diversity.
Bull Shark
Carcharhinus leucas
These shallow-water sharks are one of the most aggressive species. Bull sharks can weigh up to 500 pounds, and sometimes reach lengths of over 11 feet. The bull shark’s name comes from a penchant for head-butting prey with its short nose before biting, and from its chunky, muscular body. Bull sharks generally eat fish, dolphins and even other sharks.
Tiger Shark
Galeocerdo cuvier
Tiger sharks get their name from the dappled stripes on the flanks of young sharks. The average tiger shark is between 10 and 14 feet long, and weighs from 850 to 1,400 pounds. Tiger sharks will eat anything: turtles, trash, sea snakes and more. They’re the second-most dangerous species to humans. Thousands of tiger sharks are killed each year for their fins, skins and vitamin-rich livers.
Nurse Shark (pictured above)
Ginglymostoma cirratum
Slow-moving nurse sharks trawl the sandy ocean floor in search of tasty fish, shrimp or cephalopods. They are relatively small with long tail fins. These benthic beauties have small fleshy whiskers around their curled mouths, and their skin is soft to the touch, unlike that of some other sharks. Nurse sharks are highly social, huddling in large groups as they sleep the day away, then breaking off alone to forage at night.
Blacktip Shark
Carcharhinus limbatus
Named for its elegant black-dipped fins, the blacktip shark is relatively small, reaching maximum lengths of about 8 feet, and weighing at most just over 200 pounds. They have pointy noses and robust, barrel-chested bodies. Blacktips, like spinner sharks, are known for their elegant hunting behavior: They sometimes jump out of the water in a twirling spiral.
Atlantic sharpnose Shark
Rhizoprionodon terraenovae
The Atlantic sharpnose is a small shark, usually around 3-4 feet long. It sticks to coastal areas, often hunting for its preferred meals of mollusks, worms, small fish and crustaceans in surf zones and the mouths of rivers. While many species of requiem sharks do not thrive in captivity, the Atlantic sharpnose is well-suited to life in public aquariums.
Whale Shark (pictured below)
Rhincodon typus
At 40 feet long, whale sharks are the biggest fish in the world, and a bit of a mystery. No one has ever seen whale sharks mating or giving birth. Despite having a 5-foot-wide smile, these gentle, spotted giants don’t use their three rows of 300 teeth to eat. They slurp up vast quantities of water and filter it for krill, plankton, small fish and other marine organisms. Populations have been in decline for the past few decades.
Lemon Shark
Negaprion brevirostris
A dark-yellow coloration helps lemon sharks blend in with the sandy bottom of the coastal waters they frequent. Lemon sharks often gather in groups of up to 20 as they cruise the coral keys and mangrove forests at dawn and dusk in search of fish, crabs and rays. Lemon sharks have been seen sitting still (difficult for sharks, many of which must move to breathe) while smaller fish clean parasites off their skin.
Shortfin mako Shark
Isurus oxyrinchus
With wide, flashing black eyes and a snaggle-toothed mouth, shortfin mako sharks have a crazed look. Makos (which feed on bony fish, squid, octopuses, turtles and other sharks) catch their dinner by lunging upward at its flanks, tearing off pieces of flesh with several rows of angled teeth. These open-ocean sharks are speed demons, sometimes clocking in at 46 miles per hour. They are the fastest sharks on record.
Sandbar Shark
Carcharhinus plumbeus
This peaceful, gray-blue shark skims the seafloor in coastal areas, sticking to its diet of fish and the occasional crab. Sandbar sharks have large dorsal fins to stabilize them as they cruise through currents in shallow water, preventing them from being flipped over or rolling.
Silky Shark (pictured below)
Carcharhinus falciformis
Silky sharks’ super-soft skin lends them a metallic sheen as they slice through the pelagic zone. Measuring up to 12 feet and weighing nearly 800 pounds, silky sharks range from dark brown to silvery blue-gray, with piercing pale eyes. Like many other sharks, they eat bony fish and cephalopods; scientists often observe them sneaking around schools of tuna.
Shark facts written by Eva Frederick
More in our reef series:Deep in the Gulf | Texas Treasure Threatened | Building More Reefs | Life at an Artificial Reef | Roar of the Lionfish
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