Jan/Feb 2016For Wildlife Watchers: Great White Sharkby Rob Simbeck
Great whites cruise at ten to fifteen miles per hour and can accelerate to thirty-five.
Great white sharks should not be high on your worry list. Yes, they can kill you, but in the U.S., bees, dogs, cows, horses and rattlesnakes - in that order - are much more likely to do you in. This year's noteworthy attacks notwithstanding, on average shark attacks cause fewer than one death per year in the U.S., and of the world's one hundred or so yearly attacks - about half by great whites - there are on average six fatalities.
And yet the great white is the Elvis of predators, thanks in great measure to the 1975 thriller Jaws, which changed to this day the way we view them. Chris Fischer and like-minded colleagues are trying to change it back again.
"We've lost our connection to and awareness of the ocean," says Fischer, founding chairman and expedition leader of OCEARCH, whose information-gathering voyages are aimed at "pioneering fundamental research on sharks." Citing figures that 200,000 sharks are taken per day (many for shark fin soup), Fischer views the situation apocalyptically.
"If we lose our sharks," he says, "we lose the lions of the sea. They are key to healthy fish populations, since they cull the sick and weak, and when sharks are removed from the ecosystem, second-tier predator populations explode and wipe out the food chain below them. Unless great whites are thriving in the North Atlantic, there won't be fish to catch."
OCEARCH captures great whites, spends fifteen minutes tagging them with tracking devices and allowing scientists to draw blood and conduct other research, and then releases them. Tagging allows scientists and non-scientists alike to track the sharks in real time via maps on its website, www.ocearch.org.
The work has its detractors, who accuse Fischer of showboating and say the procedure is not without risk to the sharks. Still, OCEARCH produces useful information, and scientists and journalists clamor to join its voyages and use its data. In addition, Facebook allows thousands to follow great white sharks named Katharine and Mary Lee - both of whom spent time this year off the South Carolina coast.
The state's waters are part of a huge migratory loop that North Atlantic whites undertake every two or three years.
"We're learning day by day from OCEARCH data," says Bryan Frazier, coastal shark biologist with the S.C. Department of Natural Resources. "We used to think they would overwinter off the southern seaboard and spend summer months up north, but we're seeing that's not necessarily true. They may be closer to our shore in winter months [than we realized]. Thanks to Katharine and Mary Lee, we're kind of re-learning."
Great White Shark - Carcharodon carcharias ("sharp-toothed")
Description: Up to twenty feet, five-thousand pounds; sleek; gray above, white below.
Range and Habitat: Worldwide, between 60 degrees north and 60 degrees south latitude. Wide migratory routes. Seasonally off the South Carolina coast.
Mating: Never viewed. Young born alive, four to five feet long.
Viewing Tips: Best bet: in front of your television set during "Shark Week."
"Apex predator" seems faint praise for this monarch of the sea. It can be twenty feet long and weigh as much as five thousand pounds, although thirteen to sixteen feet and two thousand pounds is more common. Great whites cruise at ten to fifteen miles per hour and can accelerate to thirty-five.
Then there are those teeth - up to three hundred of them, triangular, razor-sharp, in rows that rotate forward as those in front break or wear off. In many species, the bottom teeth are better at gripping, the top at tearing. "In the white," says Frazier, "both upper and lower are designed for tearing." A white clamps down on prey, shaking its head side to side until it tears flesh loose, then swallows. "There's no chewing with sharks."
These are ambush hunters, taking prey from below. Its gray back helps it blend with rocky bottoms when viewed from above, while its white belly blends in with the brighter surface from below. Directing it all is a brain weighing just ounces and largely dedicated to smell, with a central cerebrum the size of a walnut. The rest is like a string of beads dedicated to separate functions.
Torpedo-shaped, with a pointed snout, coal black eyes, fins for balance and a stiff, side-to-side swimming motion powered by a tail muscular enough to power leaps out of the water, the great white is one of more than six hundred species of sharks and rays that, unlike true fishes, have skeletons made of cartilage. Their large, oily livers help produce buoyancy in place of the gas-filled bladders many bony fish rely on, and they must keep moving to keep from sinking. Five gill slits on each side extract oxygen from the water, and its muscles warm its blood, keeping the stomach, brain and other organs eight to ten degrees warmer than the water. Its skin is made of dermal denticles, which are structurally similar to teeth.
The white's migratory route seems to have a built-in reproductive rhythm. Scientists have proposed both South Carolina's and New Jersey's coasts as possible birthing sites and, says Frazier, "another likely location is off the coast of the Greater Antilles." Females look for places with good food supply and relative safety, but otherwise do not care for the young.
Eggs hatch in utero, and the embryos eat subsequently produced, unfertilized eggs, as well as their own shed teeth, reutilizing calcium and other minerals. The female gives birth to anywhere from two to fourteen live pups, each three to five feet long, after a gestation thought to take eleven months. The young eat fish, rays and other sharks until their jaws and teeth are strong enough to withstand the impact of biting adult-level prey. They are generalists and eat sea lions, seals, walruses, turtles, dolphins, tuna, other sharks and whales, among other species.
Humans simply aren't on the menu, and most human bites are thought to be sharks using the only tool they have to figure out if we're edible. They can detect minute traces of blood from three miles away and have organs that sense the electromagnetic fields generated by prey's muscle contractions and heartbeat, down to one two-billionth of a volt.
With ancestors going back 400 million years, sharks have survived all five of the planet's mass extinctions. "Orcas have been observed killing white sharks," says Frazier, "but we don't know how common that is."
As usual, humans are the threat they really have to worry about. They have been protected off South Africa, Australia and California, are listed as "vulnerable" by the World Conservation Union, and are protected under some international agreements.
"I can't overstate how important sharks are to the ocean's health," says Frazier. "A lot of fishermen hate sharks because they react to the signal put out by fish struggling on their hooks and go after them. Their brains are wired that way. That struggle tells the shark something is wrong, and that's the fish it culls. It's vital for the health of the target species. It's top-down control of the whole food web. If we didn't have sharks, we wouldn't have a healthy ocean."