Mysteries of the Great White Shark

The largest toothed-shark, the great white shark, is one of the least understood animals in California’s coastal waters. Even though this shark has been intensely studied for decades, and hundreds of divers have had the opportunity to observe this graceful beast, relatively little is known about the shark and its habits. Most of what we do know about white sharks comes from evaluating dead animals, and observing them when they feed on the surface. Until recently our opportunities to observe white sharks throughout the day and year have been limited at best. New technology is beginning to provide greater insight into what it is like to be a white shark.

White sharks are what I call “warmer blooded” animals. Instead of maintaining their body at a constant temperature like mammals, their metabolism keeps them about 23 degrees F above sea temperature. This feature allows them more energy for bursts of speed, but increases their food requirements. White sharks need calories, and fat is the most compact source of energy. White sharks seek out fatty prey.

Young white sharks feed mostly on other sharks and rays and are believed to switch to marine mammals as they grow. They are known to hunt otters, harbor seals, sea lions, and feed on whale carrion. Year-old elephant seals may be a near ideal food for adult white sharks: they are the right size to be subdued by a moderate-sized shark; they have lots of fat, and are relatively unobservant. Big, fat, and dumb—perfect prey.

No one knows how many white sharks there are, but we do know that sharks appear and disappear at regular intervals throughout the year, mainly following their prey. Biologists stationed at Southeast Farallon Island (off San Francisco) record about 95 percent of their shark sightings from September through November. Observations from the mainland peak during the summer, except at Año Nuevo where sharks are seen through the fall and winter. White sharks may be found at Guadalupe Island (south of San Diego) year around, but are most abundant in the summer and fall. The fall peak at the Farallons, Año Nuevo and Guadalupe corresponds to when yearling elephant seals come ashore. White sharks are also abundant during the summer at Guadalupe when schools of tuna are present.

But, where do they go at other times? It turns out a long, long way from California. The recent use of satellite tags has shed a great deal of insight into the previously unobservable part of a white shark’s life. Some California sharks swim to Hawaii for the winter and early spring, presumably feeding on whale carrion, and return to California during the summer. Others head south into Mexican waters.

Scott Davis (now at Shark Diving International) has studied white sharks for 10 years and has deploying satellite tags. He regularly observes animals at Guadalupe that make repeated visits to the Farallons and Año Nuevo. Scott observed that, “many sharks use Guadalupe Island as a waypoint during their trip from the Farallon Islands to points south and west.”

From dissecting animals we know that white sharks give birth to live pups as long as 4.5 feet, but no one has ever observed a great white giving birth. A male white shark reaches sexual maturity at 9-10 years old; females take a bit longer and must be 14 to 15 years old to reproduce. The age of most sharks at Guadalupe is in this range and they average about 14 feet long. The average size at the Farallones is considerable larger and 17 to 19 foot sharks are common. These big guys are many decades old.

You don’t get to be very old by being bold and reckless; you grow old by being cautious and restrained. The sharks divers observe from cages are neither excited nor frenzied, and the notion of a shark as a crazed killer is quickly dispelled when you observe them from the safety of a cage. Curious, inquisitive, and graceful are perhaps the most accurate descriptions of these sharks.

Although reef divers rarely see these magnificent predators, those seeking close encounters can safely make their dreams come true on cage diving trips to the Farallon Islands or Guadalupe. Sign up for a trip and see for yourself just how beautiful and fascinating a top predator can be.

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