The Great White Shark: Threatened Species?

Last week, Gov. Pete Wilson signed a bill by state Assemblyman Dan Hauser (D-Arcata) to prohibit the killing of great white sharks except under specific circumstances, such as for scientific or educational purposes. Exact statistics are unknown, but some experts believe that the population of great white sharks has been reduced significantly in recent years. Anecdotal reports, however, seem to indicate an increase in sightings of great whites-perhaps attributable to an increase in the populations of many marine mammals, a primary food source for sharks. Thirty-six shark species can be found off California from the foot-long pygmy shark to the 50-foot whale shark, an infrequent visitor and the world’s largest fish. Most attacks involve the great white. Here is a look at the species and some tips for avoiding contact.

Anatomy

Huge optic nerves give it excellent vision.

Water flowing through the nostrils allows detection of even very faint odors.

A “sixth sense” provided by an elaborate system of sensory tubes inside the snout-known as the ampullae of Lorenzini-can detect electrical signals from objects in the water.

Unlike other fish, it cannot pump water over its gills, relying instead on constant swimming to force water through the mouth and over the gills.

It’s torpedo-shaped body can grow to a length of more than 20 feet. Gray on top and white underneath, it is cartalaginous, having no bony skeletal structure.

Large jaws hold several rows of extremely sharp, triangular and slightly serrated teeth. When striking, the jaws extrude. The biting force is estimated to be several thousand pounds per square inch, enough to bite through a surfer and a surfboard. Open jaw size for an adult great white ranges from 2 1/2 to 3 feet.

Behavior

In August, a great-white rammed a fishing boat off Santa Cruz Island, one of the Channel Islands. Sharks do bump or attack boats, but not in the manner portrayed in the movie “Jaws”. The undersides of boats often have a small electrical field, which a shark may sense through the ampullae of Lorenzini and misread as a living organism. Sharks avoid strong electrical fields, a fact that researchers hope to use in helping people ward off attacks.

Food

Generally, feeds on large prey, including fish, seals, sea lions, sometimes other sharks and other marine animals. Other things reportedly found in the stomachs of sharks: a man in a full suit of armor, license plates, and pieces of land animals ranging from horses to buffaloes to elephants.

Steps Toward Protection

Sharks, which bear very few young in comparison to other fish, are extremely vulnerable to overfishing. Assembly Bill 522 would prohibit most commercial and recreational fishing of great white sharks. It would specifically ban severing the pelvic fin from a shark that is caught accidently unless it is brought ashore-a provision aimed at halting the killing of sharks solely for souvenirs or shark-fin soup.

Shark Attacks

Since 1926, great white sharks are suspected in a total of 69 attacks on humans in California waters, including three non-fatal attacks in 1993, all in Northern California. Seven of the 69 attacks were fatal. Recorded attacks by great white sharks in California 1984: 2 1985: 2 1986: 1 1987: 1 1988: 2 1989: 4 1990: 5 1991: 3 1992: 2 1993: 3

Safe Swimming Rules

1. Never swim, surf or dive alone.

2. Never swim with an open wound or near fishing areas. Blood may attract sharks.

3. Never swim at night or in murky water.

4. Leave the water immediately if a shark is sighted. Swim as smoothly as possible; thrashing movements may attract a shark.

5. Never grab or injure any shark, no matter how small.

6. Avoid places with a history of shark attacks.

7. Stay away from areas where marine mammals enter and leave the water. Sharks may be attracted to these areas.

8. If you do see animals rapidly leaving the water, this may be an indication that a shark is in the area. Sources: John McCosker, California Academy of Sciences; Steinhart Aquarium, San Francisco; World Book Encyclopedia Researched by NONA YATES