Although the jaws and teeth of the GW are the first things most people think of when picturing the shark, the fins come in a close second. Who can forget the image of a sharp fin slicing the surface of the water? A quick rundown of the major fins and their proper names:

It has been said that sharks don't swim through the water as much as they "fly" through it. The fins serve important roles in this action. As the shark moves the caudal fin to propel it forward, careful adjustment of the pectoral and dorsal fins keeps the shark level and on course, much as the wings and tail of an airplane do.

In addition to the major fins pictured above, the GW has a smaller dorsal fin located closer to the caudal fin, a small pair of pelvic fins (visible in the photo at the top of this page), and a tiny anal fin just in front of the caudal fin. These minor fins help improve the way water flows over the shark as it swims.

OF PREDATORS & THEIR PREY

To study the predatory behavior of the GW, scientists must travel to a location where GW's are known to hunt their prey. Luckily, about 30 miles off the coast of San Francisco are the Farallon Islands, home to a large elephant seal population - making this area the local burger shop for GW's in the neighborhood and thus a hotspot of GW research.

A regular watch began in 1987 on Southeast Farallon Island and it has produced a great deal of information about the GW's predatory habits. For example, it seems from this data that most attacks occur during the day in late summer or early winter. Furthermore, the attacks took place at around the same time each day, most likely due to the tide schedule.

To give you an idea of what a GW considers to be the ultimate meal - the Big Mac of the sea, if you will - think of those cute seals and sea lions you often see performing at a Sea World near you. They are collectively known as pinnipeds and they are the preferred food of the GW - over fish, other sharks, or your Aunt Sally.

Going back to the observational data, some interesting differences in attack strategies were noted based on the species of the shark's prey. For example, in the case of the seal, the animal is often attacked just beneath the surface by a GW rising from below. A large elongating blood stain at the surface indicates that the shark carries the seal underwater for a distance before removing a bite and releasing the carcass which then floats to the surface. When this initial attack took place near the head of the seal, an area rich with networks of blood vessels, death by exsanguination (loss of blood) or decapitation was the norm. On other occasions, the GW would disable the seal by attacking from behind, biting the strong hind flipper.  Nature is pretty grisly stuff, huh?

With the sea lion, attacks are usually observed with the sea lion at the surface of the water, the GW striking brutally - even throwing itself out of the water with the sea lion clamped in its jaws. The sea lion, lacking the same network of blood vessels flounders at the surface until the shark returns for the final kill and feeding.

Prior to the study I refer to above, a prevalent theory relative to GW predatory behavior held that a primary attack strategy of the GW is to capture and bite their prey, release them wounded but alive, and then remain nearby until the prey animal is still, indicating death or severe injury. The GW would then be afforded an easy meal. This 'bite, spit, and wait' behavior was not observed in the over 130 attacks recorded as part of this study. Does this mean it is not a valid hypothesis? Not at all - 130 attacks in a single location on a limited prey selection can hardly be called universally representative of a GW's predatory behavior. However, these same 130 observed events provide an excellent glimpse at how the GW goes after its favorite meal.

I bet you didn't know seals could talk!

Of course, they can't. This is common knowledge. So it seems would be an attack from below. After all, this is because when a shark attacks an item at the surface, any attack other than a 'Jaws'-like (and thus camera-friendly) attack at the surface would be from below. But what path does the shark take when attacking? Does the shark travel in a horizontal manner beneath its prey before striking or does it prefer the vertical attack made famous by the poster for Mr. Spielberg's most famous fish story? Turns out Hollywood got it right. The GW likes to attack from a deep angle (45-90 degrees) below the prey item. Is this because there are a limited number of other attack vectors or because this is the best way to catch dinner?

In examining this question, a couple of benefits become apparent, namely that an attacker from below is harder to spot and also to elude. Think about it - for many reasons, a shark deeper than its potential meal is less visible than a shark swimming on the same plane. The greater the angle from and the further below the shark is from a seal means the seal is going to have a tough time seeing it before it becomes a statistic in a South Farallon Island study.

At the same time, a seal's best approach to evade the GW is to bust a move quickly in the opposite direction of the shark's attack. Think of 'The Little Mermaid' when Ariel and Flounder swim horizontally away from the shark who wants to make them an appetizer. They've got lots of room and if they swim quickly, they can (and did, of course!) evade their attacker. However, a seal attacked from below can realistically only travel up . . . and there's only so far it can go in that direction!

BIBLIOGRAPHY

Klimley, A. P., Anderson, S. D., Henderson, R. P., and Pyle, P. (1996) A description of predatory attacks by white sharks on pinnipeds. In "Great White Sharks: the biology of Carcharodon carcharias" (A. P. Klimley and D. G. Ainley, eds.), pp. 175-191