Chapter 14. Tracking Jaws

Tracking Jaws

Read the article below. Then answer the questions that follow.

Hollywood horror movies might depict great white sharks as bloodthirsty, man-eating monsters. However, these elusive creates don't have a taste for humans.

In horror movies great white sharks lurk around sunny beaches, waiting to rip apart unsuspecting swimmers. In reality, white sharks almost always go about their business without paying much attention to swimmers. White sharks (Carcharodon carcharias) are rarely sighted, and humans aren’t their food type.

Humans pose a far greater threat to white sharks than vice versa. Despite an international ban, the trade of shark teeth and fins remains a big industry. Furthermore, because white sharks live long, are slow to mature and mate, and have small litter sizes, the elimination of a single individual can have a big population impact.

This is why marine biologists have been searching desperately for a sampling method to count white sharks. When scientists are concerned that a marine species may be threatened or endangered, they often do a population assesssment to determine whether or not better protection is needed. But this is easier said than done.

California white sharks keep a low profile

Despite an international ban, shark poaching continues to be a problem worldwide, with the trade of shark fins and teeth still booming.

It turns out that California white sharks are especially evasive. Researches have not been able to get a good abundance estimate because there are far fewer white sharks in California’s waters than there are fish, marine mammals, and other sharks. White sharks always have been a rare sight in California, and because they don’t come to the surface to breathe like dolphins and whales, it is difficult to get a solid count, which is needed for a population estimate.

Despite these problems, University of California - Davis and Stanford University researchers completed the first rigorous census of its kind in May 2011. Armed with cameras, the researchers piloted small boats to white shark feeding locations in the Pacific Ocean and lured sharks into photo range using a seal-shaped decoy on a fishing line. As the triangular dorsal fins skimmed the surface of the water, researchers snapped photos—the very kinds of images we associate with Jaws!

By photographing the uniquely jagged edges of the dorsal fins, the researchers were able to distinguish between individual sharks. The fin photographs prevented mistakes like double-counting the same individual.

Taking multiple photos of the same shark also helped document site fidelity. In other words, if sharks keep coming back to the same coastal locations during their migration route, they likely are true members of the California population and not visitors from afar.

Mighty sharks in small numbers

In total the researchers identified 131 individual sharks. Population models estimate there are only about 220 adult and sub-adult white sharks in the Northeast Pacific Ocean. This is far fewer than expected.

“This is why taking even a single individual could have major implications,” says Taylor Chapple, a researcher at the University of California - Davis who led the study.

To put things in perspective, there are 25,000 polar bears (Ursus maritimus) estimated to exist today; the species has been classified as endangered.

Researchers don’t have enough information to estimate the total number of white sharks in the world’s oceans. Distinct populations of white sharks can be found in South Africa and Australia/New Zealand, and one recent count conduced in Spencer Gulf, Australia, found 191 white sharks. Yet due to the aforementioned complexities of conducting a survey, such population studies are rare.

Researchers also can’t estimate how dramatically populations have plummeted. While trophy hunting, pollution, and commercial fishing practices have contributed to declines, it may be that populations of white sharks have always been small. In either case, the shark’s small numbers make it vulnerable to human impacts. With so few breeding individuals, the survival of the species may depend on human protection.

© 2015 WH Freeman and Company.

14.1 Comprehension Questions

Answer the following questions to demonstrate your understanding of the article.