But there’s something that might be just as scary as meeting up with a shark—at least from an environmental perspective. It’s the thought of what might happen if sharks disappeared from the oceans. That’s because sharks are important players in delicate food webs, suggests a new study out of Canada.

Fishing companies have been killing large sharks for decades. Sometimes they’ve done it on purpose, and sometimes they’ve done it by mistake. Because of these kills, the animals that sharks eat have boomed. And that’s bad news for the creatures even lower on the food web.

Along the East Coast of the United States, only sharks that are at least 2 meters (6.6 feet) long are tough enough to eat a lot of the medium-size sharks, rays, and skates living in those waters. Eleven large shark species in the region fit into that category.

Researchers led by Ransom Myers in Nova Scotia reviewed 17 surveys that counted big sharks and their prey during the past 35 years. They found that numbers of all 11 species have dropped since 1972.

As the big sharks disappear, most of the smaller sharks, rays, and skates have increased in number. Surveys have shown increases in 12 of 14 species of these sea creatures over the past 30 years. The populations of some of these species are 10 times as high as they were three decades ago.

Cownose rays travel in a dense horde. Each fall, such hordes from the bays of the New Jersey and Delaware region swim south along the coast for the winter.

W.S. Otwell

Researcher Charles H. Peterson recently heard fishermen in North Carolina complaining that cownose rays were eating up all the region’s bay scallops. He and his colleagues at the University of North Carolina’s Institute of Marine Sciences at Morehead City decided to test whether this was really happening.

To keep rays from eating scallops in certain areas, the scientists put a protective ring of poles around the scallops. Rays are wider than most sea creatures and won’t usually swim between poles that are spaced closely together. (The rays could turn sideways and fit through, but they don’t usually do this.) Other animals, however, swim easily through the gaps between poles.

In 2002 and 2003, at the beginning of the fall season, researchers found populations of bay scallops that were healthy and dense. But after rays migrated through, the scallops nearly disappeared in areas that were not surrounded by poles. Within protected areas, only half of the scallops were gone. It’s not even certain that the missing ones got eaten, Peterson says, since they might just have swum away.

The study suggests that efforts to replace declining populations of shellfish, such as scallops and oysters, might require extra levels of protection against predators.

The findings reinforce the message from a 1998 study of a food web in Alaska. In that area, killer whales can normally eat otters. Otters eat sea urchins. And sea urchins eat kelp. When the whales ate more otters, the study found, sea urchins thrived, and the kelp suffered.

In food webs, balance is key.—E. Sohn

Going Deeper:

Milius, Susan. 2007. Too few jaws: Shark declines let rays overgraze scallops. Science News 171(March 31):197. Available at http://www.sciencenews.org/articles/20070331/fob5.asp .

Sohn, Emily. 2003. Swimming with sharks and stingrays. Science News for Kids (Sept. 17). Available at http://www.sciencenewsforkids.org/articles/20030917/Feature1.asp .

Mother penguins and their chicks, as seen in the movie March of the Penguins.

Jérôme Maison. © 2005 Bonne Pioche Productions/Alliance de Production Cinématographique

“For some, this is not acceptable,” says narrator Morgan Freeman, describing the chicks’ reactions. “But it is nonnegotiable.”

In another scene, a penguin mother stands over her dead chick and wails at the sky. “The loss is unbearable,” Freeman explains.

In yet another scene, Freeman describes typical penguin behavior. “They’re not that different from us, really,” he says. “They pout. They bellow. They strut. And occasionally, they engage in contact sports.”

Such statements have drawn criticism from some biologists who say it’s wrong to attribute human feelings to animals. Penguin researcher Dee Boersma, however, says that this kind of anthropomorphism is a good thing.

“I think these movies are a wonderful opportunity to engage children and adults in the wonders of nature instead of the wonders of shoot-’em-ups,” Boersma says. She’s a conservation biologist at the University of Washington in Seattle.

Hard life

Inspiring people to care about penguins is important, Boersma says, because life isn’t getting any easier for the quirky-looking birds.

Penguins live on land, on ice, and in the oceans of the southern hemisphere, but global climate warming is shrinking their habitats (see “Shrinking Glaciers“). Oil slicks and other types of pollution are making them sick. More and more often, fishermen are catching penguins in their nets by mistake. And over-fishing is making it harder for the animals to find fish to eat.

Emperor penguins travel long distances each year to reach their breeding grounds.

Jérôme Maison. © 2005 Bonne Pioche Productions/Alliance de Production Cinématographique

Penguins are especially sensitive to changes in the environment because they travel long distances during their lives, but can’t fly. Environmental damage along any part of their routes can have harmful effects.

The Emperor penguins featured in March of the Penguins, for instance, walk and slide on their tummies over ice for 70 miles each year to meet at the same breeding grounds. Similarly, Magellanic penguins, which live in South America, sometimes travel more than 2,000 round-trip miles between Argentina and Brazil.

Penguins gather in huge groups when they breed, which makes it easy for scientists to see if populations are declining.

Penguins gather in large groups when they breed.

Jérôme Maison. © 2005 Bonne Pioche Productions/Alliance de Production Cinématographique

“We’re interested in using penguins as sentinels of the environment,” Boersma says. In other words, if penguins show signs of distress, that’s a sign that the environment is experiencing stress, too.

Cool birds

Boersma has been studying Magellanic penguins in the Patagonia region of Argentina for 22 years. Every year, she spends September through March at a protected reserve called Punta Tombo, which borders the Atlantic Ocean. About 200,000 breeding pairs of penguins live there.

“It’s a megalopolis of penguins,” Boersma says. “It’s like New York City.”

Biologist Dee Boersma poses with a host of penguins.

Courtesy of Dee Boersma

Even so, she says, there are 20 percent fewer penguins living at Punta Tombo now than when she started working there in 1987.

Boersma has big goals when it comes to penguin research. She wants to learn everything there is to know about penguins. To that end, she and her colleagues tag birds every year and track their migration routes with satellite technology.

The researchers also visit nests and count how many penguins return from year to year. They spend hours observing the animals every day, trying to figure out how penguins choose their mates, why they make certain noises, how oil spills affect populations, and how Punta Tombo’s 70,000 yearly human visitors affect the behavior of the birds and their ability to reproduce successfully.

“What’s mostly driving us,” Boersma says, “is to make sure penguins are going to be here for future generations.”

Penguin personalities

Studying penguins is as entertaining as it is interesting, Boersma says. “I don’t know anyone who won’t say they like penguins,” she says. “They are fun to watch. They’re comical. They walk upright. What’s not to like?”

Now that she has known some of the penguins at Punta Tombo for more than 2 decades, she has grown to appreciate their personalities. “Some are nervous,” she says. “Some are placid.”

One of her favorites is a 21-year-old male who makes a grunting “hmmph” sound every time the researchers pick him up to weigh and measure him.

Emperor penguin chicks.

Jérôme Maison. © 2005 Bonne Pioche Productions/Alliance de Production Cinématographique

I never realized how amazing penguins are until I saw March of the Penguins. The birds go to incredible lengths, I learned, to find food for themselves and their babies. In the Antarctic, they withstand brutal snowstorms and frigid temperatures, and they go for months without food, all for the sake of their chicks.

The film also gave me an appreciation for how cute baby penguins are. Afterwards, all I wanted to do was to adopt a group of the adorable puffballs and protect them from winds, cold weather, and hungry predators.

On second thought, though, that would probably be a bad idea. People may have something in common with penguins, but penguins would probably be too noisy and wild to make good roommates. My cat, by the way, agrees.

Going Deeper:

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Whether or not the story is true, the chances of catching “the big one” seem to be getting worse and worse. In response to fishing pressures, fish are becoming smaller, growing more slowly, and having a harder time reproducing, says David O. Conover of the State University of New York at Stony Brook.

In response to fishing pressures, fish are becoming smaller, growing more slowly, and having a harder time reproducing.

The average size of fish of many species has declined in recent years. That’s not surprising. Smaller fish are more likely to squirm out of nets than larger ones. And laws often require that fish smaller than a certain size be returned to the sea. People tend to catch and keep the bigger, meatier ones.

Atlantic silversides.

Courtesy of David Conover

Fishing can also induce changes in fish that are passed on from generation to generation. To check this idea out, Conover grew several generations of Atlantic silversides in six aquarium tanks. In two of the tanks, he kept removing the biggest fish, to copy what commercial fishermen do in the ocean. He found that this caused each generation of fish to grow more slowly than the one that came before it.

When Conover repeatedly removed the smallest fish from two other tanks, each generation grew more quickly than the previous one. When he removed fish at random, there was no change in how fast the fish of each generation grew.

After four generations in which large fish are harvested, the descendents tend to be smaller than they were originally (bottom). Harvesting small fish leads to fish that are larger in later generations (top).

Courtesy of David Conover

Taking only big fish penalizes fish that grow quickly. Removing these animals from the gene pool leads to breeds that grow more slowly and don’t grow to be as large.

To see if the trend is reversible, Conover then stopped fishing from his tanks. So far, it seems to take longer than expected for the fish to recover their earlier growth patterns.

It’s not practical to stop fishing altogether. Instead, Conover proposes that fishing boats be required to throw back the biggest fish along with the smallest ones. This would help preserve fast-growing fish. And your chances of catching “the big one” might actually improve.—E. Sohn

Going Deeper:

Harder, Ben. 2005. Shrinking at sea: Harvesting drives evolution toward smaller fishes. Science News 167(Feb. 26):132-133. Available at http://www.sciencenews.org/articles/20050226/fob4.asp .

You can learn more about the impact of fishing on people and fish populations at www.ourplanet.com/aaas/pages/issues05.html (American Association for the Advancement of Science).

Chartering a boat or taking your own vessel out to sea to go fishing for fun is a large industry. Yet, for a long time, people thought that all the fish caught in this way represent just a tiny fraction of the number of fish caught by commercial fishing boats and sold in markets or brought to factories.

Once targeted by both recreational anglers and commercial fishing boats, the lingcod is one of many saltwater species being overfished.

OAR, NURP, Alaska Dept. Fish and Game

The impact of sportfishing is much bigger than previously suspected, say researchers from Florida State University in Tallahassee.

When the researchers took a close look at U.S. fisheries data, collected over more than 22 years, they found that recreational fishing accounts for 4 percent of fish caught. Two types of fish, menhaden and pollack, make up the bulk of the commercial catch, however. When these two types of fish are left out of the analysis, the fraction of all other fish caught and killed in recreational fishing jumps to 10 percent.

Finally, the researchers looked just at species that have been classified as “overfished.” That’s where the numbers are more troubling. Recreational anglers account for 59 percent of red snapper landings in the Gulf of Mexico, for example, and 93 percent of red drum landings in the southern U.S. Atlantic.

In some places and for some types of fish, it might be time for stricter regulations, the researchers say. There are already limits on the number of fish that someone can catch in many locations. But regulators rarely limit the number of people allowed to go fishing.

People aren’t going to stop fishing. If they just threw back what they caught, though, the fish now at risk might be better off.—E. Sohn

Going Deeper:

Milius, Susan. 2004. There’s a catch: Recreation takes toll on marine fish. Science News 166(Aug. 28):133-134. Available at http://www.sciencenews.org/articles/20040828/fob6.asp .

You can learn more about U.S. marine recreational fisheries at www.st.nmfs.gov/st1/recreational/index.html (National Oceanic and Atmospheric Administration).

Comments:

I now know that fishing for fun can really kill. And the orcas really need help. I hate what the world is doing to all the animals!—Megan, 13