Demon Fish (2 page)

Scientists can track sharks by embedding them with satellite tags and attaching underwater cameras, technology that captures for the first time their enormous migrations across entire ocean basins. Other researchers are using DNA analysis to determine not only how sharks breed and reproduce but what species are ending up on the global fin market. Another set of scientists, moreover, are cataloging new species of sharks in areas of the world that have been off-limits to researchers for years. In other instances they have captured their behavior with exacting precision. A. Peter Klimley, a professor at the University of California at Davis who has spent years tracking great whites, can tell you how rarely great whites eat—they can survive for as long as a month and a half on a single bite—as well as how they warn away other potential food competitors by slapping their tails.

We are beginning to unravel the mystery of sharks, at just the moment when some of them are in danger of disappearing altogether.

Sharks are fish, but they differ from bony fish in many respects. All sharks belong to the taxonomic class Chondrichthyes, which signifies they have skeletons made from cartilage. Unlike bony fish, which have teeth attached in sockets, sharks have teeth that are connected to their jaws by soft tissue. Their teeth continually fall out or break off and are replaced. Every shark is a carnivore. But not all of them eat other fish: some of them consume tiny plankton, or invertebrates.

Many fish have swim bladders that provide them with neutral buoyancy. Sharks stay afloat by other means. Much of their buoyancy comes from the oil in their liver, but different species use an array of techniques to suspend themselves in the water. Sand tiger sharks suck in air when they reach the ocean’s surface and then hold it in their stomachs, allowing them to float. Many sharks gain lift from the pairs of pectoral and pelvic fins they have on their undersides, in the same way that planes rely on their airfoil wings. They can also use their pectoral fins for braking and to move up and down or to the right or left, but they cannot manipulate them to swim backward or hover. With a few exceptions—the gigantic whale and basking sharks stand out in this respect—these animals have torpedo-like bodies that allow the fastest of them to move at speeds up to thirty miles per hour. The short-fin mako ranks as the swiftest shark, with the blue shark, clocking in at roughly twenty-four miles per hour, as the second fastest. When they’re not pursuing prey, however, sharks often swim at the pace of a human engaged in a brisk walk.

Bony fish have an easy mechanism that lets them breathe underwater: they can use muscles attached to a bony plate covering their gills, known as an operculum, to bring water through their mouths and across their gills. This mechanism provides them with oxygen while allowing them to expel carbon dioxide through their gills. Some bottom-dwelling sharks can imitate this effect by moving their fins so as to create enough current to bring water in and over their gills, or by operating a pumping system where they suck in water with their gills closed and then force the water out through them. These methods allow them to rest on the seabed. But most of the largest sharks have no choice but to swim at all times, with their mouths agape, in order to obtain the oxygen they need to survive. This is one of the reasons people see sharks as so scary: cruising along as they display their sharp teeth, they look as if they’re poised to attack at any moment.
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This phenomenon—technically called ram ventilation—is what Woody Allen was referring to when his character Alvy Singer famously told Annie Hall in his 1977 classic: “A relationship, I think, is like a shark. You know? It has to constantly move forward or it dies. And I think what we got on our hands is a dead shark.”

While humans tend to fixate on the most obvious things they can observe about sharks—their constant movement, their sharp teeth, and their dorsal fins that jut out of the water—these creatures’ unique skin and extraordinary senses allow them to dominate the sea. All sharks boast an armored skin covered with denticles—a.k.a. skin teeth—made of the same material as their teeth, crowns covered with hard enamel. This amazing material, which reduces friction by forcing the water to flow in channels, has scales that flex separately from one another, and in general the cusps of the denticles’ crowns point toward the tail. This feature, which makes shark skin feel smooth when stroked from one direction and scratchy when stroked from the opposite one, allows sharks to move swiftly through the water. Even before people understood their purpose, they marveled at denticles’ scratchiness and exploited it for their own purposes. In August 1869,
The Brooklyn Daily Eagle
reported on an eight-foot shark that washed up into a pool of water near Fifteenth Street and Hamilton Avenue, describing how bystanders had killed it and dragged it onto dry land. According to the paper, “The animal was skinned by some boys, the skin being said to make excellent sand paper.”
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The types of denticles sharks have depend on the species, allowing for specialization: basking sharks have crowns that point in all directions, while short-fin mako sharks—some of the fastest swimmers in the sea—have smaller, lighter denticles than other sharks. The varying composition of these suits of body armor reflects their respective purposes: lighter denticles maximize a shark’s speed while providing slightly less protection against a predatory attack. Like sharks’ teeth, these denticles fall out routinely over time and are subsequently replaced, providing them with constant protection. They are as strong as steel and carry an added benefit: by minimizing water turbulence, they allow sharks to hunt better by moving through the sea in near silence.
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Humans have done their best to replicate denticles: the swimsuit manufacturer Speedo has made clothing out of an imitation material, Fastskin, and NASA has explored using denticles as a model for the material it could use on airplanes. Ralph Liedert, a researcher at the University of Applied Sciences in Bremen, Germany, informed his colleagues at an annual meeting of the Society for Experimental Biology that covering ships with artificial sharkskin would help them move smoothly because the material would dramatically reduce bio-fouling. Biofouling, which occurs when barnacles, mussels, and algae latch onto ships, increases a vessel’s drag resistance by as much as 15 percent. Liedert has produced an imitation sharkskin from elastic silicone that would reduce this fouling by 67 percent, and he estimates that once a ship reached four to five knots, nearly all of these critters would fly off the hull’s surface.
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After researchers from Mote Marine Laboratory’s Center for Shark Research and Boston University’s marine program discovered that sharks hunt prey by sensing the differences when their smell hits each nostril—they call it “smelling in stereo”—scientists have started exploring whether they can apply this same steering algorithm to odor-guided robots that track oil plumes and chemical leaks underwater.
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In recent years the concept of biomimicry has become increasingly popular: venture capitalists have started eyeing everything from whales’ circulatory systems to the way leaves photosynthesize as a model for commercial products. Sharks’ unique adaptive qualities, honed over millions of years, offer a range of possibilities that we’ve only begun to explore.

I didn’t grow up obsessed with sharks, as many small children do. But once I got in the water with sharks in Bimini, I started to think about them quite a bit. Part of my interest stemmed from the fact that they were incredible to look at: the muscular power they can convey just moving through the water makes them formidable swimming companions. The dizzying array of shark-related scientific papers that flooded my e-mail in-box at
The Washington Post
also piqued my interest. As I learned about how researchers are beginning to piece together how sharks live and operate, it became clear that their work is far from complete. But just as significantly, I began to see how sharks’ lives reveal much about the ocean: how it functions, and why it is now in peril.

Some like to describe sharks as “the lions and tigers of the sea,” while Rachel Graham, a Wildlife Conservation Society scientist who works in Belize, Guatemala, and Mexico, calls them “jaguars” to appeal to Central Americans’ pride. Sharks are the kinds of predators, not unlike masters of the savanna and grasslands, that are beginning to tell us about a largely invisible world to which our lives are inextricably tied. Their ancient lineage teaches us how creatures, including ourselves, have adapted to changing environments over millions of years; the toxins that now pervade their bodies show us how what we emit from industrial smokestacks permeates the air and water throughout the globe. They show us not just how we may be heading toward the abyss but also how the natural world functioned before we started undermining it. As one of the most dominant forces underwater, sharks help maintain the balance of marine ecosystems by keeping midlevel predators in check. One of their most valuable qualities, from a strictly human perspective, is that they hint at how the ocean would look if we invested in its resilience instead of plundering its depths.

While it sounds odd, for much of the twentieth century humans saw sharks—along with most other fish—as meat. They were something to be caught in a net or by hook, hauled overboard, and shipped off to market. Even scientists saw them as static creatures, for the most part: they might dissect them to examine their stomach contents, but they didn’t observe their underwater lives and contemplate how their actions affected the rest of the ocean over time. But in the same way researchers and land managers now understand that reintroducing gray wolves into Yellowstone has a slew of cascading effects along the region’s food chain, experts now understand that healthy shark populations restore the historic balance of marine life. Rather than selectively picking apart the ocean’s natural system—blasting corals in one area, fishing out tasty large fish like groupers in another, and pulling up sharks in another—we could commit ourselves to repairing this ravaged system. We have declared less than half of 1 percent of the ocean off-limits, compared with the roughly 14 percent of the planet’s terrestrial surface that enjoys protection.
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We set aside more land for conservation than for farming,
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but marine reserves don’t begin to compete with the areas where fishing lines stretch and trawlers scrape.

Plenty of evidence now exists that if we curb our worst excesses—overfishing, trawling, and polluting—when it comes to the sea, we can give it at least a chance of resisting the broader environmental threats that are well under way, such as climate change. While it’s impossible to restore the entire sea to health, protecting the most ecologically rich areas will produce diverse pockets of the sea in which a range of creatures and plants can thrive. And sharks represent an essential part of the mix.

To better understand sharks, and the men and women whose lives are inextricably tied to them, I ventured across the globe to examine places best described as the water’s edge: the areas where humans mingle with sharks. Sometimes this place was literally the land-sea boundary: the place where a Mexican shark fisherman is pulling his catch of mako and blue sharks up onto the beach, or where a Papua New Guinean elder is shoving his canoe off the shore to search for the fish that reconnects him to his ancestors. Other times the water’s edge is abstract. The place where I crowd in with shark fin traders to get a better look at the wares at a Hong Kong auction, a Fort Lauderdale lab where I examine the results of a genetic analysis of shark samples in Mahmood Shivji’s office, or the New Orleans bar where I listen to aides to a prominent American politician joke that sharks deserve to be wiped out before they claim another human life all represent different intersections between our lives and those of sharks. In some cases these moments show how we are slowly disassembling the natural world; at other times these incidents exemplify our fight to understand it and preserve it. The extent to which these individuals recognize their dependence on these creatures, of course, dictates the extent to which they are invested in sharks’ survival.

In every instance, however, I began to see how we are coming nearer to the monsters of the sea that have terrified us for centuries. This is an actual fact: because of recent advances in technology, some researchers are discovering that sharks live much closer to us than we’ve ever suspected. And the relentless push toward our coasts, whether it’s to live full-time or to spend our holidays, drives us into even closer contact. But that doesn’t mean we understand sharks better, or appreciate them more, than we did before.

Often we value things in the natural world because we see ourselves in their reflection: in how they sing, raise their babies, or travel across the countryside. On rarer occasions—when we marvel at the improbable journey of the albatross or the way male lions live apart from females—we prize them because we define ourselves by how different they are from us. But sharks matter because they exist apart from us, not because of how they stand in relation to us. Henry Beston, writer and naturalist, put it best when he wrote of animals, “They are not brethren, they are not underlings. They are other nations, caught with ourselves in the net of life and time, fellow prisoners of the splendor and travails of the earth.” Sharks, and their surroundings, merit as much exploration as the moon, but we only devote a fraction of the same resources to them. Not for reasons of conquest, or even because our fate is in part linked to theirs. Sharks are worth understanding in their own right, a source of revelations about a foreign world that abuts ours.

For the most part we still see the sea as a source of valuable commodities we can extract, whether it’s the fish we eat or the oil we drill. And for all of the modern techniques we now use to conduct it, the act of fishing itself is pre-agrarian: it’s hunting and gathering. Sharks and other commercial fish are something for humans to capture, not cultivate. We seek to defeat their wildness, rather than admire it.