Dave Freedman - Natural Selection

Normally, a shark swimming in the illuminated waters above would detect a large, apparently wounded fish thrashing in the depths. With short, rapid sweeps of its big tail, the shark would dive down to find it. As it descended into the darkened waters, however, its vision would disappear and it would sense several peculiarities. The most prominent was that there’d be no blood. But even without blood, the vibrations would continue, and the tiny-brained hunter would blindly swim closer.

The attack would come in one of two ways.

Sometimes, the shark would realize something was wrong when it was only ten feet away. Suddenly the wounded animal would be perfectly healthy—and swimming right for the shark. The shark wouldn’t see it in the darkness, but it would feel its watery wake from its massive pumping wings. Unable to slow down—sharks possess no form of braking mechanism—the shark’s momentum would carry it right into the animal, which would simply open its massive dagger-filled mouth and bite down. The bite, which was more powerful than the crushing mechanisms of most garbage trucks, would sever the entire upper third of the shark’s body. Then the others would join in.

More commonly, the predator pretending to be wounded would continue its act until the last possible moment. Sometimes, it would even allow the shark to bite it. The ray knew from experience that the shark’s teeth wouldn’t pierce its tough armorlike skin, at least not with a single nip. And a single nip would be all it would get. By then, the other creatures the shark had just swum right over would have risen from the bottom. If the shark had been paying attention, it would have known they were coming for it. But the shark never paid attention. Six or more would surround it and tear away pieces of its body, eating it alive. The bloody feast would finish in seconds.

But there were no feasts now. The sharks weren’t coming. Nothing was.

The writhing predator froze and floated down, joining the others. They were all still hungry. Unlike the growing juveniles, these animals had spent their entire lives learning how to hunt a certain way, in a certain place. But the juveniles were different. They weren’t learning how to bait sharks, read ocean currents, and hide in the depths. They were learning entirely different skills in another place.

No longer could these elder animals stop them by killing them. The younger rays regularly escaped their attacks simply by swimming into the higher waters—and staying there. The juveniles spent very little time in the depths anymore. Even at the moment, they were at the surface, more than a third of a mile away. They were too far to be seen, too far to be heard, but the animals here were watching them.

They were watching something else, too. They’d stopped their migration because of it. Food was coming. The juveniles didn’t know it yet, but that would soon change. The adults were incapable of catching what was coming; they were too large, too slow moving, and too far away. But the juveniles were none of those things. Perhaps they’d find a way to eat.

THE SMALLER rays continued shooting out of the sea, zooming everywhere. Then one of them jerked its horned head to the north. Suddenly detecting what the adults had just sensed, it pulled its wings in tight, dove back into the sea, and didn’t return. Instantaneously, the others did the same. In less than a second, the entire ocean plane was deserted.

They hung listlessly below the surface, every sensory organ tuning in. They’d just picked up a group of fifty animals, still a great distance away but swimming in their direction.

The juveniles heard them, though not with their ears and not with their lateral lines either. In a technical sense, they didn’t “hear” them at all, though hearing was the human sense that most closely approximated what they’d done. They possessed highly specialized organs in their heads known as ampullae of Lorenzini. Like an inner ear, ampullae are composed of delicate jelly-filled pores that provide magnetic detection capabilities. Land-based animals don’t have ampullae of Lorenzini, but they are common in creatures of the sea. Mantas have the strongest ampullae of Lorenzini in the known animal kingdom. Those of their unknown cousins were a hundred times stronger.

The rays didn’t move. Hanging in the moon-speckled waters, they simply tuned. The prey were still heading toward them. This particular type of prey wasn’t part of their regular diet, but the rays could be opportunistic—or at least try to be. The rays had already attempted to hunt this prey on several occasions and failed every time. But they’d learned lessons. They were concerned about the prey’s sonars. The juveniles themselves possessed sonar, sound navigation, and radar, but that of the approaching prey was far stronger. In its crudest form, sonar is an echo-location system in which a sound is emitted and its reflection, or echo, is analyzed. The approaching species used sonar by emitting a series of high-frequency clicks, commonly in the 200,000-hertz range. When these “clicks” met a fish, much like an X-ray, they passed through body tissues but reflected back against bone. But unlike the picture from a doctor’s office, these particular X-rays provided an intimate view of three entire miles of open ocean.

But still, as strong as the approaching prey’s sonars were, the rays’ ampullae of Lorenzini were even stronger. Their ampullae had a range of five miles and could detect the electrical activity in every one of the approaching animals’ muscles: front and rear torsos, necks, fins—even their hearts. Indeed, from five miles away, the juvenile rays had detected the prey’s individual heartbeats, more than fifty of them.

The rays knew the prey’s sonars would soon pick them up as well, but the prey’s sonars could be fooled. If a small pack of rays swam in a very particular way, they could effectively simulate another predator that the prey would attempt to evade. But in evading what they’d think was a single large predator, they’d actually be swimming toward thousands of smaller ones. A group of juveniles began moving.

FIFTY BOTTLENOSE dolphins zoomed out of the sea, their elegant gray bodies glistening in the pale moonlight. The mammals hung in the air for a brief moment, arching slightly, then knifed back in. A few miles offshore and moving at nearly twenty-five miles per hour, the dolphins were in the midst of a southern migration.

At the front of the herd, the leader was much larger than the rest— a twelve-footer weighing nearly 950 pounds. The animal had been studying the ocean ahead since the beginning of their migration, and until this point, its sonar had detected very little, just schools of tiny fish. But suddenly it picked up something else. The reading was foggy and unclear, but somewhere in the distance was a large creature. Made of cartilage, the creature appeared to be a shark, swimming from the west. The leader changed direction slightly, and like a flock of birds, the other dolphins followed.

They swam for nearly half a minute when the leader picked up something else: an unmoving mass spread out over a square mile. Again the reading was unclear, but the leader’s sonar indicated it had to be a kelp forest. Dolphins often swim through kelp forests to evade sharks, and this school intended to do the same.

They swam straight for it. What they thought was a kelp forest was a little more than a mile away.

THE DOLPHINS had reacted as hoped.

Most of the rays still didn’t move, however. They just floated, luring the mammals closer. They knew that if the dolphins didn’t change course soon, their fates would be sealed.

THE DOLPHINS didn’t change course. They knew instinctively that something was “off” in the ocean ahead, but they didn’t know what. As they knifed in and out of the sea, the leader’s sonar continued producing unusual readings. It now indicated the kelp forest ahead might not be kelp after all, but something else, something indeterminate. The big dolphin didn’t have time to analyze it. The large cartilaginous creature from the west was still swimming toward them, and now so was a second creature, from the east.