The Book of Eels, Patrik Svensson [bill gates best books .TXT] 📗

At first, the results looked random, to say the least. The eels’ movements traced strange patterns on the map, as though someone had tried to draw a maze blindfolded, or as though nothing was predetermined and every journey was the first. But at least one thing was made unambiguously clear: the majority of eels never make it to their spawning grounds. The long journey back to their birthplace remains for most of them a thwarted aspiration.

That may seem like a bleak outcome, both for the eels and for the scientific study. Not one of the seven hundred silver eels released could be tracked all the way back to the Sargasso Sea. It’s impossible to say if any of them reached it. Sooner or later, they disappeared into the depths, leaving the realm of human knowledge while their electronic transmitters floated up to the surface.

Nevertheless, the research team managed to draw some new and fairly remarkable conclusions from their observations. Their initial finding was that the eels’ migration is likely more complex than previously thought, but that it could be explained—at least in part. Because from the observations that at first seemed random and unpredictable, a pattern eventually appeared. Firstly, it was clear that the eel rarely takes the shortest route from its starting point to its goal. Its journey isn’t like the journeys of birds or airplanes. Nevertheless, all of Europe’s eels seem to rendezvous somewhere around the Azores, about halfway through their journey, and continue west toward the Sargasso Sea from there in much closer formation. If the journey starts in uncertainty and slight confusion, it becomes more deliberate as it progresses.

The researchers also discovered something else that complicates our understanding of the eels’ migration. When old specimens of leptocephalus larva caught in the Sargasso Sea were reexamined and compared for size and growth rate, they showed that the eel’s spawning season probably starts earlier than previously thought, possibly as early as December. That would mean breeding commences around the same time the last silver eels set off from the coasts of Europe, which only serves to make the question of how they get there on time even more vexing.

But the explanation, the researchers claimed, must, of course, be that all eels don’t make it across the Atlantic in time for the next breeding season. For some, the long journey back to the Sargasso Sea can take much longer. Perhaps eels simply adjust their speed and route according to their abilities. While some swim as fast as they can in order to reach the Sargasso Sea in early spring, some take a considerably more leisurely approach and wait for the next breeding season instead. While an eel setting off from Ireland, for instance, can travel west in an almost straight line and get there by spring, an eel coming from the Baltic Sea might aim to arrive in December, more than a year after it first set off. That would not only explain the differences in the behavior observed but also lend some kind of logic and relevance to what at first seemed random. Maybe eels are, quite simply, individuals, who not only have different abilities but also different means and methods of reaching their goal. Maybe they’re all aiming for the same destination, but no two journeys back to the origin are exactly the same.

AND THUS, ONE QUESTION REMAINS, AND IT IS ONE THAT APPLIES TO both eels and humans: How do they know which route will take them back to where they came from? How do they find their way back home?

That the eel has special abilities that make it skilled at navigating great distances has long been known. It’s well established, for example, that it has a phenomenal sense of smell. According to the German eel expert Friedrich-Wilhelm Tesch, who wrote the standard reference work The Eel in the 1970s, the eel’s olfactory sensitivity is on par with a dog’s. Put one drop of rosewater in Lake Constance, Tesch claimed, and an eel can smell it. It’s likely that eels use smell in some way during their journey across the Atlantic, either to locate the Sargasso Sea itself or at least one another. It’s also likely that the eel is sensitive to changes in temperature and salinity and that these might offer clues as to which way to go. Some scientists believe the eel’s well-developed magnetic sense constitutes its primary navigational tool. Much like bees and migrating birds, it can feel the earth’s magnetic field and is thus guided toward a certain destination.

We know what that destination is. And somehow, the eels know it, too. They know where they’re going, even if the routes they choose can be both meandering and unpredictable. But how they know is one of the mysteries still surrounding the eel question, one of the enigmas even scientists cherish.

Rachel Carson, for her part, described the eel’s inherited knowledge about its origin as something more than an instinct. In Under the Sea-Wind, she writes about how the fully grown and sexually mature eels one autumn suddenly feel a “vague longing for a warm, dark place,” and how these eels, who have lived their long lives “beyond all reminders of the sea,” in lakes and rivers, now set off into the unfamiliar open ocean, finding there something familiar, something they recognize, a sense of belonging “in the large and strange rhythms of a great water which each had known in the beginning of life.”

Do they remember where they came from and where they’re going now? Do they remember their very first journey across the Atlantic as tiny, transparent willow leaves? No, perhaps not in a human, conscious sense, not according to our definition of memory. But when the European research team who followed the more or less successful attempts of seven hundred eels to reach the Sargasso Sea tried to explain how the eels find their way back to their birthplace, they still described the experience as a kind of memory.