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

along the Atlantic coast of the continent, past Morocco and the Canary Islands, and into the Mediterranean, all the way to the Egyptian coast. He found lots of leptocephalus larvae, but they were all more or less the same size as the first one he’d caught, between two and half and three and a half inches.

After more than seven years of searching, he was still stuck on square one, and evidently plagued by a certain degree of despondency. “The task was found to grow in extent, year by year, to a degree we had never dreamed of,” he wrote. “And this work has been handicapped throughout by lack of suitable vessels and equipment, and by shortage of funds; indeed, had it not been for the private support afforded from numerous different sources, we should have had to long since relinquish the task.”

He had at least felt able to draw one firm conclusion: since all the larvae he’d found along the coasts of Europe were relatively large and evidently not newly hatched, he’d realized that eels probably do not reproduce near the coast and that his search would have to continue considerably farther out to sea. For this, the steamship Thor was insufficient; instead, Johannes Schmidt was able to enlist the aid of Danish shipping companies that sailed the Atlantic. He equipped their ships with nets and instructions, and between 1911 and 1914, twenty-three large freighters participated in the search for the tiny, transparent larvae. Their crews had no scientific training and no equipment other than the trawling nets Schmidt had given them, but they were under instruction to drag the nets along behind them, mark where they raised them and send their catches to the laboratory in Denmark. More than five hundred catches were logged by the freight ships covering large swathes of the northern part of the Atlantic.

Schmidt for his part set off in the summer of 1913 on the schooner Margrethe, which a Danish company had lent him. He scoured the waters all the way from the Faroes to the Azores, west toward Newfoundland and then south in the direction of the Caribbean.

The intensified search yielded results. Before long, Johannes Schmidt found that the eel larvae became more numerous as he moved west, while their size decreased. At one point, about halfway across the Atlantic, between Florida and West Africa, he caught a larva measuring only 1.3 inches, a new record. Eventually, pushing even farther west, he found a specimen measuring less than 0.7 inches.

Schmidt collected all the fragile leptocephalus larvae, from both his own expeditions and those of his helpers, studied them under a microscope, measured them, and kept meticulous notes: length and number, depth and date, latitude and longitude. Slowly but surely, he built up an enormous collection of data, which guided him, almost imperceptibly slowly, toward his goal. Among other things, he was able to discern a link between the tiny willow leaves’ movements across the Atlantic and the mighty ocean currents. He also found something else, almost by chance.

It was already known that the eels that swim up rivers and other waterways on the American continent belong to a different species from their European counterparts. The two types of eel are virtually identical, and they go through the same metamorphoses, but they nevertheless belong to different species of the Anguilla family. The only thing that differentiates them is that the European eel, Anguilla anguilla, has a few more vertebrae then the American eel, Anguilla rostrata.

Johannes Schmidt’s mission was, of course, to find the birthplace of the European eel, but what he discovered as he pushed farther and farther west was that more and more of the larvae caught belonged to the American species. That posed certain problems. Aside from measuring and counting the larvae, he now also had to classify each specimen. Out on the ocean, aboard a rolling and pitching ship, he had to place every last tiny willow leaf under the microscope and try to count the muscle fibers along its back; the fibers correspond to the number of vertebrae that appear in the fully grown eel. By so doing, he could determine which species the larva belonged to, and then construct tables showing where each species was more common. What he discovered was that in the western part of the Atlantic, the population was mixed. European and American larvae comingled, seemingly powerless to resist the currents, and they were caught in the same nets. That should, logically speaking, have meant that European and American eels were not only virtually identical but that they also bred in the same spot.

If that were the case—and in turn meant that Schmidt, if he could find the birthplace of the European eel, would by default also find the birthplace of the American eel—only one mystery would still remain: How do they know which species they are? How do the tiny willow leaves drifting through the Atlantic know where to go? Clearly, Schmidt wrote, larvae of both eel species travel together on the Gulf Stream, but at some point, their journeys diverge; the American larvae suddenly veer west, turn into glass eels, and wander up American waterways, while the European ones press on eastward. “How,” Johannes Schmidt wrote, “do the masses of larvae in the western Atlantic sort themselves out, so that those individuals which belong to Anguilla anguilla ultimately find themselves in Europe, while those of Anguilla rostrate ‘land’ on the shores of America and the West Indies?”

His conclusion was that the different types of larvae, similar as they may appear, are programmed from birth to seek out different destinations. Simply put, the American ones grow faster than their European cousins, meaning they have the strength to break out of the mighty ocean current as it passes the American coast, instead of drifting on toward Europe. American eel larvae undergo their first metamorphosis, turning into glass eels, after just one year, while the European ones spend two long years drifting with the currents, and become