In 1904 Johannes Schmidt, a young Danish oceanographer and biologist, got a job aboard the Thor, a Danish research vessel, studying the breeding habits of food fishes such as cod and herring. One day that spring, a larva of the European eel, Anguilla anguilla, showed up in one of the expedition's trawls west of the Faroe Islands. Was it possible that eels living in the creeks of Denmark spawned way out in the middle of the Atlantic Ocean?
A year earlier Schmidt had made what would end up being an auspicious betrothal to the heiress of the Carlsberg Brewery, a Danish company that donated generously to marine research. Outfitted with schooners capable of ocean crossings, he amassed data showing that the farther from the European coast, the smaller the eels. Schmidt asserted that eels must spawn in the southwestern part of the North Atlantic, in the Sargasso Sea. "No other instance is known among fishes of a species requiring a quarter of the circumference of the globe to complete its life history," he wrote in 1923. "Larval migrations of such extent and duration … are altogether unique in the animal kingdom."
After Schmidt's death in 1933, some scientists cast doubt on his Sargasso proposition. They showed that he had concealed certain data to make his case more plausible, and they questioned how he could say with any certainty that this was the only eel breeding ground, since he hadn't witnessed an actual hatching and had barely looked for eels anywhere else. Yet such criticism does little to diminish the profound story of eels he conveyed, which still appears to be true.
In 1991 an expedition headed by Katsumi Tsukamoto of the Atmosphere and Ocean Research Institute of the University of Tokyo that included Michael Miller, then a graduate student at the University of Maine, made another breakthrough. On a dark night in the Pacific Ocean west of Guam, the team found hundreds of larvae of the Japanese eel, Anguilla japonica, within days of their hatching, thus locating the spawning area of this species for the first time. Nineteen years later Tsukamoto and Miller are still searching the oceans for spawning eels.