No list of incredible migratory fish would be complete without a nod to the fantastic European eel. Much of their life is shrouded in mystery, and their lifecycle includes one of the most remarkable feats of animal migration observed in nature. After spawning in the Sargasso Sea, it is assumed the eggs drift on Gulf Stream currents towards Europe. They hatch into larvae and subsequently morph into tiny cylindrical fish that are almost completely transparent. These ‘glass eels’ find their way into freshwaters, and darken in colour to become ‘elvers’. Migrating upstream, they mature into the dark adult eels that people are most familiar with. They can stay in these freshwater habitats for more than 20 years before they morph again, this time into ‘silver eels’, which swim back to the Sargasso Sea to spawn.
Incredibly, no silver eel has ever been caught in the open ocean. It is still unknown to science how long it takes them to reach their spawning grounds, or what kind of percentage of silver eels that left Europe survive the epic journey to the Sargasso Sea to spawn.
Once so common that they were used in medieval Europe as currency, they now face huge anthropogenic pressures and have seen their numbers drop by up to 95% across Europe. One of the drivers of this catastrophic loss is a huge, highly organised network of criminal gangs, who illegally traffic glass eels from Europe to Asia to feed a voracious market. The species is currently listed as Critically Endangered.