In the twilight zone of the ocean, a fish that could feed the world - or destroy it

In 1789, explorers Alessandro Malaspina and José de Bustamante set out from Cadiz on the first Spanish scientific expedition around the world. For five years, Malaspina and Bustamante studied and collected animals and plants throughout the Spanish Empire, which stretched along the northern, central, and southern Pacific coasts, and westward to the Philippines. /p>

In 2010, another Spanish expedition set out from Cadiz, retracing much of the original route and studying what the oceans look like today.

< p class="dcr-1vtk2mf">The team measured pollutants, plastics and chemicals that weren't around in the days of Malaspina and Bustamante. They collected seawater and plankton samples. And throughout the 31,000 mile voyage, the ship's sonar was turned on, listening for echoes from below. Their main targets? Small, silvery fish that look like sardines or anchovies - only with larger eyes and rows of glow-in-the-dark spots.

These are lanternfish: there are about 250 species of them and they are not only the most common fish in the twilight zone but the most abundant vertebrates on the planet.Huge numbers were first noticed during World War II, when naval sonar operators saw echoes from what appeared to be a solid seabed, which rose to the surface at night and fell again at dawn.In fact, the sonic pulses echoed in the swim bladders - the internal gas-filled bubbles - of billions of lanternfish, as they gathered in dense layers hiding in the depths, then at sunset swam for thousands of meters for r feed on the surface. . Every night, along with other animals, such as squid that feed on them, lanternfish undergo the largest animal migration on the planet.

Before shipping Malaspina 2010, studies based on trawl surveys estimated that the twilight zone contains about one gigatonne (1 billion tonnes) of fish. But it turns out that was most likely an underestimate, because the lanternfish have...