September 29, 2022 — In 1789, the explorers Alessandro Malaspina and José de Bustamante set sail from Cádiz on Spain’s first scientific expedition around the world. For five years, Malaspina and Bustamante studied and collected animals and plants across the Spanish empire, which stretched along the North, Central and South American Pacific coasts, and westwards to the Philippines.
In 2010, another Spanish expedition set off from Cádiz, tracing much of the original route and studying what the oceans are like today.
The team measured pollutants, plastics and chemicals that were not there in Malaspina and Bustamante’s time. They collected samples of seawater and plankton. And all the way through the 31,000-mile voyage, the ship’s sonar was switched on, listening for echoes from below. Their chief targets? Small silver fish that look like sardines or anchovies – only with bigger eyes and rows of spots that glow in the dark.
They are lanternfish: there are about 250 species and they are not only the most common fish in the oceans’ twilight zone but the most abundant vertebrates on the planet. Huge numbers were first noticed during the second world war, when naval sonar operators saw echoes from what appeared to be a solid seabed, one that rose to the surface at night and fell back down at daybreak. In fact, the pulses of sound were echoing off the swim bladders – the internal gas-filled bubbles – of billions of lanternfish, as they congregated in dense layers hiding in the deep, then at sunset swam up thousands of metres to feed at the surface. Every night, along with other animals, such as the squid that prey on them, lanternfish undergo the greatest animal migration on the planet.
Before the 2010 Malaspina expedition, studies based on trawl surveys estimated that the twilight zone contains about a gigatonne (1bn tonnes) of fish. But this was most likely an underestimate, it turns out, because lanternfish avoid being caught by swimming away from the open nets. The Malaspina acoustic survey did not rely on nets, and in 2014 its research led to new estimates of the abundance of twilight-zone fish, ranging between 10 and 20 gigatonnes.
The prospect of such a colossal harvest raised an old question: could fish from the twilight zone help to feed a growing human population?