In the ocean’s twilight zone, a fish can feed the world – or destroy it | Marine life

IIn 1789, explorers Alessandro Malaspina and José de Bustamante set sail from Cádiz on the first Spanish 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 northern, central and southern Pacific coasts, and westward to the Philippines.

In 2010, another Spanish expedition set off from Cadiz, tracing much of the original path and studying what oceans look like today.

The team measured pollutants, plastics and chemicals that were not present in the time of Malaspina and Bustamante. They collected samples of seawater and plankton. And all the way through the 31,000-mile voyage, the ship’s sonar was turned on, listening for echoes from below. Their main goals? A small silver fish that looks like sardines or anchovies – only with larger eyes and rows of glow-in-the-dark spots.

A school of lanternfish.
A school of lanternfish. Photo: OAR/National Marine Research Program

they are lantern fishThere are about 250 species and they are not only the most common fish in the twilight zone of the oceans but the most abundant vertebrates on the planet. Huge numbers were first observed during World War II, when naval sonar operators saw echoes of what appeared to be a solid sea floor, which rose to the surface at night and fell again at dawn. In fact, the pulsations of sound reverberated from the swimming waters – the gas-filled inner bubbles – of billions of lantern fish, as they congregate in dense layers hiding at depth, then at sunset swim thousands of meters to feed on the surface. Every night, along with other animals, such as the squid that prey on them, lanternfish undergo the largest animal migration on the planet.

Prior to the 2010 Malaspina expedition, studies based on trawl surveys estimated that the aurora zone contained about gigatons (1 billion tons) of fish. But it turns out that this was likely an underestimate, because the lanternfish avoid being caught by swimming away from open nets. Malaspina’s acoustic survey did not rely on nets, and in 2014 his research led to new estimates of the abundance of twilight zone fish, which range from 10 to 20 gigatons.

The prospect of such a massive harvest raised an age-old question: Could fish from the Twilight Zone help feed a growing population?

It’s so tempting to ignore

It is unlikely that lantern fish will appear directly on anyone’s plate – it is very fatty and full of bones. However, its high oil content means that it can be pureed for animal feed, mostly for fish farms. After Malaspina’s discovery, it was suggested that if half of the estimated lower mass of Twilight Zone fish – still a huge 5 gigatons – were caught – it could theoretically be converted into enough fishmeal to produce 1.25 gigatons of farmed seafood, which equates to much more than the catch. The current annual 0.1 gigatons of wild fish.

However, even if the lantern fish harvest begins, and regardless of the other environmental impacts of many types of fish farming, such as pollution from medicines and waste, many wonder if it will achieve the virtuous goal of securing food for all.

Varieties of lantern fish.
Lantern fish come in a variety of shapes and sizes, and they all have biologically luminous organs. Photo: Paul Kieger/Woods Hole Oceanographic Institution

Much of the fishmeal is fed to salmon and prawns in food-rich developed countries, and increasingly larger amounts are being sold as a supplement in pet food. Moreover, previous attempts to create a lantern fishery failed, including by the Russian and Icelandic fleets. fishing So far it has been proven that these deep waters are very expensive, and fishmeal is very cheap.

But recently, spurred in part by high ratings for lanternfish populations, plans are being made to investigate how to make Twilight Zone fisheries profitable. The European Union funded a five-year research project to investigate such opportunities. In 2017, Norway issued 46 exploratory fishing licenses for the Twilight Zone. These fisheries are likely to seek profits, not by producing low-cost fishmeal, but by providing a more lucrative “nutrient” industry that provides products such as omega-3 supplements and fish oil pills More people are taking it despite the lack of evidence of its benefits.

These and other initiatives to develop “twilight fisheries” reflect an urgent need to hunt wild fish. Amid the talk of sustainability – and the need to “feed the world” – is the counter-assumption that leaving those fish unfished would be somehow a waste. The term “underutilized” is often used, as if the only purpose of those animals is for the benefit of humans. The idea of ​​a thousand trillion sparkling fish streaming through the twilight zone is too tempting for many to ignore.

Snakefish attack the lanternfish, which has photosynthetic organs on the tail to confuse predators.
The lanternfish, which has light organs on its tail to confuse predators, is pursued by the viperfish into the depths of the ocean. Photo: Minden Pictures / Alamy

To catch enough lanternfish and make it worth the effort, these fisheries probably need to use giant middle-water trawls and target fish during the day, as they huddle together in large shoals that are easy to find with sonar. The nets won’t touch the bottom or smash the 1,000-year-old reef, but as they sink and strain the open waters, they will catch other animals — sharks, dolphins, turtles — that already have enough problems.

Climate Consequences

Unlike slow-growing deep-sea species such as the orange rockfish, lanternfish are more likely to withstand significant fishing pressures; They grow much faster, their lives are measured in months, and some live for less than two years. However, fishing in the twilight zone can lead to a different kind of disaster by disrupting the way lantern fish and similar species help regulate the climate.

Their daily routine of swimming up and down forms vital links between surface and depth by strengthening Particle Injection Pumps. This is the process of feeding small fish in shallow water, then diving to the bottom, where they are eaten by larger fish that remain at the depths, thus “pumping” carbon dioxide from the atmosphere to the depths of the ocean where it can be stored. If the particles sink to less than 1,000 metres, the carbon can be stored for up to 1,000 years before returning to the surface. A study of the continental slope off western Ireland estimated that deep fish catch and store the equivalent of one million tons of carbon dioxide.2 year.

siphonophore hula skirt.
There are reflective bubbles filled with gas inside its body. Photo: imageBroker / Alamy

No one can be sure how quickly or how dangerous this biological carbon pump would be weakened if the twilight zone fisheries damage the surface-to-depth connection. But there is a danger that the lanternfish is such a part of the global climate system that it must be left alone.

Alarmingly, not everyone agrees with the new high number of Twilight Zone fish numbers. Even Malaspina’s 2010 study notes the uncertainty and limitations of the methods used. But the headline – that the Twilight Zone contains at least 10 times as many fish as previously thought – caught people’s attention.

Subsequent studies have looked more critically at those numbers and the assumptions they underlie. Malaspina’s study critically hypothesized that acoustic “backscattering” – the measure of sound reflected from the depths received by sonar – came entirely from fish. But they aren’t the only animals in the twilight zone with reflective, gas-filled bubbles inside their bodies. They are also found in many SiphonophoresIntricate jelly pieces identified and drawn by German naturalist Ernst Haeckel in the 19th century. Some twilight fish lack swimming bladders, so they are not detected by sonar.

A 2019 study reinterpreted acoustic data from Malaspina’s flight, taking into account these uncertainties. Estimates of fish in the twilight zone ranged from 1.8 to 16 gigatons. It’s too soon to say where the true value lies on this scale, which means it’s definitely too early to start catching lanternfish based on the risky hypothesis that there could be 20 gigatons.

Recent history tells us that when industrial fisheries sweep through new areas to hunt new species, there are always devastating environmental impacts. Can the same error be avoided in the twilight zone?

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