The battle to avoid mistakes in fishing the ocean’s twilight zone

Can we find food deeper below the ocean’s surface to feed the world’s growing population? Can we do this without repeating the mistakes of overfishing, ecosystem destruction and biodiversity loss we have made so far in shallower waters? A deep sea fishing expedition supported by the EU-funded MEESO project is exploring parts of the North Atlantic to find the answers.

The scientists are focusing on the mesopelagic zone, a dark ocean area between 200 and 1 000 metres in depth also referred to as the twilight zone. A team from DTU Aqua – the National Institute of Aquatic Resources at MEESO project partner Technical University of Denmark (DTU) – are processing some of the information collected by marine research vessels in this part of the ocean. The research is centred on two small species of fish, the glacier lantern fish and Mueller’s pearlside, whose high oil content makes them a good prospect for commercial fishing.

However, as Prof. J. Rasmus Nielsen from DTU Aqua observes in a news item posted on DTU’s website, scientists currently know “virtually nothing” about how fishing these species will affect the food chain they are part of. They also lack insight into the role the species play in the overall ecosystem. “It’s both exciting and frightening to be doing research in an area where we know so little. This means that our research is both relevant and necessary, but it’s also a huge responsibility,” Prof. Nielsen states. He adds: “The first articles in a virtually unknown area can have a huge impact on later decisions. So we really need to think it through and do work that is both quick and correct.”There has always been interest in the mesopelagic zone, where there is so little light that photosynthesis is practically non-existent. However, the results of a 2014 international study – claiming that the twilight zone contains between 10 and 20 billion tonnes of fish and shellfish – propelled this interest to new heights. “Obviously, those numbers attracted a lot of attention. And soon a number of interested parties were asking the next question: Can this be exploited?” states Prof. Nielsen.

The catch is that mesopelagic marine life plays a vital role in maintaining the planet’s carbon balance, moving 2 to 6 billion tonnes of carbon from the ocean’s surface to its depths each year. There is therefore an urgency to gain in-depth knowledge about the mesopelagic zone before the fishing, pharmaceutical and food industries begin to exploit it. “We need to act quickly, because if it suddenly turns out that there is a high-value product down there, they’re just going to go for it,” remarks Prof. Nielsen.

The research team use the data obtained on glacier lantern fish and Mueller’s pearlside to determine the stocks of the species and the dynamics of the stocks. “When we know the dynamics of a natural stock, we also know the surplus amount produced and thus how much we can sustainably take from the stock,” notes Prof. Nielsen.

The work carried out with support from MEESO (Ecologically and economically sustainable mesopelagic fisheries) could help pave the way for sustainable fishing in the future. With this goal in mind, the project has also supported sampling of parasitic species infecting mesopelagic fish in research conducted in north-west African waters.

For more information, please see:

MEESO project website