Researchers at MIT have discovered that large marine predators like tuna and swordfish rely heavily on the ocean’s twilight zone for their diet, rather than previously thought. The study found that these three species source between 50% to 60% of their diet from this dark layer of the ocean.
The twilight zone, spanning from 200 to 1,000 meters below the surface, is a previously understudied region teeming with life. It’s often referred to as the “deep-sea buffet” due to its abundance of organisms adapted to live in darkness. The researchers observed that many large predatory fish make regular dives into this zone to dine on the deep-sea bounty.
Bigeye tuna spend much of their day making short, quick plunges into the twilight zone, while yellowfin tuna dive down every few days. Swordfish, meanwhile, follow a daily migration pattern, swimming up to the surface at night and descending back into darkness at dawn.
The study’s findings have significant implications for fisheries management. As fishing industries turn their attention to the twilight zone for commerciality, these changes could negatively impact fisheries or more shallow tuna and swordfish populations. The researchers warn that any large-scale fishing in this region could lead to uncertainty around the profitability of tuna fisheries, making it essential to carefully consider impacts on the twilight zone and larger ocean ecosystem.
The study’s lead author, Ciara Willis, notes that predators like tuna need concentrated layers of food to survive, which drives their interest in the ocean’s twilight zone. With 50% to 60% of their diet coming from this region, bigeye tuna might be the most at risk from food web effects if fishing in the twilight zone becomes widespread.
Source: https://oceanographicmagazine.com/news/tuna-are-more-reliant-on-oceans-deep-sea-buffet-than-first-thought