Bottom Trawling Could Unleash Carbon Dioxide, Worsening Global Warming

A Controversial Fishing Method May Dredge Up a Climate Time Bomb

By Kate McMahon edited by Andrea Thompson

A heavy metal net is dragged across the seafloor at breakneck speed, churning up dark clouds of sediment and swallowing everything in its path. A blue-spotted stingray tries to flee, flailing its winglike pectoral fins as the trawl closes in from behind, but its efforts are in vain. This unprecedented footage—a scene in David Attenborough’s latest documentary Ocean—is the first time bottom trawling has been captured in high definition, exposing a practice rarely seen by the public.

Bottom trawling is a highly controversial fishing method, but it provides a quarter of the world’s seafood. It involves a vessel pulling a weighted net and other heavy gear, blindly and fast, along vast stretches of seabed—often in pursuit of only one or two commercially valuable species. It traps huge numbers of other organisms and bulldozes over fragile habitats, destroying centuries-old coral, scallop gardens and seagrass beds. “It’s hard to imagine a more wasteful way to catch fish,” Attenborough narrates somberly as viewers watch a pile of dead juvenile sharks and rays get swept off the deck of the fishing vessel in Ocean.

But ecological destruction is not the only concern. Emerging research points to another lesser-known problem with bottom trawling: its potential to unleash climate-warming gases by disturbing carbon stored in seafloor sediments.

On supporting science journalism

If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

The ocean is the world’s largest single carbon sink, absorbing around 30 percent of the carbon dioxide that human activity pumps into the atmosphere. Phytoplankton—microscopic plants and algae drifting near the ocean’s surface—take in CO₂ during photosynthesis, converting it into organic carbon that gets stored in their tissues. Many sink to the seafloor when they die; sediments eventually bury them and the carbon they contain, effectively locking it away.