A Net the Size of a Football Field, Dragged Across the Seafloor
Picture a weighted net as wide as a football field being hauled across the ocean bottom at several knots, scooping up everything in its path. That is essentially what bottom trawling is. A vessel drags a large, cone-shaped net behind it, held open by heavy doors and weighted rollers that keep it pinned to the seafloor. Whatever lives there, whether it is the target species or not, gets swept inside.
The technique is highly effective at catching commercially valuable fish and shellfish like cod, shrimp, and flatfish. That effectiveness is also precisely what worries marine scientists. The same physical force that fills a net can flatten coral structures that took centuries to build, crush sponge beds, and churn up sediment in ways that disrupt entire food chains.
What the Science Shows
Research on the ecological damage caused by bottom trawling has been building for decades. Studies have found that trawled areas can take years, sometimes far longer, to recover, depending on what type of habitat was disturbed. Soft sediment beds recover more quickly than complex structures like cold-water corals, which grow extremely slowly.
One concern that has gained significant attention is the carbon question. Seafloor sediments store large quantities of carbon accumulated over thousands of years. When trawl gear disturbs those sediments, some of that stored carbon can be released into the water column, and potentially into the atmosphere. Research suggests the scale of this release could be meaningful in the context of climate change, though scientists continue to debate exactly how much carbon actually reaches the atmosphere versus staying dissolved in the ocean.
Beyond habitat destruction, bottom trawling produces high levels of bycatch, meaning species caught unintentionally. Sea turtles, juvenile fish, and non-commercial invertebrates can all end up in a trawl net. In some fisheries, bycatch has historically made up a substantial portion of the total catch by weight.
There is also the issue of where trawling happens. As shallow-water fish stocks declined over the latter half of the twentieth century, fleets moved into deeper waters, including seamounts and deep-sea ridges that host ecosystems almost entirely unknown to science.
The Push to Regulate or Ban the Practice
The case against unregulated bottom trawling has grown louder in recent years, and it has found support far beyond academic circles. A number of countries have banned or significantly restricted the practice in certain zones, and international bodies have worked to protect vulnerable deep-sea habitats in areas beyond national jurisdiction.
In 2023, the European Commission set out an action plan calling on member states to phase out bottom trawling in protected marine areas by 2030, a non-binding call that some conservation groups called too weak and that fishing industry representatives argued could devastate coastal fishing communities that depend on the practice for their livelihoods. That tension is at the heart of the policy debate. Bottom trawling is not just an environmental issue; it is an economic one. In many parts of the world, small-scale fishing families rely on trawl gear because it is among the more affordable and reliable ways to bring in a catch large enough to sell.
Proponents of trawling argue that modern gear modifications, such as turtle excluder devices and modified net openings, can reduce bycatch and minimize seafloor contact. Some industry voices contend that selective bans ignore these technological improvements and unfairly target bottom trawlers while leaving other damaging practices untouched.
Scientists who study deep-sea ecosystems tend to push back on that framing. Their argument, broadly, is that even reduced-impact trawling in sensitive habitats causes harm that cannot be reversed on any human timescale, and that the precautionary principle demands protecting areas that have not yet been thoroughly studied.
A Slow-Moving Crisis With Faster-Moving Consequences
The deep ocean is easy to ignore because it is invisible. There are no photographs of a trawled seamount circulating on social media the way images of a clearcut forest might. That invisibility has historically made it easier to treat the seafloor as an inexhaustible resource.
The science increasingly suggests otherwise. Whether through expanded marine protected areas, stricter gear regulations, or outright bans in the most sensitive zones, the pressure on governments and international bodies to act has rarely been stronger. How they respond will shape the health of ocean ecosystems for generations.