Bottom trawling, a fishing method with roots in 14th-century Europe, has evolved significantly over the centuries. Initially a modest endeavor, it underwent a transformative expansion in the 19th century with the introduction of steam-powered boats. This technological leap enabled the use of larger nets and heavier gear, facilitating deeper and more extensive seabed trawling.
Today, bottom trawling is pivotal in harvesting a diverse array of groundfish species like cod, flounder, and shrimp. Its efficiency makes it a favored technique in commercial fisheries, playing a vital role in bolstering the global seafood supply.
A study published in Frontiers in Marine Science has uncovered a previously unrecognized environmental impact of bottom trawling: its contribution to atmospheric carbon emissions. The research, conducted by an international team from esteemed institutions like Utah State University, the National Geographic Society, and the NASA Goddard Institute for Space Studies, reveals that bottom trawling is not just destructive to marine life and habitats but also significantly contributes to global warming.
The study's findings are alarming: bottom trawling releases vast amounts of carbon dioxide, previously trapped in seabed sediments, into the atmosphere. Remarkably, this emission amount is estimated to be double the annual emissions from the global fishing fleet's fuel combustion. The researchers found that 55% to 60% of the carbon dioxide produced by bottom trawling will make it into the atmosphere within nine years.
Notably, areas like the East China Sea, the Baltic and North Seas, and the Greenland Sea are identified as having particularly high carbon emissions from trawling.
This revelation of bottom trawling's role in atmospheric carbon pollution necessitates urgent action. Dr. Enric Sala, a National Geographic Explorer in residence, highlighted the need for countries to include these emissions in their climate action plans. The study, also sheds light on the additional problem of ocean acidification caused by carbon remaining in the water post-trawling, further endangering marine life.
The research serves as a call to reassess policies, aiming to mitigate the multifaceted impacts of bottom trawling on both marine life and the global climate.
“We have long known that dragging heavy fishing nets -- some as large as ten 747 jets -- across the ocean floor destroys sea life and habitats,” said Dr. Trisha Atwood of Utah State University and National Geographic Pristine Seas. “Only recently, we have discovered that bottom trawling also unleashes plumes of carbon, which otherwise would be safely stored for millennia in the ocean floor. Our study is the very first to show that over half the carbon released by bottom trawling eventually escapes into the atmosphere as carbon dioxide over the span of about 10 years, contributing to global warming. Much like destroying forests, scraping up the seafloor causes irreparable harm to the climate, society, and wildlife.”
Despite its efficiency, bottom trawling raises significant environmental concerns. The method, involving dragging heavy nets across the ocean floor, can severely damage seabed habitats, upset ecological balances, and diminish biodiversity. This disruption has prompted increased regulation and a push for more sustainable fishing practices globally.
The ongoing debate seeks to find a balance between the need for efficient food production and the imperative to preserve marine ecosystems.
In addition to the direct impacts on targeted fish populations and seabed habitats, deep sea trawling nets often ensnare a variety of non-target species, a phenomenon known as bycatch. This incidental capture includes a broad spectrum of marine life, ranging from vulnerable fish species to seabirds, marine mammals, and even endangered sea turtles. For instance, trawling in certain regions has been known to inadvertently capture species such as the Atlantic bluefin tuna, known for its commercial value yet facing population pressures, and the leatherback turtle, a critically endangered species.
The issue of bycatch represents a significant challenge in marine conservation, contributing to the decline of various species populations and the disruption of marine ecosystems. It poses a particular threat to species with slower reproductive rates, as their populations are less resilient to such unintended captures. Furthermore, the loss of these species can have cascading effects on the ocean's ecological balance, impacting food chains and the overall health of marine environments.
Recognizing this critical issue, regulatory bodies and environmental organizations are increasingly focusing on developing and implementing bycatch reduction strategies. These include modifications to trawling equipment, such as the introduction of bycatch reduction devices and the establishment of marine protected areas where trawling is restricted or prohibited. These efforts are integral to ensuring the long-term sustainability of marine ecosystems and the species that inhabit them.
“There are more issues with bottom trawling than just the impacts from carbon -- biodiversity and sustainability for instance,” said Gavin Schmidt, the director of the NASA Goddard Institute for Space Studies. “But this ‘marine deforestation’ is large enough to be noted and assessed. Hopefully, this can lead to policy efforts that can try to maximize benefits across all of the impacts.”
