The world’s oceans and coasts provide a natural sink for excess carbon in the atmosphere. Scientists refer to carbon that is captured and stored this way as blue carbon. Well-known blue-carbon examples include mangroves and salt marshes—wetland ecosystems in which the soils may store carbon for thousands of years. An often-overlooked source of blue carbon, however, is large fish living in the open ocean, according to marine scientists reporting in the journal Science Advances (October 2020). Large fish are classified as being longer than 30 centimeters (12 inches) in length, and include such species as tunas, mackerels, sharks, and billfishes. See also: Carbon; Chondrichthyes; Mackerel; Mangrove; Salt marsh; Soil; Perciformes; Pisces (zoology); Tuna; Wetland
Using historical fishing data, scientists estimate that marine fisheries have released at least 0.73 billion metric tons of carbon dioxide into the atmosphere since 1950 through the sheer volume of fish captured as well as the amount of fossil fuel consumed by fishing vessels. According to these scientists, simply allowing large fish to die and sink to the bottom of the deep ocean might serve as a nature-based solution to global climate change due to storage of carbon in large fish carcasses buried on the ocean floor for time scales ranging from decades to millions of years. See also: Carbon dioxide; Fossil fuel; Global climate change; Global warming; Marine ecology; Marine fisheries
As a first step toward reducing blue carbon lost through the capture of large fish, scientists suggest that governments discontinue subsidizing fishing fleets for traveling to remote fishing grounds. Without subsidies, about half of these long-distance fishing efforts would become unprofitable. This conservation strategy has the potential to reduce carbon-dioxide emissions both in terms of reduced numbers of fish captured (blue carbon removed from the ocean) and from fossil fuels burned by fishing vessels. An added potential benefit is that depleted fish stocks in these regions might rebound as well, which, in turn, could increase the amount of carbon stored as more large fish sink to the seafloor at the end of their life. See also: Fisheries ecology; Marine conservation