Fisheries, Fishing, and Ocean Carbon Cycling

Blue Hill Harbor, Blue Hill, Maine. (Credit: USFWS via Flickr Public Domain)

In the conversation on carbon cycling and emissions, fisheries may be overlooked, but the connection between fisheries management and carbon cannot be ignored. Considering the connection between excess carbon and climate change, the role of fisheries and their exploitation is a key part of carbon management.

Fish and Carbon Removal and Production

A 2024 article published in Ocean Sustainability outlines the role of fish and fisheries in the ocean carbon cycle “through a range of biological and physical processes.” Carbon is consumed and exchanged within the food web. Some carbon is stored in the bodies of fish for their entire lifetimes, then consumed later by a predator, or passed naturally as faecal pellets.

These pellets are an efficient form of carbon that sinks through the water column and is one of the ocean’s most effective natural carbon sequestration mechanisms. These pellets sink to the bottom and slowly decompose.

The article cites that “fish-mediated active transport of carbon through diel vertical migration of mesopelagic fish has been estimated to contribute 10%-40% of deep ocean carbon export through defecation, respiration, excretion, and predation at depth.”

How Human Activities Impact Carbon Cycling in the Ocean

Because fish play an important role in carbon cycling and storage, certain maritime activities and unsustainable practices can negatively impact the ability of the ocean’s ability to sequester carbon.

Fishing alone is estimated to have halved the biomass of exploited species, leading to a reduction in fast-sinking faecal pellets and deadfalls, which alters carbon export and deep-sea carbon sequestration when fish are removed.

Overfishing interacts with other anthropogenic stressors, such as climate change and pollution, leading to lower resilience of fisheries and marine ecosystems. Targeting of key species in any ecosystem can have cascading effects, limiting or altering carbon dynamics and exchange.

Equipment and fishing practices like trawling can disturb sequestered carbon in ocean sediments, mixing and re-suspending sediments, “altering the respiration pathways of organic carbon mineralization through increased oxygen exposure, with the potential to substantially alter organic carbon cycling within seafloor sediments.” The impacts of this practice may be irreversible, permanently impeding carbon burial rates and capacity.

More than the fisheries themselves, emissions from the industry as a whole are a contributor of greenhouse gases. Between boating out to fishing areas, transporting harvest, and the energy used for fishing, the carbon footprint of fishing can add up.

Conclusion

Due to the influence of fisheries and unsustainable practices, the article concludes that good fisheries management is good carbon management. Improved sustainable management practices can help limit carbon emissions and protect the ocean’s natural carbon cycling.

Improvements to management will not only improve the carbon storage potential of the ocean but also the resilience of marine ecosystems that are already under stress due to climate change, anthropogenic threats, and other stressors.