New Study Reveals How Fishing and Climate Change Reduce the Ocean’s Ability to Store Carbon
The World Maritime University (WMU) partnered on a new international study with researchers from the University of Montpellier, the National Centre for Scientific Research (CNRS), and the University of California Los Angeles and Santa Barbara, that reveals how fishing and climate change are impacting the ocean’s capacity to trap carbon, a natural process critical in the fight against climate change. The study, “The combined impact of fisheries and climate change on future carbon sequestration by oceanic macrofauna”, is published in Nature Communications, and calls for a more sustainable management of the ocean, taking into account the impact fishing can have on ocean carbon sequestration.
Fish as a Tool Against Climate Change
Nature-based Climate Solutions (NbCS) like forest restoration are widely recognized for their ability to absorb CO₂. However, as terrestrial ecosystems face increasing threats from fires and human activities, scientists are exploring the ocean’s potential in climate mitigation. According to the joint 2021 report from the Intergovernmental Panel on Climate Change (IPCC) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), the way we manage ocean food resources must evolve so that a healthy ocean—rich with thriving fish populations—can help in the fight against climate change.
This new study seeks to answer key questions, including: How exactly does a vibrant ocean link to carbon sequestration? What are the impacts of climate change and fishing on the ability of fish to sequester carbon? And could better ocean management become an effective tool to mitigate climate change?
How Fish Sequester Carbon
Nearly 30% of all carbon sequestered by marine organisms is linked to fish. Fish consume carbon through their diet, storing some in their bodies while expelling the rest as fecal pellets. When these pellets—or fish carcasses—sink into the deep ocean, the carbon is effectively locked away for thousands of years. In 1950, commercial fish populations sequestered approximately 0.23 billion tonnes of carbon per year, mostly through fecal pellets (90%).
The Historical Impact of Fishing
Today, commercial fish populations sequester just 0.12 billion tonnes of carbon annually. The research shows this is equivalent to a decline of 47% compared to the 1950s. “We estimate that every time fishing reduces fish biomass by 1%, carbon sequestration decreases by 0.8%,” the researchers report.
Researchers found that fishing disproportionately affects long-lived fish, the primary contributors to carbon sequestration through carcasses. The research points out that in addition to the impact this may have on carbon sequestration, this reduction in the arrival of carcasses on the ocean floor also means a reduction in the arrival of food in abyssal ecosystems. “Carcasses are a much-appreciated meal for organisms living in the abyss. We may be starving a whole host of abyssal organisms that we barely know about,” the team concludes.
Climate Change and a Vicious Cycle
According to the study, climate change is projected to significantly reduce the ability of fish to sequester carbon, which will in turn amplify climate change. If global warming is limited to 1.5°C, fish carbon sequestration will decline modestly, but the decrease could reach 13.5% if temperatures rise by 4.3°C. For every additional degree of warming, a 2.46% reduction in sequestration is expected. The researchers conclude that, “Although this effect is weaker than fishing, the two drivers act together, potentially reducing sequestration by 56% by the end of the century compared to 1950.”
A New Nature-Based Climate Solution?
The research quantifies the potential benefits of restoring commercial fish populations. If restored to historical levels, these populations could sequester around 0.4 billion tonnes of CO₂ per year—comparable to the carbon capture potential of mangrove restoration. Over time, this could total 240 billion tonnes of CO₂, equivalent to six years of current global greenhouse gas emissions. Therefore, restoring populations of commercial species is an interesting NbCS avenue to consider.
However, the researchers emphasize that NbCS, including those linked to fish, cannot achieve climate goals on their own and must complement substantial reductions in greenhouse gas emissions. They caution that there are still uncertainties and gaps surrounding this new field of research which make it difficult to conclude that measures to restore fish populations are a new NbCS. Nevertheless, the researchers conclude that the results “illustrate the importance of managing the ocean more sustainably to avoid wiping out a carbon sink whose protection could bring benefits for biodiversity and the climate”.
Funding Acknowledgment
The study was partially funded by the OceanICU Horizon Europe project (grant agreement no. 101083922), which aims to understand biological carbon cycling in the ocean. Views expressed are those of the authors and do not necessarily reflect the European Union or European Research Executive Agency.
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