The ocean is one of Earth’s largest natural carbon sinks, having absorbed a substantial share of anthropogenic greenhouse gas emissions since the industrial revolution. Through its depth, stratification, and circulation patterns, the ocean can store carbon originally fixed by phytoplankton for long time scales, in some cases isolating it from the atmosphere for centuries to millennia (Gruber et al., 2019; Siegel et al., 2023).
Living marine organisms play a central role in this process through the Biological Carbon Pump, which transfers carbon from the ocean surface to deeper waters. In recent years, the role of marine vertebrates within this process has increasingly been recognized. Their contribution, often referred to as “fish carbon”, occur through ecological interactions such as the production of sinking fecal pellets, carcasses, and vertical movement within the water column, facilitating the transfer of carbon to depth (Lutz and Martin, 2014).
At the same time, the global fishing industry is operating at historically high levels, with a significant share of fish stocks being exploited beyond sustainable limits (The State of World Fisheries and Aquaculture 2024, 2024). Intensive fishing practices contribute not only to the depletion of targeted species, but also to broader ecosystem degradation, including habitat destruction, disruption of food webs, and death of non-target bycatch (Davies et al., 2009; Martin et al., 2021; Steadman et al., 2021). These dynamics are reinforced by a persistent “race for fish”, whereby fishing actors seek to maximize catches in the face of competition, even when additional effort yields limited economic returns (Scott Gordon, 1956).
Fisheries governance frameworks have traditionally focused on sustaining harvest levels and securing livelihoods, often treating fish primarily as extractable resources rather than as integral components of marine ecosystems. In this context, fish carbon represents one of several ecosystem services that emerge from maintaining healthy marine ecosystems, thus being but one co-benefit of larger fish populations.
While recent international agreements, such as the WTO Agreement on Fisheries Subsidies, the BBNJ Agreement, and the Kunming–Montreal Global Biodiversity Framework, signal a growing shift toward more sustainable and ecosystem-based approaches, the integration of marine carbon processes and broader ecosystem co-benefits into fisheries and ocean governance remains limited.
In particular, the role of fish carbon within the Biological Carbon Pump remains absent from policy frameworks, whether it be fisheries management or broader climate governance. This raises important questions regarding the extent to which fisheries policy can support, or undermine, the ocean’s role as a carbon sink. Such concerns expose a fundamental limitation of current fisheries management frameworks, which define sustainability in terms of maintaining extractable yields over time rather than preserving the ecosystem functions that fish support. As a result, existing governance systems may inadvertently undermine the ocean’s capacity to function as both a climate mitigation and adaptation mechanism, by constraining marine ecosystem resilience and reducing long-term carbon sequestration potential.
