Toward the inclusion of oceanic conservation measures in the Nature-based Climate Solution portfolio

It is clear now that Nature-based Climate Solutions (NbCS) – solutions designed to protect, restore, and sustainably manage ecosystems to mitigate climate change – are needed to achieve the net-zero climate targets. In a context where NbCS over-rely on land ecosystems, it is necessary to seek natural analogs in the ocean by focusing on components that contribute to oceanic carbon sequestration and that we can target through conservation measures, such as fish and the seabed.
Here, we estimate the past and future influence of fisheries on the carbon cycle by assessing their impact on the carbon sequestration potential of fish, as well as their contribution to greenhouse gas emissions, with the ultimate goal of discussing their potential inclusion in the NbCS portfolio.
We show that before the development of the fishing industry, fish of commercial interest induced a carbon export flux of 0.22 GtC.yr^-1 (eq. to 0.80 GtCO₂.yr^-1), and that exploitation has reduced export to 0.10 GtC.yr^-1 (eq. to 0.36 GtCO₂.yr^-1). This means that the restoration of macrofauna populations towards their historical levels has a climate change mitigation potential of 0.124 GtC.yr^-1 (eq. to 0.45 GtCO₂.yr^-1), an estimate of the same order of magnitude as the one of mangroves restoration measures. Yet, as the vast ocean also plays a pivotal role in addressing socio-economic goals such as fisheries or food security, protecting oceanic areas for climate action should not impede these socio-economic goals. Consequently, finding areas where these potential conflicts are minimized is necessary to better inform the spatial management of fisheries. Regarding epipelagic fisheries, we find that most of the opportunities to safeguard and increase fish carbon sequestration lie in the high seas. Regarding bottom-trawling fisheries, the Arctic Ocean emerged as an area of major interest. Indeed, in a context where the Arctic would be sea-ice-free by the 2030s, these new open areas where the sediment carbon is still intact would soon become new bottom-trawling fishing grounds. We show that avoiding the development of these fisheries will avoid the emission of greenhouse gas emissions from fossil fuel burning and seabed carbon disturbance, without imperilling existing bottom-trawling fisheries. Our results therefore suggest that oceanic conservation measures are options to be considered for expanding the NbCS portfolio.