Mobile bottom fishing in the Canadian Pacific and Atlantic causes disturbance and risk to remineralisation of seabed sediment carbon stocks

Mobile bottom fishing causes substantial disturbances to seabed sediments–one of the world’s largest organic carbon stores. We estimate that 2.1 and 32.0 Mt of carbon is disturbed by annual fishing activities in the Canadian Pacific and Atlantic, respectively. A net increase in carbon remineralisation from this disturbance could negatively impact the oceanic sink for CO 2 . Due to high uncertainty in estimating the scale of remineralisation, we construct a semiquantitative measure of relative carbon risk to describe potential differences between locations and fisheries. In the Pacific, shrimp trawling caused the largest total carbon disturbance and risk; groundfish trawling had large total disturbance but lowest mean disturbance and risk per unit effort (PUE); scallop dredging had the smallest total impacts but highest disturbance and risk PUE. In the Atlantic, shrimp trawling dominated total impacts; however, mean disturbance PUE was highest for scallop and clam dredging, and mean risk PUE was highest for groundfish trawling. High spatial variation in these results would allow a targeted management approach. While uncertainties remain, precautionary risk-based ecosystem management should be implemented.