The Role of Predator Removal by Fishing on Ocean Carbon Dynamics

Total ocean carbon exceeds 40,000 GT either dissolved in the water column or buried in ocean sediments, and the ocean continues to sequester carbon from the atmosphere. Selective removal of predatory fsh through extractive fshing alters the community structure of the ocean. This altered community results in increased biomass of more productive, low trophic level fsh, higher overall fsh respiration rates and lower carbon sequestration rates from fsh, despite possible decreases in total fsh biomass. High-pressure fshing on high trophic level fsh, a globally occurring phenomenon, may result in as much as a 19% increase in respiration from fsh communities overall. This increase in respiration will reduce sequestration rates and could prove highly signifcant in global carbon budgets. Preliminary estimates suggest a loss of sequestration equating to around 90Mt C.year−1 (~10% of total ocean sequestration or~1% of anthropogenic fossil fuel emissions per year). Ultimately, to reduce these carbon emissions, fshing needs to be carbon optimised, alongside other fsheries management outcomes, which may mean that fewer higher trophic level fsh are removed. This study highlights the potential magnitude of fshing on ocean carbon dynamics and presents the key uncertainties (including understanding the efects of fshing on zoo- and phytoplankton communities) we need to urgently research to accurately quantify the efects and model future fshing practices