Optimizing fisheries for blue carbon management: Why size matters

Abstract

Fish contribute to the export of carbon out of the euphotic zone. They ingest organic carbon fixed by phytoplankton, store it in their tissues for their lifetime, and contribute to long-term sequestration by producing sinking fecal pellets, respiring at depth, or via their own sinking carcasses. While the flux of carbon through fish is small relative to the export flux by plankton, humans have a direct influence on fish communities and thus on the magnitude of carbon storage and flux. We use a size spectrum model to examine the combined effect of fishing and trophic dynamics on the total carbon stored as biomass of a simulated community of fish. By sampling 10,500 possible fishing strategies that randomize fishing mortality and size-selectivity, we consider optimal strategies that balance several UN Sustainable Development Goals addressing (1) food security, (2) climate action, and (3) marine conservation. The model shows that fishery management strategies that preferentially conserve large species increase overall carbon stored in the fish community. This study presents a perspective for considering carbon storage and sequestration in fisheries management alongside alternative objectives such as food production and biodiversity conservation. Our study focused on the state (total carbon in the living community). Incorporating rate processes like fecal pellet flux, vertical migration, and natural mortality would build toward a more holistic carbon approach to fisheries management.

Re‐imagining the precautionary approach to make collaborative fisheries management inclusive of Indigenous Knowledge Systems

“…When fish die naturally, much of their carbon content is sequestered in sediments (Mariani et al, 2020). Due to metabolic scaling, larger individuals store carbon more efficiently and their potential contribution to carbon sequestration exceeds that of an equivalent biomass of smaller fish (Falciani et al, 2022). Biomass reductions allowed by the PA's provisional reference points, coupled with the lack of benchmarks against declining body sizes, likely diminish fish contributions to natural carbon stores, indirectly contributing to ocean warming and acidification (Falciani et al, 2022; Mariani et al, 2020).…”

“…For example, Howell et al (2021) outline a methodology applied to two case studies in which target fishery mortalities for individual stocks were first determined through single‐species assessments and then scaled, from the output of ecosystem models, to support broader socio‐ecological objectives. An approach like this may also use the output of ecosystem models to incorporate carbon sequestration objectives into fisheries management (Falciani et al, 2022). Additionally, open source, state‐of‐the art stock assessment models that can incorporate environmental covariates are now available (Stock & Miller, 2021).…”

“…Stakeholder support for MPAs and IKS‐compatible fisheries approaches may potentially also increase if trade‐off analyses are inclusive of broader ecosystem benefits to people. Ecosystem models, for instance, can show trade‐offs between carbon storage or other ecosystem functions and fisheries landings (Falciani et al, 2022), and methods are available for economic valuation of those trade‐offs (Luisetti et al, 2019; White et al, 2012). Additionally, most economic analyses employed in fisheries valuation account only for benefits to current generations and discount these benefits through time, potentially biasing policy decisions towards those that favour increased consumption in the present.…”

“…Though not developed here, body size criteria under IKS can further refine stock status. sequestration objectives into fisheries management (Falciani et al, 2022). Additionally, open source, state-of-the art stock assessment models that can incorporate environmental covariates are now available (Stock & Miller, 2021).…”

Carbon sequestration in aquatic ecosystems: Recent advances and challenges

“…Several management approaches, particularly the restoration and protection of vegetated ecosystems, aim to maximize aquatic carbon sequestration while minimizing greenhouse gas emissions. Falciani et al (2022) discussed how fishing strategies can enhance not only food production, but also carbon sequestration via fish harvest and fecal pellet fluxes to deeper waters. Livestock grazing is a widely used management approach to increase the biodiversity of saltmarshes, but the effect grazing on carbon sequestration has rarely been tested.…”