Realistic fisheries management reforms could mitigate the impacts of climate change in most countries

fishing effort (see Gaines et al. [19] and Costello et al. [16] for additional details and equations). Country-level fisheries outcomes We evaluated the impact of climate change and management reform on the fisheries of 156 coastal sovereign countries summing across their domestic and territorial exclusive economic zones (EEZs). We scaled the projections of Gaines et al. [19] from the global- to country-level by assuming that the proportion of a species’ overall range occurring inside a country’s EEZ (determined by the SDM) is identical to the proportion of the species’ overall carrying capacity occurring inside the country’s EEZ. This proportion was used to generate time series of bio- mass, harvest, and profit for each species in each country under all three emissions scenarios and five management scenarios. We summarized country-level projections by comparing fish- eries outcomes: (1) in 2100 relative to today under each management scenario and (2) over the entire period (2012–2100) for each of the adaptation scenarios relative to the business-as-usual scenario. These approaches allow us to, respectively, estimate the projected impact of climate change on national fisheries outcomes under the different management scenarios and the cost of failing to adapt national fisheries management to account for climate change. For Approach 1, we compared the percent difference in harvests and profits in 2100 relative to today (i.e., 2012) under each management scenario. While Gaines et al. [19] performed this

comparison using only the projection endpoints (i.e., values in 2012 and 2100), we compared mean decadal values at the ends of the projection window (i.e., mean value in 2012–2021 and 2091–2100) to reduce sensitivity to specific endpoint values. For Approach 2, we compared the percent difference in cumulative harvest and cumulative profits between the four adaptation scenarios and the business-as-usual scenario. By examining differences in cumulative harvest and profits, this approach is also insensitive to endpoints and documents the accumulated ben- efits or losses of climate adaptive management. In both approaches, we quantified the impact of climate change and fisheries management on fisheries health as the mean proportion of stocks with biomass above BMSY, the biomass that produces MSY when fished at FMSY, by century’s end (2091–2100). This is a common target for fisheries management (i.e., U.S. Mag- nuson Stevens Act, E.U. Common Fisheries Policy, and U.N. Sustainable Development Goals). This performance metric better reflects the goals of fisheries management than percent change in biomass. For example, decreasing biomass in a previously undeveloped fishery is an expected consequence of economically optimal management and should only be perceived negatively when the decrease reduces biomass below the target. Results Impacts of climate change on maximum sustainable yield Maximum sustainable yield (MSY) of the evaluated stocks is forecast to decrease by 2.0%, 5.0%, and 18.5% from 2012–2021 to 2091–2100 under RCPs 4.5, 6.0, and 8.5, respectively (Fig

1). Note that these values differ slightly from those reported in Gaines et al. [19] because we excluded mixed-species stocks and measured changes in MSY using decadal means. Across emissions scenarios, MSY is generally projected to decrease for equatorial countries and increase for poleward countries (Fig 1 and S2 Fig). Variability around this common prediction is explained by heterogeneity in local oceanographic conditions, climate velocities, and com- munity compositions [36]. Particularly dramatic reductions in MSY are predicted for the equatorial West African countries. Even under the least severe emissions scenario, nineteen countries, fifteen of which are in West Africa, are projected to experience reductions in MSY of 50–100%. The number of countries projected to experience dramatic losses in MSY, and the PLOS ONE Realistic fisheries management reforms could mitigate the impacts of climate change in most countries PLOS ONE | https://doi.org/10.1371/journal.pone.0224347 March 5, 2020 6 / 21