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

interventions. Overall, we (1) forecast the impacts of climate change on national fisheries and (2) quantify the national-scale benefits of implementing climate-adaptive fisheries reforms. We conclude with a brief overview of promising methods for achieving the benefits of climate- adaptive fisheries reform along a gradient of scientific, management, and enforcement capacities. Methods Overview We used the Gaines et al. [19] climate-linked fisheries bioeconomic model to examine coun- try-level changes in fisheries status, catches, and profits under three emissions scenarios (RCPs 4.5, 6.0, and 8.5; S1 Table) and five management scenarios (Table 1) from 2012 to 2100. Gaines et al. [19] evaluated the 915 single- and mixed-species stocks from Costello et al. [16] with the Table 1. Fisheries management scenarios evaluated in the analysis (HCR = harvest control rule; EEZ = exclusive economic zone). Management scenario Business-as-usual (no adaptation) This scenario assumes that no action is taken: management fails to account for range or productivity shifts or fix economically sub-optimal harvest rates. Thus, current fishing mortality is maintained for all static (non-shifting) stocks and gradually shifts to open access for all transboundary (shifting) stocks given the lack of transboundary agreements. HCR for static stocks: Current fishing mortality HCR for transboundary stocks: Gradual shift from current to open access fishing mortality Range shift adaptation only This scenario assumes that management adapts to spatial changes in range location by implementing

transboundary institutions that facilitate continued management of stocks as they shift into and out of EEZs. However, management does not address corresponding changes in productivity or fix economically sub-optimal harvest rates. Thus, the scenario prevents open access fishing of transboundary (shifting) stocks but does not otherwise improve fisheries management. HCR for static and transboundary stocks: Current fishing mortality Productivity shift adaptation only This scenario assumes that management is naturally adaptive to changes in productivity and fixes economically sub-optimal harvest rates by adopting an economically optimal HCR where the appropriate harvest rate adjusts based on the total biomass that year. However, this scenario assumes that management does not address transboundary issues associated with spatial range shifts. Thus, this scenario optimizes harvest for static (non- shifting) stocks but sees a shift from optimal to open access harvest for transboundary (non-shifting) stocks. HCR for static stocks: Economically optimal fishing mortality; harvest rate depends on the total biomass that year HCR for transboundary stocks: Gradual shift from economically optimal to open access fishing mortality Full adaptation This scenario assumes that management fixes economically sub-optimal harvest rates accounting for shifts in productivity and effectively prepares for range shifts by implementing transboundary institutions. Thus, this scenario assumes adaptive, economically optimal harvest rates even as stocks shift into and out of EEZs.

HCR for static and transboundary stocks: Economically optimal fishing mortality; harvest rate depends on the total biomass that year Realistic adaptation (implemented at 5, 10, and 20-year intervals) This scenario implements a more realistic representation of the full adaptation scenario by acknowledging that management rarely acts annually. Instead, this scenario assumes that management sets an economically optimal harvest rate based on the total biomass at regular assessment intervals and maintains this rate, regardless of shifts in productivity, until the next assessment. The scenario assumes that transboundary institutions maintain this management interval as stocks shift into and out of EEZs. HCR for static and transboundary stocks: Economically optimal rate in the year of assessment is maintained until the next assessment (5, 10, or 20 years later) https://doi.org/10.1371/journal.pone.0224347.t001 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 3 / 21