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

adaptation, and “realistic” adaptation (see Tables 1 and 2 for details). Productivity shift adaptations improve fisheries management by implementing a dynamic, economically- optimal harvest policy given current biological conditions, which optimally adjusts harvest mortality based on the total biomass that year, and is therefore naturally adaptive to climate- driven productivity changes. Range shift adaptations assume that transboundary coopera- tion results in the maintenance of management, rather than the degradation of management to open access, as stocks shift across boundaries. Business-as-usual management fails to implement either adaptation: it maintains current harvest rates for species that do not shift spatially, while management degrades to open access for stocks that shift across boundaries. Full adaptation assumes that both challenges are addressed: the dynamic economically-opti- mal harvest policy is implemented and maintained even as stocks shift across boundaries. Realistic adaptation refines the full adaptation scenario by implementing productivity shift adaptations at plausible management intervals: it determines the economically-optimal har- vest rates on 5, 10, or 20-year intervals and maintains these rates until the next management intervention. The economically-optimal harvest rate was implemented without error; thus, scenarios implementing this policy represent the best case for fisheries assessment and man- agement performance. In each scenario, all countries operate under the same management

paradigm (e.g., they all implement business-as-usual management or they all implement realistic adaptive management; they never implement a mixture of management paradigms). Although we acknowledge that successful implementation of the required optimal fishery reforms is ultimately dependent on a country’s scientific, management, and enforcement capacities, this was a necessary simplification given our goal of modeling the impact of trans- boundary cooperation that either maintains or fails to maintain management as stocks shift across boundaries. Profits were calculated as revenues minus costs where (1) revenues were calculated as catch multiplied by species-specific ex-vessel prices [35] and (2) costs represent the costs of fishing, which were derived for each species-stock, and were assumed to increase exponentially with Table 2. Harvest control rules used in the management scenarios�. Harvest control rule (HCR) Current fishing mortality This HCR continues the initial fishing mortality rate (i.e., F in 2012) through all years. Economically optimal fishing mortality This HCR achieves maximum net present value (NPV) over an infinite time horizon under the current climate and biological conditions. Each stock has its own optimized harvest policy where fishing mortality rate is a function of biomass. This HCR is determined using a dynamic optimization routine for each stock. Gradual shift from current to open access fishing mortality This HCR is only relevant to transboundary stocks. For these stocks, fishing mortality begins at the initial fishing

mortality rate (i.e., F in 2012), then changes at a constant rate towards open access fishing mortality (i.e., fishing mortality that achieves open access equilibrium at 30% of BMSY), which is reached in the year in which the first spatial shift into or completely out of an EEZ occurs. Fishing mortality remains at the open access rate for all subsequent years. Gradual shift from economically optimal to open access fishing mortality This HCR is only relevant to transboundary stocks. For these stocks, fishing mortality begins at the economically optimal level given biomass in 2012, then changes at a constant rate towards open access fishing mortality (i.e., fishing mortality that achieves open access equilibrium at 30% of BMSY), which is reached in the year in which the first spatial shift into or completely out of an EEZ occurs. Fishing mortality remains at the open access rate for all subsequent years. � See the Gaines et al. [19] supplementary information for more details on the management scenarios and harvest control rules. https://doi.org/10.1371/journal.pone.0224347.t002 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 5 / 21