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Governance challenges for tropical nations losing fish species due to climate change

Abstract

Climate change is driving fishery stocks out of their historical ranges. Along with the management challenge of species entering new jurisdictions, the exit of species from countries’ waters poses distinct threats to those resources and the economies that depend on them. We show that this risk is particularly acute in the tropics, where projected exits are highest and entries are fewest. We find that existing policy frameworks are poorly equipped for this challenge, and we suggest a way forward that draws on climate policy.

Main

Marine fisheries provide an important source of food, income and livelihoods worldwide, and contribute to many national economies. However, ocean warming is driving a redistribution of these natural resource endowments as fish stocks migrate towards cooler waters to maintain their preferred thermal environment1. Pinsky et al.2 stimulated an important discussion by showing how commercial species entering new national jurisdictions can pose governance problems by creating transboundary stocks and unregulated fisheries, as seen in the so-called ‘mackerel war’. However, the implications of permanent stock losses from a national jurisdiction are overlooked in this discussion, particularly in jurisdictions without new stocks entering to replace them. This loss is an externality of climate change that raises issues of distributional equity3,4 and threatens the economies of nations and communities in ways that cannot be adequately managed through conventional fishery laws alone.

We use previously projected changes in the distribution range of 779 commercial fish species5 (see Methods) to estimate the number of species exiting national jurisdictions under two emissions scenarios up to 2100. Tropical nations stand to lose the most species under these scenarios (Fig. 1, Supplementary Fig. 1), with few if any stocks replacing them (Supplementary Fig. 2). This finding is consistent with previous estimates of species entrants in the tropics2. Under the moderate emissions scenario Representative Concentration Pathway (RCP) 4.5, we found that, by the year 2100, the average tropical exclusive economic zone (EEZ) stands to lose 7% of species present in 2012. This value increases to 40% under a high emission scenario (RCP 8.5). Northwest African EEZs could lose the highest percentage of species. Under RCP 4.5, these EEZs are projected to lose, on average, 6% of their species by 2050 and 30% by 2100. Projected losses are much greater under RCP 8.5: 25% by 2050 and 58% by 2100 (Fig. 2). Southeast Asia, East Africa, and Central America and the Caribbean are also projected to experience steep declines in species under RCP 8.5. In the absence of policy interventions, tropical nations could lose not only an important natural resource but also the associated wealth, jobs and culture5,6. This will be particularly acute for small island nations in the tropics that depend heavily on fishing5,7.

Fig. 1: National loss of species.
figure1

a,b, The number of species shifting out of each EEZ by 2100 under RCP 4.5 (a) and RCP 8.5 (b).

Fig. 2: Impact to tropical regions.
figure2

a, The mean percentage of species shifting out of EEZs by tropical region ±1 s.d. were projected for 2025, 2050, 2075 and 2100 under RCPs 4.5 and 8.5. The number in parenthesis indicates the number of countries in the region. See Supplementary Methods for the list of countries. b, The cumulative mean trajectories for these percentages for 2012–2100 calculated at five-year intervals under RCPs 4.5 and 8.5. c, Summary of the characteristics from 127 existing international agreements in 5 of these tropical regions (see Methods). We used a list of climate terms to determine if the agreement had language relating to these climate-driven exits. These terms are described in the Methods.

Traditional fisheries management focuses on how to sustainably exploit fish populations8,9. Such policies assume that fish are a renewable natural resource, that their geographical range is static and that they will remain plentiful in the absence of overfishing. However, the long-term migration of species out of a country due to climate change presents a new paradigm in which fish stocks may not always be renewable in their historical jurisdictions, even if they remain renewable at the international scale. For the jurisdiction losing the stock, this creates an incentive to overfish before it exits10.

The basis for international fishery policy lies in the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which entitles countries to establish zones of national jurisdiction over resources (EEZs) and requires cooperation among nations to conserve living resources9. The 1995 United Nations Fish Stock Agreement (UNFSA) strengthens the framework of UNCLOS by calling for management and conservation of highly migratory stocks and stocks that straddle jurisdictions11. However, UNCLOS and UNFSA operate at a high level and do not mandate specific management mechanisms. Although UNFSA addresses the development of new fisheries, it does not consider the possibility of permanent stock exits, or how they might undermine the conditions for international cooperation.

This raises the question of whether any existing regional, multilateral and bilateral policies can adequately manage stock exits under climate change. To better understand the policy landscape in the tropics, we analysed 127 publicly available international fisheries agreements in the South Pacific, Southeast Asia, South Asia, Northwest Africa, and Central America and the Caribbean (Fig. 2e). These include bilateral and multilateral agreements (such as regional fisheries management organizations (RFMOs)). None of the 127 agreements contains language that is directly related to climate change, range shifts or stock exits (a full list of search terms is provided in the Methods). Some agreements may offer scope for adaptation12, such as RFMOs that provide for ecosystem-based management13. However, none of the fisheries agreements explicitly addresses the impacts of climate change, in particular the policy challenge of how to prevent overfishing by nations losing fish stocks.

We account for long-term climate trends until the year 2100 and do not take into account shorter-term climate variability, such as interannual or multidecadal fluctuations, which can also drive range shifts in fish species14. Although shorter-term variability poses serious challenges for management15, it is more plausibly accommodated under existing RFMO frameworks provided that stock movements are temporary. For example, the Parties to the Nauru Agreement uses a vessel-day trading scheme to manage the year-to-year spatial fluctuations in stocks among the participating states16. Although this mechanism is promising, it may be challenged by long-term range shifts, because countries facing exits would see diminishing benefits to cooperation unless otherwise compensated. Whether stocks are shifting temporarily or permanently may not be initially obvious, as variability could mask long-term changes. That uncertainty might initially forestall the feared ‘race to fish’ in some cases. However, the literature indicates that failure to recognize the impacts of long-term climate trends on stocks can lead to maladaptation and contribute to overfishing even at relatively short time scales17,18.

To restore the incentives for conservation, the country benefiting from the range shift may need to negotiate bilaterally with the country losing the stock. For example, the United States and Canada are managing the northward shift of cod, haddock and flounder by gradually changing the basis for catch allocations from historical catch to the geographical distribution of the stock19. The agreement gives the United States more than its ‘fair share’ of the stock in the short term, in the interest of preserving the stock in the long term. However, this agreement is not legally binding, and it is not clear that it would work as a model in settings with different geopolitical dynamics. A study using game theory showed that cooperation between two nations managing a stock shifting from one to the other may not happen without side payments10. Without compensation, tropical nations that are losing stocks may have little incentive to enter into such agreements, as few stocks are projected to replace the stocks that are exiting (Supplementary Fig. 2).

Compensation might also be obtainable from the international community through the Warsaw International Mechanism for Loss and Damage, developed at the Conference of the Parties (COP) 19 in 2013 and reaffirmed in Article 8 of the 2015 Paris Agreement as the primary vehicle for the United Nations to address the losses from climate change20. Although fisheries were not an explicit focus, the loss of stocks in tropical nations clearly falls within the concerns of the negotiators over slow-onset events, non-economic losses, and action and support21. However, Item 51 of the accompanying decision document states that nations will not be held liable for these damages22, drawing into question whether the mechanism has legal force. Compensation for loss and damage proved to be controversial at COP 25, in December 2019, particularly between tropical nations and developed countries. Going forwards, tropical nations should highlight the loss and damage to their fisheries not only in negotiations over the mechanism but also in implementing long-term climate finance, the Green Climate Fund and the Global Environment Facility. The exit of stocks from many national fisheries is inevitable, but carefully designed international cooperation could ease the impact on those nations while preserving the resource for others.

Methods

We examined the implications of two climate change scenarios on the spatial distribution of 779 globally representative exploited marine species stocks in the context of national boundaries. The projected spatial distributions were obtained from Gaines et al.5, and were created using a modified version of the climate velocity model described previously1. In this model, the range of each species expands or contracts—tracking its thermal niche—conditioned on thermal and depth tolerances. Details regarding the climate-velocity model and the species included in this study were described previously1,5.

Projected distributions were compared to 2012 distributions derived from AquaMaps (see ‘Data availability’) in five-year intervals from 2015 to 2100. Using this information, we determined the number of species that are projected to exit each EEZ23—that is, the total loss of range by the end of the century.

Climatic data used for the range projections were obtained from the Royal Netherlands Meteorological Institute Climate Explorer portal (http://climexp.knmi.nl). We used mean annual sea surface temperatures from multi-model mean ensembles for the IPCC RCP 4.5 and RCP 8.5 (further details are provide in the supplementary materials of ref. 5). These pathways represent two trajectories of radiative forcing from anthropogenic greenhouse emissions. They represent a mitigation scenario leading to stabilization (global temperature increase between 1.1 and 2.6 °C) and a high baseline emission scenario (global temperature increase between 2.6 and 4.8 °C), respectively.

To assess the ability of existing governance frameworks to address these climate-induced shifts, we collected data for international fisheries agreements. Our database includes bilateral and multilateral (for example, RFMOs) agreements that relate to the management and sustainability of shared fish resources. We identified relevant agreements (Supplementary Methods) and, for each agreement, we recorded basic agreement characteristics and whether or not the agreement text includes the following terms related to climate change and range shifts: climate, climate change, warming, global warming, cooling, global cooling, temperature, sea surface temperature, range shift and shift. In our analysis, we report on agreements that pertain to the tropics, which we identify as the most at-risk region for species exits (Supplementary Fig. 2). Additional details regarding our search are provided in the Supplementary Methods.

Data availability

The species distribution maps used to generate the range-shift projections that informed our analysis are publicly available at https://www.aquamaps.org/. Datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We thank D. Bradley, C. Cochran, D. Flores, S. Gaines, J. Lawson and Q. Lee for comments, suggestions and references. This work was supported in part by the David and Lucile Packard Foundation (grant number 2016-65300). J.G.M. is supported by the ‘Tenure-Track System Promotion Program’ of the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the JSPS KAKENHI, Grant Number 19H04322.

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Contributions

K.L.O. conceived the idea with input from all of the authors. J.G.M. developed the species loss analysis. J.G.M. and T.M. conducted the species loss analysis. K.L.O., C.C., J.S. and J.B. designed the agreement analysis. J.B., T.M. and A.L. conducted the agreements analysis. K.L.O. wrote the manuscript with input from all of the authors.

Corresponding author

Correspondence to Kimberly L. Oremus.

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C.C. is on the Board of Trustees for two environmental NGOs: Environmental Defense Fund and Global Fishing Watch. The other authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1 and 2, and methods.

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Oremus, K.L., Bone, J., Costello, C. et al. Governance challenges for tropical nations losing fish species due to climate change. Nat Sustain 3, 277–280 (2020). https://doi.org/10.1038/s41893-020-0476-y

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