The Ocean Equity Index is flawed, misleading, and lacks validation 

Arising from:

Blythe, J.L., Claudet, J., Gill, D. et al. The Ocean Equity Index. Nature 650, 123–128 (2026). https://doi.org/10.1038/s41586-025-09976-y

First, as the authors acknowledge, the OEI “does not assess the outcomes of an initiative, or its efficacy”. Its assessments are based predominantly on the design of the initiative, i.e. presence of various “processes” and “mechanisms”, not its performance in advancing social equity among impacted communities. The authors assert that it measures “status and progress” towards equity with an unsubstantiated claim that “when an OEI score is high, the likelihood of achieving positive outcomes for both people and nature increases”. The authors provide no details that back up their claims that the selected criteria in the OEI will generate equitable outcomes, and fail to consider the role of institutional power, which is fundamental to both the cause and perpetuation of inequities.

For instance, the authors assume that plans to identify and implement human rights and Indigenous rights policies will contribute to ocean equity. However, if these rights are to be implemented under the institutional arrangements (e.g., states) that have been complicit in perpetrating environmental and social harms in the past, then legal guarantees, recognition and inclusion offered may constitute perpetuation of the existing subjugative relationships³. This indifference to power and histories is also reflected in the OEI via its calls for the inclusion of “all relevant actors”, including “private sectors” and “non-human actors”, without explicit acknowledgement that these actors are historically shaped by racialized perspectives and legacies of colonial exploitation^4,5.

Second, the authors argue that the three foundational domains of the OEI (recognitional, procedural and distributional equity) are “interrelated”. Yet, by structuring the OEI as a weighted sum composite index, the authors inherit the assumption of this mathematical model, including that the components are independent⁶—a score in the recognitional domain, for example, does not interfere with scoring in the distributional domain. Scholars of environmental justice have long emphasized the interdependence of the three domains⁷; just distribution requires full recognition of diverse communities as a precondition, while just procedure demands recognition of the historical contexts of communities, such as coloniality^8,9. By assessing each criterion separately, the OEI disregards such interdependence and allows for superficial actions such as benefit-sharing mechanisms that may not recognize the most marginalized people, to be potentially scored high. In their Supplementary Materials, the authors note that “convergence or trade-offs between criteria be explored in the OEI assessment” but fail to articulate how that would be reflected in the quantitative OEI scores which cannot reflect these dynamics.

Moreover, as a composite index, the OEI assumes compensatory relationships among its twelve criteria—that a low score in one criterion can be offset by a high score in another. The framework treats human rights as equivalent in importance to factors such as communication (e.g., transparency) when assessing status and progress comparatively via aggregated OEI scores as they do in their Figure 3. However, by definition, human rights and Indigenous rights are fundamental; allowing them to be substituted by other criteria raises both ethical and technical questions about how the model functions and how the composite score is constructed.

Third, the OEI requires that a single score is assigned to each criterion based on assessors’ “perceptions and judgement”. Thus, assessors of the OEI can choose a score that best fulfills their interest, such as proponents emphasizing positive efforts over potential adverse outcomes. While the authors identify this as a limitation, we argue that this is a fundamental flaw of the framework because such “subjectivity and potential bias” is not introduced unintentionally but rather is embedded in the scoring process itself. The authors offer Kendall’s coefficient as a way of measuring variability among assessors but fail to articulate how this should be interpreted in assessing subjectivity and biases. In the case of Canada’s ecosystem-based management framework, Kendall’s coefficient found strong agreement in scores among the assessors, but this concordance should not be interpreted as the scores being less biased; rather, this should be interpreted as the result of two of the three assessors being the authors of this framework¹⁰.

The fundamental flaws of the OEI as explained above are clear when examined closely in case studies. Canada’s ecosystem-based management framework case demonstrates a failure to account for the interlink between procedural and recognition dimensions. It scores high on human rights and Indigenous rights, yet a recent study revealed a fundamental lack of capacity to consider the cultural values of First Nations, which underpin those rights¹¹. In the case of blue carbon projects in Mexico, the assessor awarded full points for Inclusion and Influence based on the ejido governance structure, despite its history of marginalizing women¹². Such scoring is a structural consequence of the OEI’s failure to account for equity outcomes. The Danish EIA framework case study illustrates the ethical concern resulting from the aggregated OEI score; this case had the highest mark (78%) despite its failure to consider human and Indigenous rights protection with no mechanism for accountability. In the case of the fish-drying project in Tanzania, the assessors represent Beach Management Units as a local, community-based organization, scoring full marks for Institution and for Inclusion and Influence; however, the legitimacy of this institution as representing community interests has been previously criticized¹³. This is a clear example of the subjectivity and bias in the OEI’s scoring framework.

In their conclusion, the authors acknowledge several caveats and limitations of the OEI, including bias, subjectivity, scope, and trade-offs. However, these acknowledgments function more as disclaimers than as safeguards. Given the stakes involved, it is irresponsible to present a model that carries such significant risks of misrepresentation and misleading conclusions. Justice and equity are among the few principles that we must never compromise on and that remain central to decision-making for safeguarding human dignity and respect. We are concerned that the authors gravely undervalue the implications of the fundamental flaws in their equity index, treating “measuring ocean equity” as a performative exercise rather than an act with real human consequences. Thus, rejecting the OEI is, in our opinion, critical if scholars, activists, and others are to align their stated values with praxis.

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Author affiliations:

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Author Contributions:

All authors contributed to the original conception of this critique. Y.O. took the lead in writing the manuscript in consultation with C.S., G.S. and W.S. All authors provided critical feedback and helped shape the manuscript. 

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Competing Interests:

The authors declare that they have no competing financial or non-financial interests as defined by Nature Portfolio. 

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Correspondence and requests for materials should be addressed to Yoshitaka Ota (yoshitaka.ota@uri.edu)

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References

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