Unbounding fish: Assessing vulnerability to overexploitation for transboundary fish populations

Abstract

SummeryGlobally coastal fisheries are managed according to political jurisdictions of nations and their provinces. This practice often results in multiple states/provinces managing a single genetically distinct fish population autonomously and without coordination. In multi-species, decentralized and data poor fisheries such management lead to poor assessment and eventually overharvest of fish. To assess overexploitation risk for such interjurisdictional populations, we propose a risk indicator IRIIS which incorporates 1) species-specific vulnerability 2) distribution of genetically-distinct populations with respect to jurisdictional boundaries and 3) differences in management practices across jurisdictions. As a case study we evaluated overexploitation risk for individual populations of nine commonly caught fish species spanning across multiple jurisdictions along Indias west coast. Our results indicate that interjurisdictional differences in management alters innate biological susceptibility. IRIIS is also sensitive to population-level differences and policy changes. Our analyses emphasize the need for population-level assessments and interjurisdictional cooperation to achieve sustainable fisheries. Science and society statementCoastal fisheries worldwide are managed through politically defined maritime jurisdictions, while fish populations are structured by biological processes such as dispersal, ocean currents, and natural barriers. This fundamental mismatch between biological population boundaries and jurisdictional management boundaries often results in the same population being exploited under multiple, uncoordinated governance regimes. In the context of the global overfishing crisis, such governance fragmentation can lead to inaccurate stock assessments and heightened risk of local population collapse. This challenge is particularly acute in developing and tropical countries, where fisheries are multispecies, data-limited, and increasingly decentralized to support community-based governance. While decentralization promotes social justice, it can inadvertently intensify the misalignment between biological and administrative boundaries, complicating sustainable management. In this manuscript, we introduce a robust framework -- the Integrative Risk Indicator for Interjurisdictional Stocks (IRIIS) -- which has a high applicability for multispecies, data-poor, and decentralized fisheries. Building on, and extending beyond, species-level Productivity Susceptibility Analysis (PSA), IRIIS integrates population genomics to delineate biologically meaningful population boundaries and combines these with fisheries policies and regulations across jurisdictions to quantify management-associated risks of overexploitation at the population level. We apply IRIIS to case studies of nine commercially important fish species harvested along the west coast of India. Our results demonstrate that the framework can (i) distinguish differential vulnerability among populations of the same species, (ii) explicitly capture management disparities across jurisdictions exploiting shared populations, and (iii) detect sensitivity to temporal changes in fisheries policies. By linking genomics, governance, and risk assessment, IRIIS provides a practical framework for identifying interjurisdictional management gaps and actionable entry points for policy coordination. This approach is particularly relevant for the Global South, where reconciling social equity objectives with ecological sustainability is both essential and challenging.