Latent vulnerability of the blue shark (Prionace glauca) in the South Atlantic: Biological constraints, conservation status, and governance challenges

Conservation assessments of highly migratory marine predators are frequently challenged by the coexistence of apparently stable stock indicators with persistent biological, demographic, and governance uncertainty. Under these conditions, conventional stock status may not fully capture processes that influence long-term conservation vulnerability. Here, we evaluate the South Atlantic blue shark (Prionace glauca) using a structured, semi-quantitative, multi-domain evidence-integration framework designed to assess whether independent evidence streams converge towards a condition of latent vulnerability. The framework synthesized biological, demographic, stock-assessment, conservation, exploitation, trade, and governance evidence using predefined indicators, ordinal contribution scores, confidence scores, robustness analyses, and structured cross-domain integration. The biology domain showed the lowest contribution to latent vulnerability, reflecting the comparatively higher intrinsic productivity of blue sharks relative to many pelagic sharks. In contrast, exploitation, trade, and removal observability produced the strongest signal, followed by conservation, demography, governance, and stock-assessment domains. Across domains, the evidence consistently indicated strong dependence on juvenile survival, sustained industrial exploitation, incomplete observability of removals, and important conditionality associated with stock assessment and governance systems, despite generally favourable biomass estimates in recent ICCAT assessments. Confidence-weighted and unweighted syntheses produced highly consistent results, supporting the robustness of the overall interpretation. Rather than contradicting existing stock assessments, the proposed framework provides a complementary weight-of-evidence perspective indicating that apparently stable stock conditions may coexist with demographic sensitivity, limited observability, and uneven governance capacity. These findings highlight the value of integrating multiple independent evidence streams when evaluating conservation vulnerability in highly exploited migratory marine species under uncertainty.