Understanding Population Sustainability and Safe Consumption Limits to Inform Cultural Harvest of Tuna Within Nelson Lakes National Park

Customary harvest plays a vital role in expressing Māori identity, maintaining relationships with place and whakapapa, and transmitting mātauranga across generations. However, re‐engaging with traditional practices can be constrained by ecological risks and regulatory frameworks, particularly in protected areas. This study presents an integrated ecological and toxicological assessment of the customary longfin tuna ( Anguilla dieffenbachii ) harvest by Ngāti Apa ki te Rā Tō at Rotoroa, Nelson Lakes National Park. A dual knowledge approach combining mātauranga Māori and biophysical science was used to evaluate sustainability and food safety. From 2022 to 2024, annual harvests were paired with tuna monitoring and biological sampling. Otolith analysis revealed a mature slow‐growing population, and production modelling indicated that harvest levels (∼2–3% of annual cohort biomass production) were within conservative ecological limits. Mercury concentrations in muscle tissue averaged 0.31 mg·kg −1 (wet weight), with estimated dietary exposure from a single meal approaching short‐term health guidelines. Mercury levels were inversely correlated with condition factor, suggesting that the selective harvest of healthier individuals may reduce contaminant risk. These findings demonstrate that tikanga‐aligned harvest, supported by scientific assessment, can enable safe, sustainable customary use within conservation settings and offer a transferable model for iwi‐led freshwater management.