Effects of customary egg harvest regimes on hatching success of a culturally important waterfowl species.
1. Customary harvests of wildlife underpin the livelihoods, cultural identities, well-being and ecological knowledge of many Indigenous peoples and local communities (IPLC), whereas government restrictions on harvests can erode these relationships. Supporting IPLC in place-based resource management, including sustainable customary harvests, can aid wildlife, their habitat and the cultures that value them. 2. Using an experiment jointly initiated by the Māori tribe Ngāi Tahu and researchers (Māori and non-Māori) in Aotearoa/New Zealand, we identified low-impact strategies for harvesting black swan (kakī anau, Cygnus atratus) eggs at an important coastal lagoon, Te Waihora/Lake Ellesmere. The experiment tested whether nest-level hatching success (number of eggs hatched) depended on nest-level harvest pressure; whether this effect was additive; and the extent to which harvest influenced post-harvest egg laying and hatching probability, relative to several control variables. 3. Nest-level harvest pressure determined nest-level hatching success and had a non-additive effect on population-level hatching success. Specifically, harvesting one-third or two-thirds of a clutch caused a loss of approximately one hatchling per egg removed, because swans tended to replace few of those harvested eggs and hatching probability of unharvested eggs was generally high (but lower in nests with two-thirds of eggs removed). Conversely, harvesting an entire clutch caused a loss of approximately one hatchling for every two eggs removed, because swans often subsequently re-laid new, albeit smaller, clutches. 4. During fixed-output harvests, removing entire clutches early during nesting could induce re-laying and prevent abandonment of unharvested eggs. Moreover, harvesting from areas of nesting colonies with low nest density, where hatching probability of unharvested eggs was lowest, could limit disturbance. Finally, restoring foraging habitat in degraded wetlands surrounding nutrient-overloaded waterbodies could offset eutrophication effects by providing plant resources that swans require to lay eggs indeterminately. 5. In addition to improving IPLC well-being, implementing strategies such as these could enhance place-based resource management by supporting IPLC engagement with nature, which increases the number and detection resolution of ecological feedbacks (e.g. population numbers, habitat conditions) and resilience to environmental change. Moreover, customary harvest could be a practical, culturally appropriate and less wasteful alternative to non-consumptive culling for mitigating human-wildlife conflict (e.g. waterfowl grazing on pasture).