Details of assessment carried out: Primary literature

Brief summary on why the use has been assessed/judged to be sustainable or unsustainable: The authors assessed that while previous egg collection regimes may have been unsustainable (particularly under the management of the European imposed Canterbury Acclimatisation Society which excluded the indigenous Ngai Tahu people), their proposed low impact harvests would be sustainable under an adaptive population model: "In this study, the effects of egg harvest on swan hatching success depended on nest-level harvest pressure and occurred primarily via direct removal of eggs and indirect, harvest-pressure- dependent impacts on post-harvest egg laying and clutch size. Specifically, harvesting one-third or two-thirds of a clutch of eggs resulted in the loss of approximately one hatchling for each egg removed, because swans tended to replace few or none of those harvested eggs, and egg hatching probability was generally high in areas unaffected by flooding (Figures 2 and 4). In contrast, harvesting an entire clutch resulted in the loss of approximately one hatchling for every two eggs removed, as swans often quickly reused empty nests to re-lay new, albeit smaller, clutches (Figures 2 and 4). Harvesting two-thirds of a clutch also impacted hatching success by reducing the probability of hatching for unharvested eggs (Figure 2b). Confidence limits around estimates for eggs within such nests were large, likely due to small sample size coupled with high variability in egg hatching probability among nests. However, the reduced hatching probability of eggs within nests that had two-thirds of eggs removed reflects the tendency of some swans to abandon nests following the removal of most, but not all, eggs. Taken together, these results clearly indicate that nest-level harvest impacts are not additive, and there is potential to adapt egg harvests to limit population-level impacts."

Details of assessment carried out: Primary literature

Brief summary on why the use has been assessed/judged to be sustainable or unsustainable: The study outlines the cultural value of egg collection of the Ngai Tahu people, improving connection with the natural world and incentivising engagement with conservation programmes: "Customary harvest can be an important way for resource users to connect with their traditional lands, ancestors, cultural identity and family and community members through sharing of resources (Lemelin et al., 2010; Lyver et al., 2009; Wilson, 2003). Maintaining those connections for future generations to use is a key motivation among IPLC for conserving wildlife and their habitat (Lyver, Ruru, et al., 2019). Likewise, restrictions on customary har- vest can undermine IPLC motivation to take part in conservation (Lyver & Tylianakis, 2017; Tyrrell, 2008)." The authors also assert that through sustainable harvest of black swan eggs, Ngai Tahu harvesters can collect valuable data on clutch size, habitat suitability and anthropogenic pressure through pollution and climate change. "Engaging more people in place-based resource management, such as customary harvests, also increases the number and detection resolution (both spatially and temporally) of ecological feedbacks (e.g. wildlife population numbers, habitat conditions), which can in- form adaptive responses to environmental change (Berkes, 2009; Cumming et al., 2017; Herse et al., 2020; Thompson et al., 2020). For instance, current management of swans by FGNZ is based on annual, regional-scale trends in adult abundance and/or harvest rates, which could obscure local ecological drivers of populations (Herse et al., 2020; Weinbaum et al., 2013). Importantly, Māori who regularly engage with swans and their habitat through sustainable customary egg harvests could continuously monitor local variability in swan numbers, nesting productivity, habitat conditions and non-harvest pressures (e.g. nest predation, flooding)."