Year-round GLS tracking of Northern Buller’s Albatross and comparison with Southern Buller’s Albatross

Fisheries risk assessments for seabird bycatch rely on accurate, year-round, and up-todate information on seabird distribution. Such information exists for virtually all albatross species that breed in Aotearoa, but not for Northern Buller’s Albatross. Addressing this data gap will improve the accuracy of estimates of bycatch risk for both Northern and Southern Buller’s Albatross in domestic Aotearoa/New Zealand and international fisheries. We deployed GLS tags on Northern Buller’s Albatross on the privately-owned Motuhara (the Forty-fours) during 2021-22 and Southern Buller’s Albatross on Tini Heke (The Snares), which ultimately resulted in 69 and 28 year-round datasets, respectively. We used these data to assess each taxon’s breeding phenology, generate population-level utilization distributions, quantify spatiotemporal overlap between taxa, and document geopolitical responsibilities for each taxon. Our results highlighted considerable spatiotemporal segregation between the two taxa. Average breeding phenology of Southern Buller’s Albatross was delayed by four months in comparison to Northern Buller’s Albatross. During the breeding period, Northern Buller’s Albatross core range was centred around the Chatham Rise, whereas the Southern Buller’s Albatross core range was centred around the south of te Waipounamu (South Island). The taxa only co-occurred in space and time during July-September off the coast of South America. Despite this spatiotemporal segregation, geopolitical responsibilities for both species were similar. Both species spent most their time in Aotearoa waters, the high seas, Chilean, and Peruvian waters. However, Southern Buller’s Albatross also spent considerable amounts of time in Australian waters. Our analyses of GLS tracking data fills a major knowledge gap and suggests that the generated information on spatiotemporal segregation of Northern and Southern Buller’s Albatross should be accounted for in future national and international fisheries risk assessments. In addition, we recommend that the information provided here is used in future integrative taxonomic assessments aimed to resolve the status of both taxa.