Breeding Population Survey of Adélie Penguins along the Northern Victoria Land Coast, Ross Sea, Antarctica

This report presents the results of aerial surveys of Adélie penguin breeding colonies along the Northern Victoria Land coast conducted from 2021 to 2024, supporting the evaluation of the Ross Sea region Marine Protected Area (RSRMPA) under CCAMLR Conservation Measure 91-05. As a key indicator species, Adélie penguins play a central role in assessing the effectiveness of spatial protection measures within the General Protection Zone (GPZ). The total number of breeding pairs across 12 colonies increased by 3.9% compared to the baseline, although substantial variation was observed among sites. According to the SMART criteria—which define a 30% decline from the baseline as the threshold for significant change—the combined number of breeding pairs at the surveyed sites remained above this threshold. Cape Hallett exhibited a long-term decline in breeding pair numbers from the 2017/18 to 2023/24 breeding seasons, with partial recovery in 2024/25. Breeding success increased until 2022/23, followed by a decline in 2023/24. In contrast, Inexpressible Island maintained stable numbers of breeding pairs and consistent breeding performance during the same period. This study addresses key data gaps in the assessment of Adélie penguin population dynamics and contributes to the scientific basis for the upcoming 10-year review of the RSRMPA.