Cryptic population decrease due to invasive species predation in a long‐lived seabird supports need for eradication

Invasive species are one of the greatest drivers biodiversity loss worldwide, and eradication invasive from islands is a highly efficient management strategy. Because operations require large financial investments, uncertainty over magnitude impacts both their removal can impede willingness decision makers to invest in eradication. Such prevalent for long-lived that display an inherent lag between life stages affected by those used population status assessments. Albatrosses amongst longest-living bird threatened on land at sea industrial fisheries. As many seabird species, usually only segment (breeding adults) assessments, making it difficult assess albatross trends potential benefit conservation action, such as predatory species. We monitoring mark-recapture data estimate past trajectory critically endangered Tristan Diomedea dabbenena accounting unobservable birds integrated model. then projected future albatrosses scenarios with or without predation house mice Mus musculus main breeding site, Gough Island. The adult remained stable 2004 2021, but success was low (31%) our model indicated total (including immature birds) decreased median 9,795 7,752 birds. Eradicating leading two-fold increase would result 1.8–7.6 times higher 2050 (median 10,352 individuals) than this intervention. Low reproductive output may lead cryptic decrease, which be obscured readily available counts pairs changes structure. Mouse necessary halt ongoing decrease albatross, even if not yet apparent size.