Uncovering genetic population structure in the Endangered northern rockhopper penguin (Eudyptes moseleyi) across islands in the Southern Atlantic and Indian oceans

Background: The northern rockhopper penguin (Eudyptes moseleyi) is a threatened species, listed as Endangered globally by the IUCN owing to rapid population decreases in the past, combined with a limited distributional range. Their breeding is confined to five islands in the central South Atlantic Ocean (Gough, Nightingale, Inaccessible, Alex (= Middle), and Tristan da Cunha) and two islands in the southern Indian Ocean (Amsterdam and Saint Paul). Non-breeding birds forage widely in these oceans and vagrant individuals have been recorded in the Falkland Islands/Malvinas, South Africa, Kerguelen Archipelago, Australia, and New Zealand. The origins of these vagrant birds are largely unknown, and it remains unclear to what extent northern rockhopper penguins move between islands and oceans. Understanding connectivity between populations is essential for developing appropriate conservation strategies, especially as some populations may be at greater extinction risk than others. Results: Northern rockhopper penguins from the two oceanic basins are genetically distinct, with minimal evidence of migration between ocean basins. No substructure was detected within ocean island groups and although low, the level of migration between islands was sufficient to prevent genetic differentiation. Differential signatures of genetic diversity and inbreeding may also suggest some island populations are at higher risk of inbreeding depression. Conclusions: This study provides the first comprehensive genetic population structure analysis of the entire breeding range of the Endangered northern rockhopper penguin. This gives an unparalleled understanding of the connectivity within and between populations breeding in the Atlantic and Indian oceans, and highlights areas for further investigation. Knowledge of genetic structure and population dynamics can inform effective conservation .