Populations of rockhopper penguins, elephant seals, and grey-headed albatrosses in the subantarctic have declined quite markedly in recent decades.
NIWA seabird ecologist Dr David Thompson describes how scientists have narrowed down the possible causes for one species: the rockhopper penguin. Using stable isotope analyses, they've identified a decline in ocean productivity as the most likely factor, although the underlying causes of this remain unknown. (7:19)