A recent study of the northern rockhopper penguin population (published in 2009), has shown that well over one million birds have been lost from the breeding colonies on the islands of Tristan da Cunha and Gough. While this equates to declines of over 90 percent on both islands, on Gough this loss has occurred in just 45 years, whereas on the main island of Tristan, it has taken almost three times longer. The reasons for the swift decline on Gough are currently unknown, but the penguin may be suffering increased levels of predation, as well as competition for food, from the rapidly rising population of Subantarctic Fur Seals Arctocephalus tropicalis
(5). Other factors may include increasing disturbance and pollution, introduced predators, reduced food supplies due to overfishing, and climate change (4).