 This ratio also holds for the most abundant species, eleven of the sixteen species being tropical.On the other hand, over 70% of tropical species occur in extremely low numbers, so low in fact that they are thought not to maintain breeding populations at the Abrolhos; rather, populations are maintained by larvae carried to the islands by the Leeuwin Current from populations further north.The Houtman Abrolhos maintains a breeding population of Australian sea lions ("Neophoca cinerea"), probably numbering between 75 and 100.