The distribution an breeding success of seabirds on and around ascension in the Tropical Atlantic Ocean

Ascension was once one of the greatest seabird colonies in the world, comparable to the largest in the Pacific and Indian Oceans, the only one in the apparently barren centre of the tropical South Atlantic. The birds have been reduced by introduced rats and cats over the last three centuries, but early accounts, guano and bones suggest there were once more, most breeding in the north of the island. Observations from the shore and at sea indicate that while some seabirds may feed offshore and in an area of marine turbulence in the lee of the island to the west, many fly north towards the Equatorial Counter-current, where there are many more birds and cetaceans than to the south. Periodically there is increased rainfall which may be accompanied by seabird breeding failures, as in 1876, 1924, 1958-59, 1963, 1991-92 and 1997, possibly associated with fluctuations in the counter-current, similar to, but not always simultaneous with, El Niño-Southern Oscillation (ENSO) events elsewhere. There is a need for world-wide monitoring and attention to the implications of these fluctuations.