Historically, their colonies were an important source of guano, the rich natural fertiliser formed from seabird excrement in arid areas. Throughout most of the 20th century, people were stationed on the gannets’ breeding islands to protect the birds and their precious guano, which was scraped up after each breeding season. As a result, we have a good record of how gannet numbers have changed since the first census was conducted in the mid-1950s.
Over this period, Cape Gannets have bred at only six islands: Mercury, Ichaboe and Possession off southern Namibia, and Lambert’s Bay, Malgas, and Algoa Bay’s Bird Island off southern Africa. In the 1950s, there were some 260 000 pairs of Cape Gannets, 80 per cent of which bred in Namibia. Today there are barely 130 000 pairs, 95 per cent of which breed in South Africa. As a result, the species is listed as globally Endangered and as Critically Endangered in Namibia.
The dramatic decline of the Namibian colonies resulted from the collapse of that country’s sardine population due to overfishing in the 1960s and 1970s. Dwindling fish stocks off the South African west coast over the past two decades have seen gannet numbers decreasing at both Lambert’s Bay and Malgas Island, and the colony on Bird Island in Algoa Bay now supports almost three-quarters of all Cape Gannets in the world. This is the only stable population – all five colonies off the west coast continue to decrease.
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