Text and photographs by Michelle du Toit
Animal Demography Unit
The Bank Cormorant is endemic to southern Africa, breeding from Hollamsbird Island, Namibia to Quoin Rock, South Africa. The non-breeding range extends further north from Hoanibmond in northern Namibia to Die Walle in the Western Cape, South Africa. They seldom range farther than 10 km offshore; their distribution roughly matches that of kelp Ecklonia maxima beds. Band recoveries show that fledglings disperse up to 459 km and adults up to 150 km from their breeding colonies.
Nests are constructed from seaweed and guano and are built in close proximity to the sea on offshore islands, raised rocks, harbour walls, jetties and guano platforms. They prey on various fish, crustaceans and cephalopods, feeding mainly amongst kelp beds where they catch Cape Rock Lobster Jasus lalandii, with Pelagic Goby Sufflogobius bibarbatus taken in mid-water.
Bank Cormorants on Ichaboe Island, Namibia
The global population numbered some 8 672 breeding pairs in 1978-80, but by 1995-1997 this number had nearly halved to 4 888 pairs. The greatest losses during this period occurred at Mercury and Ichaboe Islands in Namibia, which together supported 71% of the global population in 1980. Bank Cormorants no longer occur at eight former breeding sites. Overall, the Bank Cormorant population declined by 60% in the three most recent generations. These declines are mainly attributed to scarcity of prey. Therefore, commercial exploitation of Pelagic Goby will result in further declines in the populations at Mercury and Ichaboe Islands. A decline in Rock Lobster numbers in the southern part of their range could further impact on the species.
Eggs and chicks are taken by Kelp Gulls and Great White Pelicans, and human disturbance exacerbates this predation; this resulted in the loss of four colonies (including Bird Island in Lambert's Bay) and reductions in the populations at six others between 1978 and 1997. In addition, Kelp Gull predation may have increased in areas where gull numbers have grown through human provision of additional food. Cape Fur Seals prey on both adult and fledgling Bank Cormorants, and compete with the birds for breeding space. Between 1978 and 1997, 1 824 pairs of Bank Cormorants were displaced from Mercury Island by seals, and seals occur at a further 16 localities where they breed. The birds sometimes drown in Rock Lobster traps, and nests are often lost to rough seas. Oiling poses a considerable threat to this vulnerable species; during the Treasure oil spill in 2000, 25% of the population at Robben Island was lost. Bank Cormorants on offshore rocks may also be susceptible to disturbance by recreational fishers.
Bank Cormorant chick