|Avian Demography Unit
Department of Statistical Sciences
University of Cape Town
Bank Cormorant Phalacrocorax neglectus
The Bank Cormorant is endemic to South Africa and Namibia. Its conservation status is "Vulnerable", because of its small population size, which is decreasing, and because most of these birds are concentrated at a small number of breeding sites.
The overall distribution of the Bank Cormorant coincides broadly with the distribution of kelp Ecklonia maxima; its main feeding habitat is the sea bottom among kelp beds. It seldom occurs more than 10 km offshore.
Since the 1970s, breeding has been recorded at 52 localities, between Hollamsbird Island, which lies about halfway between Luderitz and Walvis Bay in Namibia, and Quoin Rock, which lies just west of Cape Agulhas, in the Western Cape, South Africa. Two surveys of the population size of the Bank Cormorant have been made, the first between 1978 and 1980 and the second between 1995 and 1997. The estimated number of nest sites at 44 localities occupied between 1995 and 1997 was 4888; the other seven localities where breeding had been recorded earlier were unoccupied. During the latter survey, 75% of the breeding population was in Namibia, and 75% of the population was concentrated at just five sites which had more than a hundred nests each:
The comparable figure for the total population for the earlier survey period 1978-1980 was 8672 active nest sites; the decrease over the period of 17 years between the two surveys was 45%.
Four colonies were deserted completely between the 1978-80 and 1995-97 surveys. At 25 out of 44 colonies which were surveyed in both surveys the number of nests had decreased by more than 25%. The most important causes of desertion of colonies and decreases at colonies appear to be human disturbance and shortage of food. At breeding colonies at which Kelp Gulls are present, the gulls rob nests of eggs and small chicks if the adults are disturbed off them. Another factor implicated in the decrease is competition for breeding space with increasing populations of Cape Fur Seals; seals occur at about 20 Bank Cormorant colonies, and breeding space for the cormorants is severely restricted by seals at several of these.
Two new colonies formed between the two surveys. Birds colonized the breakwater of the small harbour at the Koeberg Nuclear Power Station, which was constructed in the 1980s. Access by people to this colony is, by the nature of the place, minimal. The new colony at Stony Point, Bettys Bay, was discovered in October 1987, within a a few months of the African Penguin colony being fenced off in July of the same year. Both new colonies are characterized by the near-elimination of human disturbance.
The main food of the Bank Cormorant in Namibian colonies is the Bearded Goby Sufflogobius bibarbatus. This species is not targeted by the commercial fishery. In spite of this, stocks of Bearded Goby collapsed in central Namibia in 1994, at the time of a severe Benguela El Nino event, and the fish has not subsequently recovered. Large decreases in numbers of Bank Cormorants breeding at Ichaboe Island and Mercury Island commenced during this period. The rate of decrease on these two islands is consistent with the mortality rate of adults, and might suggest that no young birds are being recruited to these colonies. Thus it seems that adults are obtaining enough alternative food to survive, but that a combination of low breeding success and poor survival of young birds are leading to a lack of recruitment into the adult population.
Some colonies are particularly vulnerable to oil pollution. The population on the breakwater at Robben Island was reduced by about a quarter during the Treasure oil spill of June 2000. Unlike penguins, oiled cormorants are extremely difficult to catch and clean. Thus the best way to prevent mortality of cormorants during oil spills is to prevent the oil spills themselves.
Actions to improve the conservation status of the Bank Cormorant include the reduction or elimination of disturbance at breeding sites, and the prevention of displacement by fur seals.