African Penguin population trends in the Western Cape 1992-2003
Trends in the number of breeding pairs of African Penguins at 12 colonies in the Western Cape are discussed for the period of 1992 to 2003. The data come from counts made close to the peak of the breeding season each year. Of the 144 possible counts, 15 were not made. These missing values were filled in by linear interpolation between actual counts. The rate of increase was estimated using exponential growth. Comparisons were made with counts from 1956 and 1979. Over the 12-year period, the breeding population of the African Penguin in the Western Cape increased by an average of 7.4%per year. This increase was not uniform, as the population was stable from 1992 to 1997, followed by a marked increase of 12.4% per year thereafter.
Penguin breeding localities in the Western Cape
Within the Western Cape, penguin numbers at the two easternmost (Dyer and Geyser islands) and three northernmost (Lambert's Bay, Malgas and Marcus islands) colonies decreased, while the population more than doubled over the period at five colonies, including the two largest (Dassen and Robben Islands). The most significant development between 1978 and 1992-2003 was the establishment of three colonies that did not exist earlier in the 20th century: Stony Point, the Boulders and Robben Island, which now supports the third largest colony for the species.
During the period reviewed, there were two major oil spills off the Western Cape, at the peak of the penguins' winter breeding season. The Apollo Sea spill of June 1994 oiled 10 000 penguins of which 5 000 were cleaned and released; the Treasure spill of June 2000 oiled 19 000 penguins of which 16 000 were cleaned and released. The cleaning and rehabilitation of these birds was enabled by the dedicated work done by the Southern African Foundation for the Conservation of Coastal Birds (SANCCOB) and volunteers. In 2000, an additional 19 000 penguins were relocated 800 km to the east to prevent their becoming oiled.
The 12 localities discussed also support significant proportions of the breeding populations of other species of seabirds and shorebirds that face similar threats to the African Penguin.
Bird Island, Lambert's Bay
Historically, African Penguins dominated the island (breeding Cape Gannets were absent until about 1912), with 250 pairs in 1956. By 1979 there were only 50 pairs, and by the early 1990s only half this number. During the period 1992-2003, the population fluctuated between 9 and 27 pairs, with a rate of decline of 6.5% per year.
Penguin population trends, Bird Island, Lambert's Bay
Disturbance to breeding birds by visitors is at a minimum since the erection of a high-tech viewing facility in 1998, but the birds are vulnerable to predators such as dogs, cats, rats and mongooses that gain access via the causeway. Predation by Cape Fur Seals on penguins is thought unsustainable; seals are also hauling out and breeding in increasing numbers on this island, threatening to outcompete and displace birds.
The problems of predation, competition with commercial fisheries for Anchovy and Sardine, and the threat of oil pollution, need to be addressed in order to conserve this penguin population. The island is earmarked as a potential release site for "orphan" penguin chicks raised at SANCCOB, and surplus zoo fledglings, but the problems of predation by seals and terrestrial predators need first to be solved.
In 1956, there were 2 500 pairs of penguins breeding on the island, but by 1979 this number had decreased to 1 022 pairs. In the early 1990s, just fewer than 100 pairs were found to breed, and a moderate decrease of 5.4% per year took place from 1992-2003. Despite the population being markedly smaller than a few decades ago, it has been stable since 1997.
Penguin population trends, Malgas Island
Historical human impact on seabird nesting areas started with the removal of the guano cap in 1845. Guano is no longer harvested from South African islands. Low retaining walls, paths and several buildings on the eastern side of the island remain. The island is manned by officials of South African National Parks, who guard the island and its resources against poaching.
Predation by Cape Fur Seals of seabirds, notably Cape Gannet fledglings, at Malgas Island is cause for concern, especially in the light of the increasing seal population. African Penguins are particularly vulnerable to oiling at this island, which lies along shipping routes into Saldanha Bay.
In 1956, there were 4 750 pairs of penguins nesting on Marcus Island. By 1979 there was only a quarter as many. Between 1992 and 2003, numbers fluctuated, averaging 109 pairs. The population currently has a moderate decrease of 5% per year.
Penguin population trends, Marcus Island
Terrestrial predators that gain access to the island via the causeway take eggs, chicks and even adult birds. The unpredictable threat of chronic crude oil pollution is of concern for this population due to its proximity to major shipping routes and the Saldanha Bay harbour.
There were 7 500 breeding pairs of penguins on Jutten Island in 1956, and 2 878 in 1979. Between 1992 and 2003, the population remained fairly stable, averaging 933 pairs. A moderate increase of 0.9% per year occurred during this time.
Penguin population trends, Jutten Island
The vegetation has been considerably changed by European Rabbits but this has not affected breeding seabirds. The increase in the penguin population at Jutten Island may be attributable to the recovery of South Africa's Sardine stock.
In 1956, the interior of Vondeling Island housed 300 pairs of penguins. In 1979, the island held 495 pairs. Between 1992 and 2003, the breeding colony more than quadrupled, with a growth rate of 15.1% per year, and is currently at over 600 pairs.
Penguin population trends, Vondeling Island
The rapid increase in the population is attributed to the recovery of the South African Sardine stock, as well as immigration of penguins, possibly from Dyer Island. However, the expanding seal population is resulting in an increase in competition for space.
Dassen Island was home to over a million penguins at the start of the 20th century. In 1956 there were 72 500 pairs, 79% of the breeding population in the Western Cape, but by 1979 only 12 646 pairs were nesting. However, the population decline has been reversed, with the population increasing to 22 883 nests by 2002, with an annual increase of 10.9% per year between 1992 and 2003.
Penguin population trends, Dassen Island
Egg exploitation, the disturbance and habitat alteration associated with guano harvesting, overfishing, oil pollution and predation by feral cats caused the historic decline of the penguin population. The last cats have now been removed from the island. Situated along major shipping routes, Dassen Island's penguins suffered major oil pollution disasters in 1994 and 2000.
The current increase in breeding numbers is as a result of the recovery of South Africa's Sardine stock, and may be partly attributable to immigration of birds bred at other colonies.
After being exterminated on Robben Island by 1800, African Penguins recolonised this island in 1983, when nine pairs nested there. The colony has since become the second largest in the Western Cape, with over 7 000 pairs breeding there in 2002. During the period of 1992 to 2003, the number of breeding birds more than tripled, with a growth rate of 12.4% per year.
Penguin population trends, Robben Island
This rate of increase is greater than the breeding productivity of the resident penguins, and is thought to be supplemented through immigration of birds from Dyer Island. Restrictions on purse-seine fishing in Table Bay and the recovery of the Sardine stock has contributed to improved survival and breeding success.
African Penguins on Robben Island nest under alien vegetation where they are vulnerable to fires. Chicks fall prey to feral cats, and penguins have been disturbed and killed by vehicles. Due to its proximity to shipping lanes and the Cape Town harbour, the penguin colony is exceptionally vulnerable to oiling; Robben Island's penguins bore the brunt of the Treasure oil spill in 2000.
This site was established as a breeding colony of African Penguins in 1985, with two pairs nesting. By 1992, 158 pairs were breeding here, and the numbers have been increasing steadily since then, at a rate of almost 17% per year.
Penguin population trends, The Boulders
The colonisation and subsequent growth of this colony matches the re-covery of the South African Sardine stock. It is thought that birds relocated here from Dyer Island due to restrictions on purse-seine fishing in False Bay.
Feral cats and probably genets and mongooses prey on penguins at The Boulders, and penguins have been disturbed and killed by vehicular traffic. This is exacerbated by the lack of breeding space, with penguins starting to breed on the mountain side of the main road through town. Though the penguins here are remarkably tame, disturbance by tourists may be a problem. With each penguin's "life earnings" being US$1250, wildlife does pay!
Seal Island, False Bay
In about 1880, as noted by naturalist Moseley, the whole of Seal Island was a penguin rookery. In 1956 there were 250 pairs breeding there and in 1979 there were 82 nests. From 1992 to 2003, the number of breeding penguins gradually decreased at a rate of 6% per year.
Penguin population trends, Seal Island
The trend of the penguin population at Seal Island is difficult to determine, however, as counts were often undertaken outside of the main breeding season. The penguins compete with seals for breeding space, though artificial nest sites proved successful in that they were soon occupied by penguins.
Penguins colonised Stony Point in 1982, and there were about 40 nests by 1986. Between 1992 and 2003, the colony more than doubled in size, increasing at a rate of 10.4% per year. The penguins are believed to have come from Dyer Island, and the growth of the new colony is sustained by ongoing immigration.
Penguin population trends, Stony Point
The colony is accessible to terrestrial predators such as Leopard, Caracal, genets, mongooses and dogs, despite the construction of a fence to exclude predators. Penguins also nest outside of the fenced-off area, increasing their vulnerability to disturbance and predation. In the summer of 2003/04, Caracals that started preying on adult penguins at Stony Point were caught and relocated.
There were an estimated 4 000 pairs of penguins breeding on Dyer Island in 1959. This number increased almost 6-fold to 22 655 nests (55% of the Western Cape penguin population) in 1979, but has been declining since then. In 1986 there were 18 481 nests, and by the 1990s there were less than 10 000. The breeding population declined at a rate of 9.1% per year between 1992 and 2003.
Penguin population trends, Dyer Island
This annual rate of decrease is close to the adult mortality rate of 13%. It is suspected that fledglings from Dyer Island do not return there to breed, but emigrate westward to colonies such as Stony Point, The Boulders and Robben Island. This has been attributed to a "regime shift" of pelagic fish westward. Predation by certain 'rogue' Cape Fur Seals from the neighbouring Geyser Island can take a heavy toll on the penguin population, contributing to the decline. Furthermore, though Dyer Island does not lie close to a major port, the penguins here are susceptible to chronic oil pollution, with a complex system of currents moving oil spilt offshore towards the shore.
In 1956, a single pair of penguins nested on Geyser Island, but by 1979 there were 318 pairs. During the 1990s, however, the population declined to extinction. No penguins are believed to have been breeding on Geyser Island since 2000.
Penguin population trends, Geyser Island
The seals have displaced the penguins from the island. Predation by seals on penguins and an altered availability of prey may have contributed to their local extinction at this island.
The oil spills of 1994 and 2000 had their greatest effects on penguins at Dassen and Robben islands, with the loss of a total of about 7 000 birds, yet these populations more than doubled between 1992 and 2003! Successful rehabilitation of affected penguins, coupled with the recovery of South Africa's Sardine stock and subsequent immigration from other breeding colonies has contributed to the increase at these two important colonies as well as at Vondeling Island and the two mainland colonies of Stony Point and Boulders. The marked declines at the easternmost and northernmost colonies is attributed to seal predation, reduced availability of food, and emigration of birds to other colonies.
It is of importance to note the extent to which a large proportion of the African Penguin population has been concentrated at only a few colonies. The Robben Island colony, which did not exist in 1956, held 10% of the global population in 2000, when 45% of the population was concentrated at two colonies in the Western Cape (Dassen and Robben islands). Given the vulnerability to oiling incidents of these two islands, which lie along shipping routes into Table Bay and Saldanha Bay, an obvious objective for conservation management of the species is to encourage growth of the six smaller colonies that do not lie close to major ports: Lambert's Bay, The Boulders, Seal Island, Stony Point, Geyser Island and Dyer Island. However, this is not easy to implement.
After a century of retreat, it is too early to claim that we have arrested the decline in the African Penguin population, and that an upward trend is in place. We can but hope that the turning point has arrived for the conservation of the African Penguin.
Acknowledgements: We are grateful to all who have participated in the annual surveys of penguin breeding colonies. We acknowledge financial support from the Darwin Initiative, Earthwatch Institute, Marine Living Resources Fund, National Research Foundation (Sea and Shore 2 Programme) and University of Cape Town Research Committee. Transport to breeding localities and accommodation at islands was provided by Marine and Coastal Management, Robben Island Museum, South African National Parks, South African Navy and Western Cape Nature Conservation Board.
Photo Les Underhill