R. J. M. Crawford

Collapse of South Africa's penguins in the early 21st century

The number of African penguins Spheniscus demersus breeding in South Africa collapsed from about 56 000 pairs in 2001 to some 21 000 pairs in 2009, a loss of 35 000 pairs (>60%) in eight years. This reduced the global population to 26 000 pairs, when including Namibian breeders, and led to classification of the species as Endangered. In South Africa, penguins breed in two regions, the Western Cape and Algoa Bay (Eastern Cape), their breeding localities in these regions being separated by c. 600 km. Their main food is anchovy Engraulis encrasicolus and sardine Sardinops sagax, which are also the target of purse-seine fisheries. In Algoa Bay, numbers of African penguins halved from 21 000 pairs in 2001 to 10 000 pairs in 2003. In the Western Cape, numbers decreased from a mean of 35 000 pairs in 2001–2005 to 11 000 pairs in 2009. At Dassen Island, the annual survival rate of adult penguins decreased from 0.70 in 2002/2003 to 0.46 in 2006/2007; at Robben Island it decreased from 0.77 to 0.55 in the same period. In both the Western and Eastern Cape provinces, long-term trends in numbers of penguins breeding were significantly related to the combined biomass of anchovy and sardine off South Africa. However, recent decreases in the Western Cape were greater than expected given a continuing high abundance of anchovy. In this province, there was a south-east displacement of prey around 2000, which led to a mismatch in the distributions of prey and the western breeding localities of penguins.

Implications for seabirds off South Africa of a long-term change in the distribution of sardine

From 1997 to 2005, the distribution of sardine Sardinops sagax, an important prey item for four seabirds off South Africa, shifted 400 km to the south and east, influencing its availability to breeding birds. It became progressively less available to seabirds in the Western Cape Province, where the number of African penguins Spheniscus demersus breeding decreased by 45% between 2004 and 2006, survival of adult penguins decreased and penguins established a new eastern colony in 2003. In that province, the number of Cape gannets Morus capensis breeding decreased by 38% between 2001/2002 and 2005/2006 and the contribution of sardine to the diet of gannets fell from an average of 40% during the period 1987–2003 to 5–7% in 2005 and 2006. The proportions of Cape cormorants Phalacrocorax capensis and swift terns Sterna bergii breeding in the south of the province increased as sardine moved south and east. In the Eastern Cape Province, the number of penguins breeding halved between 2001 and 2003, whereas after 2002 there was an increase in the number of Cape gannets that bred and in the contribution of sardine to their diet. It is likely that in that province sardine became increasingly available to gannets but remained beyond the shorter feeding range of penguins. Management measures that may mitigate the impacts on seabirds of an unfavourable, long-term change in the distribution of their prey include the provision of breeding habitat where prey is abundant, spatial management of fisheries competing for prey, and interventions aimed at limiting mortality.

Trends of African penguin Spheniscus demersus populations in the 20th century

The entire nesting population of African penguins Spheniscus demersus was about 575 000 adults at the start of the 20th century. Numbers halved by the 1950s and continued to fall to about 220 000 by the late 1970s and about 180 000 by the early 1990s. In Namibia, there has been a 30% reduction since the late 1970s, the most severe declines being in the south, where colonies continue to decrease. Populations at Mercury, lchaboe and Halifax islands now appear to be stable. In South Africa, numbers fell by 17% between the late 1970s and early 1990s, with especially severe decreases near Saldanha Bay and at Dassen and Dyer islands. These decreases have been arrested, except at Dyer Island. Three new colonies were established in the Western Cape in the early 1980s and supported about 10 000 adult birds in 1994. At islands in Algoa Bay, numbers of adults increased by nearly 30 000 between the late 1970s and the early 1990s, with large increases at St Croix and Bird islands. Ongoing deterioration in the status o...

Initial impact of the treasure oil spill on seabirds off western South Africa

On 23 June 2000, the bulk ore carrier MV Treasure sank off western South Africa between Dassen and Robben islands, which individually currently support the largest and 3rd largest colonies of African penguins Spheniscus demersus. Subsequently, more than 19 000 penguins were oiled, almost twice the previous highest number of seabirds oiled during a single event in southern Africa (10 000 penguins after the sinking of the Apollo Sea in June 1994). About 19 000 oiled penguins were collected for cleaning and care and about 150 oiled adults died in the wild. Some 19 500 unoiled penguins were caught at Dassen and Robben islands and relocated to Port Elizabeth, 800 km to the east, to remove them from waters affected by the oil. Of all penguins caught, which amounted to 20% of the total species population, less than 2 000 died within the first month, considerably less than in the Apollo Sea spill. This can be attributed to improved transport of penguins and the rapid arrival at rescue centres of experts able to administer emergency care. However, resources were severely extended and mortality would probably have been considerably higher had large numbers of birds not been removed from the area affected by the oil. Many relocated birds returned to their home islands within a month of being released, but considerable disruption of pair bonds is expected to result from mortality, different periods in captivity and disruption of moult cycles. This is likely to result in decreased breeding success. Recruitment to colonies will also be reduced by substantial loss of chicks and eggs. Although more than 3 000 orphaned chicks were collected for captive rearing, an estimated 4 000 died at the islands before they could be rescued. Up to 20% of bank cormorants Phalacrocorax neglectus at Robben Island, the 3rd largest colony of the species in South Africa, died. There was low success in catching oiled cormorants and in saving those that were caught. Of 53 grown birds of four species of cormorant that were oiled and caught, only 17 survived. Captive rearing of bank cormorant chicks, which it was feared may have been orphaned, proved more successful. Spilt oil had minor impact on gulls, terns and shorebirds in the region.

Seabird consumption and production in the Benguela and Western Agulhas ecosystems

Seabirds were estimated to consume about 430 000 metric tons of food per annum off south-western Africa (15°S to 28°E, from the coast to the 500 m bottom contour) in the 1980s. Of this some 34 per cent was eaten by Cape cormorants, 12 per cent by Cape gannets and 7 per cent by African penguins, species that breed in the region. Among the migrant seabirds, whitechinned petrels accounted for 12 per cent of overall consumption, sooty shearwaters 9 per cent, blackbrowed albatrosses 6 per cent and shy albatrosses 5 per cent. Consumption was higher in the austral winter than in summer because of the greater number of migrant seabirds in the region in winter. Anchovy was the most important prey item, contributing about 31 per cent of all food eaten, followed by pelagic goby (18%), hakes (15%) and zooplankton (8%). Virtually all the hake component of the diet is scavenged from fishing vessels, and of the other main prey items only anchovy is targeted by commercial fishermen. It is estimated that African penguins ...

Assessing conservation priorities in the Benguela ecosystem, South Africa: analysing predation by seals on threatened seabirds

Abstract Cape fur seals ( Arctocephalus pusillus pusillus ), a protected species, have become abundant in the Benguela ecosystem off the west coast of southern Africa (present population size about 1.5–2 million animals), and are killing substantial numbers of red data book species of seabirds (African penguin Spheniscus demersus , Cape gannet Morus capensis , Cape cormorant Phalacrocorax capensis , bank cormorant P. neglectus and crowned cormorant P. coronatus ). The decision has been taken to reduce the impact of seal predation by selectively culling seals which are witnessed killing seabirds. Between 1993 and 2001 a total of 153 seals, which were killing fledgling gannet chicks, were culled.

Influences of the abundance and distribution of prey on African penguins Spheniscus demersus off western South Africa

Off South Africa, anchovy Engraulis encrasicolus and sardine Sardinops sagax are the main prey of African penguins Spheniscus demersus. The combined spawner biomass of these fish increased from less than one million t in 1996 to more than nine million t in 2001 and then decreased to four million t in 2005. The combined biomass of young-of-the-year of these species increased from 0.2 million t in 1996 to 3.2 million t in 2001 before falling to 0.4 million t in 2005. There was a large eastward shift in the distribution of sardine between 1999 and 2005. The number of African penguins breeding in the Western Cape Province increased from 18 000 pairs in 1996 to more than 30 000 pairs from 2001 to 2005 before falling to 21 000 pairs in 2006, as the availability of fish decreased near breeding localities. Numbers of penguins breeding and numbers of birds in adult plumage moulting were significantly correlated with the young-of-the-year biomass of anchovy and sardine and with the available biomass of spawning sardine. The increase in the number of penguins breeding was mainly attributable to a greater proportion of birds breeding and improved breeding success. The decrease probably resulted from high mortality. Delayed first breeding and abstinence from breeding during periods of food shortage may both increase survivorship when food is scarce and enable seabirds rapidly to take advantage of improved feeding conditions. Although long-lived seabirds are buffered against short-term variability in food supplies, environmental change that influences the abundance and availability of prey can have severe consequences for central-place foragers, such as penguins, if there is long-term displacement of prey to regions where no suitable breeding localities occur.

Regionally coherent trends in colonies of African penguins Spheniscus demersus in the Western Cape, South Africa, 1987–2005

From 1987 to 2005, numbers of African penguins Spheniscus demersus breeding in South Africas Western Cape Province increased by about 50%. Numbers decreased at the four northernmost colonies in the region: Lamberts Bay and the three colonies in Saldanha Bay, although at Jutten Island the decrease is inferred from an estimate for 1987, derived from interpolation. Numbers also decreased at Geyser Rock and Dyer Island on the South Coast. At five colonies between Saldanha Bay and Dyer Island there were large increases. At a sixth colony in that region, Seal Island, where Cape fur seals Arctocephalus pusillus pusillus limit breeding space, numbers remained stable. At two colonies that were initiated in the early 1980s, Robben Island and Boulders, increases were initially rapid (>20% per annum) and matched growth of the South African stock of sardine Sardinops sagax. Strong growth at Dassen and Vondeling islands, between Robben Island and Saldanha Bay, was observed from about 1996–2002, when there was a large increase in the biomass of pelagic fish off South Africa. Increases at colonies between Saldanha Bay and Boulders slowed after 2002, whereas the colony at Dyer Island stabilised at that time. In 2003, a new colony was initiated east of Dyer Island at De Hoop Nature Reserve. These latter trends followed an eastward shift in the distribution of sardine. Small penguin colonies may act as foci for growth in a period when the distribution of prey is changing. Hence, it is important that they be maintained, especially those that, if lost, would increase the isolation of regional populations. Some of the small colonies are less susceptible to oil spills than colonies in the proximity of harbours, and for that reason also are important.

Recent distributional changes of seabirds in South Africa: is climate having an impact?

There have been recent changes in the distributions of several seabirds in South Africa. In the mid-1990s, breeding of Leachs storm petrel Oceanodroma leucorhoa was recorded in the Western Cape, the first record for the Southern Hemisphere. There was a large eastward expansion in the breeding range of crowned cormorant Phalacrocorax coronatus sometime between the early 1990s and the early 2000s, and in that of Hartlaubs gull Larus hartlaubii between 1995 and 2000. A smaller eastward expansion in the breeding range of kelp gull Larus dominicanus was noted in 2006. In 2003, a new colony of African penguins Spheniscus demersus formed in the east of the Western Cape, but after 2004 there were large decreases of penguins at colonies in the west of this province. South Africas northern most penguin colony became extinct in 2006. In the early 2000s, there was a decrease in numbers of Cape gannets Morus capensis breeding in the Western Cape, but a large increase in the Eastern Cape. Numbers of Cape P. capensis and bank P. neglectus cormorants decreased in the north of the Western Cape in the 1990s, but increased at some southern localities in the 2000s. A similar pattern was noted for kelp gulls, except that the decreases in the north took place in the 2000s. The proportion of swift terns Sterna bergii in the Western Cape that bred in the south of this province increased markedly in the mid-2000s. Although local factors may have played a role in the distributional changes, their consistent anticlockwise nature, the broad similarity in their timing and their widespread occurrence suggest the influence of environmental change, perhaps forced by climate. This hypothesis is supported by similar displacements of other South African marine resources and congruent changes in seabird populations in the South-West Indian Ocean.

Impact of predation by Cape fur seals Arctocephalus pusillus pusillus on Cape gannets Morus capensis at Malgas Island, Western Cape, South Africa

Cape fur seals Arctocephalus pusillus pusillus were estimated to kill some 6 000 Cape gannet Morus capensis fledglings around Malgas Island in the 2000/01 breeding season, 11 000 in 2003/04 and 10 000 in 2005/06. This amounted to about 29%, 83% and 57% of the overall production of fledglings at the island in these breeding seasons respectively. Preliminary modelling suggests this predation is not sustainable. There was a 25% reduction in the size of the colony, the second largest of only six extant Cape gannet colonies, between 2001/02 and 2005/06. There has been a large increase in predation by Cape fur seals on seabirds around southern African islands since the mid-1980s, coincidental with both an increase in the seal population, altered management of the islands and an altered distribution of prey for gannets and seals. At Malgas Island, most gannet fledglings were killed between 10:00 and 18:00, the period when most are in the water around the island, from mid-January to mid-March, the main fledging period. The Cape gannet is classified as Vulnerable.