24 research outputs found
Food limitation of seabirds in the Benguela ecosystem and management of their prey base
This is the final version. Available from the Environmental Information Service, Namibia via the URL in this record.âŻFour of seven seabirds that are endemic to the Benguela ecosystem (African Penguin Spheniscus demersus, Cape Gannet
Morus capensis, Cape Cormorant Phalacrocorax capensis, Bank Cormorant P. neglectus) compete with fisheries for prey and
have an IUCN classification of Endangered. Prey depletion and food resource limitations have been major drivers of recent
large population decreases of each of these species. As populations decrease, colony sizes also dwindle rendering them
susceptible to Allee effects and higher probabilities of extinction. Therefore, it is necessary to maintain colonies at sizes that
minimise their probability of extinction. Means to ensure an adequate availability of food to achieve this goal include closing
important seabird foraging areas (often adjacent to key colonies) to relevant fishing, implementing ecosystem thresholds below
which such fishing is disallowed (which are also expected to benefit forage resources) and, should there be an altered
distribution of prey, attempting to establish seabird colonies close to the new location of forage resources.The Pew Charitable Trust
Habitat preferences of Phoebetria albatrosses in sympatry and allopatry
Competition is often proposed to drive niche segregation along multiple axes in speciose communities. Understanding spatial partitioning of foraging areas is particu�larly important in species that are constrained to a central place. We present a natural experiment examining variation in habitat preferences of congeneric Southern Ocean predators in sympatry and allopatry. Our aim was to ascertain consistency of habitat preferences within species, and to test whether preferences changed in the presence of the congener
Infection pre-Ad26.COV2.S-vaccination primes greater class switching and reduced CXCR5 expression by SARS-CoV-2-specific memory B cells
Neutralizing antibodies strongly correlate with protection for COVID-19 vaccines, but the corresponding memory B cells that form to protect against future infection are relatively understudied. Here we examine the effect of prior SARS-CoV-2 infection on the magnitude and phenotype of the memory B cell response to single dose Johnson and Johnson (Ad26.COV2.S) vaccination in South African health care workers. Participants were either naĂŻve to SARS-CoV-2 or had been infected before vaccination. SARS-CoV-2-specific memory B-cells expand in response to Ad26.COV2.S and are maintained for the study duration (84 days) in all individuals. However, prior infection is associated with a greater frequency of these cells, a significant reduction in expression of the germinal center chemokine receptor CXCR5, and increased class switching. These B cell features correlated with neutralization and antibody-dependent cytotoxicity (ADCC) activity, and with the frequency of SARS-CoV-2 specific circulating T follicular helper cells (cTfh). Vaccination-induced effective neutralization of the D614G variant in both infected and naĂŻve participants but boosted neutralizing antibodies against the Beta and Omicron variants only in participants with prior infection. In addition, the SARS-CoV-2 specific CD8+âT cell response correlated with increased memory B cell expression of the lung-homing receptor CXCR3, which was sustained in the previously infected group. Finally, although vaccination achieved equivalent B cell activation regardless of infection history, it was negatively impacted by age. These data show that phenotyping the response to vaccination can provide insight into the impact of prior infection on memory B cell homing, CSM, cTfh, and neutralization activity. These data can provide early signals to inform studies of vaccine boosting, durability, and co-morbidities
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. Keywords: Arctocephalus pusillus pusillus, Cape fur seal, Cape gannet, fledgling mortality, Malgas Island, Morus capensis, predationAfrican Journal of Marine Science 2006, 28(3&4): 681â68
Congruent, decreasing trends of gentoo penguins and Crozet shags at sub-Antarctic Marion Island suggest food limitation through common environmental forcing
Numbers of gentoo penguins Pygoscelis papua and Crozet shags Phalacrocorax [atriceps] melanogenis breeding annually at Marion Island, one of South Africaâs Prince Edward Islands in the South-West Indian Ocean, were strongly correlated over 19 split-years from 1994/1995 to 2012/2013. Both species decreased between the mid-1990s and the mid-2000s, exhibited a partial recovery in the late-2000s and then decreased to their lowest recorded levels in 2012/2013. In both instances, the partial recoveries in the late-2000s were associated with improved breeding success. At a colony of gentoo penguins, breeding success was negatively correlated with the date of arrival of adults to breed. Gentoo penguins and Crozet shags are demersal feeders in inshore waters around Marion Island and there is considerable overlap in the composition of their diets. Therefore, trends in their populations may be driven by food availability, which is likely to be influenced by benthic production around the island. We propose that, in South Africa, and based on the current assessment, the Crozet shag, which elsewhere breeds only at the Crozet Islands, is now Critically Endangered, and the more widely ranging gentoo penguin is Endangered.Keywords: breeding success, environmental change, food limitation, Phalacrocorax [atriceps] melanogenis, population decrease, Pygoscelis papua, seabirdsAfrican Journal of Marine Science 2014, 36(2): 225â23
Short CommunicationMass on arrival of rockhopper penguins at Marion Island correlated with breeding success
For rockhopper penguins Eudyptes chrysocome at Marion Island, there were significant decreases over time in the numbers breeding and breeding success at three monitored colonies from 1985/1986 to 2006/2007, and in mass on arrival for breeding of both males and females from 1994/1995 to 2007/2008. Breeding success decreased by 0.15 chicks pairâ1 yâ1 over 22 years and was significantly correlated with mass on arrival of males and females. Survival of chicks at the guard stage was low in the late 1990s; hatching success decreased in the early 2000s. It is thought that an increasingly poor parental condition caused birds to abandon breeding at a progressively early stage. Parental condition is influenced by feeding opportunities at overwintering grounds, which have probably been altered by global climate. Keywords: breeding success; climate change; Eudyptes chrysocome; parental condition; rockhopper penguin; sub-AntarcticAfrican Journal of Marine Science 2008, 30(1): 185â18
Trends in numbers of crowned cormorants in South Africa, with information on diet
During 2008–2012, the number of crowned cormorants Phalacrocorax coronatus breeding in South Africa was c. 1 900 pairs, compared to 1 700 pairs for 1977–1981. Numbers at 10 islands in the Western Cape province fluctuated around a level of 1 100 pairs from 1991/1992 to 2011/2012, 300 more than from 1978/1979 to 1990/1991. These increases are attributable to the discovery of more colonies and an increased frequency of counting at the 10 islands after 1990/1991. The overall number of crowned cormorants breeding in South Africa is thought stable in the long term. Crowned cormorants feed mainly on small, inshore fish species that are not harvested by humans. Clinidae dominated the diet at 10 colonies adjoining the open sea, whereas Gobiidae contributed most food of birds at three colonies in a lagoon. The stability of the crowned cormorant population contrasts with decreases of some other seabirds endemic to southern Africa that feed primarily on prey that is exploited by fisheries. The crowned cormorant population decreased in the Northern Cape and small numbers initiated breeding at colonies to the east of Cape Agulhas at the turn of the century, but most of the population continues to breed to the west of Cape Agulhas. In some instances the availability of suitable breeding habitat may limit numbers breeding.Keywords: breeding habitat, Clinidae, Gobiidae, Phalacrocorax coronatus, population trendAfrican Journal of Marine Science 2012, 34(3): 411–42
Collapse of South Africaâs 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 2001â2005 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.Keywords: African penguin, diet, numbers breeding, numbers moulting, Spheniscus, survivalAfrican Journal of Marine Science 2011, 33(1): 139â15
Cape cormorants decrease, move east and adapt foraging strategies following eastward displacement of their main prey
Numbers of Cape cormorants Phalacrocorax capensis breeding in South Africa decreased by nearly 50% from approximately 107 000 pairs in 1977â1981 to 57 000 pairs in 2010â2014. Although four colonies had >10 000 pairs in 1977â1981, there was just one such colony in 2010â2014. Almost all the decrease occurred after the early 1990s off north-west South Africa, between the Orange River estuary and Dassen Island. South of this, the number breeding in the two periods was stable, with some colonies being formed or growing rapidly in the 2000s. The proportion of South Africaâs Cape cormorants that bred south of Dassen Island increased from 35% in 1977â1981 to 66% in 2010â2014, with the opposite situation observed in the north-west. This matched a shift to the south and east in the distributions of two of the Cape cormorantâs main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax. In 2014, an apparent scarcity of prey in the north-west resulted in Cape cormorants attempting to take bait from hooks of fishing lines over an extended period, a behaviour not previously recorded. The number of Cape cormorants breeding in the south may be constrained by the absence of large islands between Dyer Island in the west and Algoa Bay in the east. If so, it may be possible to bolster the southern population through the provision of appropriate breeding habitat, such as platforms, or restricting human disturbance at suitable mainland cliff breeding sites.Keywords: colony size, distribution change, food availability, foraging behaviour, Phalacrocorax capensis, population decreas