Management of avian cholera<i>Pasteurella multocida</i>outbreaks on Dyer Island, South Africa, 2002–2005

Waller, LJ; Underhill, L. G.

doi:10.2989/ajms.2007.29.1.9.74

Cited by 30 publications

(20 citation statements)

References 10 publications

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“…Although Cape cormorants may move between breeding localities (Crawford et al, 1994), they also show fidelity to natal and nest sites (Berry, 1977;Hockey et al, 2005). Both African penguins and Cape cormorants have a restricted foraging range when breeding (e.g., Heath and Randall, 1989;Pichegru et al, 2010a;Hamann et al, 2012) and they suffered high adult mortality in the 1990s and 2000s in periods of prey scarcity off western South Africa (Crawford et al, 1992(Crawford et al, , 2011Waller and Underhill, 2007;Sherley et al, 2014). Cape gannets have a much greater foraging range during breeding (Lewis et al, 2006) and supplement their diet by feeding on offal discarded by fisheries when their natural prey is scarce, thereby buffering adult survival (e.g., Berruti et al, 1993;Pichegru et al, 2007;Grémillet et al, 2008;Distiller et al, 2012;Crawford et al, 2014b).…”

Section: Discussionmentioning

confidence: 99%

A changing distribution of seabirds in South Africaâ€”the possible impact of climate and its consequences

et al. 2015

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In the southern Benguela ecosystem off South Africa, there were recent shifts to the south and east in the distributions of three forage resources (anchovy, sardine, rock lobster), which probably were influenced by environmental change although fishing too may have played a part. In this study, we review information on trends in distributions and numbers of eight seabirds breeding in South Africa. For five species that feed predominantly on anchovy, sardine or rock lobster, their populations off northwest South Africa decreased markedly. For three of these species, which exhibit behavioral inertia and have restricted foraging ranges when breeding (African penguin, Cape cormorant, bank cormorant), there were large decreases in their overall populations in South Africa. Conversely, for two showing more plasticity and able to range over wide areas or move between breeding localities (Cape gannet, swift tern) there were increases. It is thought that movement of forage resources away from the northern islands led to a mismatch in the distributions of breeding localities and prey of dependent seabirds off western South Africa and to attempts by several species to establish colonies on the southern mainland closer to food resources. There also were shifts to the south and east in the distributions of three seabirds that do not compete with fisheries for prey (crowned cormorant, white-breasted cormorant, kelp gull), suggesting some environmental forcing, but decreases of these species off northwest South Africa were less severe and populations in South Africa remained stable or increased in the long term. It is likely, because many fishing plants are located in the northwest, that there was increased competition between seabirds and fisheries for prey as forage resources moved south and east. Potential interventions to mitigate the adverse impacts of distributional changes for seabirds include allocations of allowable catches of shared forage resources at regional levels, closures to fishing around impacted seabird colonies and establishment of new colonies nearer to the present location of food.

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Section: Discussionmentioning

confidence: 99%

A changing distribution of seabirds in South Africaâ€”the possible impact of climate and its consequences

et al. 2015

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“…Repeated outbreaks of avian cholera Pasteurella multocida caused extensive mortality of Cape Cormorants from 1991 to 2006, especially at Lambert's Bay, Dassen and Dyer islands. More than 14,000 Cape Cormorants were killed at Dassen Island in 1991, 7,000 at Lambert's Bay in 2002 and more than 27,000 at Dyer Island between 2002/2003(Crawford et al 1992Williams and Ward 2002;Waller and Underhill 2007). Predation by seals Arctocephalus pusillus around breeding colonies was thought to be unsustainable for African Penguins at Dyer Island and Lambert's Bay, and for Cape Gannets at Malgas Island (Marks et al 1997;Crawford et al 2001;Makhado et al 2006).…”

Section: Influence Of Food On Seabird Trendsmentioning

confidence: 99%

Food, fishing and seabirds in the Benguela upwelling system

Crawford¹

2007

J Ornithol

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The Benguela upwelling system off south-western Africa supports sardine Sardinops sagax and anchovy Engraulis encrasicolus that are harvested by purse-seine fisheries and are the main prey of three endemic seabirds: African Penguin Spheniscus demersus, Cape Gannet Morus capensis and Cape Cormorant Phalacrocorax capensis. There have been large, long-term changes in the abundance and distribution of the fish resources that have influenced seabird populations. After 1956/1957, the numbers of penguins and gannets breeding in Namibia decreased by 90% and 95%, respectively. After 1978/1979, the number of Cape Cormorants breeding in Namibia decreased by 76%. These decreases were significantly related to the biomass of sardine and anchovy in Namibia and are thought to result mainly from a greatly reduced availability of prey. In South Africa, when the sardine collapsed, it was replaced by anchovy. In the Western Cape, the numbers of Cape Gannets and Cape Cormorants were stable after the collapse of the sardine but African Penguins decreased. The sardine resource recovered in the 1980s and 1990s but, at the turn of the century, was displaced to the east, leading to increases and then decreases in the numbers of penguins and gannets in the Western Cape. In the Eastern Cape, there were long-term increases in the numbers of penguins and gannets, until a recent decrease in penguins. In South Africa, the models used to advise allowable catches for sardine and anchovy are being modified to incorporate a model of African Penguins and functional relationships linking penguins and fish stocks. Consideration is also being given to precluding fishing in areas around seabird breeding colonies.

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“…The absence of a strong pattern could be explained by (1) possible dietary plasticity of the Cape cormorant as described in other cormorants (e.g. Ainley et al 1981, Grémillet et al 1998, Kato et al 2001 despite the fact that the Cape cormorant has been considered a pelagic-fish-specialist predator (Duffy 1989, Crawford & Dyer 1995, or (2) extensive mortality from outbreaks of avian cholera that inflicted heavy mortality on Cape cormorants during the study period (Crawford et al 1992, Waller & Underhill 2007) and may have weakened any functional coupling between Cape cormorants and their prey.…”

Section: Nature Of Local Population Responsesmentioning

confidence: 93%

Differential responses of three sympatric seabirds to spatio-temporal variability in shared resources

Sabarros¹,

Durant²,

Grémillet³

et al. 2012

Mar. Ecol. Prog. Ser.

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Environmental change linked to climate and human activities may affect top predators via the food chain in marine systems. Understanding the functional link between resources and predator responses (e.g. foraging effort, reproductive success, population growth) is of crucial importance in the context of an ecosystem-based approach to fisheries. In the Benguela upwelling ecosystem located off the South African coast, both climate and overfishing may have modified the spatio-temporal availability of sardines and anchovies over the past 2 decades. These fish are prevalent prey items for 3 seabirds: the African penguin Spheniscus demersus, Cape gannet Morus capensis and Cape cormorant Phalacrocorax capensis. Species-specific responses of these 3 sympatric seabirds to the fluctuations in their shared prey are poorly understood. Here we used generalized additive modelling to examine the 'local population response' (i.e. number of breeders) of the 3 seabirds to spatio-temporal variations in prey availability from 1987 to 2007. We showed that prey fluctuations influence seabird local population responses, presumably by modulating recruitment, breeding decision and breeding performance. We also identified speciesspecific population responses to prey availability: positive in African penguins and Cape gannets, and null in Cape cormorants. These patterns could be explained by seabirds partitioning prey in time via separated breeding periods, and space via accessing different foraging grounds due to specific feeding techniques. These responses also suggest different degrees of dependency upon pelagic resources among predators, which are likely due to contrasting foraging ecologies (e.g. dietary plasticity, foraging techniques, foraging ranges).

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Management of avian choleraPasteurella multocidaoutbreaks on Dyer Island, South Africa, 2002–2005

Cited by 30 publications

References 10 publications

A changing distribution of seabirds in South Africaâ€”the possible impact of climate and its consequences

A changing distribution of seabirds in South Africaâ€”the possible impact of climate and its consequences

Food, fishing and seabirds in the Benguela upwelling system

Differential responses of three sympatric seabirds to spatio-temporal variability in shared resources

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