Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay
The Cape gannet has undergone considerable population change and redistribution over the past 50 years. This has been linked to shifts in the abundance and distribution of their dominant prey, sardine and anchovy. Five breeding colonies, along the west coast of Southern Africa, have shown rapid popu...
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Nelson Mandela Metropolitan University
2013
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ftsealsdc:vital:10725 2024-09-15T17:59:54+00:00 Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay Green, David Bruce 2013 104 leaves pdf http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10725 http://hdl.handle.net/10948/d1020790 English eng Nelson Mandela Metropolitan University Faculty of Science vital:10725 http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10725 http://hdl.handle.net/10948/d1020790 Nelson Mandela Metropolitan University Birds of prey -- Behavior -- South Africa -- Algoa Bay Gannets -- South Africa -- Algoa Bay Birds -- Breeding -- South Africa -- Algoa Bay Thesis Masters MSc 2013 ftsealsdc 2024-07-29T23:41:48Z The Cape gannet has undergone considerable population change and redistribution over the past 50 years. This has been linked to shifts in the abundance and distribution of their dominant prey, sardine and anchovy. Five breeding colonies, along the west coast of Southern Africa, have shown rapid population declines as a result of reduced prey availability. In contrast, a single colony (Bird Island, Algoa Bay) on the south coast of South Africa has, over the same period, grown fivefold and now supports approximately two thirds of the total population. Due to its conservation importance, and isolation from other breeding localities, it is important to assess the health of the Bird Island colony, and determine how foraging distribution relates to the environment to evaluate current measures of protection. This was achieved through two related studies; a long-term dietary analysis spanning 34 years, and a spatial foraging study, which related three years of tracking data to estimates of prey availability, oceanographic features and marine protected areas (MPAs). The results of the dietary study showed that the dietary constituents of Cape gannets breeding at Bird Island have remained similar over the last three decades, but the importance of sardine and anchovy has increased significantly. For sardine, in particular, this reflects an increased availability of this species (as deduced from hydroacoustic surveys) within the foraging range of the Bird Island colony. The dietary abundance of anchovy was found to be negatively correlated with that of sardine. Surprisingly,.the dietary abundance of anchovy was also negatively correlated with estimates of its availability based on acoustic surveys. The latter is likely to be due to sardine being a preferred prey item. Recent decreases in the dietary contribution of sardine (since 2005) suggest that this species is becoming less available to gannets, with profound implications in terms of nutrient gain associated with foraging. However, this has been mediated by an increase ... Master Thesis Bird Island SEALS Digital Commons (South East Academic Libraries System, South Africa) |
institution |
Open Polar |
collection |
SEALS Digital Commons (South East Academic Libraries System, South Africa) |
op_collection_id |
ftsealsdc |
language |
English |
topic |
Birds of prey -- Behavior -- South Africa -- Algoa Bay Gannets -- South Africa -- Algoa Bay Birds -- Breeding -- South Africa -- Algoa Bay |
spellingShingle |
Birds of prey -- Behavior -- South Africa -- Algoa Bay Gannets -- South Africa -- Algoa Bay Birds -- Breeding -- South Africa -- Algoa Bay Green, David Bruce Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay |
topic_facet |
Birds of prey -- Behavior -- South Africa -- Algoa Bay Gannets -- South Africa -- Algoa Bay Birds -- Breeding -- South Africa -- Algoa Bay |
description |
The Cape gannet has undergone considerable population change and redistribution over the past 50 years. This has been linked to shifts in the abundance and distribution of their dominant prey, sardine and anchovy. Five breeding colonies, along the west coast of Southern Africa, have shown rapid population declines as a result of reduced prey availability. In contrast, a single colony (Bird Island, Algoa Bay) on the south coast of South Africa has, over the same period, grown fivefold and now supports approximately two thirds of the total population. Due to its conservation importance, and isolation from other breeding localities, it is important to assess the health of the Bird Island colony, and determine how foraging distribution relates to the environment to evaluate current measures of protection. This was achieved through two related studies; a long-term dietary analysis spanning 34 years, and a spatial foraging study, which related three years of tracking data to estimates of prey availability, oceanographic features and marine protected areas (MPAs). The results of the dietary study showed that the dietary constituents of Cape gannets breeding at Bird Island have remained similar over the last three decades, but the importance of sardine and anchovy has increased significantly. For sardine, in particular, this reflects an increased availability of this species (as deduced from hydroacoustic surveys) within the foraging range of the Bird Island colony. The dietary abundance of anchovy was found to be negatively correlated with that of sardine. Surprisingly,.the dietary abundance of anchovy was also negatively correlated with estimates of its availability based on acoustic surveys. The latter is likely to be due to sardine being a preferred prey item. Recent decreases in the dietary contribution of sardine (since 2005) suggest that this species is becoming less available to gannets, with profound implications in terms of nutrient gain associated with foraging. However, this has been mediated by an increase ... |
format |
Master Thesis |
author |
Green, David Bruce |
author_facet |
Green, David Bruce |
author_sort |
Green, David Bruce |
title |
Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay |
title_short |
Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay |
title_full |
Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay |
title_fullStr |
Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay |
title_full_unstemmed |
Foraging ecology of Cape Gannets (Morus Capensis) at Bird Island, Algoa Bay |
title_sort |
foraging ecology of cape gannets (morus capensis) at bird island, algoa bay |
publisher |
Nelson Mandela Metropolitan University |
publishDate |
2013 |
url |
http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10725 http://hdl.handle.net/10948/d1020790 |
genre |
Bird Island |
genre_facet |
Bird Island |
op_relation |
vital:10725 http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10725 http://hdl.handle.net/10948/d1020790 |
op_rights |
Nelson Mandela Metropolitan University |
_version_ |
1810437021809770496 |