The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry

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dc.contributor.authorDundee, Benedictus Lissiasen_ZA
dc.date.accessioned2014-08-13T19:48:44Z
dc.date.available2014-08-13T19:48:44Z
dc.date.issued2006en_ZA
dc.descriptionIncludes bibliographical references (leaves 25-32).en_ZA
dc.description.abstractGPS telemetry in conjunction with a recent diet time series and historical dietary informationwas used in this study to obtain novel insight into the dietary trends and feeding ecology of Cape gannets Morus capensis on the Namibian islands. particularly Ichaboe and Mercury. The gannet diet has changed substantially since the 1950s. refiecting spatio-temporal changes in the availability of commercially important pelagic prey species. The more recent diet time series for Ichaboe Island (Nov 1995 to Feb 2004) showed that trawler scavenged hakes Merluccius spp and naturally foraged saury Scomberesox saw'us dominated the diet by both contribution to mass (35 and 34 %, respectively) and frequency of occurrence (34 and 25 %, respectively). In a significant contrast, juvenile horse mackerel Trachurus trachurus capensis (40 % mass, 26 % frequency) and juvenile snoek Thyrsites atun (20 % mass, 20 % frequency) were the two main prey species at Mercury Island during Oct 1996 to Feb 2004. Multivariate analysis of data showed significant time and site effects in diet composition between Ichaboe and Mercury for the period Nov 1996 to Mar 1999. Twenty-five and 15 GPS field deployments were made on birds at Ichaboe and Mercury, respectively, during the 2003/4 breeding season. Birds from both locations showed significant differences in their foraging patterns. Birds from Ichaboe had shorter foraging trips (24.3 hrs vs 29.4 hrs),traveled shorter distances away from their island (130 km vs 197 km) and had shorter foraging path lengths (422 km vs 673 km). Birds from Ichaboe foraged in two dominant directions: west. to obtain mainly scavenged fish offal, and north to obtain forage fish. Mercury birds foraged only north, overlapping their foraging zone with birds from Ichaboe in a northerly direction, between 25.8° Sand 24.4° S. Birds at all colonies - especially in the south - appear to be constrained by lower quality food and generally poor feeding conditions which seem to be a limiting factor.en_ZA
dc.identifier.apacitationDundee, B. L. (2006). <i>The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/6468en_ZA
dc.identifier.chicagocitationDundee, Benedictus Lissias. <i>"The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2006. http://hdl.handle.net/11427/6468en_ZA
dc.identifier.citationDundee, B. 2006. The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Dundee, Benedictus Lissias AB - GPS telemetry in conjunction with a recent diet time series and historical dietary informationwas used in this study to obtain novel insight into the dietary trends and feeding ecology of Cape gannets Morus capensis on the Namibian islands. particularly Ichaboe and Mercury. The gannet diet has changed substantially since the 1950s. refiecting spatio-temporal changes in the availability of commercially important pelagic prey species. The more recent diet time series for Ichaboe Island (Nov 1995 to Feb 2004) showed that trawler scavenged hakes Merluccius spp and naturally foraged saury Scomberesox saw'us dominated the diet by both contribution to mass (35 and 34 %, respectively) and frequency of occurrence (34 and 25 %, respectively). In a significant contrast, juvenile horse mackerel Trachurus trachurus capensis (40 % mass, 26 % frequency) and juvenile snoek Thyrsites atun (20 % mass, 20 % frequency) were the two main prey species at Mercury Island during Oct 1996 to Feb 2004. Multivariate analysis of data showed significant time and site effects in diet composition between Ichaboe and Mercury for the period Nov 1996 to Mar 1999. Twenty-five and 15 GPS field deployments were made on birds at Ichaboe and Mercury, respectively, during the 2003/4 breeding season. Birds from both locations showed significant differences in their foraging patterns. Birds from Ichaboe had shorter foraging trips (24.3 hrs vs 29.4 hrs),traveled shorter distances away from their island (130 km vs 197 km) and had shorter foraging path lengths (422 km vs 673 km). Birds from Ichaboe foraged in two dominant directions: west. to obtain mainly scavenged fish offal, and north to obtain forage fish. Mercury birds foraged only north, overlapping their foraging zone with birds from Ichaboe in a northerly direction, between 25.8° Sand 24.4° S. Birds at all colonies - especially in the south - appear to be constrained by lower quality food and generally poor feeding conditions which seem to be a limiting factor. DA - 2006 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2006 T1 - The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry TI - The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry UR - http://hdl.handle.net/11427/6468 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/6468
dc.identifier.vancouvercitationDundee BL. The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2006 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/6468en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherApplied Marine Scienceen_ZA
dc.titleThe diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetryen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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