Includes bibliographical references (leaves 25-32). / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/6468 |
| Date | January 2006 |
| Creators | Dundee, Benedictus Lissias |
| Publisher | University of Cape Town, Faculty of Science, Department of Oceanography |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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