Improving understanding of the ecology of Indo-pacific bottlenose dolphins (tursiops aduncus) in Algoa Bay, South Africa
- Authors: Shaanika, Titus Mwiitantandje
- Date: 2018
- Subjects: Bottlenose dolphin -- South Africa -- Port Elizabeth , Bottlenose dolphin -- Ecology -- South Africa -- Port Elizabeth Dolphins -- Ecology -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/34788 , vital:33451
- Description: Site fidelity and spatial distribution of Indo-Pacific bottlenose dolphins (Tursiops aduncus) were assesed using mark-recapture from opportunistic photographs collected between June 2008-May 2011 in Algoa Bay, South Africa. Over 10 000 photographs were collected, and assessed, resulting in 2472 photographs being catalogued and analysed. In total, 2002 individual dolphins were photographically identified. The discovery curve does not reach a plateau, indicating a large, open population, as a result, the re-sighting rate over the study period was low. 178 (8.9%) animals were re-sighted, and 32 animals these were seen three times or more. The individual which was re-sighted most often was sighted five times. The residency index averaged 0.05 and reached a maximum at 0.25. 41% of the data were collected in 2009, which skewed the identifications per unit effort (IDsPUE) across years (Kruskal-Wallis Anova, KW= 11.59 n=60, p= 0.009) and seasons (KW= 17.47, n= 60, p=0.007). Due to the relatively higher data collection in 2009, identifications across years (KW=13.29, n=60, P= 0.004) and across seasons (KW=17.81 n=60, P=0.007) also differed significantly. In contrast, there was no significant difference is re-sighting across years (KW = 6.9, n=56, p= 0.8) and seasons (KW=12.26, n=56, p=0.6). The association between the 32 individuals seen three times or more was measured using the Half Weight Index, the index ranged from 0 to 1. A dendrogram revealed two social clusters consisting of 23 and 8 animals each, with one individual having no associations. Xenobalanus was recorded on all but five surveys over the study period. Xenobalanus occurrence did not significantly differ across years (KW=1.49, n=42, p=0.68) and seasons (KW= 6.59, n=43, p=0.36). Dolphins were mostly sighted in depths of <15 metres all around the bay. Travelling (36%) behaviour was the most recorded, followed by feeding (29 %), socialising (15%), milling (11 %), Slow travel (6%), resting (2%) and fast travelling (1%). Other than milling the spatial distribution of all behaviours were similar to the general spatial distribution of sightings. The project provides information that can be used for further research and conservation management of T. aduncus. Photographs used in this project were opportunistically collected, which has resulted in the underestimation of photo-identified individuals and consequently results of this project.
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- Date Issued: 2018
Cretaceous dyke swarms and brittle deformation structures in the upper continental crust flanking the Atlantic and Indian margins of Southern Africa, and their relationship to Gondwana break-up
- Authors: Muedi, Thomas Tshifhiwa
- Date: 2013
- Subjects: Dikes (Geology) -- Africa, Southern , Joints (Geology) -- Africa, Southern , Gondwana (Continent)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10675 , http://hdl.handle.net/10948/d1020896
- Description: Permanent brittle deformation of rocks of the upper crust is often manifested in the growth of fractures, or sliding along fractures, which may subsequently be intruded by magma and other fluids. The brittle deformation structures described here include faults, joints and dykes. Brittle deformation structures along passive continental margins result from continental fragmentation and related uplift, as is seen around the southern African margins in response to Gondwana break-up. In many cases the fragmentation is accompanied by significant magmatic events, for example the Cretaceous mafic dyke swarms that form major components of the South Atlantic Large Igneous Province (LIP) and originated during the break-up of West Gondwana (Africa and South America). The magmatic events accompanying the break-up of Gondwana resulted in crustal extension and the formation of joint systems and dyke swarms that exhibit distinct geometric features that appear to display fractal patterns. This work analyses the relationship between the Henties Bay-Outjo Dyke Swarm (HOD) on the west coast of Namibia, and the Ponta Grossa Dyke Swarm (PG) on the coast of Brazil, both of which formed ca. ~130 Ma, to test for their co-linearity and fractal geometry before and during West Gondwana break-up. This was achieved by reconstructing Gondwana‘s plates that contained the PG and HOD swarms, using ArcGIS and Gplates software. The dyke analyses was complemented with a comparative study of joints of the Table Mountain Group quartzites (TMG, ca. 400 Ma) in the Western Cape Province and Golden Valley Sill (GVS, ca. 180 Ma) in the Eastern Cape Province, to compare their fractal patterns and possible relationship. Mapping of joints was carried out in the field with the use of a compass and GPS. The HOD trend is positioned largely NNE > NE, but a NW dyke trend is also common. The dominant joints in the TMG trend NNW > WSW and the GVS joints trend WNW > NNE and others. The GVS and HOD orientations appear strongly correlated, while TMG shows no simple orientation correlation with GVS and HOD. The lack of correlation is attributed to the TMG‘s formation in different host-rocks with variable anisotropy and/or the presence of different mechanical processes acting at a different time in geological history. All mapped dykes and joints were analysed to test for fractal geometry. The fractal dimension results of about 18605 HOD dykes from microscopic to mega scale (0.1 mm – 100 km) shows fractal patterns that range between Df = 1.1 to 1.9; and the fractal dimension of about 1716 joints in the TMG and about 1026 joints in the GVS at all scales range between ca. Df = 1.6 to 1.9. The similarity of the fractal patterns indicates that joints and dykes may have formed in response to similar tectonic stress events; and similar orientations may indicate that joints pre-dated the dyke intrusions. However, the data also indicate that dykes are not always related to pre-existing joints.
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- Date Issued: 2013