This study focuses on the taxonomy, biogeography and biological aspects of the fishes of Tristan da Cunha and Gough Island in the cental South Atlantic Ocean. Oceanographic measurements were undertaken to determine the position and nature of the Subtropical Convergence (STC) in the vicinity of the islands. The Tristan da Cunha group is thought to be situated on the northern edge of the STC while Gough Island is situated on the southern edge of the front. The seasonal environmental cycle at the islands is characterised by an annual sea surface temperature fluctuation of approximately 5 °C and an annual change in stratification of the water column. It is suggested that this increase in stratification at the STC, brought about in the summer by insolation warming the surface layers of the ocean, enhances primary production. The STC is identified as a unique habitat for fishes and as an important barrier to dispersal of species in the Southern Ocean. The present study has produced 18 new distributional records from the shelf waters of Tristan da Cunha and Gough Island. The fish fauna known from the shelf waters of these islands is reviewed, and a diagnosis, synonymy, and in some cases an illustration are provided. For certain species, brief notes on their biology, relative abundance and seasonal distribution are included. An analysis of the ichthyofaunal relationships between shallow water areas in the vicinity of the STC has resulted in the identification of a characteristic neritic STC ichthyofauna. The circumglobal distribution of many of these species is thought to be a consequence of a dispersive pelagic phase in their life-cycles. Biological processes in fishes at these islands are temporally and spatially affected by seasonal changes in oceanographic conditions. Seasonal sea temperature variation was identified as being an indicator of other oceanographic phenomena that may affect processes such as growth, reproduction and feeding in fishes at the islands. Most species have a summer spawning season and growth rate increased during the summer months. It was hypothesised that enhanced primary production and a related increase in food quality and availability during the summer were the major factors temporally regulating the growth and reproduction of fishes at the islands. Twenty families of neritic fishes have been recorded in the shelf waters of Tristan da Cunha and Gough Island. Most families are represented by only one species. Because of this a wide range of life-history strategies are apparent in the fauna. Nevertheless, there are a number of common life-history characteristics shared by most of the neritic species. Firstly, the early lifehistory of many species included an extended pelagic phase which might have facilitated colonisation throughout the STC zone in the past, thereby regulating extant species diversity in this region. Secondly, the common occurrence of an extended summer breeding season and iteroparity suggested that these characters also contributed to survival in what is considered to be an unpredictable environment. It would appear that these common characteristics hold the key to the success of many fishes in the STC zone. This study has contributed to our understanding of oceanic island ecosystems and has revealed distributional patterns of fishes that were unknown previously. By focusing on the biological processes of selected species the regulatory role played by local environmental conditions became apparent. The results of this study are also relevant to proposed conservation measures for Tristan da Cunha and Gough Island.

Craniometrics is a very reliable and effective tool for studying the difference in animal morphology. Previously, traditional craniometrics were conducted with the aid of calipers in two dimensional format (2D). Such discounting of actual three-dimensional 3D form may result in loss of some relevant and critical information leading to compromised and unreliable results for studies such as population variation analysis of morphology. The employment of 3D photogrammetry allows a close to complete representation of the physical dimensions of a specimen. The use of photogrammetry in mammalogy concentrated on measuring of body size/mass, but little has been done on animal skull delineation through photogrammetry. This dissertation describes advances in morphometrics and 3D photogrammetry application in craniometrics, investigates the craniometric variation between closely related species (Arctocephalus gazella and A. tropicalis), and A. tropicalis interpopulation craniometrics between two geographically distinct populations, at Marion Island and Gough Island, using Photomodeler Scanner® (PMSc®) three-dimensional (3D) modelling software to produce accurate, high resolution 3D skull models. A total of 117 3D models were created from adult male fur seal crania, and 16 traditional measurements recorded, using specimens archived at the Port Elizabeth Museum, Bayworld, South Africa. Sixteen linear measurements, (8 caliper recordings and 8 3D recordings) were used for PMSc® methodology testing, 16 (A. gazella n= 8 and A. tropicalis n= 8) used for species cranial comparison and 85 (Marion Island n= 54 and Gough Island n= 31) used for interpopulation variation. The craniometric variations were analysed using the Statistica® v11 software package, StatSoft, Inc. The comparison between linear traditional caliper cranial measurements and 3D measurements produced significantly similar results, attesting to the accuracy of the PMSc® 3D model production. Photomodeler Scanner® therefore produces accurate and high resolution 3D models of skulls which allow 3D measurements. I predicted that PMSc® would detect the existing significant differences between the skulls of adult male A. gazella and A. tropicalis and modelled and compared their 3D models, and I further predicted that PMSc® would detect any existing differences between the skulls of A. tropicalis from Gough and Marion islands by comparison of their 3D models. The Gough Island and Marion Island A. tropicalis populations could not be discriminated based on linear 3D cranial I conclude that PMSc® is a reliable and effective tool for accurate and high resolution 3D modelling. The present study confirms previous findings and contributes additional evidence that suggests that adult A. tropicalis males from Gough Island and Marion Island cannot be discriminated based on linear measurements of craniometrics, and deviates from the Bergmanian rule as applied to large mammals. The present study, however, makes several noteworthy contributions to the use of PMSc® and 3D modelling in morphometrics. Taken together, these findings suggest a role for PMSc® 3D modelling in promoting accurate digitization of museum specimens and creation of online museum libraries. This research will serve as a baseline for future studies and usefulness of PMSc® in 3D morpho-volumetric measurements. / Dissertation (MSc (Zoology))--University of Pretoria, 2014. / Zoology and Entomology / MSc (Zoology) / Unrestricted