Northern Rockhopper penguin populations, Eudyptes moseleyi, are declining globally, and at Tristan da Cunha have undergone severe declines (> 90% in the last 130 years), the cause(s)of which are unknown. There is a paucity of data on this species in the South Atlantic Ocean, therefore their trophic ecology at Tristan da Cunha was studied, specifically focusing on diet, using stomach content analysis and stable isotope analysis (SIA), in conjunction with an analysis of diving behaviour, assessed using temperature-depth recorders. In order to evaluate the influence of gender on foraging, a morphometric investigation of sexual dimorphism was confirmed using molecular analysis. Additionally, plasma corticosterone levels were measured to examine breeding stage and presence of blood parasites as potential sources of stress during the breeding season. Northern Rockhopper penguins at Tristan da Cunha displayed a high degree of foraging plasticity, and fed opportunistically on a wide variety of prey, probably reflecting local small-scale changes in prey distribution. Zooplankton dominated (by mass) the diet of guard stage females, whereas small meso-pelagic fish (predominantly Photichthyidae)dominated diet of adults of both sexes in the crèche stage, with cephalopods contributing equally in both stages. Adults consistently fed chicks on lower-trophic level prey (assessed using SIA), probably zooplankton, than they consumed themselves indicating that the increasing demands of growing chicks were not met by adults through provisioning of higher- quality prey. SIA also indicated that adults foraged in different oceanic water masses when feeding for self-maintenance and for chick provisioning, thus temporally segregating the prey consumed for different purposes. It is possible that adults ‘selected’ these higher quality prey for themselves, or this may be a reflection of opportunistic behaviour. At Tristan da Cunha sexual dimorphism was observed in culmen dimensions (length, depth, width), with males having larger beaks and feeding on larger individuals of squid and fish than females. No sexual segregation in terms of foraging habitat (i.e. different water masses, based on ð¹³N or trophic level ð¹⁵N) during the breeding season or pre-moult period was revealed through SIA, and stomach content analysis revealed no sexual differences in prey species targeted. The results of SIA of feathers indicate that during the pre-moult period birds foraged in different water masses than during the breeding period. The fact that throughout the breeding season birds foraged in similar habitats suggests no intra-specific competition, despite both sexes feeding on the same prey.Birds were generally diurnal, daily foragers (12 – 16 hr trips), with extended trips (maximum duration 35.5 hours) and nocturnal diving recorded in a few individuals. Birds dived well within their physiological limits, predominantly utilising the upper 20m of the water column, employing two different strategies to target different prey items. Long, deep (30 – 40 m), energetically costly dives were performed when targeting energy-rich prey (fish), and a greater number of shorter, shallower (5 – 20 m), energy-efficient dives were performed when targeting prey with a lower energy content (zooplankton). More than half of the sampled study population were infected with the intra-cellular blood parasite Babesia, but infection showed no relationship to body mass, corticosterone levels or breeding success. Fasting birds showed no signs of elevated corticosterone levels, suggesting they had acquired sufficient fat reserves prior to breeding. Failed breeders did not exhibit elevated corticosterone levels. Tristan skuas, Catharacta antarctica hamiltoni, were observed to be a significant cause of egg and chick mortality. The absence of sex-based differences in foraging, and the absence of any signs of stress in relation to body mass, presence of Babesia or breeding stage, suggest that there are no obvious signs of high levels of stress or food limitations during breeding at Tristan da Cunha.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Oceanography in the Faculty of Applied Sciences at the Cape Peninsula University of Technology 2014 / The Tristan lobster Jasus tristani is distributed among several isolated islands and submerged seamounts in the South East Atlantic Ocean. This species occurs only at the Tristan da Cunha group, a British Overseas Territory and the World’s most remote inhabited island, and in international waters at Vema Seamount 1680 km ENE of Tristan. All these populations are exploited commercially. The catch, processing and export of J. tristani is the most important economic activity for the inhabitants of Tristan da Cunha, providing the livelihood of many families and accounting for approximately 80% of the Island’s revenue. Sustainable harvesting of this valuable resource requires accurate long-term data on catch and effort, as well as information on the most important biological parameters such as growth, recruitment, moulting and reproductive cycles. This information is critical for robust assessments and management strategies. This thesis describes the history of the lobster fishery at the Tristan da Cunha island group, reporting on catches and trends in Catch Per Unit Effort between 1967 and 2010. A total of 247,014 lobster samples, both sexes combined, was sampled for size composition and sex ratios, as well as 1,526 lobsters for length/weight relationships, between 1997 and 2010. This confirms earlier findings that females have broader and heavier tails than males for the same carapace length (CL). Results show that males dominate catches at all islands, and their average size was larger than that of females (83.5 ± 14.46 versus 73.4 ± 8.64 mm CL, respectively). Inter-island differences in lobster population structure appear to be caused by differences of food availability as well as in density-dependent growth and survival of young lobsters. The largest lobsters were found at Gough Island (87.2 ± 15.13 mm CL), and the smallest at Inaccessible island (73.2 ± 11.39 mm). Tristan was the next largest to Gough Island (84.0 ± 12.56 mm) followed by Nightingale island (78.2 ± 11.33 mm). Lobsters caught inshore were larger than those caught offshore, although this may be related in part to differences in catches between fishing gear types. This study showed that fecundity increases in a linear manner with CL, and although larger lobsters clearly produce more eggs than smaller ones, the gain in fecundity is not as great as in some lobster species where fecundity is more closely associated with weight. The study showed no significant differences in egg size between islands, or between large and small females at one island. The egg production per gram of body weight and mean egg diameter both seem to be less than reported in an earlier study in the 1990s. While it seems likely that this is due to differences in the way in which samples were collected (with only stage 2 ova collected and measured in this study), the possibility of a decline in fecundity needs to be investigated further. A range of management measures have been developed over the history of the fishery, and important current measures include an annual total allowable catch (TAC) for each island, minimum size limits, and a closed season timed to protect egg-bearing females. The fishery has recently been awarded certification by the Marine Stewardship Council. The study has confirmed that current conversion factors are broadly correct and that different size limits established for each island are justified. Concern is raised, however, by the fall in catch per unit effort and the mean size of lobsters at the three northern islands over the past 7 years. These trends will need to be closely monitored. There are still many uncertainties over key parameters such as growth and recruitment and the intention is to increase the knowledge base and our understanding of the dynamics of the lobster stock. A research plan has been developed, so that progress can be monitored through the gradual implementation of scientifically defendable fisheries management procedures and increased research and monitoring capacity.

Nesospiza is a genus of buntings restricted to the Tristan da Cunha Islands in the central South Atlantic Ocean. They have undergone an adaptive radiation at the islands and currently two species are recognised based on morphology: the small-billed Tristan bunting (N. acunhae), which is a dietary generalist and the large-billed Wilkins' bunting (N. wilkinsi), a dietary specialist. Both species occur on Nightingale Island with no apparent hybridisation between them. On the neighbouring Inaccessible Island there appears to have been a breakdown of the species barrier and the two species hybridise extensively. Also two altitudinally segregated colour morphs of N. a. acunhae occur on Inaccessible Island. The morphological differentiation of Nesospiza is not reflected in either the mitochondrial DNA or the microsatellite data. Rather the data suggest that there are two island lineages and that the sympatric populations on each island are more closely related to each other than to their allopatric (presumed conspecific) island neighbours. The molecular data support sympatric speciation with parallel evolution in Nesospiza, possibly as a result of divergent selection, acting on the sympatric populations on each island, which could have resulted from a change in feeding ecology. Furthermore the molecular data differentiate between the two sympatric colour morphs of N. a. acunhae, which appear to be speciating as a result of assortative mating. / Dissertation (MSc (Genetics))--University of Pretoria, 2005. / Genetics / unrestricted

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.

Dans ce travail nous avons abordé l'évolution spatiale et temporelle du système d'interaction entre le point chaud de Tristan da Cunha et la dorsale de l'Atlantique Sud. Le point chaud de Tristan da Cunha et les structures associées du fond océanique (à savoir la chaîne volcanique de Walvis dans la plaque africaine et l'élévation du Rio Grande dans la plaque sud-américaine) sont parmi les plus importantes de l'océan l'Atlantique Sud. Cependant, ce système est moins étudié que les systèmes présents dans l'Atlantique Nord (par exemple Açores et Islande), et leur origine et évolution restent sujets à débat. La compilation des données de sondage bathymétrique hébergées auprès du Centre National de Données Géophysique (National Geophysical Data Center - NGDC), et les données de bathymétrie dérivées de l'altimétrie de satellites furent utilisées pour l'élaboration d'un modèle numérique de terrain (MNT) de l'ensemble de l'Atlantique Sud. Les données d'anomalie à l'air libre dérivées de l'altimétrie de satellites et les données d'épaisseurs sédimentaires furent utilisées pour le calcul de l'anomalie de Bouguer réduite au manteau (Mantle Bouguer Anomaly - MBA) et avec les données des isochrones du fond océanique furent calculées l'anomalie résiduelle de Bouguer réduite au manteau (Residual Mantle Bouguer Anomaly - RMBA), la bathymétrie résiduelle et des nouveaux pôles du mouvement relatif entre les plaques de l'Amérique du Sud et Afrique. Les données de géoïde dérivées de l'altimétrie de satellites et le Modèle Gravitationnel de la Terre (Earth Gravitational Model - EGM2008) furent utilisés pour la séparation des différentes composantes dans le signal du géoïde, grâce à des filtres retenant différents ordres et degrés d'harmoniques sphériques. À partir des reconstructions cinématiques basées sur les nouveaux pôles calculés dans ce travail, et en se basant surl'hypothèse communément admise que l'île volcanique de Tristan da Cunha se situe à l'aplomb dela position actuelle du point chaud, la chronologie des phases de mise en place des structures volcaniques a pu être précisée. Ceci a mis en évidence l'existence de plusieurs sauts d'axes et des variations périodiques de l'apport magmatique à l'axe entrainant une alternance entre périodes de construction et de rupture du plateau axial. La comparaison détaillée de la position estimée pour le point chaud de Tristan da Cunha et de la localisation des structures volcaniques de la chaine Walvis dont les âges sont connus a souligné que la formation de la chaîne Walvis ne peut pas être expliquée dans sa totalité par un modèle d'évolution faisant appel à une interaction entre la dorsale de l'Atlantique Sud et un point chaud dont la position actuelle serait l'île de Tristan da Cunha. Ensuite, nous avons évalué l'évolution temporelle de l'influence du point chaud à l'axe de la dorsale, sur aux variations de la bathymétrie résiduelle (BR) et de l'anomalie résiduelle de Bouguer réduite au manteau (RMBA), et avec l'analyse des variations du taux d'ouverture et de la distance point chaud-dorsale. Les valeurs des anomalies de RMBA et BR, lors des premières étapes d'ouverture de l'Atlantique Sud, sont plus fortes sur la plaque africaine que sur la plaque sud-américaine. Cela suggère que la position du point chaud a été sous la plaque africaine depuis le début de l'ouverture. En synthèse, on observe trois différentes périodes dans le système d'interaction entre le point chaud de Tristan da Cunha et la dorsale de l'Atlantique Sud. Une période de rapprochement de la dorsale vers le point chaud entre 115 Ma et 100 Ma, lors de laquelle on remarque l'influence du point chaud sur la dorsale sur une distance d'au moins 150 km. Ensuite, entre 95 Ma et 60 Ma, on observe que la dorsale est à l'aplomb ou très proche (< 50 km) du point chaud. Et depuis 60 Ma, un éloignement graduel et progressif de la dorsale par rapport à la position du point chaud est observé. On a pu montrer que lors des périodes de rapprochement et de proximité de la dorsale au point chaud, les variations périodiques d'apport magmatique observées sont liées aux variations du flux de panache. A partir de l'analyse de l'évolution des structures volcaniques, en association avec les données d'anomalie à l'air libre et de géochimie, les structures volcaniques ont pu être divisées en deux groupes. Un groupe formé par la bordure nord-ouest de la chaîne Walvis et appelé première phase, cohérent avec l'évolution des structures dans un contexte de transition d'une mise en place à l'axe vers une situation intraplaque, en accord avec les trois étapes (rapprochement, fixation à l'aplomb et éloignement) décrites ci-dessus. L'autre groupe, formé par la bordure sud-est de la chaîne Walvis et appelé deuxième phase, montre une signature gravimétrique caractéristique d'une mise en place intraplaque, y compris pour les structures à l'âge desquelles la dorsale est à l'aplomb du point chaud. Les deux groupes possèdent signatures géochimiques différentes en termes de rapports Zr/Nb et d'abondance en Ti. Ensuite, à partir de l'analyse comparative des différents degrés d'harmoniques sphériques du géoïde et des nouveaux résultats de tomographie sismique disponibles dans la littérature, nous avons pu montrer l'existence d'une association en profondeur entre les panaches responsables des structures volcaniques de l'élévation du Rio Grande et de la chaîne Walvis et le superpanache africain. L'identification de trois anomalies mantéliques proches des îles de Gough et RSA semblent en faire une meilleure alternative d'emplacement que l'île de Tristan da Cunha, qui est l'hypothèse communément acceptée aujourd'hui.