ABSTRACT The zebra shark Stegostoma fasciatum is an oviparous, demersal carpet shark that forms temporary aggregations and is distributed within shallow, coastal, subtropical and tropical waters of the Indo-West Pacific (IWP) region. The IWP region encompasses various densities of human habitation leading to differences in the levels of exploitation of chondrichthyan fishes, which are targeted for local consumption and export. This is reflected in the two current regional IUCN Red List classifications for zebra sharks of ‘Least Concern’ and ‘Vulnerable’. Despite the conservation concerns for zebra sharks in the vulnerable parts of their range, as well as importance within the ecotourism industry and collection for aquarium trade, little is known about this species in the wild. The aim of this thesis was to conduct the first intensive examination of population ecology in the zebra shark by: (i) investigating the population structure and environmental parameters associated with a relatively unexploited aggregation of zebra sharks in south-east Queensland, Australia; and (ii) investigating the genetic continuity between zebra shark populations in areas with differing levels of exploitation. To investigate the size and structure of the aggregation at the site The Group in south-east Queensland, photo-identification and mark-recapture methods were employed over a three year period (2003 - 2006). In total 327 individual zebra sharks were identified from 570 photographs. Numbered dart tags on 15 zebra sharks were used to confirm pigmentation patterns were unique and persistent in wild zebra sharks for up to 810 days. Pollock’s robust design resulted in an annual population estimate of 458 individuals (95% CI = 298 – 618). The mean number of zebra sharks observed on a single day was 8 (± 8 SE) and the maximum number of zebra sharks seen on a single day was 34. In total, 27% of the sharks were sighted in more than one summer aggregation period and males had greater re-capture probabilities than females. The aggregation consisted exclusively of large (>1800 mm total length) adults with an overall female sex bias of 3.8:1, though sex-ratios varied temporally. Passive acoustic telemetry techniques were employed to investigate the seasonality and residency of the sharks and the environmental parameters associated with their presence at the study site. Five VR2 acoustic receivers were deployed for a period of 21 months (December 2004 – August 2006) and recorded ten acoustically-tagged zebra sharks (seven females and three males). The sharks showed clear seasonality in their visitation patterns with greatest presence during the austral summer months of November through to February and no presence at all during the winter months from June through to October. However their presence did not coincide with peak water temperatures. Rather there appeared to be a critical minimum water temperature of approximately 22 ºC, above which zebra sharks would be present. The tagged zebra sharks displayed greater visitation during the calmest sea conditions. The sharks further displayed diel periodicity with greater during daylight hours, and may be using The Group as a resting site during the inactive diurnal period of the day. Complementing the ecological study on the aggregation, the population genetic structure of 180 zebra sharks from 13 locations throughout the IWP was investigated to test the concordance of IUCN zones with demographic units that have conservation value. A zebra shark specific microsatellite library was developed consisting of 14 polymorphic loci of which 13 were employed for the population genetic analysis along with mitochondrial ND4 sequence data. Mitochondrial and microsatellite data-sets from samples collected throughout northern Australia and south-east Asia concord with the regional IUCN classifications. However, evidence of genetic subdivision was found within these regions, including subdivision between locations connected by habitat suitable for migration. Further, parametric FST analyses and Bayesian clustering analyses indicated the primary genetic break within the IWP is not represented by the IUCN classifications but rather is congruent with the Indonesian throughflow current. This study has demonstrated that zebra sharks form a large, predictable, shallow coastal aggregation comprised entirely of mature adults as well as display high genetic subdivision in the Indo-West Pacific region with little to no recruitment into over-exploited populations from healthy populations. These findings indicate that, if zebra sharks form similar aggregations as that which occurs at The Group in regions of high fishing pressure then, without sufficient protection and management localised depletion and extirpation will eventuate for zebra shark populations in heavily-fished areas.

L’ophiolite de Nouvelle Calédonie présente une des plus grandes sections de manteau océanique obductées au monde, offrant une perspective unique pour l’étude des processus du manteau supérieur. Les roches du manteau appartiennent à une séquence ophiolitique “atypique”, dominée par des harzburgites réfractaires avec quelques lherzolites à spinelle et à plagioclase. À l'exception de quelques cumulats mafiques-ultramafiques, la partie crustale de l'ophiolite est totalement absente. Cette ophiolite a été étudiée depuis plusieurs décennies, toutefois sa nature ultra-appauvrie a rendu très difficile une caractérisation géochimique détaillée. La littérature scientifique ne regroupe que quelques données sur les éléments en trace et les données isotopiques sont totalement inexistantes. Dans ce travail de thèse, une étude géochimique exhaustive (éléments majeurs, en trace et isotopes Sr-Nd-Pb) des péridotites et des roches mafiques associées à l’ophiolite a été réalisée. Les péridotites sont des tectonites avec des textures porphyroclastiques. Les lherzolites à spinelle ont 7-8 vol.% de clinopyroxène riche en Na2O et Al2O3 (jusqu’à Na2O 0.5 wt.%; 6.5 wt.% Al2O3), teneur en Fo de l’olivine de 88.5 à 90.0 mol.%, bas valeurs du Cr# du spinelle (13-17), attestant la nature fertiles de ces roches. A l’inverse les harzburgites costituent des roches très réfractaires : ils ne contiennent pas de clinopyroxène primaire et les teneurs en Fo de l’olivine (90.9-92.9 mol.%), le Mg# de l’orthopyroxène et le Cr# du spinelle (39-71) sont élevés. Les spectres de concentrations en REE présentent des caractéristiques typiques de formation dans un environnement abyssal pour les lherzolites à spinelle, alors que les harzburgites ont des spectres en U typiques d’environnement d’avant-arc. Les compositions en REE des lherzolites à spinelle sont compatibles avec un bas degré de fusion fractionnée (8-9%) d'une source DMM, commençant dans le domaine de stabilité du grenat. Au contraire les concentrations en REE des harzburgites indiquent un haut degré de fusion d’une source DMM, en accord avec une fusion hydratée en environnement d’avant-arc. Les lherzolites à plagioclase présentent des microtextures d’imprégnation, des spinelles riches en Cr2O3 et TiO2 et un enrichissement progressif en REE, Ti, Y, Zr. Les modèles des éléments en trace indiquent que les lherzolites à plagioclase résultent des lherzolites à spinelle par séquestration des liquides MORB très appauvris au sein de la lithosphère océanique.Les roches intrusives sont des gabbronorites à olivine avec des compositions très appauvries (87.3≤Fo ol≤88.9 mol.%, 87.7≤Mg# Cpx≤92.2, An Pl=90-96 mol.%). Le haut Mg#, le bas teneur de TiO2 des pyroxènes, la composition en anorthite du plagioclase et le modèle des éléments en trace montrent que les magmas parents des gabbronorites sont des magmas primitifs, très appauvries, formés dans un environnement de subduction. / The New Caledonia ophiolite hosts one of the largest obducted mantle section in the world, hence providing a unique insight for the study of upper mantle processes. These mantle rocks belong to an “atypical” ophiolitic sequence, which is dominated by refractory harzburgites but it also includes minor spinel and plagioclase lherzolites. Upper crust is notably absent in the ophiolite, with the exception of some mafic-ultramafic cumulates cropping out in the southern part of the island. Although the New Caledonia ophiolite has been under investigation for decades, its ultra-depleted nature has made its characterization an analytical challenge, so that few trace element data are available, while isotopic data are completely missing. In this thesis a comprehensive geochemical study (major, trace element and Sr-Nd-Pb isotopes) of the peridotites and the associated intrusive mafic rocks from the New Caledonia ophiolite has been carried out. The peridotites are low-strain tectonites showing porphyroclastic textures. Spinel lherzolites are undepleted lithotypes, as attested by the presence of 7-8 vol.% of Na2O and Al2O3-rich clinopyroxene (up to 0.5 wt.% Na2O; 6.5 wt.% Al2O3), Fo content of olivine (88.5-90.0 mol.%) and low Cr# of spinel (13-17). Conversely, harzburgites display a refractory nature, proven by the remarkable absence of primary clinopyroxene, very high Fo content in olivine (90.9-92.9 mol.%), high Mg# in orthopyroxene (89.8-94.2) and Cr# in spinel (39-71). REE contents show abyssal-type patterns for spinel lherzolites, while harzburgites display U-shaped patterns, typical of fore-arc settings.Spinel lherzolites REE compositions are consistent with relatively low degree (8-9%) of fractional melting of a DMM source, starting in the garnet stability field. Conversely, REE models for harzburgites indicate high melting degrees (20-25%) of a DMM mantle source under spinel faies conditions, consistent with hydrous melting in forearc setting. Plagioclase lherzolites exhibit melt impregnation microtextures, Cr- and TiO2-enriched spinels and REE, Ti, Y, Zr progressive increase with respect to spinel lherzolites. Impregnation models indicate that plagioclase lherzolites may derive from spinel lherzolites by entrapment of highly depleted MORB melts in the shallow oceanic lithosphere. Mafic intrusives are olivine gabbronorites with a very refractory composition, as attested by high Fo content of olivine (87.3-88.9 mol.%), very high Mg# of clinopyroxene (87.7-92.2) and extreme anorthitic content of plagioclase (An = 90-96 mol.%). The high Mg#, low TiO2 concentrations in pyroxenes and the anorthitic composition of plagioclase point out an origin from ultra-depleted primitive magmas in a convergent setting. Geochemical trace element models show that the parental melts of gabbronorites are primitive magmas with striking depleted compositions, bearing only in part similarities with the primitive boninitic melts of Bonin Islands. The first Sr, Nd and Pb isotope data obtained for the New Caledonia ophiolite highlight the presence of DM mantle source variably modified by different processes.Nd-Sr-Pb isotopic ratios for the lherzolites (+6.98≤ƐNdi≤+10.97) indicate a DM source that suffered low-temperature hydrothermal reactions. Harzburgites are characterized by a wide variation of Sr, Nd and Pb isotopic values, extending from DM-type to EMII compositions (-0.82≤ƐNdi≤+17.55), suggesting that harzburgite source was strongly affected by subduction-related processes. Conversely, combined trace element and Sr-Nd-Pb isotopic data for gabbronorites indicate a derivation from a source with composition similar to Indian-type mantle, but affected by fluid input in subduction environment.

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The West Pacific Warm Pool (WPWP) plays an important role in the global heat budget and global hydrologic cycle, so knowledge about its past variability would improve our understanding of global climate. Variations in WPWP precipitation are most notable during El Niño-Southern Oscillation events, when climate changes in the tropical Pacific impact rainfall not only in the WPWP, but around the globe. The stalagmite records presented in this dissertation provide centennial-to-millennial-scale constraints of WPWP precipitation during three distinct climatic periods: the Last Glacial Maximum (LGM), the last deglaciation, and the Holocene. In Chapter 2, the methodologies associated with the generation of U/Th-based absolute ages for the stalagmites are presented. In the final age models for the stalagmites, dates younger than 11,000 years have absolute errors of ±400 years or less, and dates older than 11,000 years have a relative error of ±2%. Stalagmite-specific 230Th/232Th ratios, calculated using isochrons, are used to correct for the presence of unsupported 230Th in a stalagmite at the time of formation. Hiatuses in the record are identified using a combination of optical properties, high 232Th concentrations, and extrapolation from adjacent U/Th dates. In Chapter 3, stalagmite oxygen isotopic composition (d18O) records from N. Borneo are presented which reveal millennial-scale rainfall changes that occurred in response to changes in global climate boundary conditions, radiative forcing, and abrupt climate changes. The stalagmite d18O records detect little change in inferred precipitation between the LGM and the present, although significant uncertainties are associated with the impact of the Sunda Shelf on rainfall d18O during the LGM. A millennial-scale drying in N. Borneo, inferred from an increase in stalagmite d18O, peaks at ~16.5ka coeval with timing of Heinrich event 1, possibly related to a southward movement of the Intertropical Convergence Zone (ITCZ). An inferred precipitation maximum (stalagmite d18O minimum) during the mid-Holocene in N. Borneo supports La Niña-like conditions and/or a southward migration of the ITCZ over the course of the Holocene as likely mechanisms for the observed millennial-scale trends. In Chapter 4, stalagmite Mg/Ca, Sr/Ca, and d13C records reflect hydrologic changes in the overlying karst system that are linked to a combination of rainfall variability and cave micro-environmental effects. Dripwater and stalagmite geochemistry suggest that prior calcite precipitation is a mechanism which alters dripwater geochemistry in slow, stalagmite-forming drips in N. Borneo. Stalagmite Mg/Ca ratios and d13C records suggest that the LGM climate in N. Borneo was drier and that ecosystem carbon cycling may have responded to the drier conditions. Large amplitude decadal- to centennial-scale variability in stalagmite Mg/Ca, Sr/Ca and d13C during the deglaciation may be linked to deglacial abrupt climate change events.