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Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140?km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population. 相似文献
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The coccolith assemblages from seafloor sediments over the inner shelf in the northern region of the KwaZulu- Natal Bight on the east coast of South Africa were identified and their distribution determined. In all, 29 Recent species and taxonomic groups, as well as 29 reworked species were recorded. The distribution of the Recent species appears to be governed by environmental features that have been documented in other studies: temperature, salinity, nutrient concentration and water circulation pattern, which reveals the long-term existence of a circulation cell in the sector between Durban Bay and the Thukela River. The outer edge of the cell consists of nutrient-enriched mixed layers and is characterised by an enhanced abundance of Gephyrocapsa oceanica, whereas the central region consists of a stratified nutrient-depleted water mass with elevated abundance of Umbilicosphaera sibogae, Florisphaera profunda, and a group of umbelliform species. The elevated levels of G. oceanica, coupled with the rarity of U. sibogae, F. profunda and the umbelliform species, confirm the presence of a permanent upwelling cell off Richards Bay. The maximum abundance of F. profunda found between Richards Bay and Lake Nhlabane indicates a region of nutrient-depleted (except for nitrite) conditions. 相似文献
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We present an efficient,robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies.With appropriate mathematical treatments,the apparent numerical difficulties associated with singularities in computing elliptic integrals are completely removed.Using a boundary element discretization procedure,the governing equations are transformed into a linear algebra matrix equation that can be solved by straightforward Gauss elimination in one step without further ... 相似文献
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自然和人为的灾害每年都使远东的中国和她的周边国家蒙受了巨大的经济损失。为了能快速地对这些灾害作出反应以减少损失,有效和及时地从外层空间监测灾害已成为了一项迫切的国家需要。为了改进现行系统的覆盖范围和覆盖周期,曾建议采用地球观测卫星网。然而,常规遥感卫星的高成本至今还使得这项建议难以实施。萨瑞大学的萨瑞卫星技术有限公司(SSTL)已经研制了一套性能高、寿命长的微型卫星,该卫星利用先进的对地观测有效载荷,具有较强的星载处理能力。利用该套卫星就可以极低的成本获得从空中对地球的常规观测。每颗微型卫星只需费用约250万美元,因此,投资不到1800万美元就能构建由7颗卫星组成的卫星网(星座)。微型卫星重量轻、体积小,只需一个小的发射器就可以把整个网发射到低地球轨道中。 相似文献
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