Fluid dynamic properties of a soft shell float with open bottom

ABSTRACT:   A physical model of a soft shell underwater float with an openbottom was constructed and the float was subjected to sinusoidaloscillation in the vertical direction in order to investigate the relationsbetween the characteristic properties of the buoyancy and fluidforces in the movement of the float. No change in the fundamentalperiod of the float was seen in response to the imposed oscillation,but there was a lag in the phase of the float response of up toone-quarter wavelength. Various fluid force factors approached valuesreported for a globular buoy as the float was increasingly filledwith air, but hysteresis was very low. The drag coefficient showedmuch scatter. The dominant factor for control of vertical movementof a soft shell float with open bottom was buoyancy, not fluid resistanceforce. It was concluded that for the purposes of design and controlof these systems, only the float volumetric capacity and air capacitymust be considered.     

The life history of Tenualosa macrura in Sarawak, further notes on protandry in the genus and management strategies

Abstract  The contraction of Tenualosa macrura (Bleeker) to the Sarawak coast and a small part of Sumatra, and the decline in its fishery mirror what has happened to three other species in the genus. Little was known of this species in its last stronghold in Sarawak where it is important for management and conservation reasons to understand its biology and life history. It forms part of a multispecies fishery where effort is uniform, but catches follow a lunar cycle. Tenualosa macrura is protandrous, but low numbers of small females suggest diandry. In Sumatra Tenualosa macrura spawn throughout the year, but in Sarawak have a seasonal peak in the NE monsoon (December). This has management implications because the Sarawak fishery ceases at this time because of adverse weather, hence reducing fishing pressure on spawning T. macrura . Management measures introduced in Sarawak for Tenualosa toli (Valenciennes) may therefore not be required for T. macrura .     

Status and management of fish populations of Rawal Dam reservoir, Pakistan

Abstract Studies were conducted to determine the composition and relative abundance of commercially desirable and less desirable fish populations of Rawal Dam reservoir. Fifteen fish species belonging to 11 genera were identified. The less desirable species were abundant, constituting 62.3%, 84.8% and 78% of the total number of fish sampled on three occasions. Carnivores were represented by two species with very low percentage composition by number or weight. The ratio of total weight of forage fish to that of carnivorous fish indicated an unbalanced population in the lake. The proportion of the fish population at harvestable size suggests a balanced population, but this index may have been overestimated because of a minimum harvestable size.     

Recent changes in the trophic structure of the Black Sea

During the past few decades, the Black Sea has been subjected to various human impacts that have led to changes in the ecology of this inland sea. River runoff has introduced high levels of certain heavy metals and other toxic substances as well as detergents. Ship traffic has led to the introduction of new species, and fishing pressures have also altered the ecology of the area.
This paper reviews major ecological changes over the past 40 years. An increase in nutrients has caused eutrophication, with outbursts of phytoplankton blooms and changes in the species composition of these algae. Small-sized zooplankton species and gelatinous zooplankton have become more common, while many of the herbivorous copepods have decreased in abundance or have disappeared. The introduction of the predatory ctenophore Mnemiopsis leidyi in the 1980s has had significant impact on the plankton community and has led to a sharp decline in anchovy stocks. Decreased water transparency has led to a loss of macrophytic algae, except in shallow waters, and to a subsequent decline in the zoobenthos associated with this flora. Eutrophication has also led to decreased oxygen concentrations in the near-bottom water due to large amounts of decomposing phytoplankton, and regions of hypoxia and anoxia now appear on the shelf, with consequent reduction in benthic populations of invertebrates and demersal fish. The numbers of fish species harvested commercially have fallen from 26 to 5, but the total catch has increased, owing to increases in abundance of small fish (e.g., sprat) and horse mackerel, and to increased fishing effort.     

渔用自增强聚乙烯单丝的拉伸力学性能分析

在标准实验室环境里,对渔用自增强聚乙烯(self-reinforced polyethylene,简称SRPE)单丝的结晶形态、拉伸力学性能进行了分析。结果表明：渔用SRPE单丝结晶度、声速值比普通聚乙烯(polyethylene,简称PE)单丝均有提高,其内部生成了串晶结构;SRPE单丝断裂强度、结节强度和结强损失率比普通PE单丝分别提高了12．75％、4．82%和12．69％,而断裂伸长率降低了27．72％。结论可供渔具设计及网线材料选配时参考。     

山东省海洋渔业产业集群复杂网络分析

选择《山东省统计年鉴》与互联网中山东省海洋渔业相关企业的数据,应用复杂网络相关理论和Pajek软件对山东省海洋渔业的网络统计特征进行了相关研究,并提出了相应的对策,即推进海洋生态建设与健全渔业资源管理体制。     

Molecular species identification and population genetics of chondrichthyans in South Africa: current challenges,priorities and progress

Molecular genetic techniques, such as DNA barcoding and genotyping, are increasingly being used to assist with the conservation and management of chondrichthyans worldwide. Southern Africa is a shark biodiversity hotspot, with a large number of endemic species. According to the IUCN Red List, a quarter of South Africa's chondrichthyans are threatened with extinction. South Africa's commercial shark fisheries have increased over the last decade and there is a need to ensure sustainable utilisation and conservation of this fisheries resource. Here, we give an overview of the molecular techniques that are used to assist in the identification of species, cryptic speciation and possible interspecific hybridisation, as well as the assessment of population structure and reproductive behaviour of endemic and commercially important chondrichthyan species of southern Africa. We discuss the potential application of these techniques for management and conservation of several species affected by South African fisheries. Acquiring baseline barcode data of all chondrichthyans in southern African waters and assessing the population structure of exploited species on a local and greater regional scale are recommended as research priorities. Future prospects should also include high-throughput molecular marker development and investigation of intraspecies functional variation using next generation sequencing technology.     

The onset of spawning in the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters and its implications for management

Abstract The spawning periodicity of silver pomfret, Pampus argenteus (Euphrasen), was investigated against a background of conflicting evidence on the onset of spawning in this species. Contrary to the existing view that silver pomfret in Kuwait waters begin to spawn in March–April, evidence is presented that indicates a delay in spawning until May. Only an insignificant level of spawning takes place in April which, from the management point of view, may be ignored. The species has a prolonged spawning period extending from May to August in females, although the males mature in April and ripe specimens are encountered in monthly samples until September. There are two spawning peaks, the first one in May and the second in August.     

Developing socioeconomic indicators for an ecosystem-based fisheries management approach: An application to the Korean large purse seine fishery

Developing socioeconomic indicators for ecosystem-based fisheries management is particularly important. This is because socioeconomic factors have direct effects on ecosystems, and ecosystems have direct effects on socioeconomic factors. Therefore, it is imperative that socioeconomic indicators are developed and evaluated in order to predict changes in ecosystems and to provide advice for effective fisheries management. In this study, socioeconomic indicators have been developed to be combined with biological and ecological indicators, in order to conduct the ecosystem-based fisheries assessment. In terms of socioeconomic indicators, five socioeconomic criteria were considered as important attributes of socioeconomic changes. These were economic production, business conditions, levels of income, the state of the market, and levels of employment. In order to establish reference points for the evaluation of indicators, target reference points and limit reference points were set through a comparison with other industries or other fisheries rather than by using the Traffic Light System (TLS) method, which has been used in many previous studies. In addition, on the basis of the application of developed indicators and reference points to the Korean large purse seine fishery, the socioeconomic conditions of the fishery and the usefulness of the indicators were evaluated and management implications were discussed.