Structure and dynamics of demersal fish assemblages over three decades (1985–2012) of increasing fishing pressure in Guinea

In a context of growing fishing pressures and recommendations for an ecosystem approach to fisheries, there is a need to monitor changes in fish communities over time. In this study, we analysed data from scientific trawl surveys carried out on the continental shelf off Guinea between 1985 and 2012. We performed factorial analyses and calculated biodiversity indices to characterise the changes in the structure and composition of fish communities that occurred over the 28-year period in this area, particularly given intensive fishing activities. We show that, over the study period, fish communities on the Guinean shelf were structured primarily according to spatial factors, with temporal changes being less pronounced than expected. However, a temporal analysis of biodiversity indices and species dominance showed that the intensification of fishing had significant effects on the general ecological features of the fish assemblages under study. There was a decrease in fish density and in mean trophic level. In addition, there were changes in species dominance, whereby large, slow-growing species with high commercial value were gradually replaced by smaller, fast-growing species of lesser commercial interest. These results from field observations are in line with some conclusions from previous modelling studies in the same geographical area, and provide further support for the hypothesis of a progressive ‘ecosystem effect of fishing’ occurring in Guinean waters.     

Age and growth of redeye round herring Etrumeus whiteheadi off the South African coast

Ages of redeye round herring Etrumeus whiteheadi were estimated with associated errors and used to infer life-history information, such as age composition, age-at-maturity and instantaneous mortality rate. Samples were collected in November 2005 during a research survey aimed at estimating the biomass of spawning pelagic fish off South Africa’s west and south coasts. Replicate age estimates obtained from sagittal otoliths were collected with slight bias and relatively high precision. A von Bertalanffy model describing growth of the combined sexes, including juveniles, was L_t = 20.41(1 ? e^{?0.41(t ? 1.92)}). Kimura’s likelihood ratio test revealed no statistically significant differences between growth parameters of males and females. Results suggested that otolith length is a better predictor of age than otolith weight. Maturity estimates for E. whiteheadi were similar to those previously documented.     

Spawning of major carps in the lower Halda River,Bangladesh

Spawning biology and spawn fishery of three valuable species of Indian major carps,Catla catla, Labeo rohita andCirrhinus mrigala, in the lower Halda River, Bangladesh, were studied in 1978. The major carps spawned only in the Sonairchar oxbow-bend from April to June on or near the dates of the full moon and the new moon. The tide was then at its highest level, and there was heavy flood water runoff from the hill region with sharp increases in water level, turbidity and current velocity, as well as decreases in water temperature, dissolved oxygen, and hydrogen ion concentration. These three heterogeneric species, as a result of parallelism or convergence in evolution, overlap in their environmental requirements for spawning. The nursery ground of the major carp fry spawned in the Halda River was found to be in the Bay of Bengal. The brood stock origin is suspected to be at the Shankha River, 40 miles south of the Karnafuli River. The spawn fishery in the Halda River was intensive but inefficient. Engineering works and water management schemes are threatening the spawning habitat.     

Dynamics and seismic performance of rocking bridges accounting for the abutment-backfill contribution

The present study explores analytically the concept of rocking isolation in bridges considering for the first time the influence of the abutment-backfill system. The dynamic response of rocking bridges with free-standing piers of same height and same section is examined assuming negligible deformation for the substructure and the superstructure. New relationships for the prediction of the bridge rocking motion are derived, including the equation of motion and the restitution coefficient at each impact at the rocking interfaces. The bridge structure is found to be susceptible to a failure mode related to the failure of the abutment-backfill system, which can occur prior to the well-known overturning of the rocking piers. Thus, a new failure spectrum is proposed called Failure Minimum Acceleration Spectrum (FMAS) which extends the overturning spectrum put forward in previous studies, and it differs in principle from the latter. The comparison with the dynamic response of bridges modelled as rocking frames without abutments reveals not only that seat-type abutments and their backfill have a generally beneficial effect on the seismic performance of rocking pier bridges by suppressing the free rocking motion of the frame system, but also that the simple frame model cannot capture all salient features of the rocking bridge response as it misses potential failure modes, overestimating the rocking bridge's safety when these modes are critical.     

南海北部陆架和陆坡区小型底栖动物群落的比较研究

为了解南海北部陆架与陆坡区小型底栖动物的群落特征,以及影响群落特征的环境因素,2015年6月对南海北部海域(19.3°—21.4°N, 112.4°—115.1°E)7个站位的小型底栖动物及环境因子进行了采样,并对陆架和陆坡区小型底栖动物群落的丰度、生物量、类群组成和群落结构进行比较。结果表明,在陆架站位,小型底栖动物由13个类群组成,平均丰度为(132±130)ind./10cm2,平均生物量为(169±79)μgdwt/10cm2;在陆坡站位由8个类群组成,平均丰度为(33±14)ind./10cm2,平均生物量为(56±35)μgdwt/10cm2。单因素方差分析结果表明,陆坡区小型底栖动物的总丰度和总生物量以及线虫和多毛类的丰度均显著低于陆架区,但优势类群的相对丰度组成没有显著不同,海洋线虫占总丰度的83%,其次为多毛类和桡足类,分别占7%和3%。环境因子的主成分分析(Principal ComponentsAnalysis,PCA)将陆架和陆坡站位沿第一主分量轴分开,小型底栖生物丰度和生物量与沉积物叶绿素a和脱镁叶绿酸含量以及底层水温呈最大正相关,与水深呈负相关;聚类(Cluster)和排序(non-metric Multidimensional Scaling, MDS),以相似性系数65%将7个站位划分为2组,与按照水深划分的陆架和陆坡组基本吻合;单因素相似性分析(one-way ANOSIM)显示陆架和陆坡区小型底栖动物群落结构差异显著;生物-环境分析(Biota-Environment,BIOENV)表明影响群落结构的最佳环境因子组合为叶绿素a和底层水温。综上可知,随水深增加的食物减少和底层水温的下降是限制南海北部研究海域小型底栖动物丰度和生物量及影响群落组成和结构的主要因素。     

Screened triple-alpha reaction rate to produce carbon in stellar interiors

Recent experimental data for radiative width and resonance energy are used to find reaction rates and mean lives for triple-alpha reaction affecting screening effect. The reaction rates are found to be drastically altered. Plots of various dimensionless parameters in temperature-density plane are given. The red-giant sttage will be of short duration. The mean lives for gravitationally collapsing stars are insignificantly small. Our results at ?=10⁵ g cm^?3 greatly differ fro those of Burbidgeet al. (1957).     

Unusual Carbonatite Lavas from Active Volcano, Oldoinyo Lengai

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Unusual Carbonatite Lavas from Active Volcano, Oldoinyo Lengai     

RANK-ORDER ANALYSIS FOR ROBUST MULTIRESPONSE,MULTIBLOCK COMPARISONS:EVALUATION OF HERBICIDE INTERACTIONS

Studies of interactions among bioactive compounds are often difficult to interpret unambiguously.A priori assumptions about the nature of such interactions can seriously distort analysis of the data.Byapplying a rank order analysis appropriate to the naturally ordinal scale of response to xenobiotic insult,several co-herbicides were successfully identified from among numerous candidates in an experimentinvolving multiple blocks,rates and species.Moreover,underlying herbicide interactions weresubstantiated and identified which were not apparent by more traditional parametric analysis.     

Helium plasma: Pycnonuclear triple alpha reaction rates in stars

The plots of dimensionless parameters, for helium plasma are given, as they are of great importance for the study of physical conditions prevalent in stellar interiors consuming helium. The relevant temperature and density leading to weak and strong screening can be obtained from the plots to compute the effect of screening to enhance the thermonuclear reaction rates. To make a realistic approach, the pycnonuclear triple alpha reaction rates are found for the 7.66 (O⁺) MeV level for pair creation. The equation used here is suitable for white dwarfs satisfying 0<3/1. The rates are enhanced approximately 10⁴² times, which indicates that the mean life will be reduced by the same factor. The extent of the pycnonuclear regime is shown in diagram.