An approach to estimating rockfish biomass based on larval production, with application to Sebastes jordani

An assessment of the total biomass of shortbelly rockfish (Sebastes jordani) off the central California coast is presented that is based on a spatially extensive but temporally restricted ichthyoplankton survey conducted during the 1991 spawning season. Contemporaneous samples of adults were obtained by trawl sampling in the study region. Daily larval production (7.56 × 1010 larvae/d) and the larval mortality rate (Z=0.11/d) during the cruise were estimated from a larval “catch curve,” wherein the logarithm of total age-specific larval abundance was regressed against larval age. For this analysis, larval age compositions at each of the 150 sample sites were determined by examination of otolith microstructure from subsampled larvae (n=2203), which were weighted by the polygonal Sette-Ahlstrom area surrounding each station. Female population weight-specific fecundity was estimated through a life table analysis that incorporated sex-specific differences in adult growth rate, female maturity, fecundity, and natural mortality (M). The resulting statistic (102.17 larvae/g) was insensitive to errors in estimating M and to the pattern of recruitment. Together, the two analyses indicated that a total biomass equal to 1366 metric tons (t)/d of age-1+ shortbelly rockfish (sexes combined) was needed to account for the observed level of spawning output during the cruise. Given the long-term seasonal distribution of spawning activity in the study area, as elucidated from a retrospective examination of California Cooperative Oceanic Fisheries Investigation (CalCOFI) ichthyoplankton samples from 1952 to 1984, the “daily” total biomass was expanded to an annual total of 67,392 t. An attempt to account for all sources of error in the derivation of this estimate was made by application of the delta-method, which yielded a coefficient of variation of 19%. The relatively high precision of this larval production method, and the rapidity with which an absolute biomass estimate can be obtained, establishes that, for some species of rockfish (Sebastes spp.), it is an attractive alternative to traditional age-structured stock assessments.

东湖螅状独缩虫(纤毛门:寡膜纲)的异质性

以螅状独缩虫(Carchesium polypinumLinne,1785)为研究对象,利用RAPD技术对武汉市南湖、沙湖和东湖3个湖区的螅状独缩虫样本进行了DNA多态性比较分析,以确认种群并期望促进微型生物种群生态学研究。结果如下:(1)从120条随机引物中筛选到31条有清晰扩增条带的,其中20条引物扩增出172条条带清晰、多态性高的条带,片段大小为100~1600bp,而其余11个引物扩增出59条相对多态性差的清晰条带,片段大小为100~1500bp;(2)扩增产物经SPSS12.0与RAPDista

Ultrafast low-temperature grown AlGaAs/GaAs photorefractive quantum wells using point defects as capture centers

At a medium substrate temperature of 400 degrees C and a lower As flux, we have grown an ultrafast AlGaAs/GaAs photorefractive multiple quantum well (MQW) structure by molecular beam epitaxy. The as-grown sample exhibits strong photorefractive effect under the transverse Frantz-Keldysh geometry. A peak electroabsorption of 2100 cm(-1) is measured in the as-grown sample in an 11 kV/cm dc electric field, and the peak photorefractive diffraction efficiency can be 1.2%. After postgrowth annealing, the photorefractive effect becomes weak and disappears in samples annealed above 700 degrees C. Using optical transient current spectroscopy, deep levels are measured in these samples. It is found that deep levels are stable against annealing until 700 degrees C. Using a pump-probe technique, carrier lifetimes are measured at room temperature. We find that the as-grown sample has a lifetime of 20 ps, while the 700 degrees C annealed sample has a lifetime of more than 200 ps. The ultrafast lifetime in the as-grown sample is caused by point defects, not by As clusters. Our result show that AlGaAs/GaAs MQW structure grown around 400 degrees C has better performance of the photorefractive effect. (C) 1999 American Institute of Physics. [S0003-6951(99)04036-X].

基于SPEM的CMM软件过程元模型

软件企业在实施CMM(capabilitymaturitymodelforsoftware)的过程中面临最主要的障碍是如何将CMM软件过程模型转换成可实施的、体现组织过程特征的CMM实施过程模型.可以利用模型驱动架构MDA来支持CMM模型转换,其首要问题是建立CMM软件过程元模型.通过分析CMM软件过程,给出了面向CMM的软件过程工程元模型SPEM的扩展策略,提出了一个基于SPEM的CMM软件过程元模型——SPM-CMM.该元模型既支持CMM软件过程的抽象语法和规则语义,也支持利用UMLCASE工具操作CMM软件过程模型.