Condition assessment of lamprey populations in the Yorkshire Ouse catchment,north‐east England,and the potential influence of physical migration barriers

• 1. River lamprey (Lampetra fluviatilis) and sea lamprey (Petromyzon marinus) are designated features of the River Derwent Special Area of Conservation (SAC) and the Humber Estuary (a possible SAC). This study determined the condition of lamprey populations in the Yorkshire Ouse catchment by assessing the species composition, distribution, abundance and size‐structure of larval (ammocoete) populations in five major tributary rivers (Derwent, Swale, Ure, Nidd and Wharfe).
• 2. According to EU condition assessment criteria, Lampetra populations (assumed to be mostly river lamprey) are at present in favourable condition, with site mean (±SE) densities ranging from 2.7 (±1.2) to 160.3 (±50.5) individuals m^?2 (all river means >2 individuals m^?2), and at least two size (≈age) classes present in optimal microhabitats. By contrast, no sea lamprey larvae were recorded, suggesting that populations of this species are in unfavourable condition.
• 3. Actions to protect and enhance nationally or internationally important stocks must be implemented from at least a catchment perspective, because many of the issues affecting such species are not localized. With respect to lampreys, particular attention should be given to protecting spawning and nursery habitats, improving water quality, reducing impingement at abstraction points, preventing exploitation at spawning grounds and increasing passage at potential physical obstructions.

Copyright © 2007 John Wiley & Sons, Ltd.     

The pond's shape matters: differential growth,physiological condition and survival of epibenthic Farfantepenaeus aztecus postlarvae

As a function of the water quality provided by square, circular and oval experimental ponds, the growth, survival and oxygen requirements in epibenthic postlarvae of Farfantepenaeus aztecus were analysed in relation to their routine metabolism and apparent heat increment. Temperature, oxygen concentration, pH and salinity were measured daily in two experimental ponds of each shape. The postlarvae oxygen consumption during two 24‐h cycles, their growth, physiological condition and survival and the productivity in the ponds were estimated. Low values of pH, oxygen concentration and phytobenthos productivity, and reduced postlarvae relative growth and survival were observed in the square ponds. We suggest that the latter results from a deficient water circulation related to the effect of the pond's shape on dissolved oxygen levels and, consequently, on growth and survival. The postlarvae routine metabolism, including feeding, varied between 1.91 and 2.25 mg O₂ h^?1 g^?1 wet weight, whereas the minimum oxygen concentration needed in the ponds is approximately 4.25 mg O₂ L^?1. These conditions were achieved in the oval ponds concurrent with higher survival and growth values, in which individuals distributed randomly, for which we suggest that oval‐shaped ponds could be the most adequate for the culture of this and other penaeid species.     

福建海洋渔业产业结构调整对策的探讨

一种产业的高速发展能否得以持续,关键在于是否对该产业结构进行不断调整,使之趋于最合理状态。为再度振兴福建海洋渔业,不失时机地进行渔业结构战略性调整是唯一选择。     

不同栽培技术对马铃薯水份利用率的影响

在三种不同的栽培技术中,地膜覆盖平均WUE为1.69kg/mm较平作平均WUE1.26kg/mm提高34.13%水分利用率,垄作平均WUE为1.47kg/mm较平作提高16.67%水分利用率,脱毒马铃薯的平均WUE为1.60kg/mm,未脱毒马铃薯的平均WUE为1.34kg/mm,水分利用率提高19.35%。平作种植方式马铃薯现蕾至成熟期需水量占整个生育期到90%左右;垄作种植方式76.86~83.3%;地膜覆盖种植方式73.08~77.08%,垄作与地膜覆盖后马铃薯水分的利用趋于合理。进行地膜覆盖和垄作后能使植株健壮,单窝薯重,大中薯商品薯率高,从而提高马铃薯的产量。     

Cost minimization and input substitution in the production of gilthead seabream

Abstract

This paper studies cost minimization decisions by utilizing a simple bioeconomic model for gilthead seabream (Sparus aurata). This model is based on a biological growth model which accounts for the effects of temperature and ration size. Although the implicit production function derived from the growth model is shown to be quasiconcave, it is not homothetic nor quasilinear. Further, technology shows increasing returns with respect to ration size and harvesting time. Optimization decisions are analyzed in two different contexts, a restricted biological setting and an expanded economic problem. It is shown that the optimal ration size increases for the latter context, reaching values commonly accepted in current industrial practice. Even though the elasticity of substitution to the shadow input prices is positive at the optimal ration size, the latter is rather robust to changes in input prices. However, optimal costs show larger sensitivity to the labor price than to the feeding and managerial costs.     

Habitat associations of dolphinfish larvae in the Gulf of Mexico

The aim of this study was to investigate the role of the northern Gulf of Mexico (Gulf) as essential habitat of common dolphinfish (Coryphaena hippurus) and pompano dolphinfish (C. equiselis) during early life and to characterize conditions in which they were found. Eight ichthyoplankton surveys were conducted during the summer months from 2007 to 2010 in northern Gulf waters off Texas and Louisiana (26–28°N, 87–93°W), during which 1145 dolphinfish larvae were collected. C. hippurus, the dominant dolphinfish species, were collected in 57% of sampling sites with an overall mean density of 0.73 larvae 1000 m^?3, whereas C. equiselis were only collected at 18% of sites with a mean density of 0.12 larvae 1000 m^?3. Generalized additive models (GAMs) were used to examine the relationship between several environmental parameters and C. hippurus presence/absence and density. Both presence/absence and density GAMs indicated that catches of C. hippurus larvae increased near fronts and eddies and that increased abundances were most strongly associated with higher salinities and cooler temperatures. In addition, our models showed that C. hippurus larvae were positively associated with C. equiselis larvae, suggesting that C. hippurus and C. equiselis use similar habitats. Results of this study indicate that the Gulf may represent important spawning and/or nursery habitat of dolphinfishes and that mesoscale features and physicochemical conditions influence the distribution and abundance of C. hippurus larvae in this region.     

我国特有单种属植物蒜头果的保护与利用研究状况

蒜头果(Malaniaoleifera Chun et S.K Lee)为我国特有单种属树种,被列为国家二级保护植物,仅分布于我国云南、广西两省。调查资料表明蒜头果个体数量急剧下降,现已处于濒危状态。本文概括了我国对蒜头果的保护与开发利用研究状况,分析了在这两个方面存在的问题,并针对问题提出了建议与对策。     

国家级生态乡镇建设与农村生态经济的互动效应

创建国家级生态乡镇活动的12年多来,开展创建国家级生态乡镇活动与生态经济可持续发展之间,产生了良好的互动效应,有利于提升农村的生态文明水平,有利于实现农村经济发展与环境保护的"双赢"。该研究基于国家级生态乡镇建设指标体系的导向作用,分析了国家级生态乡镇建设的示范作用及社会效益。     

移栽期与施氮量对烟叶产质量的影响

为探究适宜陕西洛南烟区的烤烟移栽期和施氮量,试验以云烟99为供试材料,对比不同移栽期(4月25日、5月1日、5月6日)和施氮量(112.5 kg/hm~2、120 kg/hm~2、127.5 kg/hm~2)对烤烟主要生育期、农艺性状、病害发生、经济性状等的影响。结果表明,在洛南以5月1日移栽、施氮量为120 kg/hm~2时,烟叶品质最优。     

我国地下水开发利用中的水环境问题及其对策

论述了我国地下水开发利用中出现的区域地下水位下降、地下水资源枯竭、地下水水质恶化、海水入侵、地面沉降、地面裂缝和地面塌陷等水利环境问题,并提出了对策与建议,以期达到环境保护成为社会发展过程中的一个重要组成部分。