Habitat associations of upper Volga river fishes: Effects of reservoirs

Habitat associations of upper Volga river fishes are defined within a cycle of spawning, feeding and overwintering migrations. The migration cycles of resident riverine fishes are categorized as obligate rheophils, limno-rheophils and limnophils. Forty-four fish species in 14 families occurred in the upper Volga River before regulation. Four mainstem reservoirs were constructed on the upper Volga between 1937 and 1957: Ivankovo, Uglich, Rybinsk and Gorky. They are maintained in a stage of delayed and sustained annual flood pulse. Additional impacts of reservoir construction include the creation of a new pelagic habitat, replacement of floodplains by lacustrine littoral and sublittoral habitats, creation of a complex bathyal habitat from former river channels and replacement of riverine flow patterns by pelagic water mass circulations. Populations of rheophilic species declined, while a new pelagophilic fish guild developed. Forty-six fish species are now present; seven species were lost and nine introduced after impoundment. Spawning, feeding and wintering habitats are outlined for reservoir guilds. Ichthyomass increased three to four times following reservoir construction and commercial fish harvest from Rybinsk Reservoir between 1945 and 1992 ranged from 2220 to 4304 t/y. Reservoirs of the upper Volga have limited bioproductivity due to a deficiency and uneven distribution of reproductive habitats, decreasing bottom irregularity, seasonal anomalies of flooding and draining of the littoral and sublittoral and underestimating the importance of tributaries. Lack of littoral reproductive habitat can be remedied by increasing the area of protected littoral through the construction of chains of small islands, diking and reclamation of bogged areas. Improved reproduction of migrating local stocks can be achieved by removing sand bars across tributary mouths, construction of artificial spawning grounds and restoration and preservation of preferred habitats in the main channel.     

Hydrology and Nutrient Enrichment at Two Coastal Lagoon Systems in Northern Greece

The lagoons of N.E. Greece, located on the western side of NestosRiver, and of N.W. Greece, located at the lower reaches of Kalamas River, are among the most important shallow, semi-enclosed ecosystems in Northern Greece. The temporal variability of nutrients at both lagoonal systems shows the strong influence of fresh water discharge on water quality. Nutrient enrichment factors showed that nitrites and ammonium were six times higher at the lagoons of N.W. Greece than those observed at N.E. Greece, while phosphates were forty times higherat Nestos River lagoons. The flushing half-life was calculatedbased on a combination of hydrological and tidal processes, foreach lagoon of these two systems, allowing for the assessment ofwater quality changes. Proper management measures for both systems should focus on the control of fresh water quality entering the lagoons, the reduction of phosphoric fertilizers used by agriculture and the better oxygenation of the water column. One way to eliminate massive fish deaths during the winter in N.E. Greece is also the transfer of fresh, warm groundwater, while bathymetric modifications and channel wideningare needed at the lagoons of N.W. Greece.     

Catches of Larval Rainbow Smelt (Osmerus Mordax) and Alewife (Alosa Pseudoharengus) in Plankton Nets of Different Mesh Sizes

Four 0.5-m plankton nets (one each of 0.355-, 0.450-, 0.560-, and 0.750-mm mesh) were used to collect larvae of the alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) in northwestern Lake Huron and the St. Marys River. The number of larvae collected varied inversely with mesh size and the average length of larvae varied directly with mesh size. Numbers of each species caught in 0.355- and 0.450-mm mesh nets were significantly greater (P < 0.01) than the numbers caught in 0.560- and 0.750-mm mesh nets. Numbers of alewives caught were significantly greater (P < 0.01) in the 0.355- than in the 0.450-mm mesh, but numbers of rainbow smelt caught in the two meshes were about equal. Between the two larger-mesh nets, numbers of each species caught did not differ significantly. Nets with mesh larger than 0.355 mm were less effective at catching recently hatched larvae, and this reduced effectiveness accounted wholly for the smaller numbers caught in the 0.450-mm mesh net. Smaller numbers were caught in the 0.560- and 0.750-mm mesh nets not only because they caught fewer recently hatched larvae but also because they failed to retain older, larger larvae. Information on the effect of mesh size and towing speed on catches of larvae is important for making accurate estimates of larval densities.     

Gordleton磨坊小水电改造工程水能开发和环境影响评估

水能和环境影响的评估,对于判别英格兰新福里斯特区埃文河Gordleton磨坊重新安装一台改良水车或一台水轮机或一台阿基米德式螺旋水轮机的可行性和经济性是至关重要的。基于一个典型水文年份年平均径流量0.41m3/s且合理利用水资源的方案,Gordleton磨坊改造后的年电力输出为26000~30000kW·h。实地调查并记录了当前的环境变量,包括土地利用、植被、基层、水质、鱼类、无脊椎动物和噪音等。其中,鱼类洄游,特别是受法律保护的二龄鲑,将会受到工程影响,需要安装网格为1cm2的护鱼筛网并提供鱼道。噪音和振动也是主要的环境影响,采用隔音材料可以降低其负面作用。推荐采用0.15m3/s的旱季生态系统的补偿流量。     

Methods for Environmental and Economic Accounting for the Exploitation of Wild Fish Stocks and their Applications to the Case of Icelandic Fisheries

The paper discusses methods for estimating the value of commercially exploited fish stocks and the cost of exploiting them. Methods which are recommended in the System of National Accounting (SNA) satellite system and the System for Integrated Environmental and Economic Accounting (SEEA) and relevant for this task are discussed. The paper questions the relevance of some of these methods. It argues for the integration of economic accounting for wild fish stocks with estimation of efficient management of them. Using biological and economic data makes it possible to produce consistent estimates of the value of fish stocks and the cost of exploiting them. These estimates are useful for national accounting and for guiding management of fisheries. This method allows estimation of the cost of inefficiency of fisheries management besides estimation of the cost of depletion. The different methods are illustrated using data on commercial fisheries in Iceland and the fish stocks that they exploit. It is shown that even if all methods are based on market valuation and use only objective data they lead to very different outcomes.     

Estimating Larval Fish Abundances from Plankton Net Catches in Long Point Bay,Lake Erie,in 1971–78

Larval fish were sampled in Long Point Bay each summer in 1971–78 by towing ½– and 1-m diameter plankton nets at about 1 m/s. We report on the analysis of 2,576 tows, giving detailed consideration to sampling problems and statistical methods. The most common larvae were rainbow smelt (Osmerus mordax), caught in about 50% of the tows, and yellow perch (perca flavescens), clupeids, and cyprinids, caught in about 10 to 20% of the tows. Most of the data contained too high proportions of zero catches to be transformed to approximately normal distribution, and were therefore analyzed using the log-linear model rather than by analysis of variance. Except for cyprinids, larval fish seemed to be scarce in surface waters during the day. Small (4 to 10 mm long) smelt and perch larvae were caught more frequently in 526– than in 782–μm mesh nets. Very few perch and cyprinid larvae longer than 10 mm were ever caught. This, and a more rapid decline of daytime than nighttime catches of larval smelt through the mid-summer, suggests that the nets were avoided by at least the larger larvae. If avoidance of sampling gear is substantial, larval fish abundances may be overestimated in years of slow growth when the larvae remain catchable longer. We saw no evidence that the recent industrial development at Nanticoke, Ontario, has affected larval fish abundances so far. As the annual mean densities of larval fish varied 15-fold or more, it would require several years of observation to detect any but drastic future change from the current levels of abundance.     

封闭箱体海洋水产养殖系统设计工序研究

本文旨在研究海水环境中刚性封闭箱体水产养殖系统的潜在设计工序。封闭箱体水产养殖技术通过限制并操控养殖鱼类与外部水环境相互作用以将环境影响最小化。系统的箱体单元通常紧密排布并锚泊到海底。研究关注的地理区域在加拿大不列颠哥伦比亚省乔治亚海峡。本文研究了含多个单元的箱体水产养殖系统的设计构造。设计程序包括检验以下内容:当地环境条件;多个箱体单元上受到的阻力;波浪荷载;无阻尼升沉运动;锚泊设备组件;刚性控制结构的材料应力。还讨论了操作以及其它设计要素。初步研究结果表明波浪力是至关重要的。     

Dam effects on bedload transport on the upper Santa Ana River,California, and implications for native fish habitat

Dams disrupt the flow of water and sediment and thus have the potential to affect the downstream geomorphic characteristics of a river. Though there are some well‐known and common geomorphic responses to dams, such as bed armouring, the response downstream from any particular dam is dependent on local conditions. Herein, we investigate the response of the upper Santa Ana River in southern California, USA, to the construction of a large dam at the transition from mountains to valley, using calculations of bedload transport capacity on the mainstem below the dam and for major tributaries. Approximate sediment budgets were constructed for downstream reaches to estimate deposition and erosion rates for sand, gravel, and cobble particle sizes. Our results indicate that the classical response of bed armouring and erosion is likely limited to a short reach immediately below the dam. Farther downstream, though transport capacity is reduced by flow regulation by the dam, the channel reaches are likely to remain depositional but with reduced deposition rates. Persistent deposition, as opposed to erosion, is the result of the replenishment of flow and sediment supply by large downstream tributaries. In addition, the calculations indicate that the composition of the bed is unlikely to change substantially in downstream reaches. A Monte Carlo approach was employed to estimate the uncertainty in the sediment budget predictions. The impacts of the dam on the geomorphic character of the river downstream could have implications for native fish that rely on coarse substrate that supports their food base.     

Has a non‐native cichlid of the genus Amatitlania (Actinopterygii,Cichlidae) adapted to the headwaters in Brazilian semi‐arid?

Several fish species from Central America and other regions have been introduced into Brazil. In this study, we evaluated the bioecological aspects of a non‐native cichlid of the genus Amatitlania (convict cichlid) and its possible establishment in high‐altitude forest enclaves of semi‐arid Northeastern Brazil. Specimens of Amatitlania nigrofasciata (Günther, 1867) were captured in a local stream displaying abiotic conditions like those of its natural range of distribution. The individuals collected were predominantly adult, insectivorous and displayed normal length–weight relationships, although we observed some phenotypical plasticity (variation in body depth, and a morphologically abnormal dorsal fin in three cases). Our results indicate that A. nigrofasciata has successfully colonized an Atlantic forest enclave in the Brazilian semi‐arid region, making it necessary to adopt measures to prevent the species from spreading to other water bodies in the surroundings.