Growth,mortality and recruitment of Nile perch (Lates niloticus) in Lake Victoria,Kenya

This study investigated the growth, mortality and recruitment of Lates niloticus in Lake Victoria basis on length–frequency data collected during the period 2014‐2015. The asymptotic length (L _∞ ) had a value of 124 cm TL , growth curvature (K ) of 0.22 year^?1, total mortality (Z ) of 0.96 year^?1, a natural mortality (M ) of 0.42 year^?1, a fishing mortality (F ) of 0.54 year^?1, an exploitation rate (E ) of 0.57 and a growth performance index () of 3.53. Logistic selection model showed that 50% of fish of 46.09 cm TL encountering the gear are retained. There were two peak recruitment periods, a minor one in March and a major one in July, accounting for 12.04% and 22.04%, respectively, of the total fish catch. The Beverton and Holt's relative yield‐per‐recruit model indicated the indices for sustainable yields are 0.32 for optimum sustainable yield (E _0.5), 0.60 for maximum sustainable yield (E _max) and 0.51 for economic yield (E _0.1). Compared to previous findings, there is a great decline in the sizes of Nile perch stocks in Lake Victoria. Thus, managing the fishery requires strict adherence to the slot size of 50–85 cm TL , and restrictions on illegal gear and methods, by the devolved governments through monitoring, control and surveillance in liaison with the Beach Management Units (BMU s).     

马正开海(河)堤工程建设对防城湾水动力条件的影响分析

分析了防城港马正开海（河）堤工程建设对防城湾环境的影响,包括对防城湾潮流流场及滩涂演变可能造成的影响,对防城江行洪和纳潮量的影响。提出了控制和减缓环境影响的措施。     

Effects of water clarity on the length and abundance of age-0 yellow perch in the Western Basin of Lake Erie

Water clarity is an important environmental variable that may affect fish populations by altering the visual environment. Effects can change feeding ability, as well as alter predation risk. The western basin of Lake Erie provides a valuable model system for studying the effects of transparency because the two main tributaries, the Maumee and Detroit rivers, differ substantially in clarity. We used Generalized Additive Models (GAMs) to quantify the relationship between transparency and the observed abundance and length of age-0 yellow perch (Perca flavescens) in August, based on surveys from 1986 to 2006. Secchi data from June to August were included in the models that best explained the variation in yellow perch abundance and length. August values for bottom oxygen and bottom temperature also increased model fit for abundance, whereas only bottom temperature improved model fit for length. Our models indicate that transparency was positively related to the August length while abundance of age-0 yellow perch was inversely related to transparency. Highest abundance was observed in areas with the lowest transparency, with peak abundances observed in areas with less than 1 m of Secchi depth. This is in contrast to August length, which increased as transparency increased, to an asymptote at around 3 m of Secchi depth. The split nature of water clarity conditions in the western basin of Lake Erie has resulted in areas with higher growth potential, versus areas with higher apparent survival.     

Effects of dams in river networks on fish assemblages in non‐impoundment sections of rivers in Michigan and Wisconsin,USA

Regional assessment of cumulative impacts of dams on riverine fish assemblages provides resource managers essential information for dam operation, potential dam removal, river health assessment and overall ecosystem management. Such an assessment is challenging because characteristics of fish assemblages are not only affected by dams, but also influenced by natural variation and human‐induced modification (in addition to dams) in thermal and flow regimes, physicochemical habitats and biological assemblages. This study evaluated the impacts of dams on river fish assemblages in the non‐impoundment sections of rivers in the states of Michigan and Wisconsin using multiple fish assemblage indicators and multiple approaches to distinguish the influences of dams from those of other natural and human‐induced factors. We found that environmental factors that influence fish assemblages in addition to dams should be incorporated when evaluating regional effects of dams on fish assemblages. Without considering such co‐influential factors, the evaluation is inadequate and potentially misleading. The role of dams alone in determining fish assemblages at a regional spatial scale is relatively small (explained less than 20% of variance) compared with the other environmental factors, such as river size, flow and thermal regimes and land uses jointly. However, our results do demonstrate that downstream and upstream dams can substantially modify fish assemblages in the non‐impoundment sections of rivers. After excluding river size and land‐use influences, our results clearly demonstrate that dams have significant impacts on fish biotic‐integrity and habitat‐and‐social‐preference indicators. The influences of the upstream dams, downstream dams, distance to dams, and dam density differ among the fish indicators, which have different implications for maintaining river biotic integrity, protecting biodiversity and managing fisheries. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of flow on the fish communities of a regulated California river: implications for managing native fishes

We assessed the importance of flow regime to the success of native and non‐native fish species by analysing winter/spring seining data collected from 1987 to 1997 on the resident fish communities of the lower Tuolumne River, California. The data were analysed using regression models to predict the percentage of non‐native fish at a site. The regression models included various combinations of the variables longitudinal location of the site, mean April/May stream discharge in the year of sampling, and mean April/May stream discharge in the previous year. Comparison of the models indicated that the best model included longitudinal location and stream discharge in the previous year. This model is consistent with the hypothesis that flow in the previous year differentially affects reproductive success of native and non‐native species and thus the resulting community sampled in the following winter/spring. A detrended correspondence analysis of percentage abundance species data identified a co‐occurring group of native species and a co‐occurring group of non‐native species with the non‐native red shiner (Cyprinella lutrensis) grouping separately. The differing reproductive strategies of the species were consistent with the hypothesis concerning spawning success. Our results indicate that flow regime is an important determinant of the reproductive success of native and non‐native fish species in regulated rivers. Manipulations of flow regime are a potentially powerful tool for managing native fish species, but should be considered in combination with other restoration efforts and in the context of ecosystem restoration. Copyright © 2002 John Wiley & Sons, Ltd.     

Population genetic diversity and phylogeographic divergence patterns of the yellow perch (Perca flavescens)

Great Lakes populations of yellow perch have fluctuated throughout past decades to the present due to unstable recruitment patterns and exploitation. Our study analyzes genetic diversity and structure across the native range in order to interpret phylogeographic history and contemporary patterns. We compare complete mitochondrial DNA control region sequences (912 bp) from 568 spawning individuals at 32 sites, encompassing all 5 Great Lakes and outlying watersheds from the upper Mississippi River, Lake Winnipeg, Lake Champlain, and Atlantic and Gulf coastal relict populations. These broad-scale divergences additionally are compared with fine-scale patterns from 334 individuals at 16 spawning sites across Lake Erie's 4 fishery management units. We identify 21 mtDNA haplotypes, including a widespread type that totals 87% of individuals across the Great Lakes. Overall genetic diversity is relatively low in comparison with other Great Lakes fishes, congruent with prior allozyme and microsatellite studies. The largest genetic demarcation separates 2 primary population groups: one in the Great Lakes, Lake Winnipeg, and upper Mississippi River watersheds and the other along the Atlantic and Gulf coasts, together with Lake Champlain; which diverged ∼ 365,000 years ago. In addition, the watersheds house genetically separable groups, whose patterns reflect broad-scale isolation by geographic distance. A few spawning groups show some fine-scale differentiation within Lake Erie, which do not reflect fishery management units and need further study with higher-resolution markers.     

Effects of river regulation on the lower Ebro river (NE Spain)

The regulation of the Ebro River in the 1960s has changed the discharge pattern: spring floods have been reduced and, as the reservoirs are used for hydroelectrical purposes, discharge varies daily. The last 50 km of the river have been studied for two years (1986 and 1987). Our main purpose was to establish the particulate organic and inorganic transport of the river and its seasonal changes. Particulate material was sampled in surface and deep waters. Water conductivity ranges between 0.9 and 53 mS, and anoxia is common in summer situations. Particulate C ranges between 1 and 3 mg l^?1 with higher values in summer; particulate N is very similar along the year with values between 0.1 and 0.5 mg l^?1. Effects of regulation seem to be important in supplying very high nutrient content to algae and producing a high biomass and production in the lower part of the river, especially in summer. Diatoms and Chlorophyta are the most abundant groups. Phosphorus is higher than 5 μmol l^?1, with lower values in summer. Most of particulate material is very fine (between 0.45 and 50 μm). The high biomass also explains the presence of abundant filter-feeders, such as Hydropsyche and Ephoron virgo. In some parts, where light reaches the bottom, stones and boulders are covered by Cladophora. In this case, grazers such as the gastropods Melanopsis and Theodoxus are abundant.     

Effects of Water Temperature on Breeding Phenology,Growth, and Metamorphosis of Foothill Yellow‐Legged Frogs (Rana boylii): A Case Study of the Regulated Mainstem and Unregulated Tributaries of California's Trinity River

Many riverine organisms are well adapted to seasonally dynamic environments, but extreme changes in flow and thermal regimes can threaten sustainability of their populations in regulated rivers. Altered thermal regimes may limit recruitment to populations by shifting the timing of breeding activities and affecting the growth and development of early life stages. Stream‐dwelling anurans such as the foothill yellow‐legged frog (Rana boylii) in the Trinity River of northern California are model subjects for examining associations between water temperature and the timing of oviposition, hatching, and metamorphosis, and body condition and size of tadpoles and metamorphs. Breeding activity, hatching success, and metamorphosis occurred later, and metamorphs were smaller and leaner along the regulated and colder mainstem relative to six unregulated tributaries of the Trinity River. Persistently depressed summer water temperatures appear to play a seminal role in inhibited tadpole growth on the regulated mainstem and may be a causative factor in the pronounced decline of this population. Environmental flow assessments should account for the influence of the thermal regime on the development of vulnerable embryonic and larval life stages to improve outcomes for declining amphibian populations. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Effects of reservoir management on abundance,condition, parasitism and reproductive traits of downstream mussels

The large‐scale impoundment of rivers has led to global declines in freshwater mussel populations. It is important to understand the mechanisms underlying these declines to initiate an effective recovery strategy. We examined population traits of three Quadrula species (Quadrula pustulosa, Q. cylindrica and Q. quadrula) at three locations that were exposed to two different reservoir management regimes: releases that mimicked natural flow patterns and releases that were higher and colder in summer months than the natural system. We found lower mussel density, higher hermaphroditism and parasitism rates, and reduced body condition downstream of the dam with unnatural flow regimes. Sex ratios varied on a species and site basis. We found more Quadrula cylindrica females than males averaged across all three sampling sites while Q. pustulosa was male biased across all sites and at site 1. We observed approximately equal sex ratios in Quadrula quadrula. Population disturbances downstream of the more naturally‐regulated dam were not as severe. Our data indicate that dam operation can have effects on a variety of mussel life history characteristics that may ultimately reduce population viability. Copyright © 2010 John Wiley & Sons, Ltd.     

黄河洛河渭河在三门峡库区洪水遭遇预测方法的探讨

本文采用自然正交函数分析法对黄河、洛河、渭河洪水在三门峡库区遭遇进行分析探讨,得出只要预测未来时间系数就可预测未来洪水相遇的可能性大小,并得到了比较可靠的结果,在三门峡库区及其它河流的洪水遭遇分析具有重要的实用价值.     

Trophic state, fish community and intensive production of salmonids in Alicura Reservoir (Patagonia, Argentina)

The Governments of the Provinces located in Patagonia, Argentina, promote the intensive breeding of salmonids in the Andean Patagonian region. Although annual production is low (450 ton ha^–1 year^–1), some effects are significant. Waste produced by salmonid breeding (feed losses, faeces and excretion) increases nutrient and organic matter concentrations, which cause modifications of water quality, sediments and biota. A consequent risk is the elevation of eutrophication levels. Possible changes in water composition, sediments, algae and wild fish populations were studied. Sites affected by fish farming showed increased nutrient concentration, and phytoplankton and periphyton biomass. Chlorophyll a was similar at both sites (affected and unaffected by fish farm sites). Sediments clearly reflect fish farm waste inputs: total phosphorus and organic matter increased 12‐fold and fourfold, respectively. The species present in the gill‐net catches were the autochthonous Percichthys trucha, Odontesthes hatcheri, Diplomystes viedmensis, and the introduced salmonids Oncorhynchus mykiss, Salmo trutta, Salmo salar sebago and Salvelinus fontinalis. About 50% of the total catch was salmonids. A major portion of the catch per unit weight was composed of rainbow trout, followed by perch. The catch per unit weight obtained for this reservoir agrees with the range of values previously determined ( Quiros 1990 ) for Patagonian reservoirs. Compared with previous studies by Freyre et al. (1991) , a variation in catch composition exists. This consists mainly of an increase in the numbers and condition of O. mykiss and a decrease in P. trucha. Presence of fish that escaped from hatcheries, recognizable by their eroded fins, was observed; particularly in a sampling station near the fish cage systems. Variations in catches could be caused by cyclical changes in fish populations ( Wooton 1991 ), by direct and indirect effects of intensive fish farming, or by a combination of both events, and can only be understood through long‐term studies of catch variation.     

碳氮共渗钢水泵体的磨损特性研究（续）

研究了碳氮共渗钢制作的水泵体的磨损特性。介绍了用光学显微镜测定碳氮共渗渗层中化合物层厚度和孔隙，用X射线衍射仪测定化合物层组织，用表面光度仪触针检测表面粗糙度，用维氏硬度计测定渗层表面硬度和硬度分布，用销子一平盘机进行磨损试验，其磨损机理用扫描电镜进行鉴定。试验研究发现所有采用碳氮共渗工艺均能提高钢材的耐磨性。     

Effects of damming a large lowland river on chironomids and fish assessed with the (multiplicative partitioning of) true/Hill biodiversity measure

The impact of a large lowland temperate zone reservoir on chironomid and fish biodiversity was investigated in the same upstream (U) and downstream (D) sites on the same sampling occasions in spring and autumn of several post‐impoundment years. The true/Hill N1 diversity measure was used to construct diversity models of the impact, and partitioning of N1 to reveal the importance of ecological gradients. N1 is unique in being decomposable among multiple levels and easily comparable across ecosystems and animal groups. Chironomids were more diverse than fish in all community sets owing to their probably lower mobility, lower interspecific competition, opportunistic character and much shorter life spans than those of fish. Fish exerted consumption pressure on chironomids upstream by foraging mostly on benthic insects, but not downstream where they fed on microcrustaceans of reservoir origin or on epiphytic fauna (mainly Chironomidae). The reservoir impact on chironomids decreased their diversity in U and increased in D, while much the opposite was true in fish. In D in macroinvertebrates, the impact consisted in advancing over time intensification of seasonal development of submersed macrophytes, while in D in fish in a few species escaping from the reservoir after their populational explosions each year. Partitioning of diversity revealed that the spatial (upstream–downstream) gradient was the strongest factor of diversity change in chironomids as compared with season, and age of the impoundment. No gradient was dominant in fish. Comparisons of observed data with a null model testified to very strong intraspecific aggregation in both chironomids and fish. Copyright © 2010 John Wiley & Sons, Ltd.     

Diet of Invasive Adult White Perch (Morone americana) and their Effects on the Zooplankton Community in Missisquoi Bay,Lake Champlain

White perch (Morone americana) became established in Missisquoi Bay, Lake Champlain in the mid 1990s. Since that time, cyanobacteria blooms have become common in summer. Although introduced planktivorous fish often impact plankton communities through a reduction in Daphnia density, such effects can be difficult to predict in an opportunistic species such as white perch. In this study, we examined the extent of zooplanktivory exhibited by adult white perch in Missisquoi Bay. Adult white perch were collected from Missisquoi Bay on ten dates in spring and summer of 2005. White perch diet consisted of large numbers of Daphnia on dates when Daphnia densities exceeded 20 individuals/L and when Daphnia comprised more than 50% of the zooplankton assemblage. When Daphnia densities were below these threshold values, adult white perch diet consisted predominantly of benthic prey. Our results show that white perch feed on large numbers of Daphnia in Missisquoi Bay and select Daphnia over other zooplankton taxa when they are abundant. It is likely that adult white perch grazing in Missisquoi Bay has contributed to a reduction in Daphnia density which in turn may be contributing to summertime cyanobacteria dominance in this bay.     

The influence of river stage on endangered least terns and their fish prey in the Mississippi River (USA)

Spatial and temporal availability of small fishes, as forage for interior least terns (Sterna antillarum), was compared to the least tern reproductive period during 1993 and 1994 in the lower Mississippi River, Missouri. Timing of forage availability and least tern reproduction was also related to river stage and temperature regimes. Four deep-water habitats (main channel, secondary channel, side channel, and connected slough) and two shallow-water habitats (main-channel interface and side-channel interface) were sampled using a seine and neuston net, yielding 67 245 fish≤10 cm. Catch-per-volume and richness were highest in shallow-water habitats in both years. Highest catches in deep- and shallow-water habitats occurred between 56 and 64 days after peak spring flows in both years. Water temperature was increasing rapidly during the spring flood peak each year. About 80% of total fish catch consisted of taxa known to spawn in floodplain habitats, supporting the connection between the spring flood and the timing and amount of forage available for nesting least terns. Timing of least tern reproduction was related to falling river stages in May and increased forage–fish availability in June. A conceptual model integrates the abiotic factors of hydrology and sand island area to least tern reproduction and small fish availability. © 1998 John Wiley & Sons, Ltd.     

曝气条件对侧流活性污泥水解工艺脱氮性能和微生物的影响

通过改变传统厌氧/缺氧/好氧（A²/O）反应器和侧流活性污泥水解（SSH）反应器的曝气强度和溶解氧（DO）浓度,考察了曝气条件对脱氮性能的影响,并对比研究了微生物群落结构的变化规律。结果表明：相较于高DO阶段,两组反应器在中低DO阶段有更好的脱氮效果。在相同进水条件下,SSH反应器的脱氮性能优于A²/O反应器,且出水满足一级A标准。高通量测序结果表明,中低DO浓度更有利于脱氮微生物的生长。相对于A²/O反应器,SSH反应器中反硝化微生物的相对丰度更高。因此,合理控制曝气条件维持中低DO浓度有利于SSH工艺达到良好的脱氮性能及脱氮微生物的生长。     

Effects of an upland impoundment on structural and functional properties of a small stream in a basaltic plateau (golan heights,Israel)

The aim of the study was to evaluate the impact of an upland storage reservoir, typical of the series of reservoirs in the Golan Heights basaltic plateau, on structural and functional properties of the downstream ecosystem, in the vicinity of the reservoir, shortly after damming. The effect of impoundment on water quality conditions may be divided into winter-spring, and summer periods. In the former, the impoundment seems to lengthen the period of flow of runoff quality water. This is evident by the elevated winter and spring turbidities and the higher concentrations of suspended solids below the reservoir. In summer, water quality below the reservoir is controlled by the consequences of stratification in the reservoir. The hypolimnial release results in depression of the maximal temperature and narrowing of the daily and seasonal temperature variations. It supplies water enriched in nutrients and low in oxygen, suspended solids and turbidity. The macroinvertebrate community responds to impoundment in density changes and shifting of dominance. We hypothesize that the thermal effect of hypolimnial release from warm monomictic reservoirs on the invertebrate community of warm streams will differ from an equivalent thermal change caused by cold dimictic reservoirs in cold, temperate zone, streams. The effect of impoundment on functional properties of the ecosystem are most pronounced. The rate of production of benthic algae biomass below the reservoir increased by more than two orders of magnitude, but the effect diminished downstream. The rate of processing of plant material below the reservoir was lower than above the reservoir. Further investigation is needed to clarify this effect. Changes in reservoir operation are recommended to diminish the effects of impoundment.     

Effects of stream and lake regulation on reproductive success of kokanee in the flathead river system,Montana, U.S.A

Kokanee (Oncorhynchus nerka) provided an important recreational fishery in the Flathead River-Lake system (Columbia River Basin, U.S.A.-Canada) until the late 1970s when populations declined dramatically. The declines coincided with peaking river discharge from Hungry Horse Dam during the autumn spawning period and an increase in the duration of lake drawdown caused by the operation of Kerr Dam on the outlet of Flathead Lake. Redds of both river and lakeshore spawners were, therefore, dewatered in winter, causing high freezing and desiccation mortality of eggs during the incubation period. It appeared that growth rates of kokanee were density dependent. Female kokanee from strong year classes (i.e., those produced during years of favourable water levels and flow conditions during the incubation period) were smaller than those from weak year classes when unfavourable conditions for incubation prevailed. A highly significant relationship (r² = 0.929, p < 0.001) was demonstrated between female kokanee spawner length, river gauge heights, and lake levels during years which produced each year class. The close fit of the relationship was further validated by the strong correlation (r = 0.964) between actual kokanee lengths and predicted lengths. Other factors which could have influenced kokanee year class strength include hatchery plants of kokanee fry, harvest of kokanee by anglers, variations in the carrying capacity of Flathead Lake, and natural fluctuations in egg and fry mortality.     

水库及河道整治对黄河下游游荡性河道河势演变的影响

研究了修建水库及河道整治对黄河下游白鹤镇至高村游荡性河道河势演变的影响，探讨了游荡性河道向弯曲性河道转化的可能性。认为经过水库调节后，进入下游的来沙量减少，洪峰削平及中水持续时间加长，有利于游荡性河道游荡程度的降低及向弯曲方向的发展；河道整治工程对于减小河道的摆动强度，稳定流路，促使河道由游荡向弯曲方向发展的作用是显著的。在小浪底水库下泄有利水沙条件下，若能利用现有的河道整治工程，并补充必要的河道整治措施，黄河下游游荡性河道有可能逐步转化为象高村至陶城铺河段那样的限制性弯曲河道。     

Seasonal Effects of Hydropeaking on Growth,Energetics and Movement of Juvenile Atlantic Salmon (Salmo Salar)

The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water discharge (simulating hydropeaking) but with a stable water‐covered area were studied in six experimental stream channels, both during the winter and summer. Thirty fish were stocked into each channel, and the growth, body fat and movements of the fish were followed for about 2.5 months in each season. During the winter, no effect of hydropeaking was documented on performance or movement. In the summer, fish experiencing hydropeaking had lower body mass, lower body fat, and higher movement rates than the control fish. In general, effect sizes were small, and the rapid and frequent changes in water discharge and water level in the present study had small effects on the performance of juvenile Atlantic salmon. The cumulative long‐term effect at the population level is unknown, but a reduced growth rate of 10% and a reduction in body fat of 16% in the hydropeaking experiments in the summer might to some extent translate into increased smolt age and lower overwintering survival. Copyright © 2014 John Wiley & Sons, Ltd.