Effects of entrapment and cooling water discharge by the Bergum Power Station on 0+ fish in the Bergumermeer

The numbers, distribution and size of 0+ fish in Bergumermeer and in the cooling water system of the Bergum Power Station were registered from 1978 to 1981. An exponentially decreased vulnerability to entrapment by the power station was found with increasing size of fish. Because of the large water intake in relation to the lake volume, entrainment mortality of fish larvae in May and June is large and probably of the same order of magnitude as the natural mortality. In the same period the Bergumermeer can be supplied with large amounts of fish larvae, immigrating passively with the water current. Impingement mortality later on in the season is insignificant compared with natural mortality. The heated effluents from the power station influence the distribution and the size of 0+ fish in the lake. Year-class strength of pikeperch may be improved due to the larger size of 0+ pikeperch. Less water intake as a possibility to minimize entrainment is discussed.     

Fish impingement at estuarine power stations and its significance to commercial fishing

The abstraction of cooling water at power stations sited on tidal waters inevitably leads to mortalities of some fish which are drawn in with the cooling water supply and become impinged on the intake screens. These fish are predominantly 0- or I-group juveniles which, owing to their small size, are unable to resist intake currents.
Commercial fishermen often object to the fact that juvenile fish are killed in this way. Their concern stems from the fact that, in order to protect stocks, commercial fishing is restricted to fish which are above a statutory minimum landing size, whereas the majority of fish killed by impingement are below this size.
This paper considers the significance of impingement mortalities at estuarine sites in Britain for six commercially important species: cod, Gadus morhua , whiting, Merlangius merlangus , plaice, Pleuronectes platessa , dab, Limanda limanda , sole, Solea solea and herring, Clupea harengus . Life tables are used to establish expected survival trajectories for each species and to compute reproductive potential. Each fish killed on intake screens is then considered in terms of the fraction of the reproductive potential of a single adult at maturity, and is ascribed an 'adult equivalent' value. Total catches of mixed juveniles and adults are then presented as 'adult equivalent' values. The results are then compared with commercial landings data and it is shown that catches by power stations are trivial in comparison with commercial landings.     

A holistic look at minimizing adverse environmental impact under Section 316(b) of the Clean Water Act

Section 316(b) of the Clean Water Act (CWA) requires that "the location, design, construction, and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental impact." As the U.S. Environmental Protection Agency (EPA) develops new regulations to implement Section 316(b), much of the debate has centered on adverse impingement and entrainment impacts of cooling-water intake structures. Depending on the specific location and intake layout, once-through cooling systems withdrawing many millions of gallons of water per day can, to a varying degree, harm fish and other aquatic organisms in the water bodies from which the cooling water is withdrawn. Therefore, opponents of once-through cooling systems have encouraged the EPA to require wet or dry cooling tower systems as the best technology available (BTA), without considering site-specific conditions. However, within the context of the broader scope of the CWA mandate, this focus seems too narrow. Therefore, this article examines the phrase "minimizing adverse environmental impact" in a holistic light. Emphasis is placed on the analysis of the terms "environmental" and "minimizing." Congress chose "environmental" in lieu of other more narrowly focused terms like "impingement and entrainment," "water quality," or "aquatic life." In this light, BTA for cooling-water intake structures must minimize the entire suite of environmental impacts, as opposed to just those associated with impingement and entrainment. Wet and dry cooling tower systems work well to minimize entrainment and impingement, but they introduce other equally important impacts because they impose an energy penalty on the power output of the generating unit. The energy penalty results from a reduction in plant operating efficiency and an increase in internal power consumption. As a consequence of the energy penalty, power companies must generate additional electricity to achieve the same net output. This added production leads to additional environmental impacts associated with extraction and processing of the fuel, air emissions from burning the fuel, and additional evaporation of freshwater supplies during the cooling process. Wet towers also require the use of toxic biocides that are subsequently discharged or disposed. The other term under consideration, "minimizing," does not equal "eliminating." Technologies may be available to minimize but not totally eliminate adverse environmental impacts.     

Comparison of fish impingement by a thermal power station with fish populations in the Ems Estuary

On an annual basis >10 million individuals of c . 35 fish species are impinged at the EC20 unit of the Eems power station located on the Ems Estuary. The most abundant are: herring Clupea harengus , gobies ( Gobiidae ), Nilsson's pipefish Sygnathus rostellatus , three-spined stickleback Gasterosteus aculeatus and sprat Sprattus sprattus . The impingement shows a seasonal pattern which reflects the presence of the fishes in the estuary. The results are compared with other impingement studies at power stations on the Belgian and Dutch estuaries.
In 1995, the cooling water entrance was displaced from the shoreline to 300 m off the coast at the edge of the tidal channel. The effect of this relocation on the level of fish impingement, determined by comparing the ratio of fish density in the cooling water and in the estuary before (1992–1993) and after (1996–1997) the relocation of the intake canal is discussed.     

A review and assessment of the potential use of RNA:DNA ratios to assess the condition of entrained fish larvae

In rivers, lakes, and other aquatic systems throughout the world, intake pipes withdraw huge volumes of water for industrial purposes, including power plant cooling. During this process, large numbers of small-bodied, early life-stages of fish are pulled into pipes (i.e., entrained) and may be subjected to physical, thermal and chemical stress. As a result of such entrainment, these organisms can suffer direct or indirect mortality. However, given that the vast majority of larval fish are likely to die during early life due to natural processes, it is not obvious that entrainment-related mortality will have a strong influence on subsequent adult population sizes. The ability to evaluate if larval fish are dead on arrival, moribund, or in poor condition (i.e., likely to die through natural processes) at the time of entrainment could shed light on likely population-level impacts. To this end, we review the potential use of RNA:DNA ratios to index condition of entrained larval fish. Through a meta-analysis of published research studies, we demonstrate that RNA:DNA ratios of larval fish are responsive to starvation stress, with effect size increasing with duration of starvation. We relate these results to a surrogate measure of irreversible long-term negative impacts to fish populations, and demonstrate that the timescale over which RNA:DNA ratios respond to stress may not be long enough to reflect before-and-after entrainment stress. We also highlight the diverse factors contributing to variation of RNA:DNA ratios, including methodological, ontogenetic, and thermal influences. We believe that the need to account for these influences when comparing among RNA:DNA values limits the utility of broadly using RNA:DNA ratios to evaluate entrainment effects. However, the method shows promise as a quick and efficient means of determining fish condition and, used in proper context (e.g., specific to a given set of environmental conditions; in conjunction with other assessment techniques), may provide a powerful tool in assessing the effects of entrainment on fish populations. Assuming that researchers can account for sources of background variation, RNA:DNA analyses may be most useful for assessing the condition of fish larvae susceptible to entrainment (i.e., physically in the vicinity of the water intake) and/or evaluating whether fish larvae are likely to die from natural processes independent of entrainment.     

Fluktuationen der Fischfauna im Elbe-Ästuar als Indikator für ein gestörtes Ökosystem

During 1978, 22 fish species (in particularAnguilla anguilla L.,Platichthys flesus L.,Osmerus eperlanus L.,Gasterosteus aculeatus L.,Lampetra fluviatilis L.,Alosa fallax [Lacepede],Gymnocephalus cernua L.,Clupea harengus L. andSprattus sprattus L.), sampled at the intake of the cooling system in the nuclear power plant at Brunsbüttel (Elbe estuary), were analyzed for quantities and size distribution. The data obtained were correlated to abiotic factors, such as water temperature, water outflow from the upper Elbe river, salinity and oxygen content. Spawning times and seasonal migrations of the fish species investigated corresponded to appropriate temperatures of the Elbe water. The diversity of fish species from the cooling water proved to be representative for the ichthyo-fauna of this particular estuarine area. At least 190 tons of fish per year were estimated to be annihilated by the suction of cooling water into the nuclear power plant. In spite of the progressive development of regional industries and the increasing discharges of cooling water, temperature in the estuary has remained largely unaffected up till now. The oxygen content of the heavily polluted lower Elbe river, however, has become mainly dependent on the amount of fresh water flowing from the upper Elbe river. Up to 1978, oxygen levels of 80–90 % were recorded only in the mouth of the Elbe, thus meeting the requirements for the continuous occurrence of fish species typical for this estuarine area. Varying oxygen concentrations downstream of Hamburg and at Brunsbüttel are considered to be responsible for migrations of certain fish species (mainly flounder and smelt) between the Brunsbüttel region and their habitats further upstream which were occupied before the process of industrialisation initiated. This was reflected by the size of the samples taken from various fishes. During an eventual hazard of the industrial filter plants at Brunsbüttel in May 1978 an extreme oxygen depletion occurred for nearly 2 weeks. This event coincided with the death of certain age groups of fish.     

A comparison of pump sampling systems for live zooplankton collection

Simultaneous and sequential tests of pump sampling equipment showed that sampling mortality of Lake Michigan zooplankton collected from the cooling water intake of a nuclear power plant was dependent on the sampling method used. Two sampling devices and two pump types were tested to determine which combination resulted in the lowest sampling mortality. An in-line filter trap located on the suction side of the pump provided the lowest sampling mortality. Higher sampling rates were achieved with a centrifugal pump without increasing sampling mortality.     

Is Fish Oil Good or Bad for Heart Disease? Two Trials with Apparently Conflicting Results

Two successive randomized trials examined the effect of an increased intake of fatty fish, or the use of fish oil supplements, in reducing mortality in men with heart disease. The Diet and Reinfarction Trial (DART) was conducted in 2033 men who were recovering from acute myocardial infarction (MI). Those who were advised to eat fatty fish (or who opted to take fish oil capsules instead) had a 29% reduction in all-cause mortality over the following two years compared with those not so advised. The effect appeared in the first few months of the trial. The Diet and Angina Randomized Trial (DART 2) involved 3114 men with stable angina. Advice to eat fatty fish did not reduce mortality, and taking fish oil capsules was associated with a higher risk of cardiac and sudden death. The adverse effects of fish or fish oil were restricted to men not taking β-blockers or dihydropyridine calcium-channel blockers, and were greater in those taking digoxin. Evidence from other sources strongly suggests an anti-arrhythmic action of fish oil, particularly after MI or in the presence of acute ischemia. The apparently conflicting results of the two trials may reflect different actions of n-3 fatty acids in acute and chronic conditions, together with different effects of eating fish and taking fish oil capsules. A mechanism is proposed that could account for these findings.     

Behavioral and energetic costs of group membership in a coral reef fish

Animals in social aggregations often spend more time foraging than solitary conspecifics. This may be a product of the relative safety afforded by aggregations: group members can devote more time to foraging and less time to antipredator behaviors than solitary animals (the “risk reduction” effect). All else being equal, risk reduction should result in higher food intake for grouped animals. However, intragroup competition may force group members to spend more time foraging in order to obtain the same food ration as solitary individuals (the “resource competition” effect). We compared these opposing explanations of foraging time allocation in a coral reef fish, bluehead wrasse (Thalassoma bifasciatum). Aggregations of juvenile bluehead wrasse experience safety-in-numbers, and preliminary observations suggested that juveniles in aggregations spent more time foraging for copepods in the water column than solitary juveniles. However, the risk reduction and resource competition hypotheses are indistinguishable on the basis of behavioral observations alone. Therefore, we collected behavioral, dietary, and growth data (using otolith growth rings) for bluehead wrasse at multiple reefs around a Caribbean island. Despite spending more time foraging in the water column, grouped fish did not capture more prey items and had slower growth rates than solitary fish. Thus, the increased foraging time of grouped fish appears to reflect resource competition, not risk reduction. This competition may limit the size and frequency of aggregations among juvenile bluehead wrasse, which have been shown to experience reduced mortality rates in larger groups. Bluehead wrasse recruits also spent less time foraging but grew faster at sites where planktonic copepod prey were more abundant. This suggests the possibility that large-scale spatiotemporal variability in the abundance of planktonic copepods over coral reefs may produce corresponding variability in the dynamics of reef fish populations. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The critical swimming speed of the sand smelt (Atherina presbyter Cuvier) in relation to capture at a power station cooling water intake

Critical swimming speeds (CSS) of sand smelt, Atherina presbyter , were measured in a laboratory flume. Individuals of all age classes (0+ to III +) found in the vicinity of Fawley power station, Hampshire, were tested at temperatures covering the seasonal range. The median CSS was 2.7 body lengths per second (bl s⁻¹) at 5.8 °C, rising to 5.7 bl s⁻¹ at 18.5°C.
A two-variable (water temperature and body length) regression model was fitted to the data, and this was used to assess escape potential of fish coming into contact with the power station cooling water intake currents and the extent of possible bias in fish length data collected from this source. It is concluded that the sand smelt remains vulnerable to entrainment at the power station over its whole length range and over the full range of seasonal temperatures and that size-dependent swimming performance will not lead to significant bias in sample length distributions.     

Predicted survival of the bay anchovy (Anchoa mitchilli) in the heated effluent of a power plant on Galveston Bay,Texas

Synopsis The bay anchovy (Anchoa mitchilli), collected from the intake canal of the P.H. Robinson Generating Station, Bacliff, Texas, were tested for 180 min at various constant temperatures during June 1974 through September 1975 to determine if they could survive passage through the discharge canal system.Three-h survival temperatures were significantly lower, throughout the year, than the temperatures in the discharge canal both afferent and efferent to the cooling towers. This indicates that the bay anchovy entrained and entrapped from the intake canal and exposed to the heated effluent could not survive in the cooling water system. However, the cooling towers should aid survival of the fish in the canal below the towers.     

余氯对水生生物的影响

氯是滨河、滨海企业冷却水常用的防治污损生物的处理剂。总结近年来国内外氯在企业冷却水中的应用、氯对浮游植物、浮游动物、贝类、鱼类等影响的研究成果,为制定冷却水余氯排放标准和水产养殖的合理布局提供了参考,针对我国大量滨海电厂即将建立的现状,分析了余氯研究在中国海域研究的不足,提出了氯对我国海洋生物影响不同层面的研究方向。认为氯对生物种群的毒性,氯对生物群落组成、结构和生态演替的影响,以及减轻或避免余氯污染的对策是需要进一步解决的科学问题。     

Field evaluation of a sound system to reduce estuarine fish intake rates at a power plant cooling water inlet

An acoustic deterrent system producing 20–600 Hz sound was used to repel estuarine fishes away from a power station cooling water inlet. During sound emission, total fish impingement decreased by 60%. The avoidance response varied among species from no effect to highly efficient deflection. Lampetra fluviatilis and Pleuronectiformes were less affected by the sound system while the deflection of clupeoid species was particularly effective. Average intake rates of Clupea harengus and Sprattus sprattus decreased by 94·7 and 87·9%, respectively. The results were explained as a function of species‐specific differences in hearing ability and swimming performance. In general, species without swimbladders showed no or a moderate response while intake rates of species with accessory structures increasing the hearing abilities, such as a swimbladder or a functional connection between the swimbladder and the inner ear, were significantly reduced during test periods.     

Temperature effects on spawning and egg development in Eurasian perch

Spawning, egg strand development and embryo survival was studied during 1995–1996 in perch Perca fluviatilis exposed to heated effluent from two coastal nuclear power plants on the Baltic. Spawning was earlier and more prolonged in the heated areas. Although the fertilization rate was high, most egg strands sampled in the heated areas did not develop to hatching. The egg strands disintegrated within a few days of spawning, and egg mortality was very high. All samples collected from reference areas developed up to hatching. Exposure to high temperatures during the final maturation of the gonad influenced the follicular mechanism producing the jelly membrane which constitutes the matrix of the egg strand. Effects were observed in fish in open effluent areas as well as in an enclosed research basin. These results suggest that there is a conflict between optimal reproduction and temperature preference in temperate area fish. Fish are attracted to cooling water effluent, at the expense of reduced reproductive performance.     

Biotic interactions modify multiple‐stressor effects on juvenile brown trout in an experimental stream food web

Agricultural land use results in multiple stressors affecting stream ecosystems. Flow reduction due to water abstraction, elevated levels of nutrients and chemical contaminants are common agricultural stressors worldwide. Concurrently, stream ecosystems are also increasingly affected by climate change. Interactions among multiple co‐occurring stressors result in biological responses that cannot be predicted from single‐stressor effects (i.e. synergisms and antagonisms). At the ecosystem level, multiple‐stressor effects can be further modified by biotic interactions (e.g. trophic interactions). We conducted a field experiment using 128 flow‐through stream mesocosms to examine the individual and combined effects of water abstraction, nutrient enrichment and elevated levels of the nitrification inhibitor dicyandiamide (DCD) on survival, condition and gut content of juvenile brown trout and on benthic abundance of their invertebrate prey. Flow velocity reduction decreased fish survival (?12% compared to controls) and condition (?8% compared to initial condition), whereas effects of nutrient and DCD additions and interactions among these stressors were not significant. Negative effects of flow velocity reduction on fish survival and condition were consistent with effects on fish gut content (?25% compared to controls) and abundance of dominant invertebrate prey (?30% compared to controls), suggesting a negative metabolic balance driving fish mortality and condition decline, which was confirmed by structural equation modelling. Fish mortality under reduced flow velocity increased as maximal daily water temperatures approached the upper limit of their tolerance range, reflecting synergistic interactions between these stressors. Our study highlights the importance of indirect stressor effects such as those transferred through trophic interactions, which need to be considered when assessing and managing fish populations and stream food webs in multiple‐stressor situations. However, in real streams, compensatory mechanisms and behavioural responses, as well as seasonal and spatial variation, may alter the intensity of stressor effects and the sensitivity of trout populations.     

Laser impact on marine planktonic diatoms: an experimental study using a flow cytometry system

A flow cytometry system was used to evaluate the impact of pulsed laser irradiations from an Nd:YAG laser on two marine coastal water diatoms, Chaetoceros gracilis and Skeletonema costatum. Three flow speeds, i.e. 9, 18 and 27 ml min-1 and three laser fluences, i.e. 0.025, 0.05 and 0.1 J cm-2 pulse-1 were tested during this study. The reduction in cell density and chlorophyll a (chl a) concentrations were monitored by reference to non-irradiated samples as controls. Upon irradiation, the cell density and the chl a concentrations became reduced significantly compared to the control (one way ANOVA p < 0.001 for the cell density in both the species and p < 0.05 for chl a concentrations in both species). A maximum mortality of 0.77 log10 (about 83%) for C. gracilis and 0.68 log10 (about 78%) for S. costatum was observed at 9 ml min-1 flow speed and 0.1 J cm-2 laser fluence. The maximum reduction observed in the chl a concentration was about 26% (control 0.413 and sample 0.306 mg ml-1) for C. gracilis and 27% (control 0.222 and sample 0.16 mg ml-1) for S. costatum, when the flow rate was 9 ml min-1 and the fluence 0.1 J cm-2. In general, mortality increased with an increase in the laser fluence. The results thus show if the cooling water is laser-irradiated to mitigate biofouling, this could result in significant damage to the planktonic flora of the flowing seawater system, which in turn might reduce algal biofilm formation on industrially important structures. The reduction in the chl a concentration showed that the laser irradiations also could result in a significant reduction in the primary productivity of the cooling water.     

Functional and aggregative response of North Sea whiting

The functional response of whiting (Merlangius merlangus L.) to clupeid and gadoid prey was determined from estimates of food intake and prey density at five locations in the North Sea. The intake of most prey types was well described by a type II (decelerating) response, although in some cases a type III (sigmoid) response provided a slightly better fit. Though a saturation level was reached for all types of fish prey, none of the levels corresponded to the maximum digestive capacity of the predator. This was not caused by ingestion of other prey as the amount of other food and fish prey ingested were not negatively correlated. An investigation of the occurrence of fresh fish in the stomachs revealed that fish was ingested almost exclusively during dawn and dusk and the lack of negative correlation between the intake of fish and other prey may thus be a result of the limited time in which fish prey was vulnerable to predation. No aggregative response of the predators was detected towards any of the prey and catches of prey and predators were slightly negatively correlated. There was evidence of an increase in mortality with density at low clupeid densities, but mortality decreased to virtually zero at high densities. Whiting seem therefore unlikely to impose a regulatory effect on their fish prey outside a narrow range of prey densities.     

Approach velocity and impingement duration influences the mortality of juvenile Golden Perch (Macquaria ambigua) at a fish exclusion screen

Globally, the extraction and diversion of water from river systems has had substantial impacts on aquatic ecosystem health and ecological processes. One such impact is the entrainment of fish at pump offtakes that can result in vast quantities of fish being permanently removed from rivers. Exclusion screens to prevent fish entrainment at pump offtakes are therefore an important management consideration. In this study, impingement and subsequent injury and mortality of a juvenile freshwater perciform, Golden Perch (Macquaria ambigua), was assessed in the laboratory using a simulated fish exclusion screen under a range of velocities and impingement durations. A 2 mm wedge‐wire screen eliminated the entrainment of 44‐day‐old Golden Perch that were exposed to approach velocities between 0.05 and 0.3 m/s. However, impingement rates of Golden Perch increased significantly with increased approach velocities and rates of injury and mortality increased with impingement duration. Results from this study indicate the primary mechanisms to reduce fish loss at pump offtakes are to design pump offtakes, fitted with fish exclusion screens, which limit approach velocities or impingement duration. Further studies are required to examine a range of species with varying swimming ability at early life‐history stages. Such data will contribute to the growing body of knowledge that supports adaptive management plans to prevent fish loss at water offtake pumps.     

n-3 Fatty acids, cardiac arrhythmia and fatal coronary heart disease

n-3 Polyunsaturated fatty acids (n-3 PUFA) are suggested to prevent cardiac death via inhibition of cardiac arrhythmia. In this review we discuss the results of human studies on intake of n-3 PUFAs and heart disease and, more specifically, on cardiac arrhythmia. Observational studies indicate that intake of fish is associated with a lower incidence of fatal coronary heart disease in several populations. These studies are fairly consistent, but people that have a high intake of fatty fish might have a healthier lifestyle in general, and such confounding is difficult to remove completely with statistical adjustments and corrections. Evidence from trials is less clear. In two open label trials in patients with a previous myocardial infarction intake of fish or fish oil prevented fatal coronary heart disease. In contrast, a trial in patients with angina suggested a higher risk of sudden cardiac death in patients taking fish oil. Furthermore, results of trials in patients with an implantable cardioverter defibrillator (ICD) that investigated effects of fish oil on arrhythmia in patients already suffering from ventricular tachycardia are not consistent. Also, studies on relationships between intake of n-3 PUFA from fish and less life-threatening forms of arrhythmia, such as atrial fibrillation and premature ventricular complexes (PVCs) are equivocal. Thus, after 35 years of research the question whether fish prevents heart disease remains unanswered, and an anti-arrhythmic effect of fish oil remains unproven although the idea is still viable and is being actively tested in further trials.