Affect Fish Populations Research Articles

Stressor identification and health assessment of fish exposed to wastewater effluents in Miho Stream, South Korea

This study evaluated the effects of an industrial wastewater treatment plant (IWTP) and a municipal wastewater treatment plant (MWTP) effluents on a variety of bioindicators ranging from biochemical, organism, and population-level responses in pale chub (Zacco platypus) and fish community structure. The Index of Biotic Integrity (IBI) indicated that the site upstream of these wastewater treatment plant discharges is in fair-good condition and downstream of the plant is in poor condition. The EROD (ethoxyresorufin-O-deethylase) activity, condition factor, and liver somatic index were significantly increased at the downstream site compared to those of the upstream site. The most significant change observed in pale chub population in the downstream site of the Miho Stream, relative to the upstream population, was the total absence of an younger age group. Stressors impacting the downstream site were identified as mostly organic or nutrient enrichment and habitat degradation associated with wastewater treatment plants. The results of causal analysis suggest that the primary causes affecting fish population in the downstream site are through both size-selective mortality caused by ammonia toxicity and recruitment failure caused by habitat degradation and reproduction problem due to an IWTP and MWTP effluents.

Introduction to Special Section: Measurement and Analysis of the Potential Long Term Impact of Pulp and Paper Mill Effluent on Receiving Waters

Knowledge of the current condition of a waterway and watershed, as well as a clear understanding of the changes, if any, that result from human interaction with these environments—including effluent discharges from industry—is a basic requirement for developing effective environmental management strategies. Among the many lessons learned in the United States after more than 40 y of environmental regulation stemming from Earth Day and the founding of the US Environmental Protection Agency in 1970 is a proper monitoring strategy. A proper monitoring strategy for waterways is crucial to generating useful environmental and ecological data and achieving the environmental management goals set by particular industries, government agencies, and other stakeholders. Monitoring programs that have vague objectives, unspecific indicators and inadequate sampling designs have been shown consistently to provide little useful information upon which to regulate human impact on the environment. Incomplete knowledge of current conditions coupled with poor monitoring strategies invariably wastes limited stakeholder resources and leads to inadequate water quality management and ecological protection strategies. When examining the present day questions about the effects of effluents from pulp and paper mills on aquatic systems it is difficult to separate legacy issues from the challenges that this industry faces today. Two decades or more ago, the debate among scientists, industry environmental managers, and regulatory agencies in the United States focused primarily on waste waters containing residual fiber materials and oxygen-depleting organic substances released from mills directly to receiving streams and the nature and extent of the physical and chemical impairments on aquatic biota and the ecosystem. A decade or more ago, the scientific debate shifted; debate focused on the environmental significance of chlorinated organic substances in effluent, which resulted from the use of elemental chlorine in the production process at bleached kraft paper mills. Over the past 10 y production process changes at bleached kraft mills to alternate bleaching technologies has led to the near elimination of chlorinated organic substances in effluent. Although the reputation earned during these debates linger, modern pulp and paper mills in the United States, using primary and secondary effluent treatment technologies and chlorine-free processes, have significantly altered the properties of mill effluents, in most cases meeting or exceeding the goals expressed by scientists and regulators in the past for the elimination of constituents from effluents capable of harming the environment. The debate about paper mill effluent, however, has not ended. Today, new concerns have arisen concerning natural substances in trees (e.g., phytosterols) that may find their way into mill effluents discharged to waterways and adversely affect fish reproduction (Hewitt et al. 2008; Dube et al. 2008). Throughout this history of debate, the answers to questions regarding effluent effects on the aquatic environment and waterway ecosystems have been challenging. There has been an inconsistent use of monitoring tools and approaches to meet the information needs of various State and Federal regulators, local stakeholders and research groups. From time to time and in different regions of the United States, regulatory agencies and other stakeholders have opted for assessment approaches based on short-term or long-term assessment methods, shifting measurement endpoints, and/or changing management goals. In all of these instances, the approach has rarely included the consideration of ecosystem level or landscape level indicators of environmental quality or included consideration of the ecological services provided by the target waterway in any meaningful context. The use of inconsistent monitoring methodologies to assess effluent effects has resulted in considerable disparity in data availability and debate about the conclusions that have been drawn about the extent or type of impacts on the aquatic environment attributable to paper mill effluent. The debate has continued to this day—though the focus may change from fiber and oxygen-depleting substances to chlorinated substances to phytosterols. According to the Environment Canada publication EnviroZine (2004), scientists in Canada conclude with a high degree of certainty that paper mill effluents adversely affect fish populations. Yet, a series of long-term experimental streams studies of warm water (NCASI 1983) and cold water (Hall et al. 1991; Haley et al. 1995) stream communities found little indication of adverse effects on fish or aquatic food webs at effluent concentrations considerably above those found in North American receiving waters. Regardless of whether at the core of the debate among scientists, industry environmental managers, and regulatory agencies, the differences of opinion are based on scientific disagreement or poor communication, there is a great need to find common understanding of the impact of paper mill effluents on receiving waters. Facing this challenge, the National Council for Air and Stream Improvement (NCASI), an independent, non-profit research organization that focuses * To whom correspondence may be addressed: thall@ncasi.org

Food‐dependent individual growth and population dynamics in fishes*

It is long since well established that growth and development in fish individuals are heavily dependent on food intake. Yet, this dependence of individual development on food levels has only to a limited extent been taken into consideration when studying fish population and community processes. Using the modelling framework of physiologically structured population models and empirical data for a number of species configurations, how different size‐dependent processes may affect fish population dynamics and community structures are reviewed. Considering competitive interactions, cohort interactions will often give rise to cohort cycles driven by an inequality in competitive abilities between differently sized individuals. The addition of cannibalism may dampen these cycles, the extent to which is dependent on life‐history characteristics of the cannibals. The circumstance that individuals change their trophic position over their life cycle as a result of an increase in size gives rise to life history omnivory. In such omnivorous systems, food‐dependent growth demotes the potential for predatory and prey fishes to coexist. In tritrophic food chains, food‐dependent growth in the intermediate consumer may lead to the presence of bistability including sensitivity to catastrophic behaviour. These results shed new light on the drastic decreases observed in the stocks of many marine fish top predators including their inability to recover after fishing moratoria, and on the suggested presence of alternative states in freshwater fish communities.

Asymmetric impact of piscivorous birds on size-structured fish populations

Fish are frequently considered the top predator in freshwater food web models despite evidence that predatory birds can impact fish populations. In this study, we quantified bird predation rates on experimental populations of rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) created by stocking nine small lakes in British Columbia, Canada. Combining estimates of fish mortality with estimated bird predation rates allowed us to partition fish mortality into that due to birds versus cannibalism. Our results indicated that bird predators had significant impacts on age-1 trout populations, but little impact on age-0 trout. Common loons ( Gavia immer Brunnich, 1764) were the principle predator among eight predatory bird species present, apparently consuming nearly 50% of all stocked age-1 trout and explaining almost 50% of variation in mortality rates. Age-1 trout mortality did not differ significantly from zero in lakes without loons. Birds consumed a small proportion of age-0 trout, and estimated consumption explained none of the variation in age-0 trout mortality among lakes. We conclude that birds affect fish populations by asymmetric predation on different age (size) classes and can be important top predators that should not be ignored when characterizing freshwater food webs in lakes.

Are fish populations in temperate streams affected by crayfish? – A field survey and prospects

Fish populations may be affected by predation and competition from various types of organisms, among which crayfish have been suggested as important actors. We here present results from stream surveys, suggesting that neither native noble, Astacus astacus, nor introduced signal crayfish, Pacifastacus leniusculus, necessarily affect fish population densities in temperate stream communities. Comparisons of fish densities within stream sites between years with absence and presence of crayfish showed no effect of either crayfish species. A further analysis of changes in fish densities between periods without and with crayfish in low, intermediate and high densities revealed that crayfish density did neither have an effect on fish densities. Our study is one of exceptionally few that consider the above aspects in long-term perspectives in natural systems, and we discuss that previously reported divergent results of crayfish effects on fish may be highly dependent on specific species and methods used, and that the effects of crayfish on fish populations deserve further attention to enable reliable predictions of community processes in streams.

Do resource declines increase predation rates on North Pacific harbor seals? A behavior-based plausibility model

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 312:265-275 (2006) - doi:10.3354/meps312265 Do resource declines increase predation rates on North Pacific harbor seals? A behavior-based plausibility model Alejandro Frid1,*, Gregory G. Baker2, Lawrence M. Dill1 1Behavioural Ecology Research Group, Department of Biological Sciences, and 2School of Computing Science, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada *Email: ilexp@yknet.yk.ca ABSTRACT: Harbor seals Phoca vitulina and other pinnipeds in the Gulf of Alaska have declined since the 1980s. The search for causation has considered top-down and bottom-up influences as independent factors. Research on other systems, however, has revealed that resource availability and predator densities synergistically determine the predation rates experienced by intermediate consumers. From this premise we developed a dynamic state variable model of behavior for the declining harbor seal population of Prince William Sound, Alaska. We modeled separate scenarios in which seals were prey to (1) transient killer whales Orcinus orca at and near the surface and Pacific sleeper sharks Somniosus pacificus throughout the water column, or (2) killer whales only. In both scenarios, resource decrements reduced the time spent by seals at the haulout (a refuge lacking food), increased the time spent at foraging areas, and lengthened surface intervals and dive durations. Because of this behavioral compensation, per capita fish consumption remained relatively constant, but predation rates increased as resources declined, despite fixed predator densities. Foraging effort and predation rates increased further when energy stores were lower at the onset of simulation periods, but in all scenarios seals not killed by predators had achieved a high level of energy stores by the reproductive season. These behavioral mechanisms proposed by the model potentially explain—at least partially—why the population has been declining while seals have maintained good energy stores throughout temporal shifts in resource availability. More generally, simulations suggest that overfishing and other factors that reduce fish populations indirectly increase predation rates on seals, but data are needed to test this hypothesis. Our model also encompasses a broader ecosystem perspective by predicting how resource level determines the relative strength of trait- and density-mediated interactions, whereby predators of seals indirectly affect fish populations by influencing the foraging behavior and density of seals. The behavioral modeling approach presented here is an additional tool for resource managers attempting to optimize fisheries exploitation and pinniped conservation. KEY WORDS: Predation risk · Resource availability · Harbor seal · Phoca vitulina · Dynamic state variable model · Pinniped declines · Optimal diving · Prince William Sound · Indirect interactions Full text in pdf format Supplementary appendix PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 312. Online publication date: April 24, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Overcoming human obstacles to conservation of recreational fishery resources, with emphasis on central Europe

Recreational fisheries are the dominant or sole user of many coastal and most inland fish stocks in industrialized societies. Recreational angling can negatively affect fish populations, but appropriate management approaches to address these impacts are often lacking. Overall, privately-governed European recreational fisheries systems offer suitable conditions to reconcile resource use with resource conservation because access restriction is possible, decision-making structures are simple and management scales are small. This increases the hope that the race to fish may be less pronounced than in open-access commercial fisheries. To achieve harmony between use and conservation values, a thorough understanding of the human dimension is paramount, yet approaches including this are underrepresented in contemporary recreational fisheries science and management. Based on theoretical considerations, literature review and personal experiences, this paper presents key human obstacles to the reconciliation of recreational fishery resource use and resource conservation, with emphasis on private fishing rights regimes of central Europe. Nine obstacles are identified: (1) lack of social priority; (2) lack of integrated approaches; (3) lack of cooperative institutional linkages; (4) lack of systems thinking; (5) lack of research and monitoring; (6) lack of shared values and dominance of stereotyped perceptions; (7) lack of consideration for regional fish-angler dynamics; (8) lack of objective communication of scientific findings; and (9) lack of critical self-reflection among individual anglers. Potential solutions to overcome the identified constraints briefly discussed include: (1) evaluation of the socioeconomic benefits of angling; (2) rehabilitation of ecosystem structure and function on larger scales; (3) facilitation of structured cooperation between stakeholders and management units; (4) application of complex systems approach; (5) increased funding for long-term monitoring; (6) fostering of common values of different stake-holders; (7) active adaptive management of angling effort on regional scales; (8) intensified communication of research findings; and (9) conviction of anglers to meet personal targets by more restrictive regulations. Increasing research and management efforts related to the social component of recreational fisheries will improve reconciliation of resource use and resource conservation in traditional recreational fisheries management. It is a matter of societal values whether it is judged necessary to do so on a broader scale.

Fish catches from Lake Tanganyika mainly reflect changes in fishery practices, not climate

Recently it was claimed that an increase in regional temperature, related to global climate change, has resulted in substantial decline in the pelagic fish catches from Lake Tanganyika, East Africa. Surface temperatures of Tanganyika indeed show warming trends, but evidence for decreased productivity is ambiguous, and no overall decline in fish catches has been documented. In contrast, total lake-wide fish catches increased up to 1995, increased artisanal catches outweighing regional declines in industrial fisheries. We conclude that the present evidence is not sufficient to demonstrate the effects of climate change on fish stocks in Tanganyika. Evidence indicates rather that fishery intensification has been the major factor affecting fish populations.

May Organic Pollutants Affect Fish Populations in the North Sea?

The North Sea is a highly productive area with large fish populations that have been extensively harvested over the past century. North Sea fisheries remain important to the surrounding countries despite declining fish stocks over the past decades. The main reason for declining fish stocks is nearly certainly overfishing, but other environmental pressures also affect fish populations, such as eutrophication, climate change, and exposure to metals and organic pollutants, including polyaromatic hydrocat bons (PAHs), alkylphenols, and organochlorine compounds. There are three main sources of organic pollutants in the North Sea: atmospheric, land-based sources, and inputs from offshore gas and oil installations. All three sources contribute to elevated concentrations of organic pollutants in the North Sea compared to the Norwegian Sea. There is evidence that chlorinated organic contaminants were present in sufficiently high concentrations in the southern North Sea two decades ago, to alter embryonal development in fish. The results from extensive, long-term monitoring programs show that some diseases decreased whereas other increased in the southern North Sea and that, among other factors, contaminants may play a role in the temporal changes recorded in disease prevalence. Recent studies demonstrated that components in offshore effluents may affect fish reproduction and that tissues of fish near oil rigs are structurally different to tissues of fish from reference areas. Data on effluents from offshore activities have recently become available through an international workshop (BECPELAG) and follow-up studies.

Recognizing the importance of scale in the ecology and management of riverine fish

Processes affecting fish populations range in scale from local to global. Fish response is also scale-dependent, with some activities varying locally while others depend on large-scale connectivity within or between watersheds. These issues are still only partly recognized, with large-scale research often affected by non-independent sampling, weak inference, poor model testing or model over-extrapolation. Available multi-scale studies can reach different conclusions about factors affecting fishes from local studies, but results vary between examples. Potential explanations are (i) effects on fishes are context-dependent; (ii) different species or life-stages are limited in different ways; (iii) multi-scale studies are too few for generalization. We advocate improved use of geostatistical tools to guide sampling or interpret the spatial extent of management problems, and we illustrate this using brown trout in Welsh streams. Our strongest recommendation is that fish ecologists recognize the importance of interactions across scales in quantifying effects on fishes so that management decisions can be better based on evidence rather than judgement or extrapolation.

Water-borne diclofenac affects kidney and gill integrity and selected immune parameters in brown trout ( Salmo trutta f. fario)

The detection of residues of various pharmaceuticals in surface waters during the last two decades has prompted concerns about possible adverse effects of this kind of pollution on aquatic organisms. The objective of the present study was to investigate effects of the non-steroidal anti-inflammatory drug diclofenac, one of the pharmaceuticals most prevalent in surface waters, on brown trout ( Salmo trutta f. fario), a salmonid species native to German rivers. Brown trout were exposed to 0.5, 5 and 50 μg/L diclofenac for 7, 14 and 21 days, whereby the lowest exposure concentration is comparable with concentrations commonly found in the aquatic environment. Fish exposed to diclofenac displayed significantly reduced haematocrit levels after 7 and 14 days of exposure. After 21 days, trout were examined for histopathological alterations, whereby diclofenac exposure resulted in increased monocyte infiltration in the liver, telangiectasis in gills, and the occurrence of interstitial hyaline droplets, interstitial proteinaceous fluid and mild tubular necrosis in trunk kidney. Concurrent immunohistological analysis revealed an increase of granulocyte numbers in primary gill filaments, as well as granulocyte accumulation and increased major histocompatibility complex (MHC) II expression in kidney, suggestive of an inflammatory process in these organs. Moreover, the ability of diclofenac to hinder the stimulation of prostaglandin E 2 synthesis was shown in head kidney macrophages of brown trout in vitro. These findings support the hypothesis that environmental exposure of fish to diclofenac provokes the same mechanism of action in these non-target organisms as previously described for mammalian species and can thus lead to similar (possibly adverse) effects. In general, the present study suggests that exposure of brown trout to diclofenac in concentration ranges commonly found in the environment can result in adverse effects in various organs and possibly compromise the health of affected fish populations.

Impacts of New Highways and Subsequent Landscape Urbanization on Stream Habitat and Biota

New highways are pervasive, pernicious threats to stream ecosystems because of their short- and long-term physical, chemical, and biological impacts. Unfortunately, standard environmental impact statements (EISs) and environmental assessments (EAs) focus narrowly on the initial direct impacts of construction and ignore other long-term indirect impacts. More thorough consideration of highway impacts, and, ultimately, better land use decisions may be facilitated by conceptualizing highway development in three stages: initial highway construction, highway presence, and eventual landscape urbanization. Highway construction is characterized by localized physical disturbances, which generally subside through time. In contrast, highway presence and landscape urbanization are characterized by physical and chemical impacts that are temporally persistent. Although the impacts of highway presence and landscape urbanization are of similar natures, the impacts are of a greater magnitude and more widespread in the urbanization phase. Our review reveals that the landscape urbanization stage is clearly the greatest threat to stream habitat and biota, as stream ecosystems are sensitive to even low levels (< 10%) of watershed urban development. Although highway construction is ongoing, pervasive, and has severe biological consequences, we found few published investigations of its impacts on streams. Researchers know little about the occurrence, loading rates, and biotic responses to specific contaminants in highway runoff. Also needed is a detailed understanding of how highway crossings, especially culverts, affect fish populations via constraints on movement and how highway networks alter natural regimes (e.g., streamflow, temperature). Urbanization research topics that may yield especially useful results include a) the relative importance and biological effects of specific components of urban development—e.g., commercial or residential; b) the scenarios under which impacts are reversible; and c) the efficacy of mitigation measures—e.g., stormwater retention or treatment and forested buffers.

Comparing Fish Screen Performance to Physical Design Criteria

Fish screens associated with irrigation diversion structures perform a vital function by protecting rearing and migrating fishes. Irrigation diversions in the western United States were developed in the late 1800s and early 1900s with little regard to how they might affect fish populations. Fish screens were installed on some diversions beginning in the 1930s but were often ineffective. Beginning in the 1980s a “modern-era” fish screening program was initiated in the Yakima River basin in Washington State. A systematic phased approach was employed, with federal funding, to replace antiquated screens and to install screens where there had not previously been fish protection devices. Also during this time, the federal and state agencies responsible for protecting the fish resources developed regional criteria to guide design of these facilities. These criteria, developed by the National Marine Fisheries Service and used by the Washington Department of Fish and Wildlife, dictated physical metrics such as approach velocity (and mesh size) for fish screen facilities. Scientists at the Pacific Northwest National Laboratory (PNNL) developed methods for evaluating new fish screen facilities as they came “on line” to document whether the facilities were designed, constructed, operated, and maintained to be within the fish passage criteria. PNNL uses a combination of water velocity measurements, visual inspection, and underwater videography to determine whether fish screen sites are within the fish protection criteria. This annual evaluation schedule (most sites are evaluated three times/year) is a vital tool to ensure that the large initial capital investment (over $75 million USD) is being operated and maintained to protect fish.

Altered swimming performance of a benthic fish (Erimyzon sucetta) exposed to contaminated sediments.

Numerous field surveys suggest that coal combustion wastes (ash) adversely affect fish populations, but few controlled laboratory studies have evaluated the responses of individual fish to ash exposure. Available information suggests that sublethal effects of ash, including decreased growth rates and reduced fecundity, may be important manifestations of ash toxicity. Here, we hypothesized that ash may also alter swimming performance, which could ultimately have important implications for the autecology of affected species. To test this hypothesis, we measured sprint speed and critical swimming speed (U(crit)) of juvenile lake chubsuckers (Erimyzon sucetta) exposed to ash in the laboratory. Fish exposed to ash for 90-100 days accumulated significant concentrations of As, Se, Sr, and V; exhibited severe fin erosion; and had reduced sprint speed and U(crit). Compared to controls, sprint speed of ash-exposed fish was reduced by 30% at 5 cm and the percent reduction was further reduced to 104% at 20 cm. Critical swimming speed was approximately 50% lower in fish exposed to ash compared to controls. Additionally, the typical positive relationship between standard length and U(crit) was absent in fish exposed to ash. Because reductions in swimming performance could not be attributed to pollutant-induced differences in body condition or fin morphology, we hypothesize that physiological disruptions (e.g., increased energy demands, decreased oxygen uptake or transport) are responsible for the observed effects and warrant further attention.

Endocrine disruption in wild freshwater fish

Endocrine disruption has been reported in freshwater fish populations around the world. This phenomenon ranges from subtle changes in the physiology and sexual behavior of fish to permanently altered sexual differentiation and impairment of fertility. Despite widespread reports of endocrine disruption in fish (and this is well characterized at the individual level), few studies have demonstrated population-level consequences as a result of exposure to endocrine-disrupting chemicals (EDCs). An exception to this is in Lake Ontario Lake trout where precipitous declines in the population have been linked with periods of high exposure to organochlorine chemicals (known EDCs). Recently, it has been established that roach (Rutilus rutilus) exposed to treated sewage effluent (that contains complex mixtures of EDCs) in UK rivers, have a reduced reproductive capacity. This, in turn, may have population-level consequences. Evidence for a link between exposure to effluents from kraft mill (BKME) and sewage treatment works (STWs) and altered reproductive function in freshwater fish is compelling. In most cases, however, a causal link between a specific chemical and a physiological effect has not been established. Indeed, identifying specific chemical(s) responsible for adverse effects observed in the wild is difficult, given that tens of thousands of man-made chemicals enter the aquatic environment and that mixtures of chemicals can have combination (e.g., additive) effects. Some EDCs are known to act at a number of different body targets to affect a variety of physiological processes, further complicating the identification of the causative agent(s). Endocrine disruption appears to be particularly widespread in freshwater fish populations. There is little evidence, however, to suggest fish are more susceptible to EDCs relative to other wildlife. Notwithstanding this, there are some features of the endocrine physiology of fish that may be particularly susceptible to the effects of EDCs, including the processes of sex-determination and smoltification (in salmonids). Furthermore, their aquatic existence means that fish can be bathed constantly in a solution containing pollutants. In addition, uptake of chemicals readily occurs via the gills and skin, as well as via the diet (the major exposure route for most EDCs in terrestrial animals). The exposure of fish early life stages to the cocktail of EDCs present in some aquatic environments may be of particular concern, given that this is an especially vulnerable period in their development. The challenge, from the point of view of ecological risk assessment, is to determine effects of EDCs on freshwater fish populations and freshwater ecosystems. In order to meet this challenge, high-quality data are required on the population biology of freshwater fish, on the effects of EDCs on their various life history characteristics, and comprehensive and appropriate population models. Basic information on the population biology of most species of wild freshwater fish is, however, extremely limited, and needs significant improvement for use in deriving a sound understanding of how EDCs affect fish population sustainability. Notwithstanding this, we need to start to undertake possible/probable predictions of population level effects of EDCs using data derived from the effects found in individual fish. Furthermore, information on the geographical extent of endocrine disruption in freshwater fish is vital for understanding the impact of EDCs in fish populations. This can be derived using published statistical associations between endocrine disruption in individual fish and pollutant concentration in receiving waters. Simplistic population models, based on the effects of EDCs on the reproductive success of individual fish can also used to model the likely population responses to EDCs. Wherever there is sufficient evidence for endocrine disruption in freshwater fish and the need for remediation has been established, then there is a need to focus on how these problems can be alleviated. Where industrial chemicals are identified as causative agents, a practical program of tighter regulation for their discharge and/or a switch to alternative chemicals (which do not act as EDCs) is needed. There are recent examples where such strategies have been adopted, and these have been successful in reducing the impacts of EDCs from point source discharges on freshwater fish. Where EDCs are of natural origin (e.g., sex steroid hormones from human and animal waste), however, remediation is a more difficult task. Regulation of the release of these chemicals can probably be achieved only by improvements in treatment processes and/or the implementation of systems that specifically remove and degrade them before their discharge into the aquatic environment.

River regulation and fish larvae: variation through space and time

1. Patterns in abundance and distribution of larval fish in a heavily regulated and a mildly regulated Australian lowland river were compared over four breeding seasons to gain some insight into how river regulation affects fish populations.2. Larvae from a total of 13 species from nine families were recorded from the two rivers. The mildly regulated Broken River supported twice as many species as the heavily regulated Campaspe River. The two rivers shared three introduced species but only two native species. The dominant species in the Campaspe was not found in the Broken River.3. The two most abundant species in the Campaspe were classified as `opportunists'. They are small, short‐lived species, which spawn for up to 9 months, encompassing extremes in temperature and flow. The extended spawning period may place a subset of larvae in optimal conditions for recruitment and is hypothesised as being the key to the success of these species.4. Most species spawned each year, despite large interannual variation in flow and temperature conditions. Poor recruitment over several decades, rather than a failure to spawn, is considered the most likely explanation for differences in the larval fish faunas between the two rivers.5. The highly regulated section of the Campaspe River downstream of the regulating impoundment is thought to provide suboptimal habitat conditions for larvae relative to the less regulated downstream sections.6. The timing of occurrence of larvae of the dominant species varied by breeding season and may be the result of flexibility in the timing of spawning.

Modeling possible cooling-water intake system impacts on Ohio River fish populations.

To assess the possible impacts caused by cooling-water intake system entrainment and impingement losses, populations of six target fish species near power plants on the Ohio River were modeled. A Leslie matrix model was constructed to allow an evaluation of bluegill, freshwater drum, emerald shiner, gizzard shad, sauger, and white bass populations within five river pools. Site-specific information on fish abundance and length-frequency distribution was obtained from long-term Ohio River Ecological Research Program and Ohio River Sanitation Commission (ORSANCO) electrofishing monitoring programs. Entrainment and impingement data were obtained from 316(b) demonstrations previously completed at eight Ohio River power plants. The model was first run under a scenario representative of current conditions, which included fish losses due to entrainment and impingement. The model was then rerun with these losses added back into the populations, representative of what would happen if all entrainment and impingement losses were eliminated. The model was run to represent a 50-year time period, which is a typical life span for an Ohio River coal-fired power plant. Percent changes between populations modeled with and without entrainment and impingement losses in each pool were compared to the mean interannual coefficient of variation (CV), a measure of normal fish population variability. In 6 of the 22 scenarios of fish species and river pools that were evaluated (6 species × 5 river pools, minus 8 species/river pool combinations that could not be evaluated due to insufficient fish data), the projected fish population change was greater than the expected variability of the existing fish population, indicating a possible adverse environmental impact. Given the number of other variables affecting fish populations and the conservative modeling approach, which assumed 100% mortality for all entrained fish and eggs, it was concluded that the likelihood of impact was by no means assured, even in these six cases. It was concluded that in most cases, current entrainment and impingement losses at six Ohio River power plants have little or no effect at the population level.

Use of Telemetry Methods to Estimate Natural and Fishing Mortality of Striped Bass in Lake Gaston, North Carolina

Abstract Natural mortality can substantially affect fish population dynamics, but the rate is difficult to estimate because natural deaths are rarely observed and it is difficult to separate the effects of natural and fishing mortality on abundance. We developed a new telemetry approach for estimating natural and fishing mortality rates and applied it to the population of striped bass Morone saxatilis in Lake Gaston, North Carolina and Virginia. Our analyses were based on a sample size of 51 telemetered striped bass that were known to be alive and in Lake Gaston at least 1 month after capture and surgery. Relocations of live fish and fish that died of natural causes were used to estimate natural and fishing mortality rates and the probability of relocating telemetered fish. Fishing mortality rates varied seasonally, but few natural deaths were observed, so the best model incorporated a constant annual instantaneous natural mortality rate (M; ±SE) of 0.14 ± 0.02. With the uncertainty in model selection acc...

Influence of Extreme Temperatures on Consumption and Condition of Walleyes in Pymatuning Sanctuary, Pennsylvania

Temperature is an important abiotic factor affecting fish population dynamics. An unfavorable thermal regimen can restrict a species' ability to thrive in its environment. We studied the effects of an unfavorable thermal regimen on the feeding, condition, and growth of an unexploited population of walleyes Stizostedion vitreum in Pymatuning Sanctuary, Pennsylvania. We used gastric lavage to sample stomach contents of walleyes captured by electrofishing during bimonthly sampling from May through October, 1997–1998. We sampled available forage by shoreline seining and recorded water temperatures using an electronic temperature monitor. To determine the effects of temperature on walleye feeding, condition, and growth, we examined relationships among water temperature, forage availability, percentage of stomachs containing food, food consumption by number and volume, and relative weight of adults. Average daily temperature and daily minimum temperature were above the thermal optimum (22°C) for most of the summer in both years. Adult catch-per-unit-effort, percentage of stomachs containing food, average number of food items, and volume of food consumed were all lowest during summer. Average relative weight of adults was lowest during the warmest periods of summer, and was negatively related to average temperature, as was average volume of food consumed. The thermal regimen in Pymatuning Sanctuary negatively affected adult walleye feeding activity, consumption, and condition, and was thus an important factor in structuring this population.

Assessment of 316(b) impacts on Ohio River fish populations

Cooling water intake systems have the potential to adversely impact aquatic organisms though entrainment and impingement (impacts referenced under 316(b) of the Clean Water Act), yet the loss of individual fish does not necessarily mean that a population will suffer a significant decrease in number. The results of utility sponsored studies on Ohio River fish populations provide strong evidence of positive changes in the fishery due to water quality improvements. Despite these improvements, a simulation is needed to determine if a reduction in 316(b) fish losses would result in higher or similar fish population levels. Electrofishing data collected at seven power plant locations from 1981 to 1998 will be used for the population assessments. Potential 316(b) impacts on Ohio River fish populations will be modeled using site specific 316(b) data and a Leslie matrix model. The theoretical maximum population for various fish species, with and without 316(b) impacts, will be compared and the probabilistic risk that fish populations will fall below the threshold for species survival will be assessed. Historically, EPA has allowed 316(b) to be implemented on a case-by-case basis, however, the utilities believe that the first step in assessing potential adverse environmental impacts is to assess the condition of the affected fish populations.