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Brush piles (i.e., trees and large woody debris) are often installed in reservoirs to supplement fish habitat. The retention and dimensional change of brush piles after installation is important information that can be used to maximize the effectiveness of this management action. We evaluated the retention and dimensional change of 70 eastern red cedar Juniperus virginiana and bald cypress Taxodium distichum brush piles in an embayment of a drawdown reservoir up to four annual cycles of submergence and exposure. We used satellite imagery to supplement our onsite measurements of retention. We also examined spatial patterns of brush pile retention and dimensional change. Brush piles were lost at 10% per year, and their volume was lost at 14% per year. We compared our rates of brush pile retention and dimensional change with those from a holdout data set of 50 brush piles. Estimates between data sets did not differ statistically. Spatial patterns of retention and dimensional change coincided with morphological features in our study area, suggesting that retention and dimensional change is influenced by variable physical forces (e.g., wave action and flow) at installation locations. Our estimates of brush pile retention and dimensional change can be used to generally sustain desirable brush densities. For example, to maintain a fixed total volume of brush in our study embayment, roughly 23% of the total brush volume installed would need to be replaced annually. Similar research in reservoirs managed for other purposes is needed, as length and cycle of inundation could lead to variable rates of retention and dimensional change. Additionally, advancements into computer-assisted detection and volume estimation could reduce the time and effort needed to monitor brush piles.

Shallow areas of drawdown reservoirs are often devoid of adequate fish habitat due to degradation associated with unnatural and relatively invariable cycles of exposure and flooding. One method of enhancing fish habitat in these areas is to sow exposed shorelines with agricultural plants to provide structure once flooded. It remains unclear if some plants may be more suitable than others to provide effective fish habitat. To determine the fish habitat potential of various crops, we performed a replicated tank experiment evaluating the selection of agricultural plants by prey and predator fishes with and without the presence of the other. We submerged diverse treatments of potted plants in outdoor mesocosms stocked with prey and/or predator fish and monitored selection of plant species, stem density, and stem height over 0.5-h trials. Prey fish selected the densest vegetation, and selection was accentuated when a predator was present. Predators selected the second highest stem density and were more active when prey were present. Prey schooling was increased by predation risk, suggesting that cover was insufficient to outweigh the advantages of increased group size. Our data indicate that the perception of cover quality is reciprocally context dependent on predator–prey interactions for both predator and prey. Applications of the two most selected plant treatments in this study could enhance structural habitat for both predator and prey fishes in reservoirs, adding to their already reliable functionality as supplemental forage crops for terrestrial wildlife.

Climate change is the defining environmental problem for our generation. The effects of climate change are increasingly evident and are anticipated to profoundly affect our ability to conserve fish...

The spatial organization of fishes in a river system was investigated to evaluate the longitudinal distribution of uncommon species. It was anticipated that overall richness of the fish community would increase in a downstream direction together with habitat extent, but that more uncommon species would occur upstream owing to greater heterogeneity among sites. Fish were collected between 1995 and 2014 at 85 sites distributed throughout the Duck River Basin, Tennessee, USA. A site usually consisted of four habitat types: riffles, runs, pools and shoreline. Each habitat type was sampled with a multipass electrofishing protocol. In all, 136 native fish species were collected. Of these, 71% were classified as uncommon but represented only 16% of the total count of fish collected. As expected, overall species richness increased downstream, but contrary to expectation, uncommon species did too. Some uncommon species were restricted exclusively to tributaries and headwaters, some to tributaries and mainstem, many to mainstem only, but the largest fraction of uncommon species occurred throughout the basin, but even this last group increased in richness downstream. Conservation often focuses on uncommon species. This study suggests that a greater number of uncommon species can be conserved with an emphasis on large downstream reaches, which not only include more aquatic habitat to support larger concentrations of fish, but also shelter the uncommon species that tend to require the most protection.

The interspecific relationships between abundance and site occupancy have been widely studied in plants and animals, but principally in terrestrial systems. With few exceptions, a positive abundance–occupancy relationship has been reported. Few publications have included freshwater fish, possibly suggesting a general lack of abundance–occupancy patterns for this taxonomic group. We examined the relationship between abundance and the extent of site occupancy by 145 species of freshwater fish, including nine non‐indigenous species, sampled over 85 sites spread across the Duck River Basin, Tennessee, U.S.A. A distinct (r² = 0.79) positive abundance–occupancy curve was observed, with curves differing relative to feeding and size guilds, but not relative to environmental tolerance, conservation status (i.e. listed/non‐listed), or origin (i.e. indigenous/non‐indigenous). The patterns observed are consistent with those reported in many studies of terrestrial taxa. The existence of positive abundance–occupancy relationships in stream fish has at least two major implications for fish conservation. First, species that decrease in occupancy due to anthropogenic disturbances are likely to decrease in abundance, facing inflated prospects for local extinction. Second, occupancy alone may be used to index community status and the need for, or success of, conservation activities.

In shallow reservoirs, seasonal water drawdowns expose littoral areas and over time produce barren mudflats. When flooded, mudflats provide homogeneous substrates, turbid water, and eroding shorelines of limited ecological value. We hypothesized that in mudflats structurally complex habitats are occupied by more fish, smaller fish of a larger range in sizes, more species, and fish assemblages that are different from those in simpler habitats. We tested these hypotheses over two consecutive years with fish collections made in sites with varying structural complexity. Results indicated that structural complexity harbors more fish in transects and enclosures. Structural complexity did not influence median length, but length range increased with structural complexity. Average species richness increased with structural complexity. Fish assemblage composition changed as structural complexity increased. The ability of cover to provide survival, growth, and carrying capacity benefits is fundamental to programs aimed at increasing structural complexity. Results suggest observed effects on fish assemblages can lead to such benefits. Considering mudflats are a major component of reservoirs, expand as reservoirs age, and there is a potential to exert meaningful change on fish assemblages of impounded rivers by managing mudflats, we suggest additional attention is needed to develop practical habitat restoration options.

Environmental management often requires making decisions despite system uncertainty. One such example is mudflat mediation in flood control reservoirs. Reservoir mudflats limit development of diverse fish assemblages due to the lack of structural habitat provided by plants. Seeding mudflats with agricultural plants may mimic floodplain wetlands once inundated and provide fish habitat and achieve habitat management objectives. However, planting success is uncertain because of unpredictable water level fluctuations that affect plant survival and growth. Decision support tools can account for uncertainty that influences decision outcomes and reduce the risk in reservoir mudflat planting decisions. We used Bayesian decision networks and sensitivity analyses to quantify uncertainty surrounding mudflat plantings as supplemental fish habitat in four northwest Mississippi reservoirs. When averaged across all uncertainty, planting was the optimal decision only in Enid Lake. Response profiles indicated planting decisions depended on elevation contours within Enid, Sardis, and Grenada reservoirs. No planting was optimal at all elevations for Arkabutla Lake. These results provide a quantified basis for establishing best management practices and identify key system states that influence decision outcomes. The process used in this study to evaluate planting decisions can be applied to any reservoir by modifying reservoir dependent inputs to evaluate planting decisions to provide supplemental fish habitat.

Made available in DSpace on 2020-12-12T02:17:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Companhia Energética de São Paulo In a recent article, we described fitting electronic tags to the fish Prochilodus lineatus to document how a fishway connected aquatic habitats downstream and upstream of a major dam. Moreover, given that tagged fish remained upstream or downstream for periods extending months and years before returning to the fishway, and that observed patterns of passage were consistent with seasonal migratory cycles, and building on existing literature, we speculated that the fishway allows fish access to spawning habitats upstream and feeding habitats downstream. Our interpretation of the movement data resulted in several comments from Pelicice, Pompeu, and Agostinho (2020) and they outline various reasons by which, in their opinion, some of our conclusions may be mistaken. Their critique is threefold. First, they argue that the percentage of fish attracted into the fishway is too low to consider the fishway an effective link between the reservoir and the river downstream. We contend that without estimates of population size it is impossible to judge if 28% passage is “limited”; conceivably, the absolute number of fish passed may still be enough to maintain a viable population. Second, they assert that because receivers were located only in the fishway it is unknown if fish that used the fishway remained near the dam, or if they continued their migration. We counter with a brief literature review that documents P. lineatus migrating through reservoirs and spawning in tributaries. Third, they advocate for a broader conservation perspective and for additional research. We agree and, in the article, had already expressed this view that fishways are only a temporary fix and that we support their use only as an element of a broader environmental management package. We also agree with the need for more research but argue that procrastinating on conservation action may not be wise because we do not know if the research will be done, how long it will take, or what the cost may be of waiting. Sustainability Management Companhia Energética de São Paulo – CESP, SP-613 highway, km 78 Grupo de Pesquisa em Tecnologia em Ecohidráulica e Conservação de Recursos Pesqueiros e Hídricos – GETECH. Programa de Pós-graduação em Recursos Pesqueiros e Engenharia de Pesca Universidade Estadual do Oeste do Paraná – Unioeste Department of Hydraulics and Hydrology University of Valladolid U.S. Geological Survey Mississippi Cooperative Fish and Wildlife Research Unit Engineering College of Ilha Solteira Department of Biology and Zootechny Fish Ecology Laboratory Universidade Estadual Paulista – UNESP Engineering College of Ilha Solteira Department of Biology and Zootechny Fish Ecology Laboratory Universidade Estadual Paulista – UNESP

Best management practices are being implemented throughout the Lower Mississippi River Alluvial Valley with the aim of alleviating pressures placed on downstream aquatic systems by sediment and nutrient losses from agricultural land; however, research evaluating the performance of tailwater recovery (TWR) systems, an increasingly important practice, is limited. This study evaluated the ability of TWR systems to retain sediment and nutrients draining from agricultural landscapes. Composite flow-based samples were collected during flow events (precipitation or irrigation) over a two-year period in six TWR systems. Performance was evaluated by comparing concentrations and loads in water entering TWR systems (i.e., runoff or influent) from agricultural fields to water overflow exiting TWR systems (effluent). Tailwater recovery systems did not reduce concentrations of solids and nutrients, but did reduce loads of solids, phosphorus (P), and nitrogen (N) by 43%, 32%, and 44%, respectively. Annual mean load reductions were 1,142 kg solids, 0.7 kg of P, and 3.8 kg of N. Performance of TWR systems was influenced by effluent volume, system fullness, time since the previous event, and capacity of the TWR system. Mechanistically, TWR systems retain runoff on the agricultural landscape, thereby reducing the amount of sediment and nutrients entering downstream waterbodies. System performance can be improved through manipulation of influential parameters.

Fluvial geomorphology of the alluvial valley of the Lower Mississippi River reveals a fascinating history. A prominent occupant of the valley was the Ohio River, estimated to have flowed 25,000 years ago over western Tennessee and Mississippi to join the Mississippi River north of Baton Rouge, Louisiana, 750–800 km south of the present confluence. Over time, shifts in the Mississippi and Ohio rivers toward their contemporary positions have left a legacy of abandoned paleochannels supportive of unique fish assemblages. Relative to channels abandoned in the last 500 years, paleochannels exhibit harsher environmental conditions characteristic of hypereutrophic lakes and support tolerant fish assemblages. Considering their ecological, geological, and historical importance, coupled with their primordial scenery, the hundreds of paleochannels in the valley represent a national treasure. Altogether, these waterscapes are endangered by human activities and would benefit from the conservation attention afforded to...

Populations show spatial-temporal fluctuations in abundance, partly due to random processes and partly due to self-regulatory processes. We evaluated the effects of various external factors on the population numerical abundance of curimba Prochilodus lineatus in the upper Paraná River floodplain, Brazil, over a 19-year period. Panel data analysis was applied to examine the structure of temporal and spatial abundance while controlling auto-regressive processes and spatial non-homogeneity variances that often obscure relationships. As sources of population variation, we considered predation, competition, selected abiotic variables, construction of a dam upstream of the study area, water level and flood intensity during the spawning period. We found that biological interactions (predation and competition) were not significantly related to variations in curimba abundance; specific conductance was a space indicator of abundance, apparently linked to the biology of the species; intensity of floods determined inter-annual variation in abundances; Porto Primavera Dam negatively impacted the abundances at sites in the floodplain directly affected by discharges from the dam. Panel data analysis was a powerful tool that identified the need for intense flooding to maintain high abundances of curimba in the upper Paraná River. We believe our results apply to other species with similar life strategy. RESUMO As populações apresentam flutuações espaço-temporais em abundância devido a processos aleatórios e auto-regulatórios. Nesse trabalho avaliamos efeitos de vários fatores sobre a abundância da curimba, Prochilodus lineatus, em cinco ambientes da planície de inundação do alto rio Paraná, Brasil, durante 19 anos. A análise de dados em painel foi utilizada por examinar variações espaço-temporais na abundância considerando processos auto-regressivos e variâncias espacialmente heterogêneas, que por vezes dificultam a identificação das relações. Como fontes de variação na abundância da curimba foram consideradas: predação, competição, variáveis abióticas selecionadas, construção da barragem de Porto Primavera, nível da água do rio Paraná e intensidade de cheia no período reprodutivo. Foi identificado que predação e competição não foram significativamente associadas às abundâncias da curimba; condutividade específica foi indicadora espacial da abundância; intensidade das cheias foi determinante de variações interanuais na abundância; barragem de Porto Primavera influenciou, negativamente, a abundância em corpos d’água diretamente afetados. A análise de dados em painel mostrou ser uma poderosa ferramenta preditiva, que possibilitou identificar a necessidade de cheias intensas para manutenção de elevadas abundâncias de curimba no alto rio Paraná. Acreditamos que o mesmo seja válido espécies de peixes que apresentam estratégia de vida similar.

Electrofishing is widely used to monitor fish species composition and relative abundance in streams and lakes. According to standard protocols, multiple segments are selected in a body of water to monitor population relative abundance as the ratio of total catch to total sampling effort. The standard protocol provides an assessment of fish distribution at a macrohabitat scale among segments, but not within segments. An ancillary protocol was developed for assessing fish distribution at a finer scale within electrofishing segments. The ancillary protocol was used to estimate spacing, dispersion, and association of two species along shore segments in two local reservoirs. The added information provided by the ancillary protocol may be useful for assessing fish distribution relative to fish of the same species, to fish of different species, and to environmental or habitat characteristics.

Embayments are among the most widespread littoral habitats found in Mississippi flood-control reservoirs. These macrohabitats represent commonly used nursery zones for age-0 crappies, Pomoxis spp., despite barren and eroded shorelines formed over 60–70 years of annual water level fluctuations. We tested if embayments displayed microhabitat gradients linked to the effect of water level fluctuations on riparian vegetation and if these gradients were paralleled by gradients in age-0 crappie distribution. Habitat composition changed longitudinally along the embayments with the most pronounced gradient representing a shift from nonvegetated mudflats near the mouth of embayments to herbaceous material upstream. The degree of habitat change depended on the water level. Similarly, catch rates of crappies increased upstream toward the rear of embayments, differing among water levels and reservoirs, but the longitudinal pattern persisted. Our results indicate that habitat composition gradients occur in embayments o...

Managing water storage and withdrawals in many reservoirs requires establishing seasonal targets for water levels (i.e., rule curves) that are influenced by regional precipitation and diverse water demands. Rule curves are established as an attempt to balance various water needs such as flood control, irrigation, and environmental benefits such as fish and wildlife management. The processes and challenges associated with amending rule curves to balance multiuse needs are complicated and mostly unfamiliar to non-US Army Corps of Engineers (USACE) natural resource managers and to the public. To inform natural resource managers and the public we describe the policies and process involved in amending rule curves in USACE reservoirs, including 3 frameworks: a general investigation, a continuing authority program, and the water control plan. Our review suggests that water management in reservoirs can be amended, but generally a multitude of constraints and competing demands must be addressed before suc...

We examined the interaction between environmental variables measured at three different scales (i.e., landscape, lake, and in-lake) and fish assemblage descriptors across a range of over 50 floodplain lakes in the Mississippi Alluvial Valley of Mississippi and Arkansas. Our goal was to identify important local- and landscape-level determinants of fish assemblage structure. Relationships between fish assemblage structure and variables measured at broader scales (i.e., landscape-level and lake-level) were hypothesized to be stronger than relationships with variables measured at finer scales (i.e., in-lake variables). Results suggest that fish assemblage structure in floodplain lakes was influenced by variables operating on three different scales. However, and contrary to expectations, canonical correlations between in-lake environmental characteristics and fish assemblage structure were generally stronger than correlations between landscape-level and lake-level variables and fish assemblage structure, suggesting a hierarchy of influence. From a resource management perspective, our study suggests that landscape-level and lake-level variables may be manipulated for conservation or restoration purposes, and in-lake variables and fish assemblage structure may be used to monitor the success of such efforts.

We examined the relationship between fishing effort (hours fished) and average March–May water level in 3 flood control reservoirs in Mississippi. Fishing effort increased as water level rose, peaked at intermediate water levels, and decreased at high water levels. We suggest that the observed arched-shaped relationship is driven by the shifting influence of fishability (adequacy of the fishing circumstances from an angler's perspective) and catch rate along a water level continuum. Fishability reduces fishing effort during low water, despite the potential for higher catch rates. Conversely, reduced catch rates and fishability at high water also curtail effort. Thus, both high and low water levels seem to discourage fishing effort, whereas anglers seem to favor intermediate water levels. Our results have implications for water level management in reservoirs with large water level fluctuations.

Summary Estimated number of shovelnose sturgeon Scaphirhynchus platorynchus impacted annually by towboat entrainment in navigation pools of the Upper Mississippi River were compared against estimates of fishery harvest and ambient population densities to evaluate the relevance of entrainment at the population level. Mean number of sturgeon entrained per kilometer of navigation was estimated at 0.02, and mean number entrained annually considering towboat traffic was estimated at 0.38 sturgeon/ha. Losses associated with entrainment were mostly lower than fishery harvest, although differences were not large. The two sources of mortality combined could potentially reduce the mature adult population to a level where it no longer has the reproductive capacity to replenish itself. Thus, through a combination of entrainment and fishing mortality shovelnose sturgeon may be looming near unsustainable population levels. These estimates are preliminary considering the many uncertainties associated with quantifying entrainment and its effects. Additional research is needed not only to derive better estimates, but also to develop options for managing entrainment.

The presence of aquatic macrophytes is a key factor in the selection of habitats by fish in floodplain lakes because these plants enhance the physical and biological complexities of aquatic habitats. The seasonal flood pulse may influence this interaction, but there is no information in the literature about the effects that flood events may have on macrophytes assemblages and its associated effects on fish assemblages. Thus, this article aimed to investigate whether species richness, evenness and similarities in fish assemblage composition differed between littoral areas vegetated with macrophytes and unvegetated areas, before and after a flood. We sampled three lakes in the floodplain of the upper Parana River basin. Sampling was conducted before (December 2004 and January 2005) and after (early March, late March and May 2005) a flood event. Overall, species richness and evenness were higher in macrophytes-covered areas. Before the flood, the composition of fish assemblages was distinct when comparing vegetated and unvegetated areas. After the flood, the similarity in fish assemblage composition was higher, indicating a homogenization effect of floods for fish inhabiting littoral areas of floodplain lakes. After the flood, opportunistic species dominated the fish assemblages in aquatic macrophytes, apparently restructuring assemblages in the littoral, restarting a succession process. Thus, the observed homogenization effect of the flood could minimize biological interactions and could induce fish assemblages to begin a new process of structurization.

River-floodplain ecosystems offer some of the most diverse and dynamic environments in the world. Accordingly, floodplain habitats harbor diverse fish assemblages. Fish biodiversity in floodplain lakes may be influenced by multiple variables operating on disparate scales, and these variables may exhibit a hierarchical organization depending on whether one variable governs another. In this study, we examined the interaction between primary variables descriptive of floodplain lake large-scale features, suites of secondary variables descriptive of water quality and primary productivity, and a set of tertiary variables descriptive of fish biodiversity across a range of floodplain lakes in the Mississippi Alluvial Valley of Mississippi and Arkansas (USA). Lakes varied considerably in their representation of primary, secondary, and tertiary variables. Multivariate direct gradient analyses indicated that lake maximum depth and the percentage of agricultural land surrounding a lake were the most important factors controlling variation in suites of secondary and tertiary variables, followed to a lesser extent by lake surface area. Fish biodiversity was generally greatest in large, deep lakes with lower proportions of watershed agricultural land. Our results may help foster a holistic approach to floodplain lake management and suggest the framework for a feedback model wherein primary variables can be manipulated for conservation and restoration purposes and secondary and tertiary variables can be used to monitor the success of such efforts.

We surveyed the habitat and fish assemblages of four impounded and three unimpounded neighboring headwater streams, separated longitudinally into multiple upstream and downstream reaches. Instream habitat characteristics were similar between reaches of unimpounded streams and reaches above impoundments, and differed significantly from reaches below impoundments that included deeper water and more stable flows. Species richness was similar above and below impoundments, and between impounded and unimpounded streams, but fish assemblage composition and structure differed. Stream reaches above impoundments supported higher percentages of centrarchids compared to upper reaches of unimpounded streams, which had more obligate stream cyprinids. Reaches below impoundments supported mainly centrarchid species whereas lower reaches of unimpounded streams supported a balanced mix of cyprinids and centrarchids. Percina maculata (Blackside Darter) occurred throughout the study area except in upper reaches of i...

Over 6,000 crappies Pomoxis spp. were tagged in five water bodies to estimate exploitation rates by anglers. Exploitation rates were computed as the percentage of tags returned after adjustment for three sources of uncertainty: postrelease mortality due to the tagging process, tag loss, and the reporting rate of tagged fish. Confidence intervals around exploitation rates were estimated by resampling from the probability distributions of tagging mortality, tag loss, and reporting rate. Estimates of exploitation rates ranged from 17% to 54% among the five study systems. Uncertainty around estimates of tagging mortality, tag loss, and reporting resulted in 90% confidence intervals around the median exploitation rate as narrow as 15 percentage points and as broad as 46 percentage points. The greatest source of estimation error was uncertainty about tag reporting. Because the large investments required by tagging and reward operations produce imprecise estimates of the exploitation rate, it may be wor...

We investigated larval fish density and assemblage structure in mid-channel and backwater areas of Luxapallila Creek, Mississippi to better understand larval fish distribution across these two stream habitats. Our results showed backwater and mid-channel habitats not to differ with respect to total larval fish density, but rather in how larval fish taxa were apportioned across habitats. This research suggests stream alterations that reduce backwater habitats, which has occurred in Luxapallila Creek, may affect fish assemblage structure by reducing resource requirements of some fish larvae.

Eutrophication of lakes is often accompanied by wide diel fluctuations in dissolved oxygen (DO) concentrations that can influence fish assemblage composition and periodically result in highly visible fish kills. We conducted a probabilistic risk assessment to estimate the likelihood that a shallow eutrophic oxbow lake would be affected by critically low DO concentration at dawn during mid-summer. Monte-Carlo simulations with a respiration model that considered DO concentration at dusk, water respiration rate, sediment respiration rate, air–water diffusive exchange, and night duration were used to generate a depth-specific probability distribution of DO concentrations for the following dawn. This probability distribution was combined with a bathymetric model of the lake, constructed in a geographic information system using geo-referenced depth data, to predict the probability that a certain area of the lake would be affected by critically low DO concentration. The area affected was evaluated as a function of lake stage elevation. Results of the risk assessment pointed to the importance of shallow water (

A qualitative comparative approach has been used to review whether fish assemblage characteristics, such as paucity of lacustrine-adapted fish species, long food chains, and disproportionate number of piscivorous species, limit fishery yields in reservoirs of the Upper Parana River basin. The paucity of lacustrine-adapted species appears to limit fishery yields, but attempts to introduce lacustrine species have been generally unsuccessful. The food chains of species targeted by the fisheries are relatively long, but short food chains seem to be an adaptation of lacustrine species. Because reservoirs with many piscivorous species sustain high fishery yields elsewhere in the world, the hypothesis that an excessive number of piscivores limits yields is not supported. Instead, inadequacies of fish assemblages in reservoirs of the Upper Parana River basin appear to be symptomatic of an unsuitable environment for lacustrine fish species. The physical characteristics of reservoirs in the Upper Parana River basin, exacerbated by climatic patterns, may preclude the emergence of successful reservoir species from within the extant pool of riverine species. The resulting assemblages have characteristics that are neither riverine nor lacustrine, and are maladapted to support fisheries in the reservoirs. The introduction of lacustrine species is destined to failure because environmental characteristics are not lacustrine, except in reservoirs positioned high in the watershed, where increased retention times allow lacustrine conditions. Published in 2001 by John Wiley & Sons, Ltd.

In reservoirs of the Upper Parana River Basin, Brazil Paraguay, phytoplankton biomass is generally low relative to reservoirs in other parts of the world. To investigate what might be limiting phytoplankton biomass in the Upper Parana reservoirs, we used an empirical approach wherein climatic conditions in the basin as well as chemical, hydrological and morphometrical characteristics of 13 reservoirs, were compared against those prevailing in 58 reservoirs of the south-central United States. In both regions, phytoplankton biomass was correlated with chemical, hydrological and morphometrical characteristics of the reservoirs. There were no differences in phosphorus concentrations between the two regions, nitrogen levels were higher in the Upper Parana, ionic concentrations were higher in the south-central United States and there were major differences in all physical characteristics considered. In reservoirs of the south-central United States, hydraulic retention time increased and discharges decreased during the post-spawning period allowing increases in phytoplankton biomass; in the Upper Parana River Basin, discharges peaked during the post-spawning period, delaying the peak of phytoplankton blooms until after completion of the post-spawning period. Our comparison between the two sets of reservoirs suggests that hydrologic regimes dictate differences in phytoplankton biomass and that hydrology of the Upper Parana River Basin, exacerbated by climatic patterns, deter phytoplankton production despite suitable levels of essential nutrients.

We studied the relation between aquatic vegetation coverage, summer dissolved oxygen and density of sunfishes (Lepomis spp.) in 10 shallow bays of a eutrophic reservoir. The bays ranged 5.2–15.7 ha in area, 0.6–1.3 m mean depth and 6–91% vegetation area coverage. Over the 10 bays mean dissolved oxygen concentration ranged 5.8–9.0 mg l-1 in open water at least 20 m away from the vegetation, 0.8–8.1 mg l-1 at the vegetation-water edge and 0.5–7.7 mg l-1 in dense vegetation. Dissolved oxygen concentrations were inversely related to vegetation coverage. In open water, dissolved oxygen levels were consistently higher than 8 mg l-1 when vegetation coverage was

The yellow bass (Morone mississippiensis) is native to the Mississippi River drainage and some adjacent Gulf of Mexico tributaries where it inhabits backwaters, oxbows, and reservoirs. We described the diet ecology of yellow bass in an oxbow of the lower Mississippi River, assessed differences in diets between life stages, and measured diet overlap between yellow bass and coexisting species. Indices of diet breadth differed among age groups, with the diet of age-1 yellow bass being more specialized than that of larger fish. Although the yellow bass consumed a wide array of food items, it tended to rely on certain foods during different life stages. Age-1 yellow bass fed on chironomids, amphipods, and fish eggs, which accounted for 84% of the diet by weight. Age-2+ yellow bass consumed fish, fish eggs, amphipods, and benthic insects, which was over 70% of the diet by weight. Diet overlap was not significant (P > 0.20) between age-1 and age-2+ yellow bass, or between age-1 yellow bass and age-0 lar...

White crappie Pomoxis annularis and black crappie P. nigromaculatus are important freshwater sportfishes in North America. Because of erratic recruitment (the number of fish that survive to age 1 each year) fishery yields are inconsistent. We developed a simple age-structured model to help manage crappie fisheries. The model changes population biomass by age-specific somatic growth, and population abundance through recruitment and age-specific natural and fishing mortalities. Using empirical stock-recruitment data and a stochastic component to simulate the effects of abiotic environmental fluctuations on recruitment, the model simulated empirical recruitment dynamics of a crappie population over 30 years in a large impoundment. Effects of density-dependent growth and natural mortality were modeled, but did not substantially affect the yield given the observed magnitude of recruitment fluctuations. Model predictions of population biomass and yield tended to be high relative to empirical estimates, but not unrealistic. Erratic recruitment of crappie populations has made development of management strategies elusive. This model should help fishery managers examine potential management alternatives.

Degradation of reservoir fish habitat has become a serious concern. Habitat issues-such as sedimentation, excessive nutrient loadings, and lack of submerged structure-may emerge and worsen over time and are accompanied by undesirable shifts in the fish community and fisheries. To prioritize habitat rehabilitation efforts in reservoirs, we developed a classification system for large reservoirs in the contiguous U.S. We used a four-step classification approach based on over 50 variables descriptive of habitat impairment in a sample of almost 1300 reservoirs. To account for the broad geographic heterogeneity in climate and landscape, reservoirs were assigned to a spatial framework relevant to aquatic resources, selected based on how well it recognized regional differences in fish habitat. To account for differences among reservoirs within geographical regions, we used cluster analysis to identify classes of reservoirs with similar characteristics. Classes were compared regarding habitat impairment, the fish community, the recreational fishery, and other variables from an external dataset to seek support for the classification system. A method for classifying new reservoirs not included in the original sample was also developed. The resulting classification system identified nine geographical regions distributed throughout the contiguous U.S. and 24 reservoir classes within the nine regions. The system can serve as the framework for a reservoir assessment mechanism. Our approach may be applicable elsewhere a broad-scale dataset is not available and needs to be obtained quickly and inexpensively, whether in regards to fish habitat or other environmental information needs.

Fish habitat impairment resulting from natural and anthropogenic watershed and in-lake processes has in many cases reduced the ability of reservoirs to sustain native fish assemblages and fisheries quality. Rehabilitation of impaired reservoirs is hindered by the lack of a method suitable for scoring impairment status. To address this limitation, an index of reservoir habitat impairment (IRHI) was developed by merging 14 metrics descriptive of common impairment sources, with each metric scored from 0 (no impairment) to 5 (high impairment) by fisheries scientists with local knowledge. With a plausible range of 5 to 25, distribution of the IRHI scores ranged from 5 to 23 over 482 randomly selected reservoirs dispersed throughout the USA. The IRHI reflected five impairment factors including siltation, structural habitat, eutrophication, water regime, and aquatic plants. The factors were weakly related to key reservoir characteristics including reservoir area, depth, age, and use type, suggesting that common reservoir descriptors are poor predictors of fish habitat impairment. The IRHI is rapid and inexpensive to calculate, provides an easily understood measure of the overall habitat impairment, allows comparison of reservoirs and therefore prioritization of restoration activities, and may be used to track restoration progress. The major limitation of the IRHI is its reliance on unstandardized professional judgment rather than standardized empirical measurements.

We describe the fish assemblages associated with drifting macrophyte mats and consider their possible role as dispersal vectors in the Ivinhema River, a major tributary of the upper Paraná River, Brazil. Fish associated with drifting mats were sampled in the main river channel during January and March 2005, when the wind and/or the increased water level were sufficient to transport macrophyte stands. Fish in the drifting mats were sampled with a floating sieve (4 m long x 2 m wide x 0.6 m high, and 2 mm mesh size). In the laboratory, larvae, juvenile, and adult fish were counted and identified to the lowest possible taxonomic level. In four drifting macrophyte mats we captured 218 individuals belonging to at least 28 species, 17 families, and 6 orders. Aphyocharax dentatus, Serrasalmus spp., and Trachelyopterus galeatus were the most abundant taxa associated with the mats, but species richness ranged from 6 to 24 species per mat. In addition, 85% of the total number of individuals caught was larvae and juveniles. Although preliminary and based on limited samples, this study of drifting macrophyte mats was the first one in the last unregulated stretch of the Paraná River remaining inside Brazilian territory, and alerts us to the potential role of macrophytes mats as dispersers of fish species in the region.Nesse trabalho as assembleias de peixes associadas a bancos de macrófitas flutuantes à deriva foram descritas. Além disso, foi considerado o possível papel desses bancos como vetores de dispersão no rio Ivinhema, importante tributário do alto rio Paraná, Brasil. Os peixes associados aos bancos à deriva foram amostrados no canal principal desse rio, entre os meses de Janeiro a Março de 2005, quando o vento e/ou o aumento no nível da água foram suficientes para transportar os bancos de macrófitas. Os peixes foram amostrados com uma rede flutuante (4 m de comprimento x 2 m de largura x 0,6 m de altura e 2 mm de tamanho de malha). No laboratório, larvas, jovens e adultos foram contados e identificados ao menor nível taxonômico possível. Nos quatro bancos de macrófitas flutuantes a deriva foram capturados 218 indivíduos pertencentes à pelo menos 28 espécies, 17 famílias e 6 ordens. Aphyocharax dentatus, Serrasalmus spp. e Trachelyopterus galeatus foram os táxons mais abundantes associados aos bancos de macrófitas à deriva, mas a riqueza de espécie variou entre 6 e 24 espécies por banco. Além disso, 85% do total do número de indivíduos capturados foram larvas e juvenis. Embora preliminar e baseado em amostragens limitadas, este estudo, conduzido em bancos de macrófitas flutuantes à deriva, foi o primeiro no último trecho não regulado do rio Paraná em território brasileiro, e alerta para o papel potencial que os bancos de macrófitas têm como dispersores de peixes na região.