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Navigating obstacles is innate to fish in rivers, but fragmentation of the world's rivers by more than 50,000 large dams threatens many of the fish migrations these waterways support. One limitation to mitigating the impacts of dams on fish is that we have a poor understanding of why some fish enter routes engineered for their safe travel around the dam but others pass through more dangerous routes. To understand fish movement through hydropower dam environments, we combine a computational fluid dynamics model of the flow field at a dam and a behavioral model in which simulated fish adjust swim orientation and speed to modulate their experience to water acceleration and pressure (depth). We fit the model to data on the passage of juvenile Pacific salmonids (Oncorhynchus spp.) at seven dams in the Columbia/Snake River system. Our findings from reproducing observed fish movement and passage patterns across 47 flow field conditions sampled over 14 y emphasize the role of experience and perception in the decision making of animals that can inform opportunities and limitations in living resources management and engineering design.

A B S T R A C TThe Instream Flow Incremental Methodology (IFIM) has been subject to criticisms, including its apparent imprecision, inability to predict discharge-biomass relationships, lack of independence of hydraulic variables, and omission of predation/competition as variables in assessing the dynamics of aquatic populations and communities. This paper addresses criticisms of the methodology, stressing three themes. First, the development of IFIM to its present form is described. The goal of the method is to relate biotic values in equivalent terms to those used to estimate other beneficial uses of water. As such the engineering concepts of hydraulic simulation and suitability criteria play a strong role in the model. Previous studies suggest that IFIM appears to perform defensibly in coldwater systems but less well in more complex coolwater and warmwater systems. Second, the strengths of IFIM are considered and the type of environmental of IFIM are considered and the type o f environmental problems it is suited to address are described. Research suggests that biotic responses vary dramatically as certain threshold discharges are approached and it is suggested that biomass predictions are inappropriate with current versions of IFIM. Its greatest utility is shown to be in assessing the impacts of water resources development on habitat availability for aquatic organisms. Third, the limitations of IFIM are presented; those that appear to have merit and those that arise from misapplication or misunderstanding of the methodology. We suggest that suitability criteria be developed on a site specific basis and include depth-velocity dependent functions. The added predictive power by incorporation of coefficients of biological interactions to this management model is probably not justified by the expense required to obtain the data. As a tool, IFIM maximizes generality and precision at the expense of ecological reality but this does not detract from its utility to analyse water resource issues.

Over 450 dams have been constructed in the upper Paraná River basin in Brazil during the past 40 years. River regulation by these dams is considered a primary factor in the reduction of fish diversity and depletion of migratory species. In contrast to the upper Paraná Basin, only two large dams (both with upstream fish passage) have been constructed in the lower La Plata River basin. Fishery managers in the lower basin are concerned that existing and planned dams will further deplete populations of migratory fish species that constitute important recreational and commercial fisheries as has occurred in the upper basin. We assessed the sustainability of fisheries in the lower basin in the face of increased river regulation by using literature information to describe the efficiency of the fish passage systems used to mitigate river regulation impacts on fisheries. Our analysis shows that fish passage systems at both lower basin dams, Yacyreta and Salto Grande, fail to transfer sufficient numbers of upstream migrants to sustain populations of migratory species. Fish passage efficiency of target species in the fish elevators at Yacyreta is less than 2%. Fish diversity in the fish elevators is low because about 85% of the fish belong to only three nonmigratory species (Pimelodus maculatus, Oxydoras kneri and Rhinodoras dorbignyi). Large migratory species targeted for passage rarely comprise even 5 % of the fish number in the passage system. The two Borland locks at Salto Grande Dam cannot dependably pass large numbers of migratory species because passage efficiency is dependent upon interactions of powerhouse and spillway operation with tailrace elevations. Most species in the Borland system were either a small catfish (Parapimelodus valenciennis) or a engraulid (Lycengraulis grossidens). Again, the targeted migratory species were not abundant in the passage system. We conclude that existing fish passage technology in the lower basin is inadequate and that improved fish passage designs are required to conserve migratory species. These designs must be based on integrated information from geomorphology (habitat), natural fish behavior, fish swimming capabilities, and detailed population studies.Mais de 450 barragens foram construídas no alto rio Paraná, Brasil, nos últimos 40 anos. A regulação dos rios por barragens é considerada um dos fatores primários de redução da diversidade de peixes e depleção de espécies migratórias. Em contraste, somente duas grandes barragens foram construídas nos trechos mais inferiores da bacia do rio da Prata. No momento, há uma grande preocupação acerca do impacto dos represamentos sobre espécies que se constituem a base da pesca comercial e esportiva na bacia. Este artigo aborda o desempenho das passagens de peixes das barragens de Yacyreta e Salto Grande, monstrando que as mesmas falham na transferência de grandes quantidades de espécies migratórias para os trechos a montante. A barragem de Yacyreta tem dois elevadores com problemas importantes de projeto. Como resultado, a eficiência n...

The Upper Mississippi River System (UMRS) is a large and diverse river system that changes character along its 1,200 mile network of rivers and canals and 2.6 million acres of floodplain. It supports more than 30 million people in its watershed, a significant commercial waterway, more than a million acres of ''floodplain'' agriculture and about one-half million acres of river-floodplain managed for fish, wildlife, and recreation. Large-scale geomorphology and climate patterns largely determine the hydrologic characteristics of a nested hierarchy of UMRS river reaches. The human impacts above are also important drivers determining hydrologic characteristics within the hierarchy. Understanding the relationship among physical and chemical processes and ecological responses is critical to implement an adaptive management framework for UMRS ecosystem sustainability. Historic or contemporary data from 42 locations were used to examine changes in UMRS hydrology and to demonstrate the utility of a multiple reference condition analysis for river restoration. A multivariate mathematical framework was used to show how river stage hydrology can be characterized by the variability, predictability, seasonality, and rate of change. Large-scale ''geomorphic reaches'' have distinct hydrologic characteristics and response to development throughout the UMRS region, but within navigation pool hydrology is similar among all impounded reaches regardless of geomorphic reach. Reaches with hydrologic characteristics similar to historic reference conditions should be examined to determine whether those characteristics support desired management objectives. Water levels can be managed, within limits to support navigation and agriculture, to more closely resemble natural hydrology for the benefit of a variety of species, habitats, and ecological processes.

Understanding hydrodynamic cues used by outmigrating juvenile salmon (emigrants) to guide fine-scale swim path selection is critical to successful fish guidance and passage at man-made structures. We show how these cues can be inferred from channel features and complex flow fields of natural rivers through which emigrants pass. We then describe a new cue, 'total hydraulic strain', integrating properties of flow acceleration and turbulence through the spatial gradients in velocity to create a single flow field distortion metric amenable to the analysis of fish movement at the scale of large man-made structures. We explain how total hydraulic strain, together with the magnitude of velocity, provide sufficient information for any fish to distinguish between the two categories of channel features with their mechanosensory system. We demonstrate that total hydraulic strain, velocity magnitude and hydrostatic pressure can be integrated into rule-sets (the Strain-Velocity-Pressure (SVP) Hypothesis) to explain emigrant swim path selection near dams. To confirm the reasonableness of the SVP Hypothesis, we describe how its separate elements can be detected by different components of the fish mechanosensory system. We evaluate the SVP Hypothesis by (1) using it to explain the traces made by acoustically tagged emigrants overlaid on coincident total hydraulic strain and velocity magnitude fields, (2) using it to explain different passage efficiencies of competing bypass designs and (3) testing it via stepwise discriminant analysis to infer the relationship between hydrodynamic pattern and emigrant orientation. We conclude the SVP Hypothesis is a reasonable and useful approximation of the strategy used by emigrants to select their swim path through complex flow fields sufficient to serve as the basis of guidance and bypass system design. Published in

Low‐ and high‐frequency sounds were tested as a means of repelling blueback herring Alosa aestivalis in confined‐area and open‐water experiments. Confined‐area tests were performed by analyzing the response of blueback herring in floating net‐pens to sounds differing in frequency, sound pressure levels (SPLs, given in decibels [dB] in reference to l.0 μPa), and pulse width. Highfrequency sounds between 110 and 140 kHz, at SPLs above 180 dB (at 1.0 m from the transducer) and at various pulse widths, elicited statistically significant (P < 0.05) avoidance responses by blueback herring. A reduced response was observed at sound frequencies of 100 and 150 kHz. Low‐frequency sounds between 0.1 and 1 kHz at SPLs of 160–175 dB (at 1.0 m from the transducer) elicited only short‐term startle responses. Field tests were performed at Richard B. Russell Dam (on the Savannah River at the Georgia‐South Carolina border) to evaluate candidate transducers and amplifiers. In field evaluations a single high‐frequency transducer emitting 124.6‐ and 130.9‐kHz sounds at an SPL of 187 or 200 dB (at 1.0 m) partially repelled blueback herring that were approximately 60 m away from the transducer for periods of up to I h. These results suggest that high‐frequency sound may provide an effective and inexpensive method, relative to structural measures, for reducing entrainment of blueback herring at hydropower stations.

Ecosystem restoration planning requires quantitative rigor to evaluate alternatives, define end states, report progress and perform environmental benefits analysis (EBA). Unfortunately, existing planning frameworks are, at best, semi-quantitative. In this paper, we: (1) describe a quantitative restoration planning approach based on a comprehensive, but simple mathematical framework that can be used to effectively apply knowledge and evaluate alternatives, (2) use the approach to derive a simple but precisely defined lexicon based on the reference condition concept and allied terms and (3) illustrate the approach with an example from the Upper Mississippi River System (UMRS) using hydrologic indicators. The approach supports the development of a scaleable restoration strategy that, in theory, can be expanded to ecosystem characteristics such as hydraulics, geomorphology, habitat and biodiversity. We identify three reference condition types, best achievable condition (A BAC ), measured magnitude (MM i which can be determined at one or many times and places) and desired future condition (A DFC ) that, when used with the mathematical framework, provide a complete system of accounts useful for goal-oriented system-level management and restoration. Published in