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We synthesized evidence for unintended consequences and trade‐offs associated with the passage of fishes. Provisioning of fish passageways at dams and dam removals are being carried out increasingly as resource managers seek ways to reduce fragmentation of migratory fish populations and restore biodiversity and nature‐like ecosystem services in tributaries altered by dams. The benefits of provisioning upstream passage are highlighted widely. Possible unwanted consequences and trade‐offs of upstream passage are coming to light, but remain poorly examined and underappreciated. Unintended consequences arise when passage of native and desirable introduced fishes is delayed, undone (fallback), results in patterns of movement and habitat use that reduce Darwinian fitness (e.g. ecological traps), or is highly selective taxonomically and numerically. Trade‐offs arise when passage decisions intended to benefit native species interfere with management decisions intended to control the unwanted spread of non‐native fishes and aquatic invertebrates, or genes, diseases and contaminants carried by hatchery and wild fishes. These consequences and trade‐offs will vary in importance from system to system and can result in large economic and environmental costs. For some river systems, decisions about how to manage fish passage involve substantial risks and could benefit from use of a formal, structured process that allows transparent, objective and, where possible, quantitative evaluation of these risks. Such a process can also facilitate the design of an adaptive framework that provides valuable insights into future decisions.

SynopsisMorphology and resource use were compared among recently-emerged brook charr, Salvelinus fontinalis, sampled from field locations differing in current speed . Individuals from faster running water were slightly longer, and had more fusiform body shapes and larger caudal fin heights, than individuals from slower running water. In addition, individuals from faster running water also directed more foraging attempts toward the middle of the water column and fewer toward the benthos and water surface . They also ate more dipteran larvae, fewer aquatic crustaceans, and fewer insect pupae and adults . Individuals located in the slowest and fastest current speeds made fewer foraging attempts per min, on average, than individuals located in current speeds of intermediate magnitude . Dry weight of stomach contents did not vary significantly with current speed, however . The form of the relationship between body shape and current speed suggests that it is adaptive . Small-scale variation in the location of foraging sites may account for some of the individual variability in resource use often reported for stream salmonids . Variation in the locations of foraging sites may also entail a trade-off between an individual's swimming effort and the quality of prey it consumes . IntroductionStudies comparing individuals varying in morphology, physiology, or behaviour can be valuable in a variety of contexts including (i) evaluating the role that individual variation plays in the mechanisms regulating population sizes (DeAngelis et al . 1991), and (ii) establishing functional links between morphology or physiology and other aspects of an individual's ecology (e .g . habitat use, diet) (Ehlinger

Residential proximity to busy roads has been associated with adverse health outcomes, and school location may also be an important determinant of children's exposure to traffic-related pollutants. The goal of this study was to examine the characteristics of public schools (grades K-12) in California (n = 7,460) by proximity to major roads. We determined maximum daily traffic counts for all roads within 150 m of the school using a statewide road network and a geographic information system. Statewide, 173 schools (2.3%) with a total enrollment of 150,323 students were located within 150 m of high-traffic roads (greater than or equal to 50,000 vehicles/day); 536 schools (7.2%) were within 150 m of medium-traffic roads (25,000-49,999 vehicles/day). Traffic exposure was related to race/ethnicity. For example, the overall percentage of nonwhite students was 78% at the schools located near high-traffic roads versus 60% at the schools with very low exposure (no streets with counted traffic data within 150 m). As the traffic exposure of schools increased, the percentage of both non-Hispanic black and Hispanic students attending the schools increased substantially. Traffic exposure was also related to school-based and census-tract-based socioeconomic indicators, including English language learners. The median percentage of children enrolled in free or reduced-price meal programs increased from 40.7% in the group with very low exposure to 60.5% in the highest exposure group. In summary, a substantial number of children in California attend schools close to major roads with very high traffic counts, and a disproportionate number of those students are economically disadvantaged and nonwhite.

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Recently emerged brook charr foraging in still-water pools along the sides of streams tend to be either sedentary, feeding from the lower portion of the water column (a sit-and-wait tactic) near the stream bank, or very active, feeding from the upper portion of the water column (an active search tactic) away from the bank. We tested whether the search tactics used by charr in the field represent behavioural syndromes related to activity and space use. After quantifying the behaviour of fish in the field, focal individuals were captured and their behaviour quantified in novel environment experiments in the laboratory. In an aquarium, individuals that used an active search tactic in the field spent a higher proportion of time moving, spent less time near the aquarium bottom, and took less time to find their way out of an erect glass jar, on average, than did individuals that used a sit-and-wait tactic in the field. When presented with near-bank and open-water conditions over 6 days in the laboratory, individuals that used an active search tactic in the field remained active and altered their activity less, on average, than individuals that used a sit-and-wait tactic in the field. Immediate responses to a pebble dropped in the aquarium (simulated risk from above) were not correlated with field behaviour. The search tactics used by brook charr in the field reflect part of a behavioural syndrome related to general activity and space use, but not to startle responses. These initial, individual differences in behaviour provide important raw material for the initial stages of resource polymorphism.

Disruption of movement patterns due to alterations in habitat connectivity is a pervasive effect of humans on animal populations. In many terrestrial and aquatic systems, there is increasing tension between the need to simultaneously allow passage of some species while blocking the passage of other species. We explore the ecological basis for selective fragmentation of riverine systems where the need to restrict movements of invasive species conflicts with the need to allow passage of species of commercial, recreational, or conservation concern. We develop a trait-based framework for selective fish passage based on understanding the types of movements displayed by fishes and the role of ecological filters in determining the spatial distributions of fishes. We then synthesize information on trait-based mechanisms involved with these filters to create a multidimensional niche space based on attributes such as physical capabilities, body morphology, sensory capabilities, behavior, and movement phenology. Following this, we review how these mechanisms have been applied to achieve selective fish passage across anthropogenic barriers. To date, trap-and-sort or capture-translocation efforts provide the best options for movement filters that are completely species selective, but these methods are hampered by the continual, high cost of manual sorting. Other less effective methods of selective passage risk collateral damage in the form of lower or higher than desired levels of passage. Fruitful areas for future work include using combinations of ecological and behavioral traits to passively segregate species; using taxon-specific chemical or auditory cues to direct unwanted species away from passageways and into physical or ecological traps while attracting desirable species to passageways; and developing automated sorting mechanisms based on fish recognition systems. The trait-based approach proposed for fish could serve as a template for selective fragmentation in other ecological systems.

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