Over 3,300 unscreened agricultural water diversion pipes line the levees and riverbanks of the Sacramento River (California) watershed, where the threatened Southern Distinct Population Segment of green sturgeon, Acipenser medirostris, spawn. The number of sturgeon drawn into (entrained) and killed by these pipes is greatly unknown. We examined avoidance behaviors and entrainment susceptibility of juvenile green sturgeon (35±0.6 cm mean fork length) to entrainment in a large (>500-kl) outdoor flume with a 0.46-m-diameter water-diversion pipe. Fish entrainment was generally high (range: 26–61%), likely due to a lack of avoidance behavior prior to entering inescapable inflow conditions. We estimated that up to 52% of green sturgeon could be entrained after passing within 1.5 m of an active water-diversion pipe three times. These data suggest that green sturgeon are vulnerable to unscreened water-diversion pipes, and that additional research is needed to determine the potential impacts of entrainment mortality on declining sturgeon populations. Data under various hydraulic conditions also suggest that entrainment-related mortality could be decreased by extracting water at lower diversion rates over longer periods of time, balancing agricultural needs with green sturgeon conservation.

Juvenile Chinook Salmon Oncorhynchus tshawytscha from California's Central Valley must pass thousands of unscreened water diversion pipes during their out‐migration to the Pacific Ocean. The number of fish that become entrained into (drawn through) these diversions at different hydraulic and environmental conditions is currently unknown. We tested the ability of juvenile Chinook Salmon to avoid entrainment into a 0.46‐m‐diameter unscreened water diversion pipe while swimming in a large‐river‐simulation flume. Fish swimming experiments were conducted at 0.15, 0.38, and 0.61 m/s sweeping velocities (simulating the river current) with 0.42 and 0.57 m3/s water diversion rates during the day and at 0.15 and 0.61 m/s with a diversion rate of 0.57 m3/s in turbid water and during the night. The number of fish entrained during day experiments ranged from 0.8% (SE, 0.3) to 8.5% (SE, 0.3). The percentage of pipe passage events resulting in fish entrainment nearly doubled at the 0.57 m3/s water diversion rate (1.7%) compared with that at 0.42 m3/s (0.9%). In clear water conditions during the day, more fish became entrained at the higher water diversion rate (0.57 m3/s) and slower sweeping velocity (0.15 m/s), with fish entrainments starting 38.6 cm (SE, 1.6) from the center of the pipe inlet, where fish experienced an increased velocity gradient and a mean resultant velocity of 0.74 m/s. Fish entrainment was strongly influenced by the number of pipe passages per experiment, rather than by swimming orientation or time spent in the flume. More fish were entrained at the faster sweeping velocity (0.61 m/s) in turbid water during the day and at night, indicating that juvenile Chinook Salmon may use nonvisual guidance (e.g., lateral line system) to avoid water diversions in slower currents. These results help to provide a scientific basis for protecting out‐migrating juvenile Chinook Salmon exposed to unscreened water diversions.

Phytoplankton are critical component of the food web in most large rivers and estuaries, and thus identifying dominant controls on phytoplankton abundance and species composition is important to scientists, managers, and policymakers. Recent studies from a variety of systems indicate that ammonium (NH 1 4 ) in treated wastewater effluent decreases primary production and alters phytoplankton species composition. However, these findings are based mainly on laboratory and enclosure studies, which may not adequately represent natural systems. To test effects of effluent high in ammonium on phytoplankton at the ecosystem scale, we conducted whole-river-scale experiments by halting discharges to the Sacramento River from the regional wastewater treatment plant (WWTP), and used a Lagrangian approach to compare changes in phytoplankton abundance and species composition in the presence (1EFF) and absence (2EFF) of effluent. Over 5 d of downstream travel from 20 km above to 50 km below the WWTP, chlorophyll concentrations declined from 15-25 to 2.5 lg L 21 , irrespective of effluent addition. Benthic diatoms were dominant in most samples. We found no significant difference in phytoplankton abundance or species composition between 1EFF and 2EFF conditions. Moreover, greatest declines in chlorophyll occurred upstream of the WWTP where NH 1 4 concentrations were low. Grazing by clams and zooplankton could not account for observed losses, suggesting other factors such as hydrodynamics and light limitation were responsible for phytoplankton declines. These results highlight the advantages of conducting ecosystem-scale, Lagrangian-based experiments to understand the dynamic and complex interplay between physical, chemical, and biological factors that control phytoplankton populations.

KeywordsAminoglycoside antibiotics; lateral line; hair cell; ototoxicity Van Trump et al. (2010) recently demonstrated that the aminoglycoside antibiotic gentamicin, previously thought to be selectively toxic to hair cells of the canal neuromasts (CN) of the fish lateral line system, is additionally toxic to hair cells of the superficial neuromasts (SN). The authors used the fluorescent vital dyes DASPEI (2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide) and FM1-43 ((n-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide) to visualize by fluorescence microscopy the survival of hair cells in the CN and SN of zebrafish (Danio rerio) and Mexican blind cave fish (Astyanax fasciatus) treated in a solution of 0.001% gentamicin sulfate for 24h. Extensive hair cell death was observed in populations of CN and SN of gentamicin-treated animals of both species compared to control animals. On the basis of this result, the authors concluded, (p. 49), "(1) That hair cells in the SNs of the lateral line can no longer be regarded as functionally resistant to gentamicin toxicity, (2) that this drug should therefore no longer be used as a pharmacological tool for selective blocking of CN, but not SN hair cells, and (3) that the conclusions of some previous studies need to be reevaluated." Using an alternative approach to themselves reevaluate a 15-year-old assumption in the literature drawn from SEM imaging (e.g., Song et al., 1995), Van Trump et al. (2010) convincingly demonstrated that gentamicin in fact damages a high proportion of both SN and CN, similar in effect to another commonly used aminoglycoside, streptomycin (e.g., Kaus, 1987;Blaxter and Fuiman, 1989;Montgomery et al., 1997; © 2010 Elsevier B.V. All rights reserved. * (Author to whom correspondence should be addressed) Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Montgomery et al., 2003). Toward further caution in the interpretation of lateral line behavioral studies that have used aminoglycoside antibiotics to chemically ablate SN and/or CN without rigorous verification of treatment efficacy, we are inspired to share our own recent observations on limitations in the efficacy of both gentamicin and streptomycin in damaging the lateral line systems of three fish species. NIH Public AccessThe images presented here (Figs. 1-3) are drawn primarily from two projects. Images comprising Fig. 1 were obtained over the course of a series of experiments designed to examine the role of the lateral line system in swimming behaviors of goldfish (Carassius auratus) and juvenile steelhead trout (Oncorhynchu...

Water diversions pose a risk to passing fishes. We evaluated the effectiveness of several methods for preventing green sturgeon from being pulled into a simulated water diversion. We made recommendations for future management practices from the data that include considerations of fish sensory ecology as well as feasibility of implementation.

Water diversion can pose a risk to resident or migratory fishes, but fish-protection devices that reduce the entrainment of native fishes and maintain normal diversion activities exist.

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Juvenile Chinook Salmon Oncorhynchus tshawytscha traveling in river systems can become entrained by unscreened water diversions when they encounter inflow velocities that exceed their avoidance (i.e., swimming) ability. We tested the efficiency of three devices for deterring fish entrainment; the devices reduced the diversion's maximum inflow velocity by dispersing the inflow across a greater area so as to reduce fish entrainment without causing a decrease in water diversion rates. Tests were performed in a river simulation flume at a 0.15-m/s sweeping velocity in clear water conditions during the daytime and nighttime as well as in turbid water (daytime) conditions. Water was diverted at a rate of 0.57 m 3 /s through a 0.46-m-diameter pipe. The tested devices included (1) a widened box inlet (1.7 m long £ 0.76 m wide £ 0.76 m deep) with a trash rack mounted at its entrance (trash rack box), (2) a widened box inlet with a louver array mounted at the entrance (louver box), and (3) a 0.91-mdiameter cylinder perforated with 300 evenly spaced, 5-cm-diameter holes (perforated cylinder). During 2-h experiments under daytime conditions, 51.5 of 80 fish (on average) were entrained into the pipe when no device was used (i.e., control), and a fish's mean risk of becoming entrained when passing the pipe once was 14%. The mean entrainment risk during a single pipe passage event was reduced to 7% in the trash rack box treatment (i.e., 50% of the control value), 0.17% in the louver box treatment, and 0.20% in the perforated cylinder treatment. In comparison with the control, the mean number of entrained fish was reduced by 50% in the trash rack box treatment, by 97% in the louver box treatment, and by 93% in the perforated cylinder treatment. These devices *Corresponding author: nafangue@ucdavis.edu 1 Present address: Sacramento Regional County Sanitation District,