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Passage facilities at dams must accommodate a broad array of aquatic species to achieve full river connectivity. In an attempt to improve adult Pacific lamprey (Entosphenus tridentatus) passage, fishway entrance modifications were made at a large dam on the Columbia River in northwestern USA. The modifications consisted of a variable-width entrance weir and flow disrupters to create heterogeneity in water velocities near the bottom, without affecting attraction flows for adult salmonids (Oncorhynchus spp.) or alosids (Alosa sapidissima). Additionally, a lamprey passage structure (LPS) was installed to provide a lamprey-specific route from tailrace to forebay elevation (31 m). Passive integrated transponders and radio transmitters were used to monitor both Pacific lamprey and Chinook salmon (O. tshawytscha) movements. Fish use of the modified entrance was compared to that at a similar, but unmodified entrance before and after modifications. The entrance modifications resulted in increased velocity heterogeneity, but no measurable improvement in entrance efficiencies for lamprey or salmon. Lamprey successfully ascended the LPS, with annual counts ranging from 48 in 2010 to 3,851 in 2016 (0.2–8.9% of lamprey counted at the dam). Radiotelemetry indicated that tagged lamprey resumed upstream passage after LPS use and travelled at rates similar to those that used traditional fishway routes. [ABSTRACT FROM AUTHOR]

Instream barriers affect anadromous lampreys worldwide by preventing access to spawning habitat, resulting in the decline of several species. Because lampreys rely heavily on olfactory cues to choose movement paths during upstream migration in rivers, the manipulation of these cues may be used to guide individuals into the vicinity of fish passage devices and thereby mitigate the impacts of barriers during migration. However, because experimentation with imperiled species presents significant legal and ethical challenges, use of a surrogate species that exhibits similar responses may prove very useful. Our laboratory study established that (1) the odor derived from dead Pacific LampreyEntosphenus tridentatuselicits an avoidance response from invasive Sea LampreyPetromyzon marinusfrom the Laurentian Great Lakes, and (2) the magnitude of this response does not differ from the conspecific alarm cue present in Sea Lamprey. By presenting the odor on the side of a river channel opposite a lamprey fish passage device, migrating lampreys of conservation concern may be guided to fishways, if the behavioral response to the cue has evolved in these taxa. Due to their availability and well-studied chemical communication system, Sea Lamprey may prove to be a useful surrogate for identifying and producing chemosensory cues for use in guiding Pacific Lampreys towards fish passage devices and away from intakes and screens. Received December 10, 2015; accepted May 6, 2016 Published online August 31, 2016 [ABSTRACT FROM AUTHOR]

Structural or operational changes to fishways can improve fish passage efficiency, but there is often uncertainty regarding which improvements will be most effective. We developed a “bottleneck relief” model using Kaplan–Meier methods to help managers assess where remediation efforts are likely to provide the largest increases in fishway passage. The simulation model uses a matrix of observed efficiency estimates from fishway subsections and incorporates multiple passage attempts by individual tagged fish. In a case study application to test the model, we used radiotelemetry data from 2,170 adult Pacific LampreysEntosphenus tridentatusat Bonneville Dam (Columbia River, Washington–Oregon), which features multiple fishways and low lamprey passage success (mean fishway passage efficiency ∼0.50;n= 10 years). The model was run iteratively to test potential dam passage benefits from improving efficiency in 20 individual fishway segments. The highest benefits were for improvements at top-of-fishway segments and at sites where passage routes converged. Benefits were lower for segments used by fewer fish, segments located downstream from serious bottlenecks, and segments with a limited scope for improvement (i.e., efficiency was already high). The model provides a flexible and objective method for assessing complex fish passage problems and informing remediation decision making. Received December 19, 2013; accepted March 11, 2014 [ABSTRACT FROM PUBLISHER]

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Variability is a hallmark of animal behavior and the degree of variability may fluctuate in response to environmental or biological gradients. For example, diel activity patterns during reproductive migrations often differ from those in non-breeding habitats, reflecting trade-offs among efficient route selection, reproductive phenology, and risk avoidance. In this study, we tested the hypothesis that diel movements of anadromous fishes differ among freshwater migration habitats. We analyzed diel movement data from ~13 000 radio-, PIT-, and acoustic-tagged adult fishes from five Columbia River species: Chinook salmon, Oncorhynchus tshawytscha; sockeye salmon, O. nerka; steelhead, O. mykiss; Pacific lamprey, Entosphenus tridentatus; and American shad, Alosa sapidissima. All five species were active during most of the diel cycle in low-gradient, less hydraulically complex reservoir and riverine habitats. Movement shifted to predominantly diurnal (salmonids and American shad) or nocturnal (Pacific lamprey) at hydroelectric dam fishways where hydraulic complexity and predator density were high. Results suggest that context-dependent behaviors are common during fish migrations, and that diel activity patterns vary with the degree of effort or predation risk required for movement. [ABSTRACT FROM AUTHOR]

Optimization of fishways to pass multiple species is challenging because life history, swimming ability, and behavior often differ among species. For example, high fishway water velocities designed to attract adult Pacific salmon Oncorhynchus spp. at Columbia River dams inhibit fishway entrance and passage success of adult Pacific lampreys Lampetra tridentata, a species of conservation concern. We tested whether reduced water velocities (∼1.2 m/s, 0.15 m of head) at Bonneville Dam fishway openings improved entrance efficiency and other passage metrics for radio-tagged Pacific lampreys compared with control velocities (>1.98 m/s, 0.46 m of head) and near-zero (“standby”) velocities. Lamprey entrance efficiencies were significantly higher in the reduced-velocity treatment (26–29%) than in the control (13–20%) or standby (5–9%) treatment. In some years, significantly more Pacific lampreys passed through fishway collection channels and transition pools and reached the fish ladder during reduced-velocity treatment conditions, indicating that benefits extended beyond fishway entrances. However, overall passage efficiency at the dam was relatively unchanged, suggesting that additional passage bottlenecks for Pacific lampreys exist upstream from fishway entrances. The experiment demonstrated how operational changes can improve passage performance and how exploiting behavioral differences among species can improve multispecies management. Received January 6, 2011; accepted November 22, 2011 [ABSTRACT FROM AUTHOR]

Adult Pacific lampreys Lampetra tridentata migrate through areas of difficult passage and high water velocity by attaching their oral discs to substrate and then releasing and bursting upstream. In fishways at dams, this burst-and attach behavior can be ineffective, particularly where suitable attachment surfaces are unavailable. We used an experimental fishway to test performance of adult Pacific lampreys when confronted with a series of structural challenges. These included vertical steps near fishway weir orifices, squatted versus rounded orifice entrances, and floor-mounted metal grates. All experimental challenges simulated common existing structures in weir-and-orifice fishways at Columbia and Snake River dams. Most experiments were paired with field evaluations of radio-tagged Pacific lampreys or video observations of untagged individuals in situ. Field and experimental results consistently indicated that the structural challenges reduced passage efficiency and lengthened passage times. Improving Pacific lamprey passage may be facilitated by removing or modifying vertical steps and other sharp-edged corners and by providing adequate attachment surfaces. Such accommodations should be especially beneficial in areas with high water velocity. The findings demonstrate how fish morphology and behavior should be explicitly considered in the design or retrofitting of fish passage structures. [ABSTRACT FROM AUTHOR]

Adult Pacific lampreys Lampetra tridentata routinely pass through picketed leads and diffuser gratings at lower Columbia River hydropower dams and enter areas where they can be delayed, injured, or killed. We assessed the bar spacing needed to exclude adult lampreys that enter the fishways at Bonneville Dam (river kilometer [rkm] 235).The experimental fish used (n = 242) ranged from 53 to 79 cm in total length and from 282 to 800 g in weight. All were able to swim through a 2.5-cm vertical gap, 47% passed through a 2.2-cm gap, and none passed through a gap of 1.9 cm or less. In dewatering simulations, none of the additional 50 Pacific lampreys tested were able to pass through a 1.9-cm diffuser grating, while 86% were able to pass through a traditional 2.5-cm grating. Based on these results, we conclude that bar spacing of 1.9 cm or less is needed to exclude most adult Pacific lampreys in the Columbia River drainage. An initial field test of the 1.9-cm grating at John Day Dam (rkm 347) confirmed these results. [ABSTRACT FROM AUTHOR]