Passage Effectiveness at a Pool‐and‐Weir Fishway Designed to Accommodate Pacific Lampreys

Abstract

Providing passage at man‐made barriers is important to preserving migratory fish species. Fishways used to bypass barriers have historically been designed to provide passage for economically important species, with little regard given to nontarget species. Consequently, native fish species whose swimming behaviors are not well suited to these fishways have suffered from restricted access to habitat. For example, poor passage at dams has contributed to declines in populations of Pacific Lamprey Entosphenus tridentatus in the Columbia River basin. Pool‐and‐weir fishways typical of Columbia basin dams are well suited to salmonids but not to anguilliforms like the Pacific Lamprey. We evaluated the passage efficiency of Pacific Lampreys through a new pool‐and‐weir fishway at River Mill Dam on the Clackamas River, Oregon, that was designed to facilitate Pacific Lamprey passage. Rounded corners at the fishway entrances, flush‐mounted weir gates, chamfered corners on orifices and weir walls, and orifices flush with the floor were all included in the fishway design specifically for Pacific Lampreys. In 2013 and 2015, Pacific Lampreys were radio‐tagged and PIT‐tagged to assess passage success. Dam passage efficiency estimates ranged from 84% to 98%, roughly 10–50% higher than Pacific Lamprey passage efficiency estimates at other dams in the Pacific Northwest. The median passage time through the fishway was 0.87 d in 2013 and 0.71 d in 2015. The high passage efficiency of Pacific Lampreys at River Mill Dam is likely due to the design elements incorporated specifically for Pacific Lampreys. These features could inform future fishway designs and modifications at locations where Pacific Lamprey passage is a consideration.

Updating the consensus on fishway efficiency: A meta‐analysis

“…Landsman et al, 2018), as well as variants of the Ice‐Harbour design (e.g. Ackerman et al, 2019). Vertical‐slot fishways included any baffled or Hell’s Gate style fishway (e.g.…”

Considerations for Multi-Species Fish Passage in California: A Literature Review

“…Laboratory experiments indicated that attaching a 0.305-m-wide metal plate over the grating (diffuser plates) allowed lamprey to attach near, and pass through, an orifice opening with > 2.4 m s -1 velocity flow (Daigle et al 2005; Figure 3). In a field study of a pool-and-weir fishway designed to pass lamprey, Ackerman et al (2019) found that with rounded corners with a radius of 1.15 m, flush-mounted weir gates, chamfered corners, and flush orifices, passage efficiency ranged from 84% to 98%. Daigle et al (2005) found that few lampreys passed a weir using the overflow section, although those that did so passed the weir more quickly, in 38 s, than those passing via submerged orifices, averaging 3 m 20 s ( Figure 3).…”

“…Lampreys, the weakest swimmer reviewed (Figures 1 and 4), typically swim up highvelocity corridors by using their oral discs to attach to suitable substrates in a burst-and-attach behavior. Lamprey-friendly structures need adequate smooth anchorage surfaces and rounded edges with a radius of no less than 0.15 m, to allow them to use their unique burst-andattach behavior (USFWS 2014;Ackerman et al 2019). Lampreys are most vulnerable in the time between successive attachments.…”

“…• Round the corners of edges and transition angles with a radius of at least 0.15 m to improve lamprey passage efficiency (CRBLTW 2004;Ackerman et al 2019).…”

Rapid Migration and High Survival of Adult Pacific Lampreys in Reservoirs

“…A recent exception was a new fishway in the Clackamas River (Oregon), where adult Pacific Lamprey behaviors were explicitly considered in the design process, and preliminary passage efficiency estimates were 84–98% (Ackerman et al. ). Low dam passage success has been far more common, however, and has been associated with high water velocity and turbulence in dam tailraces and fishways (Johnson et al.…”