Development of Pacific lamprey fishways at a hydropower dam

Abstract

Abstract Traditional fishways do not accommodate the passage needs of all migrating species. In the north-western United States, structures designed to aid adult Pacific lamprey, Lampetra tridentata (Gairdner), passage are critically needed. The structures described here were fabricated in modular units and installed at Bonneville Dam on the Columbia River (235 km). They featured a series of aluminium ramps interspersed with rest boxes that prevented lamprey from moving back downstream. The effects of various design changes and structure operation (water volume delivered) were assessed using lamprey counts and passive integrated transponder detections. Up to 40% of the lamprey entered the structures and 90–100% of these passed through to the exit. Lowering water volume pumped to the structures had little effect on lamprey performance, but passage improved when a 3.8-m-long, steep (40°) ramp was replaced with two, 1.4-m-long, 45° ramps. Pacific lamprey ascended the 8- to 9-m-high structures and entered the dam forebay in less than 1 h. The success of these prototypes was attributed to site selection and attention to lamprey-specific performance.