Trap-and-Haul Facilities for Managing Anadromous Salmonids and Other Species: A Pacific Northwest Review

Anadromous salmonid recovery faces major challenges at high-head dams where volitional passage is limited. For obsolete structures, dam removal may be the only sustainable long-term solution, but at active hydroelectric dams, trap-and-haul facilities remain one of the few viable options for restoring fish passage connectivity. These facilities provide an assisted migration strategy, enabling juvenile transport downstream and adult transport upstream, and thus serve as a two-way conservation tool. Despite their increasing use, there remains considerable uncertainty about what "trap-and-haul" entails. Facilities range from simple, seasonal barriers and traps used to estimate run size, migration rates, behavioral patterns, and restoration effects, to highly engineered systems incorporating technical fishways, sorting facilities, and water-to-water transfer. The latter allows programmatic review, population-specific management, and adaptive strategies. We reviewed 37 trap-and-haul facilities in the Pacific Northwest (North America) to summarize key design and operational elements, including: (1) facility information; (2) species transported and numbers; (3) attraction and fishway flow rates and water sources; (4) trapping system types; (5) hydraulic drop per pool and energy dissipation factors; (6) attraction water diffuser type and source; (7) intake screen and cleaner types; and (8) presence of water-to-water transfer. Because existing data can guide development of new facilities, this review offers valuable insights not only for the Pacific Northwest but also for European hydropower operators facing similar challenges under the European Union Restoration Law, Habitat Directive, Water Framework Directive, and Eel Regulations.