By Robert A. Lusardi and Peter B. Moyle
Dams are ubiquitous in the United States and have disconnected migratory fishes from important historical habitat. Trapping fish and moving them around dams (trap and haul) is a common strategy to manage Pacific Coast salmonids. Usually, juveniles or adults are moved in one direction, but there is growing interest in two-way trap and haul (TH2), where both adults and out-migrating juveniles are captured and transported over dams. Despite recent technological advances, no TH2 program is an unequivocal success. Our review indicates that uncertainties associated with TH2 programs exist and include delayed effects from transportation, maintenance of above-dam populations, out-migrant capture efficiency, and the role of hatchery supplementation. Two-way trap and haul programs should (1) clearly define measurable and objective success metrics, such as the 10 we provide; (2) proceed experimentally under an adaptive management framework to determine risk–benefit trade-offs; and (3) be part of comprehensive conservation strategies that consider the entire life cycle of each species. Two-way trap and haul is proposed as a high-priority recovery strategy for Chinook Salmon Oncorhynchus tshawytscha populations in California. Our findings indicate that any such TH2 program should proceed with extreme caution.
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