DTE received an email from the University of Idaho regarding a group of scientists at the school who studied young fish transportation programs as a means to bypass dams during migration. They learned salmon and steelhead trout along the Columbia and Snake rivers, had lower survivorship, compared to fish that migrated naturally. To wit: "University of Idaho Scientists Study Ways to Preserve Native Fish Populations" By Sue McMurray There’s no such thing in this world as a “free” ride – even for fish. A University of Idaho fisheries research group recently investigated how juvenile salmonids transported downstream on boats can lose the ability to migrate back to their breeding grounds, reducing their survivorship and altering adaptations in the wild. When dams block rivers, migrating fish – especially juveniles – can have a tough time traveling past dams. Though juvenile transportation programs have been in place for more than three decades to improve the survival of fish that hatch in rivers, Matthew Keefer, College of Natural Resources fisheries scientist, has found that this free ride can create problems when the juveniles grow up. Keefer and his colleagues, Christopher Caudill, Christopher Peery and Steven Lee, tracked the movement patterns of adult salmon and steelhead trout along the Columbia and Snake rivers in Washington and Oregon. They found that, when compared to fish that migrated naturally, transported juveniles had lower survivorship as adults and were less likely to find their way home. “Adult fish usually move steadily upstream toward their spawning grounds, but some instead will move back downstream over dams,” said Keefer. This phenomenon, called fallback by fisheries managers, occurs more often in adults that were barged out as juveniles than in those that migrated naturally. Fallback behavior reduces adult survival, both because fish can be injured as they pass downstream over dams and because extra time and energy is needed to for fish to re-ascend dam fish ladders. “It’s not clear if they’re just running out of steam swimming up the river or if they get disoriented and move back downstream in search of cues from their home river,” Keefer said. The scientists believe that being carried on a barge prevents young fish from learning about important environmental signals during a formative time of their juvenile lives. A barge can take them the same distance in two to three days that would normally take them several weeks, Keefer explains. Traveling great distances – at least 215 miles – appears to garble the natural cues these fish use to find their way home. The study results also suggest that transported fish are more likely to stray from their home tributary. If these lost fish – often from hatchery populations – breed with another wild population, the resulting gene flow can reduce that population’s evolutionary fitness. “Salmon have a life history that represents a long legacy of adaptation to local conditions,” Keefer said. “The fish are well-adapted to specific rivers, and when you dilute their unique genetic makeup, it can reduce the productivity of the overall population.” A satisfactory solution is difficult to find. Managers could barge fewer juveniles, but then more fish would die while trying to pass the dams. They also could release more water over dam spillways to help juveniles pass downstream, but that would reduce the amount of energy the dams produce. A third option is to slow down the barges so the trip resembles the time it takes juveniles to swim to the ocean. But boats are a stressful environment for fish, and the close quarters within the barges increase the risk of disease. “It’s tough to find a solution that could handle all the challenges in this system,” Keefer said. Scientists and salmon managers hope to find the ideal solution: one that would preserve native fish populations and maximize their survival while keeping the integrity of energy-producing dams. The groups’ study, “Transporting Juvenile Salmonids around Dams Impairs Adult Migration,” recently was published in the December issue of Ecological Applications, a scientific journal published by the Ecological Society of America. Contact: Sue McMurray, College of Natural Resources, (208) 885-6673, suem@uidaho.edu; or Matthew Keefer, Idaho Cooperative Fish and Wildlife Research Unit, (406) 556-0639, Mkeefer@uidaho.edu

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