Evaluation of Imprinting and Methods to Reduce Straying By Barged Juvenile Steelhead

In an effort to increase survival, juvenile salmon are barged though the Columbia River hydrosystem during their migration to the ocean. Barged salmon stray at higher rates than fish that migrated naturally and present significant conservation concerns. We hypothesize that barging interferes with the process of imprinting wherein, juveniles learn olfactory waypoints during their migration to the sea that are later used by returning adults to identify their natal streams. In this study we assessed imprinting of barged and in-river migrants by monitoring changes in physiological function and gene expression as indicators of imprinting success. In-river migrants displayed increases in ATPase (smolting), decreases in thyroxine (smolting, imprinting) and increases in odorant receptor mRNA expression (imprinting) during their downstream migration. These responses were significantly decreased in the barged groups consistent with the hypothesis that barging impairs imprinting. We also identified key environmental parameters (e.g. novel tributary water) that may be important for imprinting success in barged fish. Exposure to as little as 10% novel tributary waters for 12 hours was sufficient to elicit increases in imprinting associated markers suggesting that delaying at tributary junctions for short periods may improve imprinting and reduce straying.