Migration characteristics of hatchery and natural-origin <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> from the lower Mokelumne River,California |
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Authors: | S Casey Del Real Michelle Workman Joseph Merz |
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Institution: | (1) East Bay Municipal Utility District, One Winemasters Way, STE K-2, Lodi, CA 95240, USA;(2) United States Fish and Wildlife Service, 4001 N. Wilson Way, Stockton, CA 95205, USA;(3) Cramer Fish Sciences, 13300 New Airport Road, Suite 102, Auburn, CA 95602, USA |
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Abstract: | The lower Mokelumne River (LMR), located in the California Central Valley, supports a population of natural-origin Oncorhynchus mykiss. In addition, the Mokelumne River Fish Hatchery (Hatchery) contributes hatchery produced O. mykiss to the system annually. We conducted a 3 year acoustic tagging study to evaluate the migratory characteristics of LMR hatchery
and natural-origin O. mykiss to the Pacific Ocean. Specifically, we analyzed downstream movement and migration rates, routes, and success of acoustically
tagged O. mykiss of hatchery and natural origin under variable release locations in non-tidal and tidal habitats. Results from our study suggest
there are significant differences in the proportion of hatchery and natural O. mykiss that demonstrate downstream movement. Fish origin, size, and release location all had a significant effect on whether an
individual demonstrated downstream movement. Mokelumne origin O. mykiss that initiated downstream movement utilized numerous migration routes throughout the Delta during their migration towards
the Pacific Ocean. We identified four primary migration pathways from the lower Mokelumne River through the Sacramento-San
Joaquin Delta while the Delta Cross Channel was closed. However, several other pathways were utilized. Origin had a significant
effect on O. mykiss success in reaching key points in the Delta and through the Estuary. Fish size had a significant effect on whether an individual
reached the marine environment. Of the 467 O. mykiss tagged, 34 successfully reached the Pacific Ocean (Golden Gate Bridge), and of these, 33 were hatchery-origin and 1 was natural-origin.
A higher proportion of hatchery-origin fish (10% of tagged) migrated to the ocean compared to natural-origin fish (<1%). Our
study provides valuable information on the differences between hatchery and natural-origin O. mykiss migration characteristics as well as unique insight into the migratory behavior of little studied non-Sacramento River origin
salmonids. |
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