Abstract
Author(s): Nielsen, Jennifer L.; Pavey, Scott A.; Wiacek, Talia; Williams, Ian | Abstract: Genetic variation at 11 microsatellite loci described population genetic structure for Oncorhynchus mykiss in the Central Valley, California. Spatial and temporal variation was examined as well as relationships between hatchery and putative natural spawning anadromous stocks. Genetic diversity was analyzed at two distinct spatial scales: fine-scale within drainage for five populations on Clear Creek; between and among drainage diversity for 23 populations. Significant regional spatial structure was apparent, both within Clear Creek and among rainbow trout populations throughout the Central Valley. Significant differences in allelic frequencies were found among most river or drainage systems. Less than 1% of the molecular variance could be attributed to differences found between drainages. Hatchery populations were shown to carry similar genetic diversity to geographically proximate wild populations. Central Valley M = 0.626 (below the M l 0.68 threshold) supported recent population reductions within the Central Valley. However, average estimated effective population size was relatively high (Ne = 5066). Significant allelic differences were found in rainbow trout collected above and below impassable dams on the American, Yuba, Stanislaus and Tuolumne rivers. Rainbow trout sampled in Spring Creek were extremely bottlenecked with allelic variation at only two loci and an estimated effective population size of 62, suggesting some local freshwater O. mykiss stocks may be declining rapidly. These data support significant genetic population structure for steelhead and rainbow trout populations within the Central Valley across multiple scales. Careful consideration of this genetic diversity and its distribution across the landscape should be part of future conservation and restoration efforts.
Highlights
Anadromous steelhead (Oncorhynchus mykiss) were broadly distributed throughout the Sacramento and San Joaquin River drainages (McEwan 2001)
In an attempt to demonstrate the spatial dynamics of diversity over several scales within and among watersheds, this study presents genetic analyses of multiple samples of O. mykiss at different life history stages; i.e., fish collected above and below dams, putative natural spawning anadromous and freshwater populations, and hatchery rainbow trout strains found in the Central Valley, California
This study focused on the genetic population structure of Central Valley steelhead and rainbow trout populations at two distinct scales
Summary
Anadromous steelhead (Oncorhynchus mykiss) were broadly distributed throughout the Sacramento and San Joaquin River drainages (McEwan 2001). Steelhead hatcheries in the Central Valley (Coleman, Feather River, Nimbus and Mokelumne River) produce and release about 1.5 million yearlings each year (Brown 2005). Despite this abundance, there has been a substantial decline of Central Valley steelhead over the last 150 years, due primarily to lost spawning and rearing habitats, changes in water quality, and within-basin dams and diversions (Busby and others 1996; McEwan 2001; May and Brown 2002). Recent studies demonstrated that non-anadromous rainbow trout introduced into Argentina gave rise to anadromous fish (Pascual and others 2001), with the source of these fish derived from early Sacramento River stocks, most probably from McCloud River Hatchery fish that had been transplanted around the world at the beginning of the 20th century, including Argentina (Riva Rossi and others 2004)
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