William C. Harrell

Habitat Use and Stranding Risk of Juvenile Chinook Salmon on a Seasonal Floodplain

Abstract Although juvenile Chinook salmon Oncorhynchus tshawytscha are known to use a variety of habitats, their use of seasonal floodplains, a highly variable and potentially risky habitat, has not been studied extensively. Particularly unclear is whether a seasonal floodplain is a net “source” or a net “sink” for salmonid production. To help address this issue, we studied salmon habitat use in the Yolo Bypass, a 24,000-ha floodplain of the Sacramento River, California. Juvenile salmon were present in the Yolo Bypass during winter–spring; fish were collected in all regions and substrates of the floodplain in diverse habitats. Experimental releases of tagged hatchery salmon suggest that the fish reared on the floodplain for extended periods (mean = 33 d in 1998, 56 d in 1999, and 30 d in 2000). Floodplain rearing and associated growth are also supported by the significantly larger size of wild salmon at the floodplain outlet than at the inlet during each of the study years. Several lines of evidence sugge...

Importance of Flood Dynamics versus Intrinsic Physical Habitat in Structuring Fish Communities: Evidence from Two Adjacent Engineered Floodplains on the Sacramento River, California

Abstract We examined the factors structuring fish communities at two adjacent engineered floodplain systems on the Sacramento River, California: Yolo and Sutter bypasses. We intensively sampled fishes at each location during January–June 2002 and 2004 by rotary screw trap, collecting a total of 126,635 fish comprised of 29 species. Nonmetric multidimensional scaling indicated that distinct fish communities persisted between the locations during our study, despite nearly identical hydrographs and water temperature regimes. Regression models evaluated with an information-theoretic approach also indicated that location was an important factor explaining the abundances of selected species. Overall, Yolo Bypass had more species and a greater proportion of native species than did Sutter Bypass. Sutter Bypass had a greater proportion of species classified as freshwater, while Yolo Bypass had a greater proportion of species classified as either estuarine or anadromous. We believe these results are related to subs...

Spawning and Rearing of Splittail in a Model Floodplain Wetland

Abstract The splittail Pogonichthys macrolepidotus, which has been listed as threatened by the U.S. government, does not produce strong year-classes unless it has access to the floodplain habitat of the San Francisco estuary and its tributaries. In this small-scale, single-year study, we tested the hypothesis that managed inundation of a floodplain can be used to support splittail reproduction in dry years, when this habitat type is not readily available. Adult splittails were captured on their 2001 upstream spawning migration and transferred to a 0.1-ha model floodplain wetland. Our results suggest that adults will successfully spawn if they are provided access to floodplain habitat in dry years. In snorkel surveys, progeny showed a significant association with the lower portion of the water column. Young splittails (15-20 mm fork length (FL)) concentrated in edge habitat near an inflow during the day but at night moved into deeper-water habitats, including open water and habitats with submerged vegetati...