The Sacramento River produces four distinct races of chinook salmon (Oncorhynchus tshawytscha) : fall, late fall, winter, and spring, based upon their appearance in tide-water (Fisher, 1994). Chinook salmon originating in the Sacramento River account for 90 percent of the San Francisco-to-Monterey commercial catch, 40 percent of the North Coast, and 5 percent of the Oregon catch (DFG, 1978). All races have declined substantially from historic populations. The winter run was listed as "endangered" by the State of California in 1989 and by the National Marine Fisheries Service in 1994. The spring run, once the most abundant chinook in the Central Valley (Reynolds et al. 1990), persists at dangerously low numbers in a few tributaries and has just been added to the California threatened list. In order to reverse the decline of chinook salmon stocks, we need to fully define the habitat used by the different races.
Much of the Sacramento River drainage basin has been lost as salmon habitat due to migration barriers. The remainder has been substantially degraded as rearing habitat for juvenile chinook. Erosion control has resulted in loss of sinuosity and braiding, thereby reducing total area of habitat and degrading the remaining habitat by increasing mean velocity. Current flood control practices require peak flood discharges to be held back and released over a period of weeks. Consequently, the mainstem of the river often remains too high and turbid to provide quality rearing habitat (Upper Sacramento River Fisheries and Riparian Habitat Advisory Council, 1989). Because of this loss of habitat quantity and quality, it is important that all remaining rearing habitats be evaluated and measures taken to preserve or enhance important components.
A component of rearing habitat which was ignored until recent years is the lower ends of small tributaries that have insufficient flow to be used consistently by spawning adults (Maslin, et al., 1996, 1996b, 1997; Moore, 1997). Valley reaches of many intermittent tributaries of the Sacramento River are used by juvenile chinook as rearing sites, (See Table 1.).
Rearing of juvenile chinook in nonnatal tributaries has been reported in other river systems. Murray and Rosenau (1989) suggest that the dispersal and migratory patterns of young chinook salmon increase the use of available rearing areas, and that movements of young salmonids from spawning areas to rearing areas consist of complex local migrations (upstream, downstream, or both) that are genetically and environmentally controlled. Scrivener et al. (1994), concluded that seasonally high sediment levels and cold temperatures in the Fraser River may induce juvenile chinook to move into small, nonnatal tributaries to feed and clear their gills of sediment. Juvenile chinook may also migrate into the tributaries to exploit food resources (Williams, 1987); and to escape unfavorable environmental conditions which occur periodically in the mainstem, such as high turbidity and cold temperatures (Upper Sacramento River Fisheries and Riparian Habitat Advisory Council, 1989). Richards and Cernera, (1992) had some success in development of off-channel habitats to increase rearing habitats for juvenile chinook.
In this study we provide more information about non-natal rearing in small and intermittent Sacramento River tributaries. The main objectives this year were:
1. To provide a rough estimate of the number of juvenile chinook rearing in non-natal streams.
2. To use genetic analysis to verify presence of winter chinook.
3. To provide further information on the spatial and temporal extent of non-natal rearing.
4. To evaluate the quality of rearing habitat based on the condition of the tributary-rearing juveniles.
To: Procedure
Introducton
Last Updated February 27,1999