A very informative article from the California Sport Fishing Blog about our local salmon.
The American River is one of the larger tributaries of the Sacramento River (Figure 1). Its watershed runs from the central Sierra Nevada range, from which it runs through the city of Sacramento to join the Sacramento River. The American River’s lower 20 miles are a tailwater of the Central Valley Project’s Folsom Dam. This tailwater supports a major run of fall-run Chinook salmon that produces 15-20% of the total Central Valley fall-run Chinook salmon population.
American river run size (adult escapement) has ranged from 6,000 in 2008 to 178,000 in 2003 (Figure 2). The CVPIA long-term average goal for the American River fall-run is a contribution of 160,000 adult fish to the overall goal of 750,000 for the Central Valley. Many of the American River spawners are from the American’s Nimbus hatchery, or are strays from other Valley hatcheries. However, a large part of the run spawns naturally in the upper ten miles of the lower American River below Nimbus dam within Sacramento County’s urban parkway. The hatched fry of natural spawners rear by the millions in the lower river and in the Delta. Each spring, about 5 million Nimbus hatchery smolts are trucked to the Delta or Bay and released.
The American River fall run is often considered a hatchery run, with the 20 miles of river described as a mere conduit to the hatchery. The hatchery smolts are nearly always trucked to the Bay or lower Delta because of the high potential risk from water diversions or predation in the river or the upper Delta. Trucked and Bay pen-acclimated hatchery smolts generally have a relatively high survival-contribution rate and low straying rate compared to other Central Valley hatchery tagged fish.1
Brown 2006 reviewed the status of the American River population during its peak 2000-2005 runs. He attributed the strong runs to a variety of improvements at the hatchery:
- Changes in fish ladder operations to bring fish into the hatchery later in the fall to minimize temperature problems.
- Change in egg incubation and size at release (to all smolts).
- Elimination or control of early disease problems with the help of DFG pathologists.
- Elimination of most bird depredation within the hatchery through deployment of exclusion nets over the raceways.
- Change in the DFG approach to hatchery operations since 1999 when the National rine Fisheries Service (NOAA Fisheries) urged DFG to adopt standard operating procedures.
- Change in release location to San Pablo Bay and change in the method of release to net pens in place of direct releases from the transport trucks to the Bay.
Others offered additional reasons for the improvement in the fall Chinook runs in the Central Valley, including the following:
- Gravel and rearing enhancement (enhancements to spawning and rearing habitat had occurred under the CVPIA Program).
- Better hatchery practices (mentioned above)
- Good ocean conditions
- Reduced ocean fisheries
- Better instream conditions (1995-2000 were wet years)
- Some combination of the above