This study began in the spring of 1994. The goals of the initial investigation were to determine distribution and relative abundance of fishes within the lower 23 miles of Putah Creek. Eight sites were chosen to reflect changes in downstream habitat:
Each of these sites was sampled once a month for the first year, using hand seines, electroshocking (where appropriate), and gill nets. For all subsequent years, each of these sites has been sampled once a month during late spring (May) through late summer (Oct.). The first two years of data were used extensively during the Putah Creek trial (Feb-March 1996).
- directly below Putah Diversion Dam (PDD),
- the reach where Dry Creek enters Putah,
- below the Highway 505 bridge,
- UC Davis’ Russell Ranch property,
- downstream of the Stevenson Road bridge,
- the UC Davis picnic grounds,
- the Old Davis Road bridge, and
- downstream of Mace Boulevard bridge.
At each sampling date, fish are collected using the methods above. The following data is recorded for all fish caught: species, standard length, weight, and relative number of external parasites. The aquatic habitat is evaluated (substrate, aquatic cover, habitat types) and the following environmental data is recorded: pH, turbidity (NTU), conductivity (umhos), temperature (°C) and flow (cfs). All of this data is entered into a computer database for analysis.
The continued monitoring of the fishes of Lower Putah Creek is part of a larger project to examine the distribution and abundance of native fishes and fish communities in low elevation streams in California. The study is designed to investigate the following questions:
The larger project is part of the dissertation research of Mr. Marchetti.
- Is native fish abundance linked to stream flow?
- How does this link vary from year to year?
- How are fish communities structured in regulated streams?
- What factors (biotic and abiotic) influence native fish distribution and abundance?
- What factors (biotic and abiotic) influence non-native fish distribution and abundance?
During the spring and summer of 1997 the standard monitoring schedule was continued. The following observations were made:
- High flows uncovered large areas of spawning sized gravels during the winter of 1996-97. Many of these areas were in the middle reaches of the lower creek (Russell Ranch - Pedrick Rd). These gravel areas had been heavily silted in before the flows.
- Flows in the creek were high during the early spring and continued above average through the entire summer. Much of the added flow (above releases from PDD) is believed to have originated through ground water inflow, again due to the large amount of rain early in the season.
- The creek maintained continuous flow out into the Yolo Bypass throughout the year.
- Native fish spawning was extensive and large numbers of juvenile fish were observed and recorded (predominately Sacramento pikeminnow, Sacramento sucker and prickly sculpin). This large recruitment may have been due to the increased spawning gravels and increased flows. A particularly large increase in native fish was observed in the Russell Ranch and Stevenson Road area.
- Non native fish abundance was down. The decreases occurred mainly for the introduced centrarchid (sunfish) species such as bluegill, green sunfish and largemouth bass. These decreases may have been due to the large flushing flows (45 days >1000 cfs) early in the year.
- A significant increase in smallmouth bass abundance was noted for the last two years (1996, 97). This increase was noted mainly at the Stevenson Rd and Russell Ranch sites. Smallmouth bass used to be widely distributed in the lower creek and typically require cooler water temperature and more regular flows indicative of the pre-PDD condition.
- A number of Pacific lamprey ammocetes were captured in the PDD area. These ammocetes were extremely small and would likely have been spawned in the winter/spring of either 1996 or 1997 indicating successful recruitment in recent years. Lampreys are anadromous, like salmon.