For years, Peter Moyle, U.C. Davis Professor and California fish expert, dreamed of the day when people could watch salmon spawning in Putah Creek from the Winters pedestrian bridge. Last year, his dream came true when a determined pair of salmon set up housekeeping immediately upstream of the construction crossing for the new Winters car bridge. Easily observed from the west side of the pedestrian bridge, this pair surprised many by spawning despite the construction activity and constant human presence.
These salmon were just two of an estimated 200 fall-run Chinook salmon that migrated up Putah Creek in December 2014 to spawn. That was almost triple the highest number of fish ever recorded in any year over the previous 30 years, surprising everyone involved in the restoration of Putah Creek. In a typical year, observers find fewer than 10 salmon in the creek.
This year, the salmon run in Putah Creek is estimated to be over twice last year’s count! Ken Davis, an aquatic biologist who monitors the annual salmon run for the Lower Putah Creek Coordinating Committee (LPCC), estimates that upward of 500 salmon have come up Putah Creek since the Los Rios check dam in the Yolo Bypass was removed in mid-November. Adding to everyone’s excitement are about 40 salmon that are spawning in the realigned and enhanced sections of Winters Putah Creek Park, including another fearless pair or two under the nearly completed car bridge.
Why so many salmon all of a sudden and where are they coming from? We don’t know conclusively why the number of salmon spawning in Putah Creek the past two years has been so much greater than in the recent past, but it is likely the result of at least three things: spawning flows, hatchery salmon responding to the drought, and habitat restoration.
Spawning Flows Attract Salmon
By the 1990s, it was clear that small numbers of Chinook salmon moved up Putah Creek in late fall. To attract and support these salmon, Putah Creek Council worked with Dr. Moyle to develop a salmon spawning flow regime. These enhanced flows were incorporated into the 2000 Putah Creek Accord, which established environmental flows in Lower Putah Creek.
The spawning flows involve two steps. First, around December 1, farmers remove the Los Rios check dam. They also breach and widen a temporary crossing of the creek to allow unrestricted flows downstream and unimpeded access for salmon to migrate upstream. Then the Solano County Water Agency (SCWA) releases enough water from the Putah Diversion Dam to maintain 50 cubic feet per second (cfs) flow for five consecutive days at the confluence of Putah Creek and the “Toe Drain.” The Toe Drain connects the mouth of Putah Creek to Prospect Slough, the Sacramento River, and the Delta.
This flow “pulse” attracts salmon moving up the Toe Drain into Putah Creek. After five days of increased flows, SCWA maintains flows at the creek’s confluence with the Toe Drain through mid-December. This allows additional salmon to move up Putah Creek, especially when there are big storms that produce natural “attraction flows.”
Hatchery Fish and the Drought
Many of the Chinook salmon coming up Putah Creek are probably stray fish that were reared in the Feather River Hatchery. To improve their survival, these hatchery fish are released “off-site” in the San Francisco Bay Estuary rather than directly into unfavorable conditions in the Feather and Sacramento rivers.
When these hatchery-raised salmon mature and return from the ocean to the Sacramento River system to spawn, they don’t have a natal stream to home in on. The Putah Creek spawning flows are an attractive option to the low flows in the drought-impacted Sacramento River and the fish easily take a wrong turn into Prospect Slough and move up the Toe Drain.
In 2014, and again this year, large numbers of these salmon swam up Putah Creek past Davis immediately after the Los Rios check dam was removed. And, most importantly, as the salmon passed above the Pedrick Road overcrossing, they found good habitat for spawning.
Successful Habitat Restoration
Past gravel mining and channel straightening for flood conveyance in Putah Creek have removed or bypassed the gravels that salmon need to spawn and eliminated floodplains and side channels. But 15 years of dedicated restoration by the LPCCC has dramatically improved habitat conditions.
Rich Marovich, Putah Creek Streamkeeper, landowners, SCWA and Putah Creek Council have resized and realigned sections of creek channel, created floodplains and side channels that connect to the creek, installed rock weirs and log revetments, enhanced spawning gravels, controlled erosion, removed trash and invasive weeds, and established native riparian habitat.
The cumulative success of these restoration projects in Putah Creek has made a big difference. And no place on the creek exemplifies this success better than Winters Putah Creek Park, formerly the site of a derelict percolation dam, gravel extraction pits, and sewage aeration ponds. The City of Winters, Winters Putah Creek Committee, LPCCC, SCWA and Putah Creek Council have worked together for 10 years to transform this reach into a publicly accessible river parkway with suitable habitat for spawning salmon and other native fishes. The 40 salmon observed in the park this year are a wonderful beginning. After the new car bridge is completed and the last section of the creek is improved, there could be many more salmon spawning in the park in late November each year.
Although recent Putah Creek salmon runs are probably mostly hatchery strays, Dr. Moyle believes that the offspring can return as wild salmon. Every year, surveys by UCD students find juvenile salmon moving downstream in the spring. And a recent study by DWR suggests that the Toe Drain is actually a better place for salmon rearing than the Sacramento River. Assuming these fish will grow large and migrate to the ocean, they can return to Putah Creek in 2-4 years to spawn. If they don’t get swamped out each year by less-fit hatchery strays, we could develop a wild Putah Creek salmon run.
From the habitat enhancement successes thus far, and the prospects for future restoration, the goal for spawning salmon in Putah Creek could be thousands. A tenfold increase in spawning habitat is possible by restoring a more natural form to additional reaches of the creek.
As Dr. Moyle recently stated in a California Water Blog post, “Putah Creek as a salmon stream – hold that thought!”