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Monday, November 17, 2008

Chinook Salmon Return to the Russian River

Every year we anxiously await our salmon's fall return to our rivers, and hope that there is enough water left to aid their journey home to spawning grounds. This year we have been blessed with rain at just the right time. Is it enough rain? Probably not -but something is better then nothing.

The following report comes in from the Sonoma County Water Agency who monitor our fish and the flow of the Russian River. This summer they asked Sonoma County residents to conserve water so there would be enough water in our reservoir lakes to release this fall for the salmon's return. Here's is what they have learned this year and the story so far.

Chinook Salmon in the Russian River

2008 Chinook/ Wild Steelhead Migration Count:

11/03/08 - 576 Chinook

11/03/08 - 1 Wild Steelhead

The 2008-09 spawning season has begun. Thanks to two underwater video cameras located in fish ladders adjacent to the Agency's rubber dam on the Russian River, we are able to count the amount of Chinook, coho and steelhead migrating. Over the 2005-2006 spawning season, more than 2,563 Chinook salmon were counted swimming through the Agency's fish ladder, which allows the migrating salmon to bypass the rubber dam.

Each year as the seasons change from summer to fall, Chinook salmon begin their annual migration up the Russian River to their natal spawning habitat. However, until quite recently, the Chinook run in the Russian was relatively unknown. Few people knew that Chinook inhabited the Russian and no one knew how many returned to the river annually. This all changed when the Sonoma County Water Agency began conducting research on the effects of its water diversion facilities on fish, and more importantly, ways to avoid impacting fish in the Russian River Basin. Much of this research stems from our Section 7 consultations (Endangered Species Act requirements) that the Agency has participated in with the National Marine Fisheries Service and the Army Corps of Engineers. This research has significantly increased our knowledge of Chinook salmon inhabiting the Russian River.

We reviewed historical documents on salmon and steelhead populations in the Russian River from 1880 to the present to try and determine if Chinook were native to the Russian River. The oldest report mentioning Chinook salmon in the Russian River were stocking records from 1881. We also found reports from the late 1880's describing an in-river commercial fishery for "salmon" on the Russian River. However, the reports that specifically identified the catch as occurring in the river did not include Chinook salmon jumping up the Agency's Mirabel Inflatable Damthe species captured (referring to the fish as "salmon"), and those that identified the fish as Chinook salmon did not specifically refer to the location of capture as the Russian River. The time of year that the commercial fishery operated was mentioned only once, when the fishery occurred between October and March. This time period overlaps the time of year when Chinook, coho, and steelhead are migrating in the river. Thus, all three of these species could have been captured in the fishery.

During the 1940's and 50's, CA Department of Fish and Game (CDFG) documents indicated that the general consensus among local biologists was that few Chinook inhabited the river, and those that did were the results of stocking activities. Chinook salmon were first stocked in the river in 1881, and stocking efforts continued sporadically until 1982, when CDFG began a serious, but largely unsuccessful effort to establish a run at the Warm Springs Fish Hatchery. Approximately 8 million fry and 5 million smolts were released from the hatchery between 1982 and 1996. Adult returns to the hatchery ranged between 0 and 304 fish during this time. CDFG ended its Chinook hatchery program in 1996.

Against the historical backdrop, in 1999 we began studying fish populations in the Russian River with the general mindset that Chinook salmon were present in the basin at very low numbers. Surprisingly, the most abundant fish captured in our downstream migrant traps that year (and every year since) were juvenile Chinook salmon. This discovery ran counter to the historical documents that we had reviewed.

Our monitoring program consists of five interrelated studies assessing adult and juvenile salmonid passage around the Agency's inflatable dam, spawning habitat distribution, seasonal water temperature conditions in the study area, and predator populations above the dam. Here we report on the results of the upstream adult monitoring program and spawner surveys.

Adult fish passage is provided at the inflatable dam in the form of two Denil style fish ladders. Although the ladders have been in place since the dam was installed, their effectiveness had not been assessed. We installed a video system consisting of ultra-high resolution monochrome video cameras with wide-angle lenses housed in waterproof cases at the upstream end of each fish ladder. Images are recorded on two time-lapse videocassette recorders. The Chinook salmon swimming through the Agency's fish laddercameras are operated continuously 24 hours a day from at least mid-August until the dam was deflated (mid-November through mid-January, depending on the water year). Videotapes are reviewed on high quality VCRs having a wide range of slow motion and freeze frame capabilities. Video cameras have been operated from 1999 until the present.

The video cameras provide fairly high quality images under most flow conditions (see image at right). The image quality is significantly degraded during periods of high turbidity associated with rain events. Another factor limiting counts is the cameras are only operational when the dam is in place. The dam is deflated during high flow periods which have ranged from mid November to mid January, depending on rainfall patterns in the basin. In addition, some Chinook salmon spawning has been reported in tributaries located downstream of the dam. Thus the results of our video counts reflect a minimum number of Chinook salmon in the Russian River.

An often-asked question is: why is it that when most salmon and steelhead populations are decreasing across their range that the Chinook salmon in the Russian River appear to be increased over historical populations? We truly have no satisfying explanation. One possibility is that the populations could have built up since the advent of the Potter Valley Project began discharging a stable flow into the river. The stable flow conditions during the fall months could have allowed the population to enter into the river each year and spawn. This sounds like a reasonable explanation except that these flows were present in the 1940's and 1950's when CDFG reports suggested that few Chinook inhabited the river. A second possibility is that access along the Russian is poor over a large section of the river, particularly during the 1940's and 1950's, and that the fish were just missed. It is true that there were no definitive studies conducted in the river to determine the presence or absence of Chinook salmon during this time period. While this is certainly plausible, the Russian River is (and was) a popular steelhead stream. Chinook are a large fish that would have been hard to miss by steelhead fisherman. A third possibility is that the current run of Chinook salmon are strays from other river systems or that they are remnants of the Warm Springs Fish Hatchery. However, genetics work conducted by the Bodega Bay Marine Lab reported that these fish are not related to populations in Central Valley rivers, the Eel River, or from the Warm Springs Hatchery.

So, while many aspects of Chinook in the Russian remain unresolved, what we currently know is positive: the river currently supports a fairly large population of Chinook; and that these fish appear to be native to the river. We are hopeful that continued research will help us better understand these fish, and help with the recovery of this fishery.

For the complete story with all the graphs and links - please go to the Sonoma County Water Agency web site:

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