Napa River - Ecology

Ecology

Known for the vineyards in its valley, the river also supports a remarkable diversity of fishes and recovering salmonid populations, especially Chinook salmon (Oncorhyncus tshawytscha) and Steelhead trout (Oncorhyncus mykiss). In 2003 the Napa County Resource Conservation District began an ongoing salmon monitoring program, and have recorded a run of approximately 400 - 1000 fall-run Chinook salmon the past several years. The Chinook run begins in late October through January. Conclusive evidence of historical Chinook salmon populations in the Napa River basin have not been established, but the river provides appropriate habitat for salmon and its location near the entrance to the Sacramento/San Joaquin Rivers make it likely that salmon would have at least ventured into the Napa River. The Napa River basin is estimated to have historically supported a spawning run of 6,000–8,000 steelhead, and as many as 2,000–4,000 Coho salmon (Oncorhyncus kisutch). By the late 1960s, coho salmon were extirpated from the watershed and the steelhead population is now reduced to less than a few hundred adults. Flow reductions in key rearing streams have reduced food availability for juvenile steelhead, causing reduced growth and survival. Recently, a Chum salmon (Oncorhynchus keta) was caught in the river.

Although diminished, the Napa River basin continues to support a fish community of greater diversity than even the Sacramento and San Joaquin River systems, including a nearly intact community of sixteen native fish species, including Steelhead, fall-run Chinook salmon, Pacific (Lampetra tridentata) and River lamprey (Lampetra ayresi), Hardhead (Mylopharodon conocephalus), Hitch (Lavinia exilicauda), Tule perch (Hysterocarpus traski), and Sacramento splittail (Pogonichthys macrolepidotus). Because of this diversity the Napa River has been prioritized for special protection. White sturgeon (Acipenser transmontanus) and many other native and non-native fishes currently utilize the Napa River watershed.

The California Golden Beaver (Castor canadensis subauraticus) was historically extant. Recently beaver have recolonized the Napa River and have been documented near Rutherford and Oak Knoll.