Navarro River Working Hypotheses
The Institute for Fisheries Resources (IFR) was retained by the Sonoma County Water Agency (SCWA) to acquire, integrate, and interpret watershed information in support of the State and Federal Recovery Planning efforts for Pacific salmon. The IFR team drew upon available data concerning fisheries, water quality, watershed conditions, and restoration efforts to build a comprehensive database for the Navarro River using Klamath Resources Information System (KRIS) software. KRIS projects point out patterns in watershed data in the form of working hypotheses. The IFR hypotheses below do not necessarily reflect endorsement of SCWA or the other agencies with State and Federal responsibility for Endangered Species Act compliance, the California Department of Fish and Game and National Marine Fisheries Service (NOAA Fisheries), respectively.
Where there appears to be substantial evidence connecting Navarro River conditions to the health of aquatic habitat and fish communities, the IFR team formulated "working hypotheses" to explain these connections. A hypothesis, according to Webster's Dictionary, is a "formula derived by inference from scientific data that explains a principal operating in nature. Hypothesis implies insufficiency of presently attainable evidence and therefore a tentative explanation...." The IFR team used a weight-of-evidence approach rather than a formal, statistical analysis. The rationale for these working hypotheses is, however, based on the current scientific literature concerning Pacific Coast salmon watersheds. Each of the hypothesis web pages is framed in the same way. Regional and local literature that provide the analysis background are provided followed by presentation of information from KRIS Navarro that are consistent with the hypothesis, including charts, pictures and maps. This is followed by the presentation of an alternative hypotheses and, finally, suggestions for testing the preferred and alternative hypotheses are offered.
Hypothesis #1: The distribution and abundance of coho salmon in the Navarro River basin has diminished over recent decades.
Hypothesis #2: Coho salmon production is limited by high water temperature in some reaches of the Navarro River.
Hypothesis #3: A reduced supply of large wood has contributed to the loss of pool habitat and the decline of coho salmon in the Navarro River basin.
Hypothesis #4: High sediment yield in Navarro River basin has caused aquatic habitat changes which limit coho salmon and steelhead production.
Hypothesis #5: Surface flows in the Navarro River basin have been diminished in recent decades, which reduces salmon and steelhead productivity.