Hypotheses Concerning Salmon and Steelhead Limiting Factors in the Gualala River
The Institute for Fisheries Resources (IFR) was retained by the California Department of Forestry and Fire Protection (CDF) to acquire, integrate, and interpret watershed information in support of the State's North Coast Watershed Assessment Program (NCWAP). The IFR team drew upon available data concerning fisheries, water quality, watershed conditions, and restoration efforts, which were augmented by agencies participating in NCWAP, to build a comprehensive database for the Gualala River using Klamath Resources Information System (KRIS) software. KRIS projects point out patterns in watershed data in the form of working hypotheses.
IFR KRIS Gualala Hypotheses
Where there appears to be substantial evidence connecting Gualala 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. First the hypothesis is stated. Next, support for the hypothesis from the regional salmon watershed literature, including the available Gualala River basin literature, is provided. The data from the Gualala River basin that are consistent with the hypothesis are presented, 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.
The IFR hypotheses below are not to be confused with the NCWAP Gualala River Watershed Assessment Report working hypotheses. The NCWAP working hypotheses are available by clicking here NCWAP Gualala Working Hypotheses. The entire NCWAP Gualala report is available at the NCWAP website (http://www.ncwatershed.ca.gov/).
Hypothesis #1: The distribution and abundance of coho salmon and steelhead trout in the Gualala River basin have been diminished.
Hypothesis #2: Elevated levels of sediment in the Gualala River limit coho salmon and steelhead trout production.
Hypothesis #3: Continuing sediment contributions to the Gualala River and its tributaries from recent land use (1985-2001) are preventing recovery of coho salmon and steelhead habitat.
Hypothesis #4: Elevated water temperatures in Gualala River tributaries limit coho salmon and steelhead trout production.
Hypothesis #5: Recent riparian timber harvest has exacerbated water temperature problems in western Gualala River sub-basins.
Hypothesis #6: Reduced surface flows are limiting salmon and steelhead production in the Gualala River.
Conclusions and data presented in KRIS Gualala do not necessarily represent the endorsement of NCWAP State agencies, including the California Geological Survey and the California Department of Fish and Game.