Working Hypotheses Concerning Salmon and Steelhead Limiting Factors in the Big 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 the Fort Bragg area (Noyo, Ten Mile and Big Rivers) prior to the inception of the State's North Coast Watershed Assessment Program (NCWAP). CDF is trying to strengthen understanding of cumulative watershed effects in order to improve watershed protection and promote the recovery of coho salmon. The IFR team drew upon available data concerning fisheries, water quality, watershed conditions, and restoration efforts to build a substantial database for Big River using Klamath Resources Information System (KRIS) software.
Where there appeared to be substantial evidence connecting Big River conditions to coho salmon numbers, 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 Big River basin literature, is provided. The data from the Big River basin that is consistent with the hypothesis are then presented. This is followed by the presentation of an alternative hypotheses and, finally, suggestions for testing the preferred and alternative hypotheses.
Hypothesis #1: The distribution and abundance of coho in the KRIS Big River project area has been diminished by historic and recent land use.
Hypothesis #2: Coho salmon production is limited by high water temperature in some reaches of the Big 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 Big River basin.
Hypothesis #4: High levels of sediment in Big River and its tributaries have caused habitat changes which limit coho salmon and steelhead production.
Conclusions and data presented in KRIS Big River do not necessarily represent the endorsement of NCWAP State agencies, including the California Geological Survey and the California Department of Fish and Game