Working Hypotheses Concerning Salmon and Steelhead Limiting Factors
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 as part of the State's North Coast Watershed Assessment Program. 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 using Klamath Resources Information System (KRIS) software.
Where there appeared to be substantial evidence connecting Ten Mile 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 Ten Mile River basin literature, is provided. The data from the Ten Mile 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 are offered.
Hypothesis #1: In the Ten Mile River basin, coho salmon have decreased in distribution and abundance to where the long term viability of a self-sustaining population is at risk.
Hypothesis #2: High levels of sediment in Ten Mile River tributaries have caused habitat changes which limit coho salmon production.
Hypothesis #3: High water temperatures in some reaches of the Ten Mile River basin limit coho salmon production.
Hypothesis #4: A Reduced supply of large wood has contributed to the loss of pool habitat and the decline of coho salmon in the Ten Mile River basin.
Hypothesis #5: Alteration of riparian stands has increased airflow over the stream and caused stream warming even where direct shade has been retained.