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 Noyo River watershed information as part of a pilot project for the State's North Coast Watershed Assessment Program. CDF is trying to strengthen the 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 sources 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 Noyo River conditions to coho salmon numbers, the IFR team has presented these relationships as "working hypotheses". An 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 approach taken here is then a weight-of-evidence one rather than a formal, statistical analysis. The rationale for these working hypotheses is, however, based on the scientific literature concerning Pacific Coast salmon watersheds available at this time, including studies brought to the attention of the IFR team by KRIS Noyo peer reviewers.
Each of the hypothesis webpages 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 Noyo basin literature, is provided. The data from the Noyo watershed that is consistent with the hypothesis is then presented. Alternative hypotheses are then provided and, finally, suggestions for strengthening the preferred and alternative hypotheses are offered.
By offering these working hypotheses the KRIS/Noyo project provides a starting point for more fine-grained watershed assessment. Users are encouraged to perform their own hypothesis-testing using the data in KRIS/Noyo and that from other sources. While the relationship between the fish populations and watershed conditions as presented here may trouble some, including land managers, IFR believes that the use of the scientific process can shift the discussion from one that is largely accusatory to one that is more rational and, ultimately, more productive.
Hypothesis #1: Both the distribution and abundance of coho salmon in the Noyo River basin have been reduced significantly between the 1960s and 1990s.
Hypothesis #2: High levels of sediment in Noyo River tributaries have caused habitat changes which limit coho salmon production.
Hypothesis #3: Coho salmon production is limited by high water temperature in the Noyo River.
Hypothesis #4: Reduced large wood supply has contributed to the loss of pool habitat and the decline of coho salmon in the Noyo 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.
Hypothesis #6 Excluding grilse from brood stock at the Noyo River Egg Collecting Station is decreasing genetic diversity.