No systematic, scientific studies have examined the size or health of salmonid populations in the Western Subbasin. However, historical accounts and stream surveys conducted in the 1960s by CDFG indicate that the subbasin supported populations of Chinook salmon, coho salmon, and steelhead trout. Recent biological stream surveys indicate the presence of steelhead trout throughout the subbasin and coho salmon in a few tributaries. Low salmonid populations throughout the Mattole Basin indicate that salmonid populations in the Western Subbasin are also likely to be depressed at this time. However, populations have a good chance to recover due to public land stewardship that is actively engaged in improving watershed and stream conditions. In addition, salmonid rearing activities within the subbasin are working to supplement native stocks as habitat conditions improve;
Instream sediment in several stream reaches in this subbasin may be approaching or exceeding levels considered unsuitable for salmonid populations. Macroinvertebrates data indicate good conditions. Additionally, amphibians sensitive to fine sediment were present in most stream reaches surveyed in this subbasin;
Riparian Water Temperature
Available data suggest high summer temperatures are deleterious to summer rearing salmonid populations in some streams in this subbasin; in others it is good;
In-stream habitat diversity and complexity, based on available survey data (i.e. pool depths, cover, and large woody debris) may be adequate for salmonid production. Additionally, recent surveys indicate instream habitat appears to be improving. Large woody debris recruitment potential is poor in this subbasin;
Available data from sampled streams suggest that suitable amounts and distribution of high quality spawning gravel for salmonids is lacking in some reaches in this subbasin;
The upper reaches of Bear, Mill (RM 2.8), North Fork Bear, South Fork Bear, Big Finley, and South Fork Big Finley creeks, and the tributary to North Fork Bear Creek, are considered good refugia, and this will continue due to BLM and cooperative private land owners and current management policies in key headwater reaches. In fact, Bear Creek was the only creek in the Mattole Basin determined to provide high quality refugia.
Although the Western Subbasin encompasses the dramatic relief of the King Range, with the highest proportion of steep slopes in the basin, approximately half of the subbasin is underlain by hard terrain and it is second only to the Southern Subbasin in terms of stable areas. Slope instability is focused primarily in the abundant areas with steep to very steep slopes and the limited area of soft terrain;
Based on features indicative of excess sediment production, transport and storage, the pattern of impacts to stream conditions is similar to that observed in the Eastern Subbasin, and is highly variable throughout the subbasin. Considering the low degree of impact by features indicative of excess sediment production, transport and storage observed in the adjacent upstream Southern Subbasin, it appears that the stream features observed in the Western Subbasin must be derived either internally within the subbasin or from the adjacent Eastern Subbasin;
As a result of past timber harvest and conversion activities, almost 60% of the Western Subbasin is occupied by small diameter (twelve to twenty-four inches diameter at breast height) forest stands. Another 20% is in forest stands greater than twenty-four inches;
Forty square miles, or nearly half of this subbasin are in public ownership managed by the Bureau of Land Management as part of the King Range National Conservation Area, designated as late seral reserve. Timber harvesting has occurred on less than one percent of the area in the last ten years and has been at low levels for decades. Privately owned acres carrying grassland are grazed while smaller, residential parcels are concentrated along the main county roads. Old roads, many abandoned, are common across the landscape;
Based on information available for this subbasin, the NCWAP team believes that salmonid populations are currently being limited by reduced habitat complexity, high sediment levels, high water temperatures, and embedded spawning gravels.
Based upon the latest science on placement of large woody debris in stream channels, managers in the Western Subbasin should work to improve channel structure and function for salmonids. Pool shelter has the lowest suitability for salmonids in Mill Creek (RM 2.8) Tributary #1 and South Fork Big Finley Creek;
Establish monitoring stations and train local personnel to track in-channel sediment and aggraded reaches throughout the subbasin and especially in the lower reaches of major tributaries and Squaw, Honeydew, Finley, Big Finley, Woods and Bear creeks;
Continue efforts such as road improvements and decommissioning throughout the basin to reduce sediment delivery to the Mattole River and its tributaries. Road inventories have been completed for much of this planning basin, and it is recommended that this effort be continued until a complete inventory is compiled. CDFG stream surveys indicated Mill Creek (RM 2.8) and Bear Trap Creek have road sediment inventory and control as a top tier tributary improvement recommendation;
Monitor summer water and air temperatures to detect trends using continuous 24 hour monitoring thermographs. Continue temperature monitoring efforts in Stansberry, Mill (RM 2.8) Clear, Squaw, Woods, Honeydew, Bear, North Fork Bear, South Fork Bear, Little Finley, Big Finley, and Nooning creeks, and expand efforts into other subbasin tributaries;
Ensure that near stream forest projects retain and recruit high canopy densities in riparian areas to reduce solar radiation and moderate air temperatures;
Where current canopy is inadequate and site conditions, including geology, are appropriate, use tree planting and other vegetation management techniques to hasten the development of denser and more extensive riparian canopy. Canopy density has the lowest suitability for salmonids in Squaw Creek. Use cost share programs and conservation easements as appropriate;
The three cooperative salmon rearing facilities in this subbasin should be continued as needed to supplement wild populations while the improvements from long-term watershed and stream restoration efforts develop;
Initiate a systematic program to monitor the effectiveness of these fish rescue and rearing activities, and determine the need for the continuance of cooperative, supplemental fish rearing efforts on an ongoing, adaptive basis using the best available science;
The nature and extent of naturally occurring unstable geologic terrain, landslides and landslide potential (especially Categories 4 and 5, page 89) must be considered when planning potential projects in the subbasin;
Encourage the use of appropriate Best Management Practices for all land use and development to minimize erosion and sediment delivery to streams;
In order to protect privacy on private lands in this subbasin while developing data, the possibility of training local landowners to survey streams and conduct salmonid population status surveys is advisable;
Ensure that high quality habitat within this subbasin is protected from degradation. The highest stream reach condition as evaluated by the stream reach EMDS and refugia analysis were found in Bear, Mill (RM 2.8), North Fork Bear, South Fork Bear, Big Finley, and South Fork Big Finley creeks and the tributary to North Fork Bear Creek.