Eighteen Northern Subbasin streams were rated as salmonid refugia areas. Refugia categories were defined as:
High Quality – relatively undisturbed habitat, with the range and variability of conditions necessary to support species diversity and natural salmonid production;
High Potential – diminished but good quality habitat with salmonids present, currently managed to protect natural resources with the possibility to become high quality refugia;
Medium Potential – degraded or fragmented instream and riparian habitat, with salmonids present but reduced densities and age class representation. Habitat may improve with modified management practices and restoration efforts;
Low Quality – highly impaired riparian and instream habitat with few salmonids (species, life stages, and year classes). Current management practices and conditions have significantly altered the natural ecosystem and major changes are required to improve habitat.
Salmonid habitat conditions in the Northern Subbasin on streams surveyed by CDFW are generally rated as medium potential refugia, with 11 of 18 streams surveyed in that category. Squaw and Bull creeks provide the best salmonid habitat in this subbasin, with Squaw Creek being rated high quality habitat and Bull Creek as high potential habitat.
These streams are both within the boundaries of Humboldt Redwoods State Park, and management priorities include tree planting in areas with intensive historic timber harvest, instream restoration projects (installing and improving instream structures), and road decommissioning projects. Squaw Creek is a high quality salmonid stream flowing through areas of old growth coast redwood forest, with excellent riparian condition and low management impacts (disturbed terrain, displaced vegetation, and diversion). Bull Creek was rated as a high potential refugia stream because although the vegetation and riparian conditions in some areas are relatively high quality, overall pool quality and shelter are low due to extensive fine sediment input in upstream areas, unstable geology, and historic practices such as logging and instream wood removal.
Five streams were rated as low quality refugia: Cuneo, South Fork Cuneo, Salmon, Fish, and Ohman creeks for the following reasons:
Cuneo and South Fork Cuneo Creek receive a great deal of fine sediment input from active landslides and unstable geology on surrounding slopes. Canopy density, pool depth and shelter, and embeddedness values are all low in the upper Bull Creek watershed;
Salmon Creek is heavily diverted for residential use and marijuana cultivation, and pool quality is low throughout the drainage;
A culvert on lower Fish Creek has a steep (7.6%) slope and is a partial barrier to adult salmonids and likely a complete barrier to juveniles. This culvert needs to be replaced and modified, and although the project has been proposed in the past, funding has not yet been secured.
Ohman Creek has a very limited anadromous reach due to a 15’ waterfall approximately 1500’ upstream from the confluence with the SF Eel River. The team split this creek into two sections (at 1800’ upstream from the confluence of the mainstem SF Eel River) because of significant differences in conditions and salmonid use between lower and upper areas. The upper section was rated as low quality refugia habitat and the lower section as medium potential habitat.