CHIMACUM WATERSHED
TARGETED LAND-USE PRACTICE IMPACTS TO COHO AND CHUM RUNS
1) Channelization – 20% reduction in coho summer rearing area in the east fork, a 37-50% reduction in the west fork, and a 20% reduction in winter rearing areas in both forks; reduced spawning area in the east fork by 51% and in the west fork by 18%. (Prior to channelization the stream provided 43.7 km of coho summer and winter rearing habitat and 17.4 km of spawning habitat. Existing channel length available for rearing habitat 31-35 km and spawning habitat 13.6km.)
2) Draining ponds, wet prairies, and beaver marshes – reduced the use of such habitat in both forks for summer and winter rearing by 95-99%. Prior to draining stream channel area provided 15.4 hectares of summer and winter rearing and now provides 10-13 hectares. The swamps provided an additional 180 hectares of summer rearing and 540 hectares of winter rearing. This habitat has now been reduced to 1 to 7 hectares depending on the area.

3) Habitat degradation: a) increased temperatures - weekly measurements at four stream sites from 1992 to 1994 showed frequent temperature elevations exceeding the 20? C threshold recommended for salmonids); b) reduced dissolved oxygen levels - EPA (1986) reports salmonid production impairment at dissolved oxygen levels below 8 mg/L. Ten of twenty-two sites measured at minimum dissolved oxgen levels below 8 mg/L with two sites measuring less than 5mg/L. This condition is exacerbated by invasive non-native grasses such as reed canary grass invading streamsides and wetland areas; c) reduced channel complexity - due to reduced input of LWD, d) increased nutrient input at points along both forks, livestock have unfenced access to the stream; e) increased episodic and chronic fine sediment deposition – episodic fine sediment deposition from road failures and chronic fine sediment deposition occurring at points along the creek due to tree and vegetation removal coupled with changes in sediment transport systems decreasing stream sinuosity have produced a dangerously high percentage of fine sediments, estimated to be as high as 60% silt and sand, in the chum spawning beds (Bahls and Rubin 1996). Evidence supports the findings of Koski (1966, 1975) and others that a percentage of 20% and above greatly reduces chum survival rates. Studies have found that a 60% level of fine sediments reduces embryo survival to near 0 for five species of Pacific salmon. (Tappel and Bjornn 1983; Irving and Bjornn 1984).
 
4) Barriers to fish migration - seven culverts have been identified as impassable to migrating coho salmon. Two impassable culverts are under county roads, one is under a State highway (Beaver Valley Road) and three are under small private roads. In several cases, culverts were constructed prior to agricultural ditching with post-ditching culverts left hanging above the water surface.