SALMON POPULATIONS 

 IN THE SOUTH FORK DRAINAGE 



Adult Chinook salmon, Onaorhynchus tshawytsaha (Walbaum), ^ and steelhead trout, 

 Salmo gairdneri Richardson, returning from the ocean to the South Fork Salmon River 

 (SFSR) have steadily declined in numbers since 1957. This decline resulted in sport 

 fishing closures on both species. Summer chinook salmon are approaching the status of 

 a "threatened species" in the Salmon River drainage. There is no evidence that their 

 populations have stabilized or that the downward trend will not continue. Decline of 

 salmon populations in the Salmon River Drainage has been caused mainly by impoundments 

 in the lower Snake and Columbia Rivers. In the South Fork of the Salmon River, erosion 

 triggered by past logging has probably contributed to the decline by silting and filling 

 in sections of the streambed. If degraded habitat is to improve, land managers must be 

 able to identify streams critical to summer chinook salmon survival. 



Adult summer chinook salmon runs into the SFSR are monitored by the Idaho Fish and 

 Game Department by conducting annual salmon redd counts. However, there is little 

 knowledge of the status and needs of the juvenile stage of the summer chinook salmon's 

 life cycle in the SFSR drainage. In the past it has been assumed that the rearing of 

 salmon juveniles was almost entirely in the main SFSR. This report evaluates the use 

 and importance of small tributaries for rearing summer chinook salmon. 



SURVEY OF SOUTH FORK TRIBUTARIES 



study Sites and Methods 



The SFSR is a major tributary of the Salmon River, draining a 1,270 mi^ (3,290 km^) 

 watershed representative of much of the forested mountainous terrain found in central 

 Idaho (fig. 1). The study area includes 397 mi2 (1,028 km2) of watershed along the 

 upper 52 miles (84 km') of the river. The study area topography ranges in elevation from 

 9,000 feet (2,740 m) around the headwaters, to 3,700 feet (1,130 m) at the river's con- 

 fluence with the East Fork-South Fork Salmon River. Most slopes are steeper than 40 

 percent and slopes more than 65 percent are common. Waters draining from the watershed 

 are low in mineral content (averaging 60 mg/liter total dissolved solids) because of the 

 dominant granitic bedrock in the watershed (Platts 1974) . 



^ Scientific names according to the American Fisheries Society (1970) list of 

 common and scientific names of fishes. 



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