SPECIES BIOLOGY 



The Chinook salmon is noted for the hlact; spotting on back, dorsal fin. and both lobes of caudal 

 fin. black pigment along the bases of the teeth and loose conical teeth in mature individuals. 

 Salmon over 14 kg are likely to be chinooks. 



The Sacramento River winter-run chinook salmon spawns in the upper Sacramento River 

 primarily between Red Bluff Diversion Dam and Keswick Dam from late April to mid-August. 

 The juveniles emerge in late June through September, beginning their downstream migration 

 within several weeks of hatching. 



SPECIES DISTRIBUTION 



The distribution of Sacramento River winter-run chinook salmon has been dramatically reduced 

 to a portion of its former range. The construction of Shasta and Keswick Dams blocked access to 

 all of the winter-run's historic spawning grounds in the McCloud. Pit and Little Sacramento 

 rivers. Current spawning takes place primarily between Red Bluff Diversion Dam and Keswick 

 Dam. During migration. Sacramento River winter chinook migrate from the Sacramento-San 

 Joaquin Delta up to the Upper Sacramento River. 



Critical Habitat 



Critical habitat for Sacramento River winter-run chinook salmon includes: The Sacramento 

 River from Keswick Dam. Shasta County (River Mile 302) to Chipps Island (River Mile 0) at the 

 westward margin of the Sacramento-San Joaquin Delta; all waters from Chipps Island westward 

 to Carquinez Bridge, including Honker Bay, Grizzly Bay. Suisun Bay. and Carquinez Strait; all 

 waters of San Pablo Bay westward of the Carquinez Bridge; and all waters of San Francisco Bay 

 (north of the San Francisco/Oakland Bay Bridge) from San Pablo to the Golden Gate Bridge. 



MAJOR IMPACTS 



Water development has blocked and inundated habitat: increased delay of juvenile migration 

 through the Sacramento River; and increased delay of adults on their way to spawning grounds. 

 Water withdrawal and storage, irrigation diversions, siltation and pollution from sewage, 

 farming, grazing, logging, and mining have also degraded the Sacramento River salmon habitat. 



Although winter-run chinook are subjected to a lower harvest rate than other Sacramento River 

 chinook salmon, due to the timing of their run compared to the timing of the chinook salmon 

 fishery, over-utilizafion continues to threaten this species. 



The impacts of numerous bacterial, protozoan, viral, and parasitic organisms on Sacramento 

 River winter-run chinook salmon are largely unknown. Predators include squawfish and striped 

 bass. The extent to which predation is a factor causing the decline of the winter-run chinook 

 salmon is unknown. 



There are numerous unscreened or inadequately screened diversions on the Sacramento River. 

 These result in an unknown loss of outmigrating juvenile salmon as a result of entrainment in 

 unscreened diversions or impingement on inadequately designed diversions. NMFS has initiated 

 a rule making process to require screens on all diversions. 



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