Fall chinook salmon were believed to return to the Umatilla subbasin as salmon were known to be captured from spring through the fall by Native Americans and early settlers. Natural production potential is theoretically large based on the juvenile life history patterns of fall chinook.
State and tribal authorities began hatchery releases of fall chinook salmon in 1982 with Tule stock, and switched to Upriver Bright stock in 1983 (Evans 1984). The suitability of the Umatilla subbasin for the natural production of fall chinook in its current condition has remained a critical uncertainty. Returns of hatchery produced adults has often been low with the largest adult return in 1999 of 737 adults. Low returns and the need for broodstock has limited harvest and natural spawning in most years (Table 23). However, outplanting of adult hatchery fall chinook from other mid-Columbia hatcheries has produced good survival to spawning and good redd numbers (Contor et al. 2000). Production of fry has also been documented, even though redds have been scoured by high flow events and impacted with fine sediment (Contor et al. 2000). ODFW (Knapp et al. 2000) estimated that 141,000 fall chinook fry migrated from the Umatilla River in 1998. Fry survival has been severely compromised by warm water temperatures during outmigration below Westland Dam, where most of the early summer flows are extracted. Additional water has been released into July during the last several years to assist down stream migration and enhance survival (Figure 33).
Fall chinook spawning has been observed primarily from the mouth of the Umatilla to the confluence of Meacham Creek (RM 79.0) with most of the spawning in the Barnhart (RM 42) to Yoakum (RM 37.0) reach. CTUIR estimates that most of the spawning occurs just below Barnhart where the majority of adult spawners are released.
Table 23. Umatilla fall chinook adult returns, disposition and spawning escapement, 1988-2000.
Figure 33. Life history chart of naturally produced Umatilla fall chinook salmon; shaded ovals represent areas and times where redds are at risk from scouring and/or sedimentation during high flows; shaded rectangles and red arrows represent times and areas where high water temperatures may be limiting (Contor et al. 1998).