Coho salmon were released from 1966 through 1969 and from 1987 to the present, and have been primarily Tanner Creek stock. Broodstock for the program are collected at Bonneville Hatchery and reared at Cascade and Lower Herman Creek Hatcheries. Some broodstock have been collected from the Umatilla River at Three Mile Falls Adult Trap during several recent years due to broodstock shortages at Bonneville. Smolt releases have been variable but the current program releases 1,500,000 smolts annually into the mainstem Umatilla River
Adult returns to Three Mile Dam have been variable and have ranged from 356 adults in 1992 to 4654 adults in 2000. More than 3000 adults returned in both 1998 and 1999 (Table 24).
Spawning survey crews have observed many coho redds and spawned-out adult carcasses through the years in the Umatilla River from the mouth to Meacham Creek. Water conditions often prevent extensive and accurate counts, but redds and carcasses are observed each year. Coho have been observed in low numbers in some of the mid-basin tributaries such as Squaw Creek, Buckaroo Creek and Meacham Creek. Naturally produced juvenile coho have been observed throughout the lower mainstem and in the lower portions of many of the mid-basin tributaries (McKay Creek, Mission Creek, Moonshine Creek, Buckaroo Creek, Squaw Creek, Tutuilla Creek and others).
Figure 34 summarizes the habitat utilization of naturally produced coho salmon in the Umatilla Basin. Prior to 1999, summer rearing conditions in the Umatilla in and around the coho spawning areas was unsuitably warm for a number of weeks each summer. Juvenile coho were frequently observed in the lower reaches and were always associated with spring seeps or other thermal refuge. Fish were often in poor condition. However, since the summer of 1999, additional summer rearing habitat has been available from the mouth of McKay Creek (RM 50.5) downstream approximately 20 miles (depending on water temperatures). Cool water is released from McKay Reservoir for irrigation use during most of each summer. In the past, water released from McKay Reservoir fluctuated during early and late summer depending on irrigation needs. Water temperatures were often suitable for juvenile coho throughout the reach during all but one or two weeks during the summer. Beginning in 1999, flows were augmented during those times so that water temperatures remained suitable. This represents a significant increase in suitable mainstem summer rearing habitat. Monitoring in 1999 and 2000 indicates the areas were utilized by many juvenile coho salmon. Coho juveniles have been in excellent health and are of large size for a given age (Contor et al. Report in progress). The management of lower McKay Creek has also been changed and now flows perennially since July of 2000. In the past many juvenile coho were stranded, lost and salvaged from the lower six miles of McKay Creek after McKay dam was shut off in the fall to store water for the following irrigation season. A minimum flow of 10 cfs is now maintained and flows are ramped down to encourage outmigration and reduce stranding of salmonids.
Harvest has been minimal as harvest conditions have been poor and coho are often difficult to catch. Variable returns have limited the interest of dip net fisheries by Tribal Fishermen.
Figure 34. Life history chart of naturally produced Umatilla coho salmon; shaded ovals represent areas and times where redds are at risk from scouring and/or sedimentation during high flows; shaded rectangles and redd arrows represent times and areas where high water temperatures may be limiting (Contor et al. 1998).