Draft Imnaha Subbasin Summary November 30, 2001 Prepared for the Northwest Power Planning Council Subbasin Team Leader

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Artificial Production

Spring Chinook

(The following discussion is taken from USFWS 2001 where not otherwise specified)

Historic artificial production of spring chinook in the Imnaha subbasin dates back to 1949 when the Oregon Game Commission initiated a spring chinook egg-take program in an effort to supplement Imnaha chinook into the Umpqua subbasin in southwest Oregon (Ashe et al. 2000). Between July and August 1951, 152 male and 6 female chinook were collected from spawning beds in the mainstem Imnaha and from a weir constructed at Coverdale (Mundy and Witty 1998). Fifteen years later, 119 adult spring chinook collected from Hells Canyon Dam were outplanted into the Imnaha (Neeley et al. 1993). In 1976, Congress authorized the production of hatchery spring chinook under the auspices of the Lower Snake River Compensation Plan (Ashe et al. 2000). The LSRCP was initiated in the Imnaha subbasin in 1982. The first releases of hatchery produced juvenile spring chinook occurred in 1984.

The LSRCP supplementation program was initiated using only adult salmon returning to the Imnaha River and each year naturally-produced fish are incorporated into the hatchery broodstock (NPT et al. 1990). Until recently, two facilities were used for the chinook production program; the Imnaha River satellite facility (located near Gumboot Creek) for adult collection, adult holding, and smolt acclimation, and Lookingglass FH for incubation and rearing of juveniles. Adults collected at the Imnaha weir are held or transported to Lookingglass FH, where they are held and spawned. LFH was designed to serve as the incubation and rearing facility. Currently, however, due to facility limitations, equipment failure and malfunction at Lookingglass Hatchery all eggs are shipped to Oxbow Hatchery (near Bonneville Dam) or Irrigon Hatchery for incubation and early rearing of juveniles. Following rearing for about five months, juveniles are transported back to LFH for another 9 months before smolts are transported back to the acclimation facility where they are held for one month prior to release in April. Exceptions to releases of fish from the acclimation facility or directly into the mainstem Imnaha, were in 1987 when Imnaha smolts were released at Lookingglass Hatchery because of disease concerns, 1990 when smolts were also released in Big Sheep Creek, and 1994 when presmolts were released in Big Sheep Creek, Little Sheep Creek, and the Imnaha River (Beamesderfer et al. 1997).

Artificial production of Imnaha River chinook salmon began as a mitigation as a program, however, beginning in the early 1990s, the co-managers recognized that the Imnaha population was at imminent risk of extirpation and immediate action was necessary. As a result, the NPT and ODFW cooperatively developed a program redirecting existing production occurring under LSRCP from mitigation to conservation and restoration. The current program is operated under Section 10 ESA permit authorization and Nez Perce Tribe/ODFW co-management agreement. The program is focused on natural population recovery and genetic conservation. Wild chinook adults were initially collected for broodstock beginning in 1982. Wild fish comprised the majority of the broodstock until 1989 when significant numbers of hatchery fish began to return. Currently, hatchery and natural fish are used for broodstock each year. Broodstock management is guided by a sliding scale management plan that places emphasis on minimizing demographic risk at escapement levels below a minimum adult spawner escapement (threshold) and minimizing genetic risk of the hatchery program at escapement levels above threshold. The proportion of natural fish that are retained for broodstock, the proportion of natural spawners that are hatchery origin, and the proportion of broodstock that must be natural origin varies depending on escapement levels.

Smolt production levels have been highly variable and typically well below the goal of 490,000 because of the abundance of natural fish and broodstock management criteria. Currently smolt production has been reduced by 25% due to the facility limitations at Lookingglass FH. Smolt-to-adult survival rates have been below the goal of 0.65% with a maximum value of 0.58% for the 1988 broodyear. Substantial smolt mortality occurs from release through the mainstem river corridor, which is a major constraint on smolt-to-adult survival. Life history and genetic characteristics are similar for hatchery and natural fish, with the exception of age composition at return. Hatchery fish return a greater proportion of age 3 males and fewer age 5 fish. Progeny-to-parent ratios for natural fish have been below replacement (1.0) since the 1983 broodyear and have averaged 0.5. In contrast, the ratio for hatchery fish has been above 1.0 in most years and has averaged 4.0. Model results indicated that presently a greater number of total fish and natural spawners in the basin, attributable to the hatchery program. ODFW has made a substantial number of adaptive management changes to improve the program including reduced emphasis on smolt production goals and increased emphasis on genetic conservation, gene banking, implementation of sliding scale management plan, aggressive fish health protection, low density rearing, and more natural smolt size-at-release (25/lb.).

Future Plans (refer to Appendix I for ODFW HGMP)

Co-managers plan to continue managing the chinook salmon hatchery program as a conservation/restoration tool to prevent extinction, enhance natural production, and assess supplementation as a tool for recovery. The program will be operated under ESA authorization and future decisions resulting from CRFMP negotiations will, in part, determine changes in future direction. Co-managers also plan to place increased emphasis on conservation hatchery management, genetic analysis (DNA), continued gene banking, improved rearing (possibly in the Imnaha River subbasin), and rearing natural size smolts in a natural environment. The Northeast Oregon Hatchery project is designing new facilities and identifying modifications to Lookingglass FH necessary to meet program requirements and conservation objectives.


Steelhead supplementation efforts in the Imnaha subbasin have occurred through the Lower Snake River Compensation Plan (LSRCP) since 1982. The preferred stock for hatchery use is Imnaha River Stock and no outside introductions are planned (NPT et al. 1990).

Three facilities are used for the steelhead production program. The adult collection/smolt acclimation facility is located in the Imnaha River subbasin on the Little Sheep Creek, a tributary to the Big Sheep Creek. Adults are collected and spawned at Little Sheep Creek, embryos are initially incubated at Wallowa Hatchery and then transported to Irrigon Hatchery. Final incubation and rearing to the smolt stage occurs at Irrigon FH. Following 10 – 13 months of rearing, smolts are transferred back to the acclimation facility for 30 days of acclimation prior to release in April and May.

Wild summer steelhead were initially collected from Little Sheep Creek for broodstock beginning in 1982. The goal of the program was to incorporate naturally-produced fish into the broodstock on an annual basis, so that an adequate escapement of natural fish to Little Sheep Creek would be reestablished. Since 1987, returns of naturally produced adult steelhead to Little Sheep Creek have amounted to less than 20% of the total return in spite of substantial supplementation with hatchery produced adults. Smolt production goals have, however, generally been achieved in all years except 1997. Prior to 1998, releases had only occurred at the Little Sheep Creek facility and in the mainstem Imnaha River. In 1998, fry were planted in other tributaries, and since 1999, adults have been outplanted in Big Sheep Creek. Smolts have also been released in Big Sheep Creek since 2000. Smolt-to-adult survival rates have varied, but have typically been below the goal of 0.61%. Life history and genetic characteristics of adult hatchery and natural fish have remained similar.

A consumptive steelhead recreational fishery was re-opened in 1986 after being closed since 1974. Catch rates in the Imnaha River are high and better than historic values. Imnaha hatchery steelhead contribute to fisheries throughout the Columbia Basin. Despite meeting many production goals, the following obstacles to achieving management objectives remain: low smolt-to-adult survival, apparently low carrying capacity of Little Sheep Creek, low abundance of natural fish in the Little Sheep Creek and lack of information on steelhead population dynamics in the Imnaha River.

Evaluation of stock status of wild steelhead in the Imnaha River subbasin were initiated in 2000 with operation of an adult escapement weir in Lightning Creek. This effort has been expanded to Cow Creek in 2001. Efforts to identify population structure through genetic information for O. mykiss are underway. A sample collection strategy was developed and initiated in 1999 to allow DNA genetic analysis of stock structure for steelhead in Imnaha and Grande Ronde subbasins. Twenty areas were targeted for sample collections. These sample collections are scheduled to continue for at least four years (through 2002). A long-term genetics monitoring (perhaps with reduced effort) is expected to occur as long as supplementation of steelhead populations in the system occurs.

Future Plans (refer to Appendix I for ODFW HGMP)

The steelhead program will continue to be managed to mitigate for lost sport and tribal harvest resulting from construction of lower Snake River dams. Co managers will continue to monitor the success of the program at meeting LSRCP goals and the success of supplementing Little Sheep Creek with hatchery steelhead.

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