*U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications*

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**NOAA F/NWC-187 - Status and Future of Spring Chinook Salmon in the Columbia River Basin—Conservation and Enhancement**

**ESTIMATING, SPRING CHINOOK PARR AND SMOLT ABUNDANCEIN WILD AND NATURAL PRODUCTION AREAS**

C. E. Petrosky

Idaho Department of Fish and GameBoise, Idaho 83707

The Idaho Department of Fish and Game (IDFG) began in 1984 to monitor the abundance of chinook salmon and steelhead trout (*Oncorhynchus mykiss*) juveniles in the Salmon, Clearwater, and upper Snake River subbasins. Status and trends of wild and natural anadromous fish populations in Idaho were monitored through three programs.

The first, a parr density and physical habitat monitoring program, was established in 1984 to determine benefits of Bonneville Power Administration (BPA) habitat improvement projects implemented in Idaho as off-site mitigation for downstream hydropower development on the Snake and Columbia Rivers under the Northwest Power Planning Act. A parallel IDFG-funded monitoring program was established in 1985 to index parr densities in the remainder of the wild and natural production areas not sampled by the BPA project. Together, these two programs form a data base that includes a total of 236 monitoring sections sampled annually. The third program, begun in 1986, is a BPA-funded research study to define the numerical relationships between spawning escapement and numbers of parr and smolts produced for two natural production areas, the upper Salmon River and Crooked River.

Juvenile chinook salmon monitoring in Idaho provided data with several levels of resolution and applications. Parr densities were compared among years, populations, drainages, habitat conditions, redd densities, and with carrying capacity ratings developed for subbasin planning by the Northwest Power Planning Council (NWPPC). Total parr abundance (standing stock) estimates and redd counts were used to estimate egg-to-parr survival in different streams and habitats. Where hatchery chinook salmon fry were stocked into vacant habitat above BPA barrier removal projects, total abundance and fry-to-parr survival were estimated.

The upper Salmon River and Crooked River research studies monitored adult escapements past weirs, estimated escapements by redd counts, and estimated total parr abundance and smolt production (yield). Smolt production was estimated from migrant trapping at weirs, and the tagging and recovery of PIT tags (passive integrated transponder; Prentice et al. 1986). Recapture and interrogation of PIT-tagged juveniles at the weirs and at Snake and Columbia River dams provided data on migration characteristics and parr-to-smolt survival.

Parr density estimates were obtained in most streams by visual counts made by snorkeling in established sections during the summer low flow period (July-August). We compared estimates obtained by visual counts and electrofishing removal in 1986 in five stream sections of different size and conductivity. Predepletion estimates were obtained by snorkeling 1 day before electrofishing. On day 2, we block-netted section boundaries and removed fish in three passes (Seber 1982). We then snorkeled a second time before releasing catches and removing block nets. Consistent with Hankin and Reeves (1988) findings for coho salmon (*O. kisutch*), visual estimates of chinook salmon abundance were similar to electrofishing estimates in four of five tests. Contrary to Hankin and Reeves, who consider electrofishing more accurate, the fifth electrofishing estimate accounted for only 18% of the total number of parr that were estimated visually before and immediately after depletion. The bias was due to inefficient electrofishing in low conductivity water (40 �mho/cm).

Monitoring of chinook salmon parr density during 1984-88 documented the depressed status of wild and natural populations of spring and summer chinook salmon in Idaho (Petrosky and Holubetz 1989). Densities were highly variable and reflected habitat conditions and escapements. Highest densities occurred in low gradient C-channels (Rosgen 1985) of both wild and supplemented streams. Mean densities of wild chinook salmon in the Middle Fork Salmon River increased during 1984-88, and reflected the general rebuilding trend for the period. On the other hand, parr densities in some streams remained at extremely low levels. We have not documented presence of spring chinook salmon parr in Snake River tributaries of Hell's Canyon since monitoring began in 1985.

Chinook salmon parr density correlated (r = 0.75) with redd density the previous year in Salmon River streams. Redd densities in the wild and natural index areas were low, ranging from 0 to 8.9 redds/ha. By contrast, the 1960s mean for the Marsh Creek drainage (Middle Fork Salmon River tributary) was 18.7 redds/ha.

We inferred chinook salmon carrying capacity from annual monitoring, the literature, fry outplants specifically designed to test carrying capacity in different habitats, and NWPPC subbasin planning estimates. Fry outplants in 1987 fully seeded stream reaches in undisturbed habitat in portions of the upper Lochsa River drainage. C-channels supported a density of chinook salmon parr (108/100 m2) that averaged 60% higher than in B-channels (67/100 m2). Sekulich (1980) estimated a similar potential parr density for low gradient streams in the Idaho batholith (120/100 m2). We calibrated the NWPPC smolt capacity ratings to IDFG estimates of chinook salmon parr carrying capacity. The calibrated habitat capacity ratings in terms of parr were excellent = 108/100 m2; good = 77/100 m2; fair = 44/100 m2; and poor = 12/100 m2.

We estimated seeding level as the observed density divided by the carrying capacity estimate. Overall, the mean 1984-88 seeding levels (unweighted mean, all monitoring sections and years) for wild spring, natural spring, wild summer, and natural summer chinook salmon were 11.5, 17.4, 11.4, and 19.0% of estimated carrying capacity, respectively (R. J. Scully, IDFG, unpubl. data). Estimated mean seeding levels in C-channels (21.0%), which included the major spawning areas, exceeded those in B-channels (5.5%) nearly fourfold.

Total parr abundance estimates and redd counts in upper Salmon River and middle fork of Salmon River streams were used as the basis to estimate and compare egg-to-parr survival rates in streams with different sediment levels and riparian degradation. The Shoshone-Bannock Tribes (Richards and Carriers. 1987) provided data for Bear Valley and Herd Creeks for this analysis. Egg-to-parr survival estimates ranged from 1.2% in Bear Valley Creek a highly sedimented stream, to 29% in two cleaner streams. Percent survival correlated strongly (r = -0.97) with percent surface sand.

We estimated total parr abundance in the vicinity of outplant sites where chinook salmon fry were introduced into vacant habitat using systematic stratified sampling. Fry-to-parr survival rates averaged 20% (range, 11-30%). Based on 75% green egg-to-fry survival in hatcheries, estimated egg-to-parr survival for outplanted fry was 15% (range, 8-22%), similar to estimates for natural spawning.

PIT tagging and outmigration monitoring of spring Chinook salmon began in the upper Salmon River in 1987 (Kiefer and Apperson 1989). Total parr abundance was estimated in July-August using stratified sampling. Parr were PIT tagged in August with assistance from National Marine Fisheries Service (NMFS) personnel. Field observations, live-box tests and studies by NMFS indicate that mortality due to the tagging operation is low. A scoop trap was installed at the Sawtooth Hatchery weir to estimate total outmigration and to tag and recapture migrants. Peak outmigration occurred in September-October and March-April (R. B. Kiefer, IDFG, unpubl. data). An estimated 73% of the summer parr population migrated past the weir, most during the fall (67%). Parr-to-smolt survival for fish that overwintered in the study area was conservatively estimated as 26%. PIT-tag recaptures will be analyzed to determine parr-to-smolt survival for fall migrants and for the total summer parr population. During the poor migration flow years of 1988-89, approximately 2-4% of the PIT-tagged parr were detected****as smolts at Lower Granite Dam. An irrigation diversion that dewatered the upper river until mid-September reduced the survival of fall migrants.

PIT tagging and outmigration monitoring of Crooked River spring Chinook salmon began in 1988 using similar methods as in the upper Salmon River. An estimated 47% of the summer parr migrated past the Crooked River weir, predominately during the spring. Estimated parr-to-smolt survival of juvenile Chinook salmon that overwintered in Crooked River was 31%. Less than 2% of the PIT-tagged parr from Crooked River were detected at Lower Granite Dam. in spring 1989.

**References**

Hankin, D. G., and G. H. Reeves. 1988. Estimating total fish abundance and total habitat area in small streams based on visual estimation methods. Can. J. Fish. Aquat. Sci. 45:834-844.

Kiefer, R. B., and K. Apperson. 1989. Intensive evaluation and monitoring of chinook salmon and steelhead trout production, Crooked River and Salmon River sites. Subproject II. Annual report, 1987. Idaho Department of Fish and Game. Bonneville Power Administration Contract No. DE-A179-84BP13381, Project 83-7.

Petrosky, C. E., and T. B. Holubetz. 1989. Idaho habitat evaluation for off-site mitigation record. Subproject I. Annual report, 1987. Idaho Department of Fish and Game. Bonneville Power Administration Contract No. DE-A179-84BP13381, Project 83-7.

Prentice, E. F., D. L. Park, T. A. Flagg, and A. S. McCutcheon. 1986. A study to determine the biological feasibility of a new tagging system: 1985-86. National Marine Fisheries Service. Bonneville Power Administration Contract No. DE-A179-84BP11982, Project 83-319. (Available from Northwest Fisheries Center, 2725 Montlake Blvd. E., Seattle, WA 98112-2097.)

Richards, C., and P. J. Cernera. 1987. Salmon River habitat enhancement. Annual report, 1986. Shoshone-Bannock Tribes. Bonneville Power Administration Contract No. DE-AI79-84BP14383, Project 83-359. (Available from BPA, U.S. Department of Energy, P.O. Box 3621, Portland, OR 97208.)

Rosgen, D. L. 1985. A stream classification system. *In*Riparian ecosystems and their management: Reconciling conflicting uses. The First North American Riparian Conference, 16-18 April 1985, Tucson, AZ, p. 91-95. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, General Technical Report RM-120.

Seber, G. A. F. 1982. The estimation of animal abundance. MacMillan, New York, NY. 654 p.

Sekulich, P. T. 1980. The carrying capacity of infertile forest streams for rearing juvenile chinook salmon. Ph.D. dissertation. Univ. Idaho, Moscow, ID.

**QUESTIONS AND ANSWERS**

- Q:
- What is your feeling about the low estimated parr-to-smolt survival based on the NMFS's PIT-tag data?

- A:
- I am surprised at the apparent low survival to Lower Granite Dam.

- Q:
- Could this be attributed to the tagging process?

- A:
- We saw about 30% overwintering survival, which was lower than we expected. Maybe it is worse in the winter than we expected. We need to look at this more carefully; the PIT tag can give us data on groups leaving vs. groups staying, but it is too soon to tell much about this.

- Q:
- Did you have PIT-tag data from Little Goose Dam to compare with data from the other detector sites?

- A:
- Yes; Little Goose Dam, was 30% and McNary Dam was 10% of the Lower Granite Dam values.

- Q:
- You said you were surprised at the overwintering survival—what did you expect?

- A:
- I thought it would not be very different from the steelhead survival, based on size, especially the 1- to 2-year-old fish. This has been about 60% overwintering survival from August smolts. But there are key missing pieces, and the PIT tag may provide that information.

- Q:
- In estimates of smolt carrying capacity, it appears that for some streams (e.g., Bear Valley Creek) you indicate only fair to good production, but they continue as viable producing/spawning areas—might the fish he overwintering somewhere else?

- A:
- In Bear Valley Creek, there are indications of a lot of early outmigration after emergence. The egg-to-parr survival is very different from that in cleaner streams, and therefore some must leave. We do not find them in the summer.

- Q:
- If there is outplanting at a given point, one sees poor outmigration of juveniles. I note great ranges (2.5 to 15%) for egg-to-smolt survival in good habitat—is that the correct range?

- A.
- Yes.

- Q:
- The subbasin plane are using higher survivals than that—do you agree?

- A:
- If you approach the carrying capacity, the literature suggests that this declines to about 6%. In the subbasin plane, the egg-to-smolt survival is indicated as 20-25%.

- Q:
- What if you separate overwintering survival from the egg-to-smolt survival?

- A:
- That would compare favorably with a 20% egg-to-smolt survival at low density.

- Q:
- How would this differ from the estimates from the Yakima River?

- A:
- The Yakima River gets 4% egg-to-smolt survival, based on 50% mortality from the headwaters to Prosser.

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