2004 Juvenile Salmonid Production Evaluation Report: Green River, Wenatchee River, and Cedar Creek

Declining salmon populations in the 1980s and 1990s has resulted in the listing of a number of Washington State salmon populations under the Endangered Species Act (ESA). Most of these listings occurred between 1997 and 1999, impacting fisheries and land management over the entire state. To better monitor the status of these listed species and their production trends, the Washington Department of Fish and Wildlife (WDFW) expanded its salmon freshwater production monitoring (smolt monitoring) program. The new sites established during this period included monitoring of lower Columbia steelhead in Cedar Creek in 1998, Puget Sound chinook in the Green River, and upper Columbia spring chinook in the Wenatchee River in 2000. Continuation of this work has relied on funding provided by the Salmon Recovery Funding Board (SRFB). The SRFB has funded smolt monitoring on the Green River, Wenatchee River, and Cedar Creek since 2002. This annual report describes the smolt monitoring activities that occurred on these three streams during the 2004 field season.

Fish were captured using a rotary screw trap on all three streams. The Green River trap, located 55 km upstream of the mouth, was operated from February 3 to July 14, 2004. The focus of this project was to estimate the number of naturally produced Puget Sound chinook originating from this river system. Over this period, 11,185 naturally produced subyearling chinook were captured. As in previous years, the timing distribution of chinook outmigrants was bimodal, with the majority migrating as fry between February and early-to-mid-April. The fork length of these fish averaged less than 45mm. A smaller production component reared upstream of the trap and migrated as smolts from mid-May through June. The fork lengths of these larger migrants averaged between 65 and 90-mm.

Forty four releases of marked chinook were made upstream of the Green River trap to estimate the proportion of downstream migrants captured (trap efficiency). During the February to April fry migration period, trap efficiency averaged 7.7% when flows were between 29 and 43 cms, and 4.0% when flows were above 43 cms. During the later smolt migration period when the migrants were larger, stream discharge had little influence on trap efficiency, averaging 3.0%. Using these efficiency estimates at these flows resulted in an estimated 238,000 naturally produced age 0+ chinook migrated during the trapping period. The 95% confidence interval for this estimate was 187,261 to 289,482 age 0+ migrants. By extrapolating for chinook migrating outside the trapping period, we estimate the total production above the trap site at 271,000.

Accounting for chinook spawning that occurred downstream of the trap and production from Big Soos Creek estimates the total Green River chinook production at 423,000 migrants. Based on the number of parent brood spawners, we estimate the Green River chinook egg-to-migrant survival at 1.9% for the 2003 brood.

A secondary objective for the Green River trapping project is to monitor naturally produced coho and steelhead smolt production. Over the season we captured 3,064 unmarked coho smolts, however, an unknown proportion of these were of hatchery origin. We also captured 239 naturally produced steelhead smolts. Large numbers of hatchery fish were released during the period when most of the naturally produced coho and steelhead were migrating past the smolt trap. Moreover, a large proportion of the hatchery coho were unmarked and indistinguishable from naturally produced migrants. These releases required the suspension of trapping for extended periods to avoid causing mortality to hatchery fish. As a result, we were unable to estimate the natural production of coho and steelhead from the basin.

On the Wenatchee River, screw traps are operated in three locations. A trap on the lower Chiwawa River is used to estimate production of spring chinook from this basin. Another trap below the outlet of Lake Wenatchee estimates sockeye smolt production from the lake. Finally, a third trap is operated low in the system, near the town of Monitor, to measure production from the entire Wenatchee basin. This report presents results from trapping the Monitor site, which is funded by this project.

The Monitor trap, located 9.6 kilometers upstream of the confluence with the Columbia River, was operated from February 13 to July 29. As in previous years, chinook from two broods were captured. Based on differences in life history, yearling chinook (2002 brood) were considered to be spring chinook and subyearling (2003 brood) were considered to be summer chinook. Spring run chinook from the Wenatchee River make up a portion of the endangered Upper Columbia Spring Chinook ESU. The summer run is not listed.

A total of 1,064 naturally produced yearling chinook were captured in 2004. The majority (90%) of the fish were captured by May 17. The majority of subyearlings migrated between May and June. There was some overlap in migration timing, but scale analysis confirmed that the two age classes could be differentiated by fork length, which averaged over 90 mm for yearlings and less than 60 mm for subyearlings.

A total of 24 efficiency tests (10 with yearling hatchery chinook and coho, and 14 with subyearling chinook) were conducted for two trap positions at the Monitor trap site over the season. Recapture rates ranged from 0.00% to 2.33% (0.94% average) for yearling fish and 0.38% to 3.82% (1.46% average) for subyearling chinook. Regression-based models using streamflow were developed to estimate trap efficiency for yearling and subyearling chinook.

An estimated 200,000 yearling Upper Columbia spring chinook migrated from the Wenatchee River in 2004. Due to low trap efficiency and since river discharge was outside the data range used to develop the regression model, confidence intervals were deemed too wide to be useful and not reported.

In addition to yearling spring chinook, we estimated 19 million subyearling chinook, 45,000 wild steelhead smolts, and 8,700 wild coho smolts which were recently reintroduced into the Wenatchee system. A total of 5.8 million sockeye smolts were estimated to have migrated past the Lake Wenatchee trap.

Trapping in a major tributary of the Wenatchee, Chiwawa River, provided some additional insight into spring chinook production and survival from the Wenatchee basin. Of the spring chinook redds created the Wenatchee system in 2001, 30.3% were found in the Chiwawa River subbasin. Yearling smolt production from the Chiwawa subbasin was 64,300, or 32% of the total Wenatchee basin production.

The Cedar Creek trap was operated from March 16 to June 26, 2004. Located 4.0 kilometers upstream from its confluence with the North Fork Lewis River, this trap monitors the steelhead production from Cedar Creek. This stream’s production makes up part of the listed Lower Columbia steelhead ESU. In addition to steelhead, coho and cutthroat productions are measured in the system. ESA listed Lower Columbia chinook are also present in Cedar Creek, but current funding is insufficient to monitor their production.

During the trapping period, a total of 1,080 steelhead pre-smolts and smolts were captured. Steelhead fork length averaged 176 mm, with a declining trend in weekly mean steelhead sizes observed (187 mm to 158 mm fork length) over the season. Of the steelhead captured, 1,067 were marked by fin coloration using a Panjet inoculator and released upstream of the trap to assess trap efficiency. Mark placement was changed weekly and 11 groups were marked. A total of 3,260 +/- 228 (95% CI) steelhead smolts were estimated to have migrated past the Cedar Creek trap using a pooled Peterson estimate.

In addition to steelhead, 34,999 +/- 1,728 (95% CI) naturally produced coho, 1,970 +/- 917 (95% CI) RSI produced coho, and 2,157 +/- 249 (95% CI) cutthroat smolts were estimated to have migrated past the trap. In addition to these estimates, 49,554 chinook, 2,977 coho, and 104 trout fry were captured, as well as 73 cutthroat, 99 rainbow/steelhead, and 100 coho parr.