2003 Juvenile Salmonid Production Evaluation Report: Green River, Wenatchee River, and Cedar Creek

Declining salmon populations in the 1980’s and 1990’s 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. Among the new monitoring sites established during this period, monitoring of lower Columbia steelhead began in Cedar Creek in 1998. WDFW also began monitoring listed 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 2003 field season.

Fish were captured using a rotary screw trap on all three streams. On the Green River, the trap, located 55 km upstream of the mouth, was operated from February 3 to July 13, 2003. The focus of this project was to monitor the production of naturally produced Puget Sound chinook from this river system. Over this period, 17,792 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 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 late May through June. The fork lengths of these larger migrants averaged between 70 and 82mm.

Twenty releases of marked chinook were made upstream of the Green River trap to estimate the proportion of downstream migrants captured (trap efficiency). Trap efficiency averaged 12.6% when flows were between 8.3 and 57 cms, and 1.0% when flows were above 57 cms. Using these efficiency estimates at these flows resulted in an estimated 535,000 naturally produced age 0 chinook migrated during the trapping period. By extrapolating for chinook migrating outside the trapping period, we estimate the total production above the trap site at 674,000. The precision of the estimate was very poor as a result of the very low efficiencies measured at higher stream flows, which primarily occurred during the fry migration period. Precision of the smolt estimate of 14,800 migrants was much better. Accounting for chinook spawning that occurred downstream of the trap and production from Big Soos Creek estimates the total Green River chinook production at 1.36 million migrants. Based on the number of parent brood spawners, we estimate the Green River chinook egg-to-migrant survival at 4.0% for the 2002 brood.

In addition to chinook, we estimated 156,000 naturally produced coho smolts and 12,600 naturally produced steelhead smolts. A large number of unmarked hatchery produced coho were released upstream of the trap. These fish were indistinguishable from the naturally produced coho smolts, making the estimation of wild coho difficult. As a result, the precision of the estimate could not be assessed and our confidence in the coho estimate is low.

We also estimated the survival to the trap for several hatchery releases of steelhead, coho, and chinook. Survival estimates ranged from 0.1% for Keta Creek steelhead to 33.9% for the combination of Icy Creek, Palmer, and Flaming Geyser steelhead releases. We estimated Keta coho smolts survived at 21% and Icy Creek yearling chinook at 10.5%.

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 21 to July 30. As in previous years, chinook from two broods were captured. Based on differences in life history, yearling chinook (2001 brood) were considered to be spring chinook and subyearling (2002 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 1,619 naturally produced yearling chinook were captured in 2003. The majority (90%) of the fish were captured by May 20. 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 nearly 50 mm for subyearlings.

A total of 30 efficiency tests (14 with yearling hatchery coho and sockeye and 16 with subyearling chinook) were conducted at the Monitor trap site over the season. Recapture rates ranged from 0.00% to 3.02% (0.79% average) for yearling fish and 0.24% to 2.73% (1.86% average) for subyearling chinook. A regression-based model using streamflow was developed to estimate trap efficiency for yearling chinook based on the result from tests conducted with yearling coho and sockeye. Two trap positions were operated during the 2003 season. Results from the 2003 efficiency tests were used to model trap efficiency for the trap position used most of the time. However, these tests along with trials from previous years were incorporated in modeling trap efficiency when the trap was fished in the �"out” position.

An estimated 319,000 yearling Upper Columbia spring chinook migrated from the Wenatchee River in 2003. 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 45 million subyearling chinook, 44,000 wild steelhead smolts, and 37,000 wild coho smolts which were recently reintroduced into the Wenatchee system. A total of 5.4 milllion 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, 49% were found in the Chiwawa River subbasin. Yet the Chiwawa produced an estimated 248,000 yearling smolts or 75% of the spring chinook production from the entire Wenatchee system. Assuming the estimates of smolt production and redd distribution are accurate, the Chiwawa is extremely productive relative to other spring chinook streams such as the Icicle, Peshastin, and Ingalls subbasins. This is not surprising since habitat quality in the Chiwawa subbasin is considered much better than in these other streams.

The Cedar Creek trap was operated from March 19 to June 26, 2003. 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 582 steelhead pre-smolts and smolts were captured. Steelhead fork length averaged 176 mm, with a declining trend in weekly mean steelhead sizes observed (202 mm to 158 mm FL) over the season. Of the steelhead captured, 561 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 13 groups were marked. Trap efficiency data was analyzed and population estimates were made using Stratified Population Analysis Software. A bootstrap methodology was used to estimate the variance of migration estimates. A total of 1,727 +/- 193 (95% CI) steelhead smolts migrated past the Cedar Creek trap in 2003.

In addition to steelhead, 35,095 +/- 2,481 (95% CI) naturally produced coho, 8,476 +/- 1,639 (95% CI) hatchery coho, and 2,548 +/- 321 (95% CI) cutthroat smolts are estimated to have migrated past the trap. In addition to these estimates, 361 chinook, 1,026 coho, and 65 trout fry were captured, as well as 27 cutthroat, 47 rainbow/steelhead, and 101 coho parr. Numerous non-salmonid species were also captured including western brook lamprey and Pacific lamprey.

Considerable effort was made in the Cedar Creek project to evaluate the conditions that researchers must assume to make fish population estimates using this approach. Results from these tests indicate the estimates are unbiased and were deemed to have sufficient precision for management and research use.