2005 Juvenile Salmonid Production Evaluation Report: Green River, Dungeness River and Cedar Creek

Declining salmon populations in the 1980s and 1990s 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 freshwater salmon production monitoring (smolt monitoring) program. The new sites established during this period included Cedar Creek in 1998 to monitor Lower Columbia River steelhead, the Green River in 2000 and the Dungeness River in 2005 to monitor Puget Sound chinook. Funding for the Dungeness Chinook Project was made possible through short-term (one-year) reserves from the Agency General Fund monies. Continuation of this work has relied on funding by the Salmon Recovery Funding Board (SRFB). The SRFB has funded smolt monitoring on the Green River and Cedar Creek since 2002. This annual report describes the smolt monitoring activities that occurred on these three streams during the 2005 field season.

Green River
The Green River screw trap, located 55-km upstream of the mouth, was operated from January 10, earlier than in previous seasons in order to capture the start of the migration, through July 15, 2005. The focus of this project is to estimate the number of naturally-produced Puget Sound chinook originating from this river system. Over this period, 18,579 naturally-produced subyearling chinook were captured. As in previous years, the timing distribution of chinook outmigrants were bimodal, with the majority migrating as fry between January and mid-April. The fork lengths measured on captured fry averaged 40-mm. A smaller production component reared upstream of the trap and migrated as smolts from mid-May through the end of the season. Fork lengths measured on these later migrants averaged between 76 and 92-mm.

Thirty-three marked chinook groups were released upstream of the Green River trap to estimate the proportion of downstream migrants captured (trap efficiency). Using these efficiency rates, an estimated 465,531 naturally-produced age 0+ chinook migrated during the trapping period. The 95% confidence interval for this estimate was 393,931 to 537,131 age 0+ migrants.

Accounting for chinook spawning that occurred downstream of the trap and production from Big Soos Creek estimates the total Green River chinook production at 607,000 migrants. Based on the number of parent brood spawners, we estimate the Green River chinook egg-to-migrant survival at 2.2% for the 2004 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 834 unmarked coho smolts and a total of 260 steelhead smolts. Unknown portions of both species were of hatchery origin, as a large proportion of hatchery coho were released unmarked, indistinguishable from naturallyproduced migrants. Also, large numbers of hatchery fish were released during the period when most naturally-produced coho would be migrating past the smolt trap; trapping was suspended for extended periods after these releases to avoid mortalities due to overcrowding in the live box. As a result, we were unable to estimate natural production of coho and steelhead from the basin.

Dungeness River
The Dungeness River screw trap was operated from March 8 through August 5, located just 1.6- km upstream from the mouth of the river. The focus of this project is to monitor annual production of Dungeness chinook, which are part of the Puget Sound Chinook Evolutionarily Significant Unit (ESU). Over the trapping season, we captured a total of 9,323 naturally-produced 0+ chinook migrants. As observed at other study sites, the timing distribution of chinook out-migrants were bimodal, with and early migration as fry in March-April, and the majority migrating as smolts between May and August. Chinook fork lengths averaged less than 40-mm for the fry component, and greater than 80-mm for smolts. The season average fork length was 69.1-mm.

A total of 47 marked chinook groups were released upstream of the trap to measure trap efficiency. These groups were rearranged into 14 strata, based on flow condition, to increase confidence in our estimates. Recapture rates averaged 14.5% for the combined groups and ranged from 9.8% to 28.6%. There was no apparent relationship between trap efficiency and flow.

Over the season, we estimated 69,881 naturally-produced 0+ chinook migrated past the trap, with a 95% confidence interval of 66,754 to 73,007 chinook. Because the fry migration was well underway when trapping began, we selected a migration start date of February 15. Extrapolating the migration back to this date estimates an additional 2,232 chinook fry would have migrated before trapping began. Total production in 2005 is estimated at 72,113 naturally-produced 0+ chinook.

In addition, this project also monitors naturally-produced coho, chum and steelhead smolt production. We captured a total of 3,136 coho smolts, which includes 432 of the total 7,880 naturally-produced fin-clipped coho released by the Jamestown S’Klallam Tribe from their weir on Matriotti Creek, a tributary to the Dungeness River. We used these marked fish as the basis of our capture efficiency estimates. The resulting catch estimates the coho capture rate at 5.5%, assuming all of the marked Matriotti coho survived to pass the screw trap. Applying this efficiency to the catch results in a production estimate of 57,096 smolts, with a 95% confidence interval of 52,242 to 61,950 smolts.

We captured a total of 329 naturally-produced steelhead smolts and 587 steelhead parr, and 365 out of the 9,825 ad-marked hatchery steelhead released from the Dungeness Hatchery. Using the proportion of hatchery fish caught to estimate the steelhead capture rate (4.5%), we estimate natural-production at 9,192 smolts.

The chum migration was already underway when trapping began. We captured a total of 49,227 chum fry over the season, with an estimated missed catch of 1,669 fry. Weekly mean sizes ranged from 33-mm to 55-mm over the season, and averaged 38.4-mm. Trap efficiency for chum averaged 11.0%, resulting in a production estimate of 484,525 fry, with a 95% confidence interval of 420,220 to 548,829 fry. In addition, we estimated 13,952 chum fry migrated before trapping began, for a total basin production estimate of 498,477

Cedar Creek
The Cedar Creek screw trap was operated from March 11 through June 26, 2005. Located 4.0 km 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 trout pre-smolts and smolts were captured. Steelhead smolt fork lengths averaged 176.2-mm, with a declining trend in weekly mean sizes observed (188-mm to 156-mm) over the season. A total of 635 steelhead trout were marked by fin coloration using a Panjet inoculator and were released upstream of the trap to assess trap efficiency. Mark placement changed weekly, with 12 mark groups released. A total of 2,374 ± 420 (95% CI) steelhead trout were estimated to have migrated past the Cedar Creek trap using a pooled Peterson estimate.

In addition to steelhead, 58,921 ± 3,081 (95% CI) naturally-produced coho smolts, 9,151 ± 1,785 (95% CI) RSI-produced coho, and 5,085 ± 1,064 (95% CI) cutthroat trout were estimated to have migrated past the trap. The trap also captured a total of