Fish/Shellfish Research and Management - Wild Salmon Population Monitoring
Date Published: August 2008
Number of Pages: 136
Publication Number: FPA 08-05
Author(s): Pete Topping, and Lori Kishimoto, WDFW Fish Science Division and Josua Holowatz, Dan Rawding and Michelle Groesbeck WDFW Fish Program, Region 5
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. The SRFB has funded smolt monitoring on the Green River and Cedar Creek since 2002, and included the Dungeness River in 2006. This annual report describes the smolt monitoring activities that occurred on these three streams during the 2006 field season.
The Green River screw trap, located 55-km upstream of the mouth, was operated from January 24, through July 17, 2006. The focus of this project is to estimate the number of naturallyproduced Puget Sound Chinook originating from this river system. Over this period, 3,528 naturally-produced sub-yearling Chinook were captured. As in previous years, the timing distribution of Chinook out-migrants were bimodal. In 2006, early fry migrants (January and mid-April) were outnumbered by later parr migrants (May through July), at 31% and 69%, respectively. The fork lengths measured on captured fry averaged 40-mm, while later parr migrants averaged between 74 and 94-mm.
In total, 102 marked Chinook groups were released upstream of the Green River trap to estimate the proportion of downstream migrants captured (trap efficiency). These groups were pooled into 18 strata, to increase confidence in the abundance estimates. Using these efficiency rates, an estimated 102,278 naturally-produced Chinook migrated during the trapping period. The 95% confidence interval for this estimate was 78,330 to 131,910 fry. Based on the number of parent brood spawners, the Green River Chinook egg-to-migrant survival was estimated at 1.47% for the 2005 brood.
A secondary objective for the Green River trapping project is to monitor and estimate natural production for the other salmonids migrating from the system. This was accomplished for coho and steelhead smolts, as well as chum and pink fry.
In total 1,422 unmarked coho smolts were capture, with an average fork length of 106.9-mm. Production of natural coho from above the trap was estimated at 31,460 smolts, ± 10,317 (95% CI).
Over the season 390 natural-origin steelhead smolts were captured, with an average fork length of 151.1-mm. Production of natural steelhead from above the trap was estimated at 16,748 smolts.
In addition 32,308 chum fry and 294.293 pink fry were captured. Production was estimated at 914,285 chum fry ( ± 258,852 , at 95% CI), and over 7-million pink fry.
The Dungeness River screw trap was operated from February 2, through August 17, located just 0.5-RKm 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 6,533 naturallyproduced 0+ Chinook migrants. As observed at other study sites, the timing distribution of Chinook out-migrants were bimodal, with an early migration as fry in February through mid- April, and the rest migrating as parr between May and August (57% fry, 43% parr). 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 57.9-mm.
A total of 85 groups of marked Chinook were released upstream of the trap to measure trap efficiency. These tests were separated into three groups based on trap position; these three groups were further arranged into 29 strata based on similar environmental conditions, to increase confidence in our estimates. Recapture rates averaged 9.86% for the combined groups and ranged from 1.3% to 27.9%. Over the season, 124,928 naturally-produced 0+ Chinook were estimated to migrate past the trap, with a 95% confidence interval of 95,362 to 154,494 Chinook.
In addition, this project also monitors natural-origin coho, chum and steelhead smolt production. A total of 1,964 coho smolts were captured; this included 170 of the 5,663 naturally-produced upper caudal (UC) fin-clipped coho released by the Jamestown S’Klallam Tribe from their weir on Matriotti Creek, a tributary to the Dungeness River. These marked fish were used to estimate the proportion of marked fish recaptured in the traps, 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 43,888 smolts, with a 95% confidence interval of 37,860 to 49,916 smolts.
A total of 425 naturally-produced steelhead smolts were captured over the season. As with the coho, the steelhead migrating from Matriotti Creek were UC-marked (497 total). Of these, only 29 were recaptured at the trap. This resulted in a recapture rate of 5.8%, which estimates natural steelhead production at 6,158 smolts ± 2,037 (95% CI).
In addition, 38 out of the 10,500 ad-marked hatchery steelhead released from the Dungeness Hatchery were captured The resulting low capture rate (0.36%) of hatchery fish indicates that heavy otter predation during rearing may have reduced the actual number released.
The chum migration was already underway when trapping began. A total of 28,457 chum fry were captured over the season, with an estimated missed catch of 4,285 fry. Weekly mean sizes ranged from 37.4-mm to 52.9-mm over the season, and averaged 40.1-mm.
A total of 12 marked chum fry groups were released upstream of the trap to measure trap efficiency from mid-March to early May. As with Chinook, these groups were combined into ten strata, resulted in a production estimate of 194,721 fry past the trap ( ± 31,354 , at 95% CI).
The pink fry migration was just starting when trapping began. For the season, an estimated 92,489 fry were captured, with an additional 19,000 fry estimated during periods when trapping was suspended. Weekly mean sizes ranged 32-mm to 43-mm, and averaged 34-mm over the season. A total of five mark-efficiency groups were released; two groups were combined to create four strata. Application of these rates to the expanded catch estimates a production of 696,642 fry ± 253,492 (95% CI).
The Cedar Creek screw trap was operated from February 20, through June 27, 2006. Located 4.0-Rkm 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 787 steelhead trout pre-smolts and smolts were captured. Steelhead smolt fork lengths averaged 175.6-mm, with a declining trend in weekly mean sizes observed (186-mm to 163-mm) over the season. A total of 756 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 14 mark groups released. A total of 1,914 ± 196 (95% CI) steelhead trout were estimated to have migrated past the Cedar Creek trap using a pooled Peterson estimate.
In addition to steelhead, 43,008 ± 1,008 (95% CI) naturally-produced coho smolts, 7,584 ± 348 (95% CI) RSI-produced coho, and 5,720 ± 458 (95% CI) cutthroat trout were estimated to have migrated past the trap. The trap also captured a total of 1,339 Chinook fry, 101 cutthroat, 42 rainbow/steelhead, and 72 coho parr over the season.