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For more information on species & ecosystem science:

Wildlife Science
360-902-2515
wildthing@dfw.wa.gov

Fish Science
360-902-2700
fishpgm@dfw.wa.gov

Habitat Science
360-902-2534
habitatprogram@dfw.wa.gov

 
 

Lead Scientist: Peter Topping

   
  Click on map to enlarge
Click on map to enlarge
   

Freshwater Production and Survival of Puget Sound Salmonids

Green River Juvenile Chinook Evaluation

Project Description

Location: Juvenile trap is located on the mainstem Green River at river mile 34.5, near Auburn, upstream from the mouth of Big Soos Creek (RM 33.7) and the Soos Creek Hatchery (see map)

History: The Green River study was initiated in 2000 with a focus on freshwater production and survival of Chinook salmon but has also provided a description of the abundance and juvenile life history of steelhead as well as coho, chum, and pink salmon in this watershed. Information on Green River Chinook and steelhead contribute to ongoing status evaluations for Puget Sound Chinook and steelhead, both listed as threatened under the Endangered Species Act by the National Marine Fisheries Service. In addition, freshwater production estimates for all species provide a baseline to evaluate impacts of the Additional Water Storage project for Howard Hansen dam. The Water Storage Project will increase water supply to the City of Tacoma and includes a number of operational and mitigation elements that may affect salmon and steelhead production in the Green River basin. In 2011, the Green River juvenile trap results also contributed to the Genetic Mark Recapture program conducted by WDFW Fish Science to validate escapement methodologies in Puget Sound watersheds.

In 2000, WDFW began a long-term project to quantify freshwater production of naturally produced salmon and steelhead from the Green River. Downstream traps were operated on the mainstem Green River and Big Soos Creek (RM 1.5) in 2000. The Big Soos Creek trap was operated for one year and measured the production of naturally-spawned hatchery Chinook. The Green River trap has been operated from 2000 to present.

Objectives

WDFW objectives:

  • The primary objective for this study is to evaluate freshwater production and survival of sub yearling Chinook in the Green River watershed.
  • The secondary for this study are to improve understanding of Puget Sound Chinook life history diversity and to estimate freshwater production of coho, chum, pink salmon and steelhead in the Green River watershed.

Methods

A five-foot screw trap on the main stem Green River is operated continuously from January through July. The trap catches a portion of the downstream migration during this period. Two times a day, downstream fish migrants are collected, identified to species, and counted. Each week, fork lengths are measured for a sub sample of the catch. In order to estimate the total migration, the trap is calibrated with a series of efficiency trials. Efficiency trials are conducted on a daily basis. Fish are marked and released upstream of the trap. Marks include a small fin clip or dye that allows technicians to quickly distinguish them from the rest of the catch. Trap efficiency is estimated based on the numbers of marked fish that are recaptured. Most of the marked fish are recaptured within 24 hours.

Green River screw trap above Highway 18
Click on photo to enlarge

Green River screw trap above Highway 18
  On-board view of Green River screw trap
Click on photo to enlarge
On-board view of Green River screw trap

Key Findings
Click on graphs to enlarge

Green River Wild Chinook Sub-Yearling Production Graph
  • Downstream migrants of Green River Chinook are mostly subyearlings (travel to sea in their first year), although yearling migrants are also caught each year.
  • Green River Chinook freshwater production has declined since trapping began in 2000.
  • Average freshwater production between 2000 and 2012 has been 326,929 migrants per year.
  • Bars show precision of the measure (95% confidence interval). Measures with smaller bars are more precise than those with larger bars.

Green River Coho Production Graph
  • No coho production estimates for 2004, 2005 and 2008 due to suspension of trapping during their peak migration and large amounts of unmarked hatchery fish released during those years.
  • Green River natural-origin coho freshwater production has been variable but without a notable trend since trapping began in 2000.
  • Average production between 2000 and 2012 has been 77,912 migrants per year.
  • Bars show precision of the measure (95% confidence interval). Measures with smaller bars are more precise than those with larger bars.

Green River Wild Steelhead Production Graph
  • No steelhead production estimates for 2004, 2005, 2008 and 2011 due to suspension of trapping during their peak migration and no directed trap efficiency releases for steelhead during those years.
  • Average production between 2000 and 2012 has been 29,405 migrants per year.
  • Bars show precision of the measure (95% confidence interval). Measures with smaller bars are more precise than those with larger bars.

Green River Wild Pink Production Graph
  • No pink production estimates prior to 2006 due to very low catches of pink salmon.
  • Pink salmon fry are caught in even years and correspond with the odd-year spawning returns to the Green River.
  • Green River pink salmon freshwater production has been relatively similar for the 3 outmigration years (2006, 2008, 2010).
  • Average production between 2006 and 2012 has been 9,990,335 migrants per year.
  • Bars show precision of the measure (95% confidence interval). Measures with smaller bars are more precise than those with larger bars.

Data - data is in MS Excel format

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