Categories:
- Fish/Shellfish Research and Management
- Fish/Shellfish Research and Management -- Management and Conservation
Published: January 2020
Pages: 62
Publication number: FPA 20-01
Author(s): Peter C. Topping and Joseph H. Anderson
Executive Summary
This report provides the 2018 results from the juvenile salmonid monitoring study conducted on the Green River in central Puget Sound, Washington. The primary objective of this study was to estimate the juvenile abundance of natural-origin Chinook salmon in the Green River. Additional objectives were to estimate the number of juvenile migrants and life history characteristics of other salmonid species. Juvenile salmonids were captured in a five-foot screw trap located at river mile 34.5 (55 rkm). Catch was expanded to a total migration estimate using a time-stratified approach that relied on release and recapture of marked fish throughout the outmigration period.
The trap was operated from January 18 through June 22, 2018. During this period, the trap fished 92% of the time. We estimated the freshwater production (juvenile abundance) of Chinook (subyearling), coho, pink and steelhead. (Table 1).
Table 1. Catch, freshwater production, fork length (mm), and out-migration timing of natural-origin juvenile salmonids caught in the Green River screw trap in 2018. Data represent freshwater production above the juvenile trap, which is located at river mile 34.5
| Species/Life Stage |
Catch | Production (% CV) |
Avg Fork Length (± 1 S.D.) |
Median Migration Date |
|---|---|---|---|---|
| Chinook -- Subyrlg | 5,086a | 315,886 (19.90%) | 58.21(±21.80)a | 19-Feb |
| Chinook -- Yrlg | 6 | |||
| Coho -- Yrlg | 1,271 | 58,011 (21.75%) | 105.21(± 10.66) | 7-May |
| Steelhead -- Smolt | 133 | 6,025 (21.90%) | 168.02(±17.37) | 12-Mayb |
| Chum | 73,577c | 6-Aprb |
- This figure includes hatchery and natural origin fish.
- This catch is median catch date which is not adjusted for trap efficiency and therefore serves as an index of migration timing.
- Unable to distinguish between natural origin and hatchery production.
Chinook salmon spawn above and below the juvenile trap. A basin-wide production estimate was derived by applying estimated survival above the trap to spawning below the trap. Egg-tomigrant survival of Green River Chinook for the 2018 outmigration (2017 brood) was estimated to be 2.32%, yielding a basin-wide production estimate of 349,324 natural origin juveniles. Unlike previous years, there was no production from Soos Creek because no adult Chinook were released above the hatchery rack in the fall of 2017.
Juvenile migrant Chinook in the Green River are predominantly subyearlings. Outmigration timing of natural origin subyearling Chinook was multimodal. The fry (≤ 45 mm fork length) represented 87% of the natural subyearling migrants and peaked in early-February. Parr migrants (>45 mm fork length) represented 13% of the migration and peaked in mid-May and again in mid-June