Categories:
- Fish/Shellfish Research and Management
- Fish/Shellfish Research and Management -- Fish/Shellfish Research
Published: June 2022
Pages: 40
Publication number: FPA 22-08
Author(s): Adam P. Lindquist, Peter C. Topping, and Joseph H. Anderson
Executive Summary
This report provides the 2021 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 29 through June 25, 2021. During this period, the trap fished 93% of the time. We experienced two multi-day outages, one in mid-February due to heavy lowland snow conditions and one in late February due to the high water due to the melting snow. We estimated the freshwater production (juvenile abundance) of natural origin subyearling Chinook salmon (Table 1).
| Species/Life Stage | Catch | Production (% CV) |
Avg FL (± 1 S.D.) |
Median Migration Date |
|---|---|---|---|---|
| Chinook - Subyearling |
4,743 | 203,830 (16.31%) |
46.37 (±11.67) | 6-Mar |
| Chinook - Yearling | 0 | |||
| Coho - Yearling | 1,670 a | 119.2 (±14.22) | 6-May b | |
| Steelhead - Smolt | 27 | 165.78 (±11.77) | 19-May b | |
| Chum | 80,340 a | 5-Apr b |
a Includes natural-origin and unmarked hatchery-origin fish.
b Median catch date- not adjusted for trap efficiency, serves as an index of migration timing.
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-to-migrant survival of Green River Chinook for the 2021 outmigration (2020 brood) was estimated to be 2.91%, yielding a basin-wide production estimate of 229,194 natural-origin juveniles.
Juvenile migrant Chinook in the Green River are predominantly subyearlings. Outmigration timing of natural origin subyearling Chinook was bimodal. The fry (≤45 mm fork length) represented 82% of the natural subyearling migrants and peaked in the late February. Parr migrants (>45 mm fork length) represented 18% of the total abundance and their migration peaked two times, once in mid-April and again, for several weeks, from mid-May to the first week of June.