Upper Skagit Tribe FY 21 Chum Hatch and Emergence Timeline for Natural and Hatchery Origin Fish

The objectives of this study were; 1) assess the time required for natural origin (NO) and

hatchery origin (HO) Chum salmon in the Skagit River and Marblemount hatchery, respectively, to hatch based

on temperature units (TU’s), 2) assess when natural and hatchery origin Chum salmon fry emerge and

outmigrate, 3) assess the size at outmigration of natural fry, and 4) compare temperature regimes in the upper

Skagit River to other areas in the basin during the Skagit River Chum incubation time period. Each objective is

addressed individually below.

1.Time for hatchery and wild chum to hatch

The timing and accumulated temperature units (ATU’s) were assessed for natural origin Chum in 2023

by identifying peak spawning activity from WDFW Chum spawning survey data and identifying peak juvenile

Chum presence by sampling known Chum spawning locations. Collection and sampling of juvenile Chum was

conducted via backpack electrofishing and beach seining in an effort to identify peak juvenile Chum presence to

estimate the time and ATU’s necessary for natural origin Chum to hatch and emerge. Sites for juvenile

collection were based on spawning ground survey results of the previous year to focus on known Chum

spawning locations.

2. When hatchery vs wild chum emerge and outmigrate

Juvenile Chum stocking data was used to compare abundances of natural and hatchery origin juvenile

Chum in the natural environment. The timeline of natural juvenile Chum abundance is discussed above, and

those timelines will be compared to that of hatchery origin juvenile Chum here. In 2022, hatchery Chum

releases began on March 27, peaked on March 27, and concluded on April 20. Compared to natural origin

Chum, it appears in 2022 that Chum stocking followed a similar timeline to when natural juvenile Chum

collections peaked. In 2023, hatchery origin Chum releases began on April 3, peaked on April 26,

and concluded on May 10. In comparison to natural origin juvenile Chum, hatchery origin Chum releases

peaked almost a month after natural origin juvenile Chum abundance was found to be highest.

3. Size differences between natural and hatchery origin chum

Hatchery and natural origin juvenile Chum were measured for fork length (FL) in 2022 and 2023 and

natural origin juvenile Chum were measured for FL in 2023.

4. Compare temperature regimes of spawning areas and hatchery

In 2022 and 2023, temperature loggers were deployed in five locations to assess water temperature

during Chum incubation time periods. Temperature loggers were deployed in two artificial spawning channels

(Taylor and Illabot Channel), two tributaries of the Skagit River (Illabot Creek and Pressentin Creek), and one

in the lower Skagit River near O’toole Creek. Water temperature data from USGS gauging stations was

obtained for the Skagit River at Marblemount (USGS gauge #12181000) and the Sauk River downstream of

Darrington, WA (USGS gauge #12189500). Temperature loggers were deployed from February 10 – May 31 in

2022 and from November 1 – June 10 in 2023.

This will enable the tribe to create a relative abundance curve for chum salmon fry; enabling determination of emergence timing, migration timing (based on relative abundance), and size.