Chinook salmon spawner abundance data are collected annually by WDFW and tribal co-manager staff as part of baseline monitoring and data collection efforts.

Washington Department of Fish and Wildlife (WDFW), Salmon Population Indicators (SPi) abundance data

Northwest Fisheries Science Center. 2015. Status review update for Pacific salmon and steelhead listed under the Endangered Species Act: Pacific Northwest.

Biologists typically estimate annual spawner abundance by counting the number of redds (gravel nests) in a river each year. Redds are counted by walking the stream or from boats or aircraft. In many populations, some hatchery-origin salmon are present on the spawning grounds along with natural-origin salmon, complicating the estimates of natural-origin abundance. The proportions of spawners that were of natural versus hatchery origin are typically estimated based on the composition of carcasses of each origin. These proportions are applied to the total spawning population to estimate the number of natural-origin versus hatchery-origin spawners. 

Chinook salmon population spawner abundance is reported here as the number of natural-origin fish estimated on the spawning grounds (spawning naturally) for all populations except in the Skagit River basin (Suiattle, Cascade, Upper Sauk, Lower Sauk, Upper Skagit, and Lower Skagit populations), for which total spawner abundance is reported. However, the proportion of hatchery-origin, naturally-spawning fish in these populations is expected to have been consistently low (e.g., < 5 percent) since 1999 based on information and estimated values in the Marblemount Hatchery Spring Chinook Hatchery and Genetic Management Plan (HGMP) and that hatchery's Summer Chinook HGMP. Thus, we chose to use the available data for total number of naturally-spawning Chinook salmon in these analyses. We will continue to try to gather natural-origin, naturally-spawning Chinook salmon abundance data from these populations for future analyses.

Our analysis of abundance change over time answers the question:

Has the spawner abundance of each Chinook salmon population changed compared to their abundance in 1999 when Puget Sound Chinook were listed by NOAA Fisheries under the Endangered Species Act (ESA)?

We chose ESA listing in 1999 as the baseline reference period because this date denotes the start of deliberate management efforts to improve the status of the population. It should be noted that the 1999-2003 period was one of relatively favorable ocean conditions (i.e., a “cool” PDO phase) for Puget Sound Chinook salmon, where we would expect better marine survival than during a warm PDO phase.

In this trend evaluation, we fit a multivariate autoregressive state space random walk with drift (MARSS-RWD) model to the log of population spawner abundance data for all populations from 1999 to 2023. The model structure was identical to that used by NOAA Fisheries’ Northwest Fisheries Science Center in its 5-year status review with a few exceptions (Northwest Fisheries Science Center, 2015). The slope of each population's smoothed abundance values was converted to percent change per year. If data were not available during these periods for a given population, data from the first or most recent years with available data were used.

To assess each population’s spawner abundance levels, we compared their recent 5-year geometric mean (“geomean”) of smoothed abundance data from the MARSS-RWD model to their low productivity planning target for abundance to get a percent of target abundance. Planning targets for Chinook abundance have been estimated for both low and high productivity scenarios. At low productivity, the population needs to be larger compared to that at high productivity in order to survive and be resilient to poorer habitat and environmental conditions, changes, and catastrophes. We evaluated the recent 5-year geomeans relative to the low productivity planning targets because the populations are thought to be in a low productivity phase and it is a more conservative assessment. Find more information on Chinook planning targets for abundance and productivity in chapter four of the “Technical Recovery Criteria and Goals for Puget Sound Chinook Salmon of the Puget Sound Salmon Recovery Plan (2007).” Please note that the planning targets for abundance were adopted by NOAA Fisheries and are distinct from the Vital Sign indicator recovery target.

For more information about the methods used for this indicator, please see the Status and Trends Analysis of Salmon Abundance Data methods report.

References:

Northwest Fisheries Science Center. 2015. Status review update for Pacific salmon and steelhead listed under the Endangered Species Act: Pacific Northwest.

National Marine Fisheries Service, Shared Strategy for Puget Sound. 2007. Puget Sound Salmon Recovery Plan, Volume 1.

• Natural-origin fish: fish produced by parents spawning in natural environments (not in a hatchery)
• Natural-origin adult fish on the spawning ground: fish produced by parents spawning in natural environments that themselves returned to spawn in a natural environment
• Population spawner abundance: number of natural-origin Chinook salmon estimated on the spawning grounds in a population (for instance, the North Fork Nooksack River)
• Hatchery-origin fish: fish produced by parents spawned in a hatchery
• Endangered Species Act (ESA): Puget Sound Chinook salmon were listed as Threatened under the ESA in 1999. There are 22 NOAA Fisheries-defined distinct independent populations (DIP; generally known as “populations”) in the Puget Sound Chinook evolutionarily significant unit (ESU)
• MARSS-RWD: multivariate autoregressive state space random walk with drift model, which was the statistical model used in our analyses