Steelhead 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. 

Steelhead population spawner abundance is reported here as the number of natural-origin fish estimated on the spawning grounds (spawning naturally). Data were available at the necessary spatial scale for 12 of the 32 Puget Sound steelhead populations.

Our analysis of abundance change over time answers the question:

Has the spawner abundance of each steelhead population changed compared to their abundance in 2007 when Puget Sound steelhead were listed by NOAA Fisheries under the Endangered Species Act (ESA)?

We chose ESA listing in 2007 as the baseline reference period because this date denotes the start of deliberate management effort to improve the status of the population.

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 2007 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, 2022). 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 steelhead 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 steelhead planning targets for abundance and productivity in chapter 4 of the ESA Recovery Plan for the Puget Sound Steelhead Distinct Population Segment (Oncorhynchus mykiss; 2019). Please note that the planning targets for abundance were adopted by NOAA Fisheries and are distinct from recovery targets developed for Vital Sign indicators.

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. 2022. Biological Viability Assessment Update for Pacific Salmon and Steelhead Listed Under the Endangered Species Act: Pacific Northwest.

•           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 steelhead estimated on the spawning grounds in a population
•      Hatchery-origin fish: fish produced by parents spawned in a hatchery
•      Endangered Species Act (ESA): Puget Sound steelhead were listed as Threatened under the ESA in 2007. There are 32 NOAA Fisheries-defined distinct independent populations (DIP; generally known as “populations”) in the Puget Sound steelhead distinct population segment (DPS)
•      MARSS-RWD: multivariate autoregressive state space random walk with drift model, which was the statistical model used in our analyses