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Winter-Run Salmon Update – March 2019

This post updates a 7/25/18 post on the status of the endangered winter-run Chinook salmon population of the Sacramento River. Figure 1 is an updated figure showing the influence of water supply conditions on the spawner-recruit relationship of winter-run during the recruits’ first year of life in the Sacramento River. The relationship is also influenced by hatchery contributions that began in 1998 and continue today.1 Other factors, including water temperature control improvement at Shasta Dam and changes to permits and water quality plans (not depicted), are also likely unaccounted-for factors. Figure 2 depicts raw run numbers by spawning year.

What the relationship shows is that there is a strong positive spawner-recruit relationship heavily influenced by water supply conditions and hatchery contributions. The recent estimates of >70% contribution from the hatchery to the population recruits1 reflects the importance of the hatchery role and the underlying problem of declining “wild” spawner contribution. Note that the spawner numbers for 2018 (recruits from critical year 2015 spawners) are as yet unpublished. Hatchery smolt production and releases were doubled in 2015, the third critical year of the 2013-2015 drought.

Figure 1. Spawners versus recruits (spawners three years later) transformed (logx minus 2). Year is spawner year. For example, 2014 is spawning year with 2017 recruits. Color denotes water-year type in spawning year: bold red is critical year, non-bold red is dry year, green is normal year, and blue is wet year. For example, red 13 represents critical water year 2013. Squares around numbers indicate the presence of hatchery contributions (begun in 1998).

Figure 2. Spawning population estimates of adult winter-run salmon in the upper Sacramento River from 1974 to 2017. Source: CDFW.