The spring-run Chinook salmon in Butte Creek had extremely low spawning runs in 2023 and 2024 (Figure 1).

In part, this was because all Sacramento River Valley salmon populations are collapsing due to the direct and indirect effects of the 2020-2022 drought and related management actions, on top of climate change and catastrophic fires.¹ Drought conditions in 2021 and 2022 in the spawning rivers, lower Sacramento River, Delta, Bay, and ocean all contributed to poor juvenile salmon survival.

The poor number of Butte Creek spawners in 2024 is also related to the high pre-spawn mortality of adult salmon in Butte Creek in 2021,² as a result of drought conditions during the winter-spring upstream migration and summer-fall holding and spawning.

Despite the failures of brood years 2020 and 2021, there is optimism for brood year 2022 and its spawning run in 2025 (Figure 2). Water year 2023 was a wet year, with good young survival conditions for juvenile salmon. Though brood year 2022 had only about 3700 spawners, , the returning adults were able to migrate and spawn with minimal stress in a drought year.

The uncertainty that remains is the survival of brood years 2023 and 2024, because of their potential small number of returning spawners in 2026 and 2027. Water year 2024 was a above-normal water year, but it was not without its stresses.³ Early indicators suggest 2025 could be a dry year. The potential for small runs to lead to strong brood years also leaves room for doubt given that four recent years of poor spawners led to poor recruitment (four dots at lower left in Figure 2).

The poor spawner numbers in 2023 and 2024, coupled with the uncertain forecasts for runs in 2025-2027, represent a serious population threat that calls for strong actions to save the species and rebuilding the spawning stock.

Winter Actions

Winter fry-fingerling emigration down lower Butte Creek past the Parrot-Phelan Diversion Dam and the primary screw trap counting station occurs in earnest beginning in mid-December, with a peak in January. The peak in fry emigration (the main element of juvenile salmon production from Butte Creek) occurs during early winter precipitation events. The fry, often still feeding on their yolk sac, leave the cold turbid creek heading for warmer, low-velocity food-rich floodplain waters of the Butte Basin and the Sutter Bypass, and for the tidewater of the Bay-Delta.

Strong winter growth is essential for good survival (good growth rates, and lower rates of starvation and predation). Strong winter growth promotes early smoltification and entry to the ocean. The main success factors in winter are adequate transport flow, access to and from floodplain habitats in the Butte Basin and Sutter Bypass, and low predation rates.

Spring Actions

Pre-smolt, sub-yearling smolts, and yearling smolts emigrate in modest numbers from Butte Creek in spring. These late migrants contribute to population numbers and genetic diversity. Success of these late migrants depends on high transport rates, low water temperatures, minimal diversion to often excessively warm floodplain habitats, minimal entrainment into unscreened water diversions, and minimum flow-through rates from river to floodplain habitats.

Adult spring-run salmon migrate from the Bay to upper Butte Creek in spring. They require adequate flows and water temperatures often not available in drought years, especially in late spring.

Specific Winter and Spring Actions to Consider:

1. Minimize water diversions at Parrot-Phelan Diversion Dam (and other creek diversions). In early winter, prioritize flow in Butte Creek over diversions for waterfowl pond flood-up and rice field decomposition (Figure 3), except in high runoff conditions. In spring, maintain flow in Butte Creek at the highest levels possible for attraction and holding except in early spring flood conditions.
2. Minimize the flow split into Sanborn Slough at bifurcation weir. Do not force more than 30% of Butte Creek flow into Sanborn Slough, which reduces important benefits of floodplain access and inundation.
3. Minimize diversions in Butte Basin and Sutter Bypass.
4. Keep Butte Slough Outfall closed except under Butte Creek flood relief conditions; instead, maximize flow through Butte Basin and Sutter Bypass.
5. In the event of dry-drought conditions, capture juvenile salmon at screw trap locations and Parrot Phelan Screen Bypass, and transport them to the mouth of Butte Creek, Verona, a conservation hatchery, downstream floodplain habitat, or a Bay-Delta location.
6. Maintain adequate transport flows in the lower Yolo Bypass and lower Sacramento River, and into and out of the Delta in winter, to maximize survival to the Bay and ocean.