Linking Flow Regime Metrics to Spawning Migration Behavior of Threatened Green Sturgeon: Implications for Water Management in Regulated Rivers

ABSTRACT

Flow regime alteration is among the most pervasive threats to freshwater ecosystems globally, and migratory species are particularly vulnerable to these impacts. Despite this, specific aspects of flow regimes that shape spawning migrations remain poorly understood for most threatened species. Functional flow frameworks offer a promising tool for identifying ecologically meaningful flow targets, especially for threatened species, like the Sacramento River population of green sturgeon ( Acipenser medirostris ). Aspects of this species' life‐history are highly flow‐dependent, and its migratory corridor overlaps with heavily regulated waterways, making it an interesting case study for understanding how flow dynamics shape migratory behavior. We used an acoustic telemetry dataset (2007–2022) to explore how river flows impact spawning migration behavior of green sturgeon ( n  = 220) through the California Sacramento‐San Joaquin Delta. A cluster analysis identified three migration patterns: mainstem Sacramento River routing, Delta routing, and incomplete migrants. Increased discharge during migration was positively associated with migration success and fish selecting the Sacramento River, with a threshold near 10,000 cfs, below which fish frequently routed through the Delta where water diversions and altered hydrology may pose additional risks. Higher pre‐migration temperatures were positively correlated with greater Delta use and strongly negatively correlated with migration success. Functional flow metrics related to wet season magnitude, wet season timing, and spring recession characteristics were the strongest predictors of route selection, migration success, and duration. Overall, this study demonstrates how functional flow frameworks combined with telemetry can uncover critical linkages between flow dynamics and spawning migrations, with direct implications for management in regulated rivers.