Modeling Delta Smelt Distribution for Hypothesized Swimming Behaviors

Delta Smelt, Hypomesus transpacificus, is an endangered pelagic fish native to the San Francisco Estuary. The distribution of Smelt in estuary shifts landward from low-salinity habitat freshwater before spawning. This spawning migration often coincides with first substantial inflow during winter. To accomplish this shift distribution, are believed use tides by swimming faster-moving currents flood and then repositioning themselves slower-moving reduce seaward movement on ebb tides. Studies have hypothesized that behavior period influenced environmental conditions such as salinity turbidity. details these behaviors—including extent which flows, salinity, turbidity affect behaviors distributions—are uncertain. management interest because increase observed counts at South water-export facilities has coincided roughly many years. In study, we investigated a range using three-dimensional particle-tracking model for water year 2002 migration, compared predicted distributions inferred catch data. Our goal was improve understanding influence and, ultimately, develop modeling tool help agencies identify associated entrainment losses. Predictions varied greatly among behaviors. Without swimming, would be rapidly transported Suisun Bay, while continuous tidal move them deep into interior Delta. These simple turbidity-driven inconsistent observations, more complex rules allowed improved predictions.