Spatial Heterogeneity in Prey Availability, Feeding Success, and Dietary Selectivity for the Threatened Longfin Smelt

Abstract Food availability is a key determinant of the nursery value given habitat for larval and juvenile fishes. Growth, survival, recruitment success are often inter-correlated influenced by prey associated feeding success. This likely true threatened population Longfin Smelt ( Spirinchus thaleichthys ) in San Francisco Estuary (SFE) which has collapsed recent decades along with its preferred prey. In years high precipitation freshwater outflow, found shallow wetland habitats throughout SFE, but variation food these remains unexplored. To examine spatial trophic different rearing habitats, we quantified availability, success, selection captured restored tidal marshes, sloughs, open-water northern southern SFE. Prey abundance varied spatially, densities approximately tenfold greater sloughs ponds relative to habitats. Feeding was positively correlated both fish length density. Larval fed selectively on copepod Eurytemora affinis , larger individuals (> 25 mm total length) exhibiting an ontogenetic diet shift mysid shrimps. Our results suggest that across SFE vary greatly their value, previously unexplored highest foraging Smelt.