Examination of Predation on Early Life Stage Delta Smelt in the San Francisco Estuary Using DNA Diet Analysis

Abstract

We examined predation by nonnative Mississippi Silversides Menidia audens, other small fishes, and invertebrates on the early life stages of the endangered Delta Smelt Hypomesus transpacificus, which is endemic to the Sacramento–San Joaquin Delta in California. Mississippi Silversides and other putative predators were collected primarily via boat electrofishing in the northern reaches of the upper San Francisco Estuary, an area targeted for substantial tidal wetland restoration to enhance habitat for Delta Smelt and other endangered fishes. Predators’ digestive tracts were removed and analyzed for the presence of Delta Smelt DNA by using quantitative PCR TaqMan assays. Across all sites, 69 of 550 Mississippi Silversides tested positive for Delta Smelt DNA. The number of sampled Mississippi Silversides that were positive for Delta Smelt DNA was significantly greater in offshore habitats than in nearshore habitats. Delta Smelt DNA detection data indicated that a wide variety of other species were also predators of Delta Smelt. Additionally, we used generalized linear modeling to analyze the relationship between Delta Smelt predation detections in Mississippi Silversides and concurrently collected habitat parameters. Turbidity was identified as a significant predictor of predation, as Delta Smelt DNA was detected more often in Mississippi Silverside samples from clearer water. These results suggest that restoration efforts designed to increase turbidity in the estuary may be beneficial in reducing Mississippi Silversides’ predatory impacts on Delta Smelt.Received August 24, 2015; accepted February 3, 2016 Published online June 15, 2016

Consequences of temperature and temperature variability on swimming activity, group structure, and predation of endangered delta smelt

“…Testable study ques- Mahardja, Conrad, Lusher, & Schreier, 2016;Schreier, Baerwald, Conrad, Schumer, & May, 2016) and may compete for similar resources; therefore, Mississippi silversides are likely to be susceptible to similar predation pressures as delta smelt. Testable study ques- Mahardja, Conrad, Lusher, & Schreier, 2016;Schreier, Baerwald, Conrad, Schumer, & May, 2016) and may compete for similar resources; therefore, Mississippi silversides are likely to be susceptible to similar predation pressures as delta smelt.…”

“…The overall goal of this study was to characterise individual and group movement behaviour of delta smelt and determine if high temperature increases predation vulnerability. Testable study ques- Mahardja, Conrad, Lusher, & Schreier, 2016;Schreier, Baerwald, Conrad, Schumer, & May, 2016) and may compete for similar resources; therefore, Mississippi silversides are likely to be susceptible to similar predation pressures as delta smelt. The present study tested chronic and acute exposures to 21°C, a moderate thermal challenge well within tolerance limits (Davis et al, 2019;Jeffries et al, 2016;Komoroske et al, 2014) of fishes that will provide relevant information to current and future habitat conditions.…”

Individual‐Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary III. Effects of Entrainment Mortality and Changes in Prey

“…For example, Mississippi Silversides Menidia beryllina prey upon Delta Smelt larvae (Schreier et al. ) and have increased greatly in abundance in shallow waters (Bennett ), but they are not quantitatively sampled by any monitoring program. The most likely predators on juvenile and adult Delta Smelt are Striped Bass (Nobriga et al.…”

“…However, information is lacking on fine-scale population densities and feeding rates of likely predators of Delta Smelt (Nobriga et al 2013). For example, Mississippi Silversides Menidia beryllina prey upon Delta Smelt larvae (Schreier et al 2016) and have increased greatly in abundance in shallow waters (Bennett 2005), but they are not quantitatively sampled by any monitoring program. The most likely predators on juvenile and adult Delta Smelt are Striped Bass (Nobriga et al 2013) and Largemouth Bass Micropterus salmoides.…”

Is Extinction Inevitable for Delta Smelt and Longfin Smelt? An Opinion and Recommendations for Recovery

“…Striped Bass diet studies have revealed that very few smelt are eaten, although DNA techniques have identified Delta Smelt DNA in the stomachs of many species, including Striped Bass (Baerwald et al 2012;Schreier et al 2016). Predation by large predators does not (Grossman 2016).…”