Detection of Threatened Delta Smelt in the Gut Contents of the Invasive Mississippi Silverside in the San Francisco Estuary Using TaqMan Assays

Abstract

In the San Francisco Estuary, predation of the threatened delta smelt Hypomesus transpacificus by the invasive Mississippi silverside Menidia audens has been hypothesized but unconfirmed in the wild due to difficulties in reliably identifying egg or larval fish remains in gut contents. This study describes the use of TaqMan assays to examine the gut contents of wild Mississippi silversides for the presence of delta smelt DNA. The species‐specific delta smelt assay was found to be highly sensitive and, in feeding trial experiments, capable of detecting delta smelt DNA in Mississippi silverside gut contents up to 36 h postingestion for some individuals. A substantial percentage (41%) of the 37 Mississippi silversides caught in the wild with midchannel trawling were positive for delta smelt DNA in their gut contents. Conversely, none of the 614 Mississippi silversides caught in the wild in nearshore beach seining contained delta smelt DNA in their gut contents.

Predation on Fishes in the Sacramento-San Joaquin Delta: Current Knowledge and Future Directions

“…Sixth, it is well known that even non-predatory fishes will consume both fish eggs and larvae, yet these resources typically are only available for weeks or a month, and are frequently missed in dietary studies. It is possible that some species such as Mississippi Silversides may prey significantly on eggs or larvae of species such as Delta Smelt (Baerwald et al 2012). Finally, recent DNA analyses of stomach contents of Delta fish predators may allow a species' diet to be quantified accurately and quickly (Baerwald et al 2012;Brandl et al 2015, unreferenced, see "Notes";Smith et al 2015), but cannot quantify the energetic importance of a given prey to the predator, and, concomitantly, the number of prey eaten by an individual predator.…”

A real-time PCR assay to estimate invertebrate and fish predation on anchovy eggs in the Bay of Biscay

“…Fox et al, 2005Fox et al, , 2008Minegishi et al, 2009). Examples of real-time PCR application to characterize marine animals diet include copepods (Nejstgaard et al, 2008;Troedsson et al, 2009;Durbin et al, 2008Durbin et al, , 2011, decapods (Töbe et al, 2010;Albaina et al, 2010Albaina et al, , 2012Cleary et al, 2012;Redd et al, 2014), fishes Fox et al, 2012;Baerwald et al, 2012) and mammals (Bowles et al, 2011).…”

A Conceptual Model of the Aquatic Food Web of the Upper San Francisco Estuary

“…Abundant larvae and juveniles are likely to provide a major source of food for other fishes such as striped bass, largemouth bass, and catfish. The alien Mississippi silversides may be an important predator of Delta smelt eggs and larvae, because of the foraging characteristics of silversides and overlap in distribution with presumed smelt spawning habitat, but no quantitative data exist (Bennett and Moyle 1996;Bennett 2005;Baerwald et al 2012). Linkage 6.12 shows the periodic but poorly understood availability of larval fish to planktivorous fish.…”