Invasion
Invasion Description
1st Record: Manteca/CA/San Joaquin River (1971, Cohen and Carlton 1995; Dill and Cordone 1995). 1st nontidal record CA/Clear Lake, Lower and Upper Blue Lakes (1967, 9,000 fish planted for insect control, Cohen and Carlton 1995; Dill and Cordone 1995).
Geographic Extent
CA/Sacramento-San Joaquin Delta (1971, Cohen and Carlton 1995; Dill and Cordone 1996); Brown and Michniuk 2007); CA/Suisun Marsh (1999, Matern et al. 2002); Coon Island/CA/Napa River (2004, Cohen and Bollens 2008, 38°11’36’’N; 122°19’09’’W), Bull Island/CA/Napa River (2004, Cohen and Bollens 2008, 38°13’03’’N; 122° 18’ 17’’ W) and Pond 2A/CA/Napa River (2004, Cohen and Bollens 2008, 38°09’09’’N; 122°19’10’’W). Alviso/CA/Alviso Slough Salt Ponds, south San Francisco Bay (Mehia et al. 2008); Nontidal records CA/Clear Lake, Lower and Upper Blue Lakes (1967, 9,000 fish planted for insect control, Cohen and Carlton 1995; Dill and Cordone 1995); Alameda County/San Francisco Bay watershed (1969, Cohen and Carlton 1995; Dill and Cordone 1995); Campbell, Santa Clara County/CA/Coyote Creek drainage (1969, Cohen and Carlton 1995; Center for Aquatic Resource Studies 2009); Fremont/CA/Lake Elizabeth (1969, Cohen and Carlton 1995; Center for Aquatic Resource Studies 2009);
Vectors
| Level | Vector |
|---|---|
| Probable | Biocontrol |
Regional Impacts
| Ecological Impact | Predation | |
| DNA surveys of Mississippi Silversides have detected DNA from the endangered, endemic Delta Smelt (Hypomesus transpacificus). In one survey, 41% of the 37 Mississippi Silversides caught by trawling had DNA of Delta Smelt in their guts, but none of the 614 silversides caught by beach seining had traces of Delta Smelt, suggesting that the Smelt were using the deeper, channel habitat (Baerwald et al. 2012). In a later study sampling multiple habitats by multiple methods, 69 of 550 Mississippi Silversides tested positive for Delta Smelt DNA. Predation was more common at sites with clearer water. Reduced water turbidity has favored increased predation on Delta Smelt (Schreier et al. 2018). | ||
| Ecological Impact | Competition | |
| Mississippi Silversides have a broad diet, including zooplankton, benthic invertebrates, and some fish. While Delta Smelt are primarily planktivores. Nonetheless, the two species have a substantial niche overlap. In mixed species aquarium experiments, both species fed on brine shrimp (Artemia sp.) nauplii, but 20 Silversides grew more twice as fast as Delta Smelt, with 100% survival, while six Delta Smelt died. These lab experiments must be applied with caution but suggest the potential for competition between the species (Bennett 2005). | ||
| Ecological Impact | Food/Prey | |
| Mississippi Silversides are a frequent prey of such predatory species of Striped Bass (Morone saxatilis), Largemouth Bass (Micropterus salmoides), and the native Sacramento Pikeminnow (Ptychocheilus grandis) (Nobriga and Feyrer 2008). However, Mississippi Silversides have not increased the abundance of predatory fishes, and are part of the overall phenomenon of 'Pelagic Organism Decline' in San Francisco Bay. | ||