Invasion
Invasion Description
1st Record (tidal): CA/Sacramento-San Joaquin Delta (1974, Swanson et al. 2000; Leidy 2007, single fish in 1974, 1982, 1985, established by 1995, Dill and Cardone 1995); 1st Watershed Record: Plumas County/CA/Almador Reservoir, North Fork Feather River (1972, Dill and Crodone 1995, Center for Aquatic Resource Studies 2009). When this fish was introduced to upstream reservoirs, it was considered to be conspecific with the native Delta Smelt, s H. transpacificus, now an endangered species (Swanson et al. 1999).
Geographic Extent
CA/Sacramento-San Joaquin Delta (1974, Swanson et al. 2000; Leidy 2007)); CA/Lower American River (Dill and Cordone 1995); CA/Cache Slough, Sacramento River (1995, Dill and Cordone 1995; Aasen et al. 1998); CA/Suisun Bay (2002, Center for Aquatic Resource Studies 2009); CA/Suisun Marsh (1999, Matern et al. 2002); CA/lower Napa River (2001, Leidy 2007, 1 fish); CA/San Pablo Bay (Aasen et al. 1998); Watershed Record: Plumas County/CA/Almador Reservoir, North Fork Feather River (1972, Dill and Crodone 1995; Center for Aquatic Resource Studies 2009), Most San Francisco estuary captures have happened at 1-10 PSU (Aasen 1998).
Vectors
| Level | Vector |
|---|---|
| Probable | Fisheries Intentional |
Regional Impacts
| Ecological Impact | Competition | |
| The Wakasagi (Hypomesus nipponensis) is considered a probable competitor with the native Delta Smelt (H. transpacificus), an endangered species (Aasen et al. 1998; Swanson et al. 1990; Bennett 2005) | ||
| Ecological Impact | Hybridization | |
| Hybridization of the Wakasagi (Hypomesus nipponensis) with the native, endangered (Delta Smelt,H. transpacificus) is a concern, but Trenham et al. (1998) found only 2 F1 hybrids in a sample of 280 fish from the Delta. However, in one sample of 280 Delta Smelt, only one F1 hybrid was found (Trenham et al. 1998). Despite their morphological similarity, the two species are genetically distinct, making introgression unlikely (Stanley et al. 1995). In a later survey of 384 fish, 125 specimens that were morphologically identified as Delta Smelt, were genetically identified as Wakasagi. Three fish were F1 hybrids, and 2 were F2 backcrosses. All the hybrids had Wakasagi as the maternal parent, suggesting that the introgression was occurring from Delta Smelt to Wakasagi, but at very low rates, and not affecting the Delta Smelt genotype (Benjamin et al. 2018). | ||