Invasion
Invasion Description
1st Record: OR-WA/Columbia River (1880, Chapman 1942, Lampman 1946)
Geographic Extent
OR-WA/Columbia River (1880, Chapman 1942, Lampman 1946); Crimms Island (downriver from Longview WA/OR/Columbia River (Haskell and Tiffin 2011); Albany/OR/Willamette River (1880, Chapman 1942, Lampman 1946); Astoria to the Cascades, 240 km upstream/OR/Columbia River (1896) (Chapman 1942; Lampman 1946; Sol et al. 2021); Granite Dam/ID/ Snake River, 600 km from the Ocean (Pearcy and Fisher 2011)
Vectors
| Level | Vector |
|---|---|
| Probable | Fisheries Accidental (not Oyster) |
Regional Impacts
| Ecological Impact | Competition | |
| Zooplankton predation by American Shad are expected to affect food availability for native fishes, including Pacific salmon (Oncohrynchus spp.) (Haskell et al. 2013). | ||
| Ecological Impact | Predation | |
| The increased population of American Shad in reservoirs of the Columbia River appears to have altered the zooplankton population, reducing the abundance of large zooplankton such as Daphnia spp. American Shad are estimated to consume an average of 23% of daily zooplankton production (Haskell et al. 2013). | ||
| Ecological Impact | Parasite/Predator Vector | |
| The increased population of American Shad in reservoirs of the Columbia River appears to have amplified the population of a native protistan parasite, Ichthyophonus spp. in freshwater reservoirs of the river. The parasite is regarded as a threat to native Pacific salmon, although prevalence was very low (~4%) in spring Chinook Salmon (Hershberger et al. 2010). | ||
| Economic Impact | Fisheries | |
| 'Several hundred thousand shad are landed annually by commercial and sport fisheries in the Columbia River (Petersen et al. 2003', cited by Pearcy and Fisher 2011). | ||
| Ecological Impact | Trophic Cascade | |
| Migration by American Shad has partially replaced the transport by native Salmon of nutrients (N and P) from the marine environment to the Columbia River Basin. At present, shad import 2% of the total phosphorus load to the John Day Reservoir, on the lower Columbia. Nutrient imports by shad roughly equal those of native salmon at present, but are much smaller than those from historic salmon population (Haskell 2018). | ||