Evolution of non-native species

American shad

Click here for video of American shad fieldwork in California.


Click here for video of American shad passing through a fish ladder on the Snake River in eastern Washington.


The spread of non-native species has resulted in substantial environmental and economic cost, and constitutes a serious threat to global biodiversity, ecosystem functioning, and the long term persistence of indigenous biota. These impacts are of particular concern where they involve interactions with designated conservation units, and resources of substantial commercial value. These considerations apply to non-native American shad (Alosa sapidissima) and their potential effects on native Pacific salmonids (Oncorhynchus sp.).


American shad rapidly dispersed following their introduction to the Sacramento River in 1871, and have since been reported in rivers from Mexico to Russia. Using advanced molecular techniques, habitat data, and otolith microchemistry, my colleagues and I are resolving the distribution of self-sustaining shad populations among Pacific coastal rivers, and identifying the source population(s) of migrants for the colonization of additional drainages. We are also exploring the potential for range expansion under climate change scenarios, identifying habitats susceptible to future shad colonization, and predicting time lines of invasion for specific rivers.


Species introduced to novel environments can exhibit rapid evolutionary changes. Because evolutionary adaptations may contribute to future establishment and spread of non-native taxa, understanding the life history variation exhibited by American shad along the Pacific coast is an important aid to the effective management of this species. My colleagues and I are examining the implications of extended freshwater residency in several Pacific coast rivers, including the formation of a landlocked population in California, and the formation of 'mini-shad' in the Columbia River.

Fisheries cover



Russian River mouth





Figure: Photograph of the typical anadromous life history form of American shad (top) and several representative 'mini-shad' (bottom) from the Columbia River.