The Rapid Establishment, Dispersal, and Increased Abundance of Invasive American Shad in the Pacific Northwest

American shad (Alosa sapidissima) were repeatedly introduced into two Pacific coastal rivers in the late 1800s. They rapidly established, dispersed, and expanded their range over 5,000 km of coastline from Mexico to Russia. American shad also increased dramatically in abundance and now comprise the largest spawning run of anadromous fish in the Columbia River (>4 million fish annually). Despite constituting a remarkable biological invasion, invasive shad have not been the subject of much scientific investigation and remain relatively obscure in the Pacific Northwest. In this first of two complementary articles, we attempt to raise the profile of invasive American shad among fisheries professionals and generate scientific interest in this biological invasion. We provide an overview of the history of their introduction and discuss the mechanisms that may have contributed to the species' establishment, rapid dispersal along the Pacific coast, and its increased abundance in the Columbia River. In the second accompanying article we discuss the possible ecological consequences of the invasion in Pacific coastal ecosystems but also its inherent value to studies of ecology and evolution. These articles are designed to be read in succession.