Pre‐impoundment fish migrations in the Mobile Basin, Alabama

Abstract

Assessing the status of several migratory fishes in the Mobile River Basin, Alabama, has been complicated due to a general lack of historical data on their life history, habitat requirements, and distributions. Whether distributions were restricted by natural or man‐made barriers to migration is difficult to answer because few scientific collections were made before dams were built, and the earliest dams were built at the largest biogeographic barrier in the basin: the geological fall line. Therefore, we used what information was available, including anecdotal information, primarily records from archived newspapers and government reports, to describe the ranges of six migratory species prior to the construction of dams in the Mobile Basin. We describe the complicated history of Alabama Shad Alosa alabamae and show that range declines may have been masked by the stocking of American Shad Alosa sapidissima in the late 19th century. We show that Gulf Sturgeon Acipenser oxyrinchus desotoi probably migrated well above the fall line in the Coosa River, and may have been sympatric with Lake Sturgeon Acipenser fulvescens. We found no records of Alabama Sturgeon Scaphirhynchus suttkusi above the fall line. American Eel Anguilla rostrata migrated above the fall line in every Mobile Basin river before dams were built. Finally, Paddlefish Polyodon spathula may have once occurred above the fall line in at least two rivers, but they persist today in impounded reaches in the coastal plain, unlike some other species. We hope that future work will continue to consider archival sources of information to re‐trace the histories of imperilled species.

Biodiversity connections—‘ties that bind’

“…Reconstructing the native distributions of lesser-known migratory fishes, particularly at the scale of individual river basins with scattered historical records, poses a problem that could hamper efforts to restore fish passage. Hershey et al (2024) tackle this challenge by combining data scoured from archived newspaper reports with more recent collection records to recreate historical distributions for six migratory fishes in the Mobile River Basin, one of the most biodiverse freshwater systems in North America (Abell et al, 2000). Their analysis provides evidence that prior to dam construction, migratory fishes historically traversed a putative geographic barrier (the Fall Line, an area of steep river gradients separating the Coastal Plain from upland regions), thereby connecting physiographically distinct portions of the basin.…”