Historical changes in the ichthyofaunal assemblages of the upper Cahaba River in Alabama associated with extensive urban development in the watershed

The upper Cahaba River in Alabama has experienced extensive urban development in its watershed in recent years. To assess the effects that these developments have had on the ichthyofauna, we compared data from samples made at 12 stations by other researchers prior to 1984 to data from samples collected by us at the same sites between 1995-97. Historical collections produced a total of 44 species, whereas recent samples produced 42. Two species, the blue shiner (Cyprinella caerulea) and the Alabama shad (Alosa alabamae), have been extirpated from this system. Relative abundances of the various taxa in recent samples correlated poorly with those of historical samples, indicating that the compositions of the ichthyological communities have changed. Disturbance-tolerant cyprinids (minnows) have generally increased in percent relative abundance (PRA) in recent collections, whereas the disturbance-sensitive cyprinids have generally decreased. The PRA of percids (:darters) has decreased in recent collections, especially the disturbance-sensitive species such as the coal darter (Percina brevicauda) and the green breast darter (Etheostoma jordani). The ichthyofaunal diversity, as measured by several indices, has decreased in recent samples. These changes in the fish populations have occurred concurrently with extensive urbanization and resultant degradation of water and habitat that has taken place in the watershed over the last 20 years.