Mechanisms of Urbanization Impact on a Sensitive Lithophilic Spawner, River Chub (Nocomis micropogon)

Fish exhibiting lithophilic spawning behavior exhibit sensitivity to urbanization. The specific causative mechanisms underlying this pattern are rarely reported. Hypotheses regarding the impact of urbanization on river chub (Nocomis micropogon) were investigated in streams in and around Baltimore, Maryland. River chub construct nests that serve as nesting habitat for other local lithophilic spawners, and they can be considered to be a keystone species in the fish community. Field experiments and observations on river chub were conducted in urbanized and less urbanized streams in the Baltimore area. While suitable substrate was found to be present in urbanized streams where they are absent, field experiments revealed that artificial nests placed in urbanized streams remained intact for a significantly shorter period of time than those placed in less urbanized streams. Artificial and natural nests were monitored in the vicinity of USGS flow gauges in order to determine threshold stream flow discharges which result in river chub nest disruption. Results support the hypothesis that frequent high flows found in urban streams are responsible in part for the elimination of river chub in Baltimore. Restoration and protection strategies for keystone species such as river chub can benefit through the determination and quantification of impact mechanisms.