Life History Characteristics of Three Obligate Riverine Species and Drift Patterns of Lower Brazos River Fishes
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I examined various life-history characteristics of the shoal chub Macrhybopsis hyostoma, ghost shiner Notropis buchanani and silverband shiner Notropis shumardi from the lower Brazos River, Texas. Monthly or bimonthly collections were made from three sites on the lower Brazos River during January 2004 through December 2005. Shoal chub, ghost shiner and silverband shiner have similar life history characteristics, including rapid growth, short life spans and early reproductive maturity. In addition, these species produce multiple cohorts of eggs during prolonged spawning seasons lasting from early spring until late fall. Diets of the shoal chub and silverband shiner consisted primarily of aquatic invertebrates, while ghost shiners consumed aquatic invertebrates and a large proportion of detritus. The life history characteristics of the shoal chub, ghost shiner and silverband shiner allow survival in highly variable aquatic systems such as the lower Brazos River.
I also examined larval and juvenile drift patterns of substrate, pelagic broadcast and adhesive broadcast spawning guilds in the lower Brazos River during 2004 and 2005. Relatively higher drift densities were observed during the high flow year for all reproductive guilds and among life stages within reproductive guilds. Substrate, pelagic broadcast and adhesive broadcast spawners also had higher drift densities at night and in near shore areas. Increased metalarvae and juvenile drift densities indicated higher survival and recruitment of larval fishes during the high flow year. Similar night time and near shore drift density patterns demonstrated concurrent use of habitat and resources among life stages and reproductive guilds, suggesting biotic factors such as competition may influence survival of larvae and recruitment of riverine fish.