Long-Term Changes in Seasonal Fish Assemblage Dynamics in An Adventitious Desert Stream

Tornillo Creek, a tributary of the Rio Grande in Texas, USA, historically is an important nursery and spawning habitat for certain native fish taxa in the Rio Grande system. We examined long-term (1967–1970 vs. 2009–2011) seasonal fish assemblage changes and contemporary assemblage-environmental associations in Tornillo Creek in order to understand the historical importance of the tributary for fish taxa, and which environmental factors are associated with fish abundance and occupancy patterns. Our results indicated that seasonal fish assemblage variability and composition from the two time periods were significantly different. The relative abundance and persistence of Campostoma ornatum, a state-listed threatened species, have significantly decreased in the creek. In contrast, the relative abundances and persistence of tolerant, invasive species have significantly increased, leading to the decrease in seasonal fish assemblage variability in the creek. The contemporary seasonal fish assemblages were linked to the local environmental factors such as water temperature and stream depth, suggesting that the maintenance of stream flow and connectivity might be important for immigration and emigration of certain riverine fishes.