Native Fish Abundance and Population Structure Pre- and Post- High Magnitude Flooding Event in an Arizona River
The Verde River native fish assemblage has experienced significant declines, due in part to nonnative species introductions and an altered flow regime. High magnitude floods, an important component to the natural flow regime of arid-land river systems, have been decreasing in frequency. Native fish species have adapted to survive flood events as regular occurrences, while high magnitude floods have been shown to reduce nonnative fish populations. On February 16, 2019, the Verde River experienced its 5th largest flood in recorded history, with flows approaching 50,000 cfs. We hypothesized that following this flow event, we would see an increase in the density of native fishes and a reduction in the density of nonnative fishes. To investigate, we sampled the fish community at 382 random locations through the “Scenic” section of the Verde River with the use of prepositioned areal electrofishing devices (PAEDs). Data from this study was compared to data collected using this same method in 2017. Our research revealed a significant increase in the density of native fishes with the greatest increase observed in Roundtail Chub, Gila robusta, and Sonora Sucker, Catostomus insignis. Most native fish were young-of-year, suggesting that a successful spawning event occurred following the late-winter/early-spring flooding event. These results demonstrate the importance of large spring-floods to the persistence and recovery of Verde River native fishes. Results were prepared for a thesis and an article was published on this work.