Roundtail chub population assessment in the lower salt and Verde rivers, Arizona

Roundtail chub Gila robusta were collected during spring and fall 2003 in the lower Salt and Verde rivers to determine population size and size structure. We collected and passive integrated transponder-tagged 262 roundtail chub using a combination of experimental gill nets and canoe electrofishing. The majority of roundtail chub were collected in the upper 16 km of the study area. Length-frequency distributions indicate that the population is comprised almost entirely of large adults with minimal recruitment. The estimated population size of roundtail chub in the lower Salt and Verde rivers during 2003 is 1,657 (95% confidence interval = 1,097-2,742), which represents a 74% decrease from 3 years ago. Based on these results, we conclude that the roundtail chub population in the lower Salt and Verde rivers is declining rapidly due to low recruitment and high natural mortality. We recommend that immediate management actions be taken to ensure the persistence of this population of roundtail chub.