Precision of Hard Structures Used to Estimate Age of Riverine Catostomids and Cyprinids in the Upper Colorado River Basin

Abstract

Understanding the population dynamics of native and nonnative fishes is critical for guiding and evaluating management activities, but obtaining information on population dynamics is often dependent on identifying structures that provide precise estimates of age. We examined age estimation using various hard structures for native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, and roundtail chub Gila robusta, and nonnative white suckers C. commersonii, creek chub Semotilus atromaculatus, white sucker × bluehead sucker hybrids, and white sucker × flannelmouth sucker hybrids in a small headwater stream of the upper Colorado River basin (UCRB) in Wyoming. We evaluated between-reader precision (i.e., between two readers) and agreement of otolith age estimates with estimates from scales, fin rays, cleithra, and opercular bones. Exact agreement between readers was highest for otoliths (66–96% among species) and fin rays (61–92%) and lowest for opercles (25–69%), cleithra (21–41%), and scales (15–48%). Age estimates from fin rays were almost exactly the same as those from otoliths for all species except creek chub, for which fin ray estimates were consistently lower than otolith estimates. Age estimates from scales were generally 1–4 years lower than those from otoliths for most species, and most discrepancies occurred when otolith ages were greater than 5 years. We recommend that fin rays be used to estimate age of native catostomids and roundtail chub in the UCRB because fin rays provide accurate estimates of otolith age and can be obtained without sacrificing fish. We further recommend that otoliths be used to estimate age of creek chub in the UCRB because accuracy of fin rays was poor and because sacrificing this nonnative species may benefit native fishes of the UCRB.