Otolith analysis reveals long-lived population demographics of quillback Carpiodes cyprinus and river carpsucker C. carpio in Colorado

The carpsuckers (Carpiodes spp.) are a little-studied genus within the Ictiobinae, a subfamily of Catostomidae that also includes the buffalofishes (Ictiobus spp.). Both quillback Carpiodes cyprinus and river carpsucker C. carpio were recently discovered to live in excess of 40 years in Minnesota, and this prompted interest in their study in Colorado. We collected 162 Carpiodes from northeastern Colorado from 2021 to 2023 and identified 143 as quillback, 15 as river carpsucker, and 4 unidentified fingerlings using a suite of morphological characters. No single character worked to separate and identify the two species in all cases. Cluster analysis helped identify six specimens where examination of the suite of characters did not allow identification to the species level. We extracted otoliths for age analysis from 159 individuals to quantify age-score precision, size at age, recruitment dynamics, and sexual maturity. Ages were very precise for both species with evidence of longevity near a half century (quillback 49 years, river carpsucker 40 years) as well as pronounced asymptotic growth. We also found that otolith mass explains significant variation in Carpiodes age, and can be used to predict quillback and river carpsucker age in Colorado. In addition, Colorado quillback mature larger and earlier than populations assessed in other regions. Finally, the historic database of Carpiodes in Colorado reveals range contraction as well as decades of skewed size structure indicative of long-lived species. Clearly, this long-neglected group of fishes requires further study, including genetic analyses to explain and validate systematics of this genus. Management attention is also needed across the declining range of this genus because their life histories are longer-lived and more complex than previously realized.