Species identification of members of the Genus Gila within the Gila River Basin: A case study of complexity

Authors: Crowder, Clayton D.*1, Carter, Julie Meka1, Leavitt, Daniel1, Hickerson, Brian1, Makinster, Andrew1

Year: 2015 (xlvii)

Abstract

Game and Fish Department). The Gila robusta complex, comprised of Roundtail chub, G. robusta, Gila chub, G. intermedia, and Headwater Chub, G. nigra, as described by Minckley and DeMarais (2000)[Copeia 1:251-256], have overlapping morphologic and meristic characters used to identify species. We wanted to test the accuracy of observers using the key as developed by Minckley and DeMarais (2000) to identify members of Gila complex to species. For this test, a panel of 10 observers with at least 10 years of experience working with the Gila complex in Arizona or New Mexico was convened. We compared the success rate of identification for three species of Gila using 89 fish collected from 15 separate sites in the Gila River Basin. We calculated a success rate of 53.4% with 244 correct identifications on 451 trials utilizing the available key. No species was perfectly identified and this pattern differed from random chance (G = 131.98; p < 0.0001). By species, G. intermedia was most frequently identified correctly (67.9%), G. robusta was the second most frequently identified correctly (62.7%), and G. nigra was the least frequently identified correctly (32.7%). Gila nigra were most commonly misidentified as G. intermedia (45.1%) and occasionally as G. robusta (22.2%). Similarly, observers identified two species at all localities and 13 of 15 localities had all three species identified. The result of our study demonstrates the challenges of accurate species identification using the recognized key, whereby one of two scenarios is true; (1) multiple species identifications from the same collection locality are accurate, and Gila sp. are sympatric in most cases or (2) only a single species is present at each locality and multiple species identifications result from morphologically indistinguishable G. intermedia, G. nigra, G. robusta.