Conservation and the Historical Distribution of Gila Trout

Authors: David Propst, Thomas Turner, Jerry Monzingo, James Brooks, Dustin Myers

Year: 2018

Abstract

Restoration of a species to historically occupied habitats is a common conservation strategy, especially for interior North American salmonids. An essential early, if not first, step is to determine the historical range of target organism. For many southwestern fishes this has proven difficult as historical habitats were compromised or destroyed by European settlers before scientific investigations catalogued the native fauna of the region. Further complicating accurate delineation of native ranges were paucity of historical collections, introduction of nonnative species, and the shifting taxonomic designations of remnant populations. Following its description in 1950, Gila Trout Oncorhynchus gilae was the presumptive native trout of the entire Gila River drainage in New Mexico and Arizona. But the description of Apache Trout O. apache from a Gila River tributary in 1972 interjected uncertainty to the historical range of Gila Trout. Was Gila Trout limited to the upper Gila River in New Mexico and were the native trout of the Agua Fria and Verde drainages taxonomically distinct from Gila Trout? Absence of uncompromised specimens from Arizona streams precludes definitive resolution of this question, but historical accounts and several museum specimens support a close affinity of these populations with Gila Trout. Consequently, Gila Trout conservation efforts should continue to include its restoration to suitable habitats throughout the Gila River drainage, exclusive of Apache Trout streams.