TAXONOMIC ANALYSIS OF GILA AND GILA x RAINBOW TROUT IN SOUTHWESTERN NEW MEXICO BY ROBERT EARL DAVID, B.S. A Thesis submitted to the Graduate School in partial fulfillment of the requirements for the Degree Master of Science Major Subject: Wildlife (Fishery) Science New Mexico State University Las Cruces, New Mexico May 1976 "Taxonomic Analysis of Gila and Gila x Rainbow Trout in Southwestern New Mexico," a thesis prepared by Robert Earl David in partial ful- fillment of the requirements for the degree, Master of Science, has been approved and accepted by the following: Dean of the Graduate School Chairman of the Examining Committee Date Committee in Charge: Dr. Douglas B. Jester Dr. G. Morris Southward Dr. Bradley A. Blake Mr. Paul R. Turner 11 ACKNOWLEDGEMENTS Financial support for this study was contributed by the New Mexico Department of Game and Fish and the U. S. Fish and Wildlife Service. I would like to express my appreciation to Dr. Douglas B. Jester, Associate Professor Fishery Science, for continued support and en- couragement throughout this project. Special thanks are extended to Mr. Paul Turner, Assistant Professor Fishery Science, Kim Mello, Gregg Schmitt, Allen Campbell, Becky Campbell, and many undergraduates who assisted in collecting specimens. Thanks are due Dr. Robert J. Behnke, Colorado State University, for continued advisement on taxonomic problems. Thanks also go to Dr. John Hubbard and other employees of the New Mexico Department of Game and Fish whose support made this project possible. A deep appreciation goes to my wife Kathy for her devotion and encouragement. 111 VITA September 20, 1950 - Born in Prescott, Arizona May 1968 - Graduated from Sandia High School, Albuquerque, New Mexico May 1972 - B.S., Wildlife Science, New Mexico State University, Las Cruces, New Mexico 1972-1974 - U.S. Army 1974-1976 - Graduate Teaching Assistant, Department of Fishery and Wildlife Sciences, New Mexico State University PROFESSIONAL AND HONORARY SOCIETIES The Wildlife Society American Fisheries Society iv' ABSTRACT TAXONOMIC ANALYSIS OF GILA AND GILA x RAINBOW TROUT IN SOUTHWESTERN NEW MEXICO BY ROBERT EARL DAVID, B.S. Master of Science in Wildlife (Fishery) Science New Mexico State University Las Cruces, New Mexico, 1976 Doctor Douglas B. Jester, Chairman Samples of trout from 19 streams in the Gila National Forest, New Mexico, were collected and analyzed to determine taxonomic status. Of 23 taximetric characters, ten were selected as key distinguishing characteristics. Main Diamond Creek was selected to represent a pure population of Gila trout, and Turkey Creek at Corral Canyon was used to represent a pure population of rainbow trout. Student's t-test with pooled variances was used to compare the means of 10 key taximetric characters of an un- known population with means of characteristics from the Main Diamond Creek population. Samples found to represent pure Gila trout were from populations in Main Diamond, South Diamond, McKenna, Iron, and Spruce Creeks. Upper Sheep Corral and McKnight Creeks, containing introduced populations of Gila trout, were not analyzed. Evidence indicates that Spruce Creek, previously believed to be an introduced population of Gila trout, may represent a native population of the San Francisco drainage. Data suggests a hypothesis that the Spruce Creek population represents an intergrade between Gila and Arizona trout. Tributaries of the San Francisco River that contain hybrid popu- lations are Whitewater, Dry, and Lipsey Creeks. Influence of either Arizona or cutthroat trout is seen in these populations. Tributaries of the Gila River which were found to contain Gila x rainbow trout hybrids were Black Canyon, Sycamore, White, Langstroth, Trail Canyon, upper Mogollon, upper Turkey, and West Fork of Mogollon Creeks. Streams containing pure populations of rainbow trout were lower Sheep Corral Creek and Turkey Creek at Corral Canyon. vi TABLE OF CONTENTS Page ....... LIST OF TABLES viii ......... LIST OF FIGURES ix .......... INTRODUCTION 1 .......... ME'tHODS 3 .......... STUDY AREA 9 ......... RESULTS 11 ......... DISCUSSION 21 ......... South Diamond Creek 21 ......... McKenna Creek 23 ......... Iron Creek 24 ......... Spruce Creek 24 ......... Black Canyon Creek 28 ......... Sycamore Creek 28 ......... Whitewater, Lipsey, and Dry Creeks 29 ......... Langstroth, White, and Upper Mogollon Creeks 31 Trail Canyon, West Fork of Mogollon, and Upper Turkey Creeks ......... 32 Lower Sheep Corral Creek ........• 32 SUMMARY ......... 33 LITERATURE CITED ......... 35 vii LIST OF TABLES Table Page 1. Measurements of 23 characteristics of Gila trout (Main Diamond Creek) and rainbow trout (Turkey Creek at Corral Canyon), showing sample sizes, ranges, and means (Main Diamond Creek in parentheses) ................................ 8 2. Regression and correlation showing proportional increases in length of morphometric characters with increase of standard length of Gila trout in Main Diamond Creek (top) and rainbow trout in Turkey Creek at Corral Canyon (bottom). Required r for Gila trout is 0.735. Required r for rainbow trout is 0.708 ................ 14 3. Means of 10 characteristics from each of 19 populations sampled. Populations exhibiting occasional basibranchial teeth are marked with an asterisk ......................... 15 4. Computed t for means of 10 characteristics from each of 18 populations compared to Main Diamond Creek. Degrees of freedom are shown in parentheses. Computed t's which are not significantly different from Main Diamond Creek (Pr < 0.05) are marked with an asterisk . • 18 viii LIST OF FIGURES Figure Page 1. Electrofishing on Spruce Creek 4 2. Ten morphometric measurements used in taxonomic analysis .......................... 5 3. Construction of sampling grid and location of sampling sites for use in spot density analysis .......................... 7 4. Study area in southwestern New Mexico. Sampling sites are indicated by 0 .............. 10 5 Hyoid apparatus of four specimens of Gila trout from Spruce Creek showing location of basibranchial teeth (indicated by "x") ............... 16 6. Means and 95 percent confidence intervals for 10 characteristics from 19 populations of trout ........................ 20 7 Gila trout from South Diamond (upper), Main Diamond (middle), and Spruce Creeks (lower), showing typical spotting patterns from each stream ....................... 22 8. Trout from Lipsey (upper and middle) and Dry Creeks (lower), showing typical spotting patterns from each stream ...................... 30 ix INTRODUCTION The Gila trout, Salmo gilae Miller 1950, is one of two native salmonids of New Mexico. Present distribution is restricted to the headwaters of the Gila and San Francisco Rivers in New Mexico and Gap Creek, tributary of the Verde River, Arizona. The Arizona population resulted from a 1974 transplant from Main Diamond Creek, Gila National Forest, New Mexico. The Gila trout is listed as an endangered species by the United States Department of the Interior (1973) and the New Mexico Department of Game and Fish (1975). An Interim Gila Trout Recovery Team was formed in May, 1974, and is attempting to restore the Gila trout to selected native streams in the Gila National Forest, New Mexico. Research has been done on both ecology (Regan 1964, 1966, Jester 1965, Hanson 1971, LaBounty and Minkley, 1972) and taxonomy (Cope and Yarrow 1875, Miller 1950, 1961, 1972, Huntington 1955, Needham and Gard 1959, Simon 1964, Behnke 1967, 1970a, 1970b, 1973, Legendre and Behnke 1972). The description of the species (Miller 1950) contains information which is no longer valid. The Arizona trout, Salmo apache Miller 1972, had not been described and populations of Arizona trout were listed as Gila trout. Origin of the Gila trout is subject to speculation because an adequate fossil record has not been discovered. The most popular hypothesis (Miller 1950) correlates the origin with late Pliocene or early Pleistocene events. At that time, the ocean temperatures were cold enough to allow a southern migration of Pacific salmonids to enter the Gulf of California. Further movement of one of these salmonids led 1 it up the Gila River into the headwaters where effects of isolation and inbreeding produced what is recognized now as the Gila trout. Prior to this study, Gila trout populations were known to exist in six streams of the Gila National Forest, New Mexico: Main Diamond Creek, South Diamond Creek, McKenna Creek, Spruce Creek, and intro- duced populations in McKnight Creek and Sheep Corral Creek. A seventh population was discovered in 1975 in the headwaters of Iron Creek, a headwater tributary of the Middle Fork of the Gila River. Objectives of this study were to determine purity of previously known and recently discovered Gila trout populations and identify streams containing Gila x rainbow trout hybrids. This thesis is presented to define more accurately the status of the Gila trout in order to facilitate restoration or other management. METHODS Population samples were taken by electrofishing (Fig. 1). Speci- mens were fixed in 10 percent formalin containing three to four ml of Ionol (Shell Chemical Company) per gallon as a color-preserving anti- oxidant. Fixed specimens were stored in 40 percent isopropyl alcohol. Each specimen was marked with a numbered opercular strap tag for in- dividual identification. All meristic and morphometric measurements were reviewed with Dr. Robert J. Behnke, Colorado State University, in order to conform with standard measuring techniques in trout