Biology and Management of Threatened and Endangered Western Trouts August 1976 USDA Forest Service General Technical Report RM-28 Rocky Mountain Forest and Range Experiment Station Forest Service U.S. Department of Agriculture Fort Collins, Colorado 80521 Abstract Behnke, R. J., and Mark Zarn. 1976. Biology and management of threatened and endangered western trouts. USDA For. Sew. Gen. Tech. Rep. RM-28, 45 p. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo. Discusses taxonomy, reasons for decline, life history and ecology, and sug- gestions for preservation and management of six closely related trouts native to western North America: Colorado River cutthroat, Salmo clarki pleuriticus; green- back trout, S. c. stomias; Lahontan cutthroat, S. c. henshawi; Paiute trout, S. c. seleniris; Gila trout, S. gilae; and Arizona native trout, S. apache. Meristic characters, distribution and status, habitat requirements and limiting factors, protective measures, and management recommendations are presented for each taxon. Keywords: Native trout, Salrno clarki pleuriticus. Sali?zo ckurki stoi~zius. Sulnzo clarki herzshawi, Salmo clarki seleniris, Salrno gilue. Sulrno uprrchc. USDA Forest Service General Technical Report RM-28 August 1976 Biology and Management of Threatened and Endangered Western Trouts R. J. Behnke Colorado State University Mark Zarn Conservation Library Denver Public Library Information reported here was prepared under contract by the Conservation Library of the Denver Public Library, through the Rocky Mountain Forest and Range Experiment Station. The report is printed as prepared by the authors; opinions are not necessarily those of the U.S. Forest Service. TABLE OF CONTENTS I . GJ3NERAL MANAGEMENT GUIDELINES FOR RAE3 AND ENDANGJIRED WESTERN TROUTS Introduction ........................... Taxonomy ............................. Reasons for Decline .................... .... Life History and Ecology ..................... Preservation. Restoration and Management Programs ......... Potential Role of Native Trout in Fisheries Management . .... Summary ............................... Authorities ............................ References ............................ 11 . COLORADO RImR CUTTHROAT TROUT. Salmo clarki pleuriticus Typical Meristic Characteristics. * ........... Species Description .................. Distribution ..................... Status and Population Trend .............. LifeHistory ..................... Habitat Requirements and Limiting Factors ....... Protective Measures .................. Recommendations .................... Authorities ...................... References ...................... I11 . WNBACK CUTTHROAT TROUT. Salmo clarki s tomias Typical Meristic Characteristics....... Species Description ............. Distribution ................ Status and Population Trend ......... Life History ................ Habitat Requirements and Limiting Factors . Protective Measures ............. Recommendations ............... Authorities ................. References ................. IV . LAHONTAN CUTTHROAT TROUT. Salmo clarki henshawi Typical Meristic Characteristics ....... Species Description ............. Distribution ................ Status and Population Trend ......... Life History ................ Habitat Requirements and Limiting Factors . Protective Measures ............. Recommendations ............... Authorities ................. References ................. V . PAIUTE TROUT. SaLmo clarki seleniris Typical Meristic Characteristics ...................... 32 Species Description ............................ 32 Distribution ............................... 33 Status and Population Trend ........................ 33 Life History ...............................34 Habitat Requirements and Limiting Factors ................. 34 Protective Measures ............................ 34 Recommendations .............................. 34 Authorities ................................. 35 References ................................ 35 TABLE OF CONTENTS (CONT'D) VI . GILA TROUT. Salmo ailae Typical Meristic Characteristics. ..................... 36 Species Description ............................ 36 Distribution ............................... 38 Status and Population Trend ........................ 39 Life History ............................... 39 Habitat Requirements and Limiting Factors ................. 39 Protective Measures ....... Recommendations ......... Authorities ........... References ........... VII . ARIZONA NATIVE TROUT. Salmo apache Typical Meristic Characteristics . .... Species Description ....... .... Distribution .............. Status and Population Trend ... .... Life History .......... .... Habitat Requirements and Limiting Factors Protective Measures ........... Recommendations ......... .... Authorities ............... References ........... .... BIOLOGY AND MANAGEMENT OF THREATENED AND ENDANGERED WESTERN TROUTS occur with anadromous steelhead trout (5. gairdneri) does coexistence occur naturally This report discusses the biology and without hybridization. In all instances where management of six closely related trouts the rainbow trout has been established beyond native to western North America. All sharg its native range and stocked with Gila trout, many common ecological and genetic attributes; golden trout or any of the interior subspecies all have suffered catastrophic declines in of cutthroat trout, hybridization has invariably abundance due to essentially similar factors. resulted. The indiscriminate stocking of The folLowing section presents general in- untold millions of rainbow trout and several formation applicable to all of these trouts subspecies of cutthroat trout into virtually and relevant to any meaningful preservation, every habitable water throughout the West, and restoration and management efforts. Succeed- subsequent hybridization with the native trout ing chapters present more specific biological fauna, has been the primary cause for the and management considerations for each taxa. almost complete elimination of pure populations of most of the taxonomic categories of native trouts in the interior regions of the West. Man still lacks complete knowledge of The presence of all degrees of hybridi- the evolutionary history which resulted in zation greatly confounds the work of correctly the diverse array of western North American identifying and evaluating the purity of exist- trouts of the genus Salmo. Earlier thought ing populations of native trout in most regions, considered that all western trouts either and the recognition of pure stocks of any of belonged to or recently derived from two the six trouts considered in this report is evolutionary lines or species: the rainbow not a simple matter. Although one can acquire trout, Salmo gairdneri, and the cutthroat sufficient familiarity with the subtle varia- trout, 2. clarki. Recent studies have demon- tions among the different species and sub- strated that the true situation is much more species of western trouts to distinguish the complex; several distinct groups including various taxa, the average field worker cannot the Gila trout (S-. gilae), Arizona native be expected to accurately differentiate the trout (5. apache), Mexican golden trout true native trout of a given area from hybrid (Salmo chrysogaster) , California golden trout populations. Taxonomic criteria exist for all (Salmo aguabonita) and redband trout (not the trouts in this report, but the sorting and officially named) do not fit the diagnosis of evaluation of specimens collected during survey either the rainbow trout or the cutthroat work to determine the status of a native trout trout and probably represent distinct evolu- and to locate pure populations remains an in- tionary lines of their own which sprang from volved process of detailed examination and a common ancestor to all western Salmo comparison of twr~ycharacters. (Behnke 1972b, Schreck and Behnke 1971, Miller 1972). So unless an agency is dealing with "certified" pure popqlations in a rare trout Despite such evolutionary diversity, all management program, it will ultimathll confront western trouts are closely related to the the problem of identification. Possibilities extent that they can interbreed freely with for additional refinement of information useful each other to produce fertile hybrids. Only in taxonomic identification exist; these in- in Pacific Coast rivers, where rainbow trout clude biochemical techniques such as protein and the coastal cutthroat, 5. c. clarki, electrophoresis and karyotype examination-- reside together and in the Salmon and Clear- the determination of chromosome number and water drainages of the Columbia River basin morphology. Yet the investigator should use of Idaho where resident interior cutthroat caution in utilizing these modern techniques to determine the relative purity of trout also favor the displacement of native trouts populations, for they require both a Icnowledge by more tolerant introduced species, notably of basic principles of taxonomy and a familiar- the brook trout (Salvelinus fontinalis) and ity with the natural range of variability of the brown trout (Salmo trutta). the trout under study. Often, if the extent of hybridization has reached a level where it Most pure native trout populations in can be detected by electrophoresis or altera- the interior regions of the West persist only tions in the chromosome compleaent, it will in small isolated headwater stream situations also show up in the form of changes in den- in essentially undisturbed