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~.II~'~ :,ACT When white explorers first entered the Bonneville Basin they encountered a multitude of wildlife species. One organism which was particularly noticeable was the resident trout Salmo clarki utah. These early explorers found cutthroat trout in nearly all aquatic environments encountered in their journeys through the Bonneville Basin drainage. Cutthroat trout found in area streams and lakes were descendants of a large spotted cutthroat that entered the Bear, Yellowstone and Colorado river drain- ages sometime prior to formation of Shoshone Falls, Idaho. Movement into the Bonneville Basin occurred with the diversion of Bear River into its present drainage system. Lake Bonneville provided an extremely large environment allowing the new cutthroat population to expand into areas of suitable habitat. Final desiccation of Lake Bonneville left many drainages isolated from each other and allowed for slight differences between the various populations. Within a short time following colonization of the Bonne~~ille Basin, cutthroat populations began to decline. Lake populations were impacted by unregulated commercial fishing and stream populations were affected by irrigation di- versionswhich dewateredmany miles of stream channel. Nearly all populations were finally impacted by the introduction of non-native trout forms, particu- larly rainbow trout. This decline and replacement of cutthroat populations resulted in near extinction of the unique Bonneville cutthroat. Relic popula- tions, however, have been located in a few small isolated streams in Utah, Wyoming and Nevada. These populations have developed in and adapted to these marginal habitats. Programs to protect these populations are being developed and use of this endemic cutthroat form in modern fisheries management is being evaluated. Many of the characteristics exhibited by Bonneville cutthroat may prove bene- ficial in developing additional fisheries in marginal waters. DISTRIBUTION, SYSTEMATICS AND BIOLOGY OF THE BONNEVILLE CUTTHROAT TROUT, SAI,MO CLARKI UTAH BRUCE E. MAY, Utah State Division of Wildlife Resources, Southern Region, Cedar City, Utah 847201 JOHN D. LEPPINK, Utah State Division of Wildlife Resources, Southern Region, Cedar City, Utah 84720 RICHARD S. WYDOSKI, U.S. Fish and Wildlife Service, Cooperative Fish Unit, Utah State University, Logan, Utah 843222 INTRODUCTION The original range of cutthroat trout (Salmo clarki) extended from Alaska to Northern California, throughout the Intermountain area and east to the Upper Missouri, Platt, Colorado, and Rio Grande drainages. Native stocks were also found in the headwaters of South Saskatchewan River, Alberta, Canada (Sigler and Miller 1963). Cutthroat trout found throughout this very large range represented a number of subspecies (Table 1). 'Present address: U.S. Forest Service, Salmon National Forest, Salmon, Idaho 83467 2Present address: U.S, Fish and Wildlife Service, National Fishery Center - Leetown, Rt. 3, Box 41, Kearneysville, W. Virginia 25430