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<br />~ <br />U~ <br />Otl <br />'t"'4 <br />C) <br />a <br /> <br />CHAPTER 1 : <br /> <br />INTRODUCTION <br /> <br />BACKGROUND <br /> <br />This document describes the results of 7 years of research on the biological, physical, and chemical <br />resources of the San Juan River. The research focused on methods of recovering two endangered fish <br />species, the Colorado pikeminnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus). <br />Although the research was focused on these two endangered species, the entire native fish community was <br />considered in the studies, because a healthy native fish community is important for recovery of the two <br />endangered species. Research encompassed a variety of biological, physical, and chemical studies, from <br />intensive studies of native and nonnative fish population structure and movement to studies of the effect of <br />storm events on important fish habitats. Final research reports were prepared for each study undertaken <br />and are cited throughout this document as the basis for analyses contained herein. This document is a <br />companion document to Flow Recommendations for the San Juan River (Flow Report) (Holden [Ed.] <br />1999), which also used information from research summarized in this document. The Flow Report <br />concentrated on the research results pertaining to the goal of developing flow recommendations. This <br />report swnmarizes the research results pertaining to limiting factors for the two endangered fishes and other <br />components of the native fish community and provides the basis for setting the future direction of the SJRIP. <br /> <br />Colorado pikeminnow and razorback sucker were widespread and common throughout much of the Upper <br />Colorado River Basin (Upper Basin), likely including the San Juan River, during the settlement and initial <br />development of the western United States (circa I 870s to I 950s) (Jordan 189 I, Koster 1957, Quartarone <br />1993, Stanford 1994). Jordan (1891) noted that settlers reported both species in the San Juan River <br />system upstream as far as Durango, Colorado. Three juvenile Colorado pikeminnow were collected in <br />1936 in the portion of the San Juan River now inundated by Lake Powell (platania 1990). Several other <br />adult and juvenile Colorado pikeminnow were collected in the river during the mid-20th Century (Koster <br />1960), some of which were collected during studies associated with the completion of Navajo Dam (Olson <br />1962). No fish collection studies encompassing the entire river were conducted until 1978, 16 years after <br />Navajo Dam was completed. VTN Consolidated, Inc. and the Museum of Northern Arizona (1978) <br />sampled the river from near Navajo Dam to Lake Powell in 1978, and they collected one juvenile <br />Colorado pikeminnow and reported (secondhand) the occurrence of razorback sucker from an irrigation <br />pond connected to the river. This study showed that both species still existed in the river but suggested that <br />neither species was abundant in the system. <br /> <br />The current population sizes of these fish species are greatly reduced compared with earlier times, <br />and recruitment is limited throughout the Upper Basin, including the San Juan River. Decline <br />of the endangered Colorado pikeminnow and razorback sucker in the Colorado River Basin, including <br />the San Juan River, was attributed to habitat fragmentation and loss, alteration of historical flow <br /> <br />September 2000 <br /> <br />1-1 <br /> <br />Program Evaluation Report <br />