Laserfiche WebLink
<br />001596 <br /> <br />CHAPTER 1: <br /> <br />INTRODUCTION <br /> <br />BACKGROUND <br /> <br />.---- --._------"-~_._~_.-~---_._-------- <br /> <br />~Thi~ument describes the results of? ;: ~f research on the biologicall1h~sic~, and c~em~~:J) <br />C ;esources of the San Juan River./rhe researcfi focuseo on methods of recovenng two endangered <br />. --- <br />. fish species, the Colorado pikeminnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen <br />texanus). Although the research was focused on these two endangered species, the entire native <br />fish community was considered in the studies, because a healthy native fish community is <br />important for recovery of the two endangered species. Research encompassed a variety of <br />biological, physical, and chemical studies, from intensive studies of native and nonnative fish <br />population structure and movement to studies of the effect of storm events on important fish <br />habitats. Final research reports were prepared for each study undertaken and are cited throughout <br />this document as the basis for analyses contained herein. This document is a companion document <br />to Flow Recommendations for the San Juan River (Flow Report) (Holden [Ed.] 1999), which also <br />used information from research summarized in this document. The Flow Report concentrated on <br />the research results pertaining to the goal of developing flow recommendations. This report <br />summarizes the research results pertaining to limiting factors for the two endangered fishes and <br />other components of the native fish community and provides the basis for setting the future <br />direction of the SJRIP. <br /> <br />Colorado pikeminnow and razorback sucker were widespread and common throughout much of <br />the Upper Colorado River Basin (Upper Basin), likely including the San Juan River, during the <br />settlement and initial development of the western United States (circa 1870s to 1950s) (Jordan <br />1891, Koster 1957, Quartarone 1993, Stanford 1994). Jordan (1891) noted that settlers reported <br />both species in the San Juan River system upstream as far as Durango, Colorado. Three juvenile <br />Colorado pikeminnow were collected in 1936 in the portion of the San Juan River now inundated <br />by Lake Powell (Platania 1990). Several other adult and juvenile Colorado pikeminnow were <br />collected in the river during the mid-20th Century (Koster 1960), some of which were collected <br />during studies associated with the completion of Navajo Dam (Olson 1962). No fish collection <br />studies encompassing the entire river were conducted until 1978, 16 years after Navajo Dam was <br />completed. VTN Consolidated, Inc. and the Museum of North em Arizona (1978) sampled the river <br />from near Navajo Dam to Lake Powell in 1978, and they collected one juvenile Colorado <br />pikeminnow and reported (secondhand) the occurrence of razorback sucker from an irrigation pond <br />connected to the river. This study showed that both species still existed in the river but suggested <br />that neither species was abundant in the system. <br /> <br />I. <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 of <br />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 />