REC-ERC-77-11 OBSERVATIONS ON THE STATUS OF THE DEVIL'S HOLE PUPFISH IN THE HOOVER DAM REFUGIUM Prepared and submitted to the Bureau of Reclamation by J. E. Williams Department of Biological Sciences University of Nevada, Las Vegas September 1977 Applied Sciences Branch Division of General Research Engineering and Research Center Denver, Colorado SI METRIC UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION ACKNOWLEDGMENTS Funding for this project was provided by the Division of General Research of the Bureau of Reclamation. Engineering and Research Center, Denver, Colo. (Purchase Order No. 6-01-ER-03376/Research Project DR-397) and by the Department of Biological Sciences, University of Nevada, Las Vegas. Thanks are due Herb Guenther and Gary Bryant of the Bureau of Reclamation in Boulder City, Nev., and Robert Furtek of the University of Nevada, for their assistance in monthly population counts. Dr. J. E. Deacon of the University of Nevada is thanked for his comprehensive review of this manuscript and the use of unpublished population data from Devil's Hole. A final technical review was performed for the USBR by J. F. LaBounty. CONTENTS Page Introduction 1 Application ........................................................................................................... 2 Summary ............................................................................................................... 2 Conclusions ........................................................................................................... 2 Description of the Hoover Dam refugium 3 Methods ............................................................................................................... 3 Results 3 Discussion of fish refugia 4 Bibliography 5 TABLES Table 1 Morphometric comparison of Hoover Dam refugium and Devil's Hole populations ........................................................................ 1 4 2 Meristic comparison of Hoover Dam refugium and Devil's Hole populations 15 FIGURES Figure 1 Underwater photograph of Cyprinodon diabolis in the Hoover Dam refugium ...................................................................................................................................... 6 2 The Hoover Dam refugium located just below Hoover Dam ........................... 7 3 Longitudinal profile of the Hoover Dam refugium ........................................................ 8 4 The tapped hot springs being piped to the refugium 9 5 The outflow box (left) of the Hoover Dam refugium ......10 6 Comparison of monthly population fluctuations from Hoover Dam refugium and Devil's Hole populations of Cyprinodon diabolis ................... 11 7 Comparison of sex ratio fluctuations in Hoover Dam refugium and Devil's Hole populations ....12 8 The shallow end of the refugium showing substrate and associated algal mats of Mastigocladus lamiriosa 13 INTRODUCTION portion of the Death Valley National Monument in 1952. Miller [1], in observing the fact that only about During the 1960's, agricultural development, 1 00 fish species occur naturally in the United with its associated pumping of underground States west of the Rocky Mountains, described water supplies, began affecting Devil's Hole by this fauna as depauperate, characterized by lowering the water level on the critical shelf area. relicts, monotypic genera, and large amounts of When the relationship between pumping of endemism. In recent years, this unique and ground water and the falling water level in Devil's specialized fish fauna has come under Hole, and between the falling water level and considerable pressure from the introduction and reduced pupfish reproduction was established, establishment of exotic fish species and a the Department of the Interior requested that reduction in habitat, usually via human demand pumping be stopped from four nearby wells. The on the water supply [1, 2]. request was ignored; so in July 1973, the Department of Interior requested the This problem has become particularly intense in Department of Justice to initiate litigation to the southwestern United States where prevent the continued withdrawal of ground agricultural pumping and diversion of water by pumping. This battle led to the U.S. watercourses coupled with the establishment of Supreme Court where, in 1976, the justices exotic fish species is threatening many native upheld a lower court decision which "favored" fishes. During the past 35 years, man's activities the pupfish by ordering a water level which have apparently caused the extinction of four would allow the pupfish to survive and species and six subspecies of fish within reproduce successfully. However, in the early California, Nevada, and Arizona [2]. Additionally, 1 970's (and presently for that matter), the 50 species of fish, including the Devil's Hole survival of the pupfish in Devil's Hole was in pupfish, within the eight Great Basin states and doubt, therefore, a search began for a possible northern Mexico are listed by the Department of transplant site. In 1971, a spring was located the Interior as threatened or endangered [3]. below Hoover Darn which appeared to have a temperature similar to the water of Devil's Hole, The one species which has received the most 33 °C. By August 1972, a triparty agreement publicity and in many ways has spearheaded between the U.S. Fish and Wildlife Service, the endangered species recovery work is the Devil's Bureau of Reclamation, and the Nevada Hole pupfish, Cyprinodon diabolis. The Devil's Department of Fish and Game resulted in the Hole pupfish, until the recent transplant into the completion of a water-filled cement pool, known Hoover Dam refugium, was restricted to a single as the Hoover Dam refugium. spring source in Ash Meadows, Nye County, Nev. This single spring, named Devil's Hole, is located In September 1972, substrate material, (metres) below the land approximately 15 m planarians Dugesia, hydrobiid snails Tryonia, surface in a collapsed cave. Devil's Hole is part of elmid beetles Stenelmis, and the green algae an underground water cavern system which is Spirogyra, all from Devil's Hole, were placed in known to exceed 100 m in depth. While the the Hoover Dam refugium. On October 2, 1972, cavern system is extensive, the pupfish use a very seven Devil's Hole pupfish were placed in the small portion of it. A small 2- by 3-m shelf area refugium. A 96-hour bioassay period was near the surface was found to be the site of initiated to examine the pupfish in their new virtually all pupfish reproductive and feeding home. Two pupfish were lost shortly after activity [4]. transfer. However, the remaining five apparently thrived, so 20 additional fish were transplanted Devil's Hole is, according to the National Park into the refugium on October 13, 1976. One Service, the most restricted habitat of any dead pupfish was removed two days later. On vertebrate species in the world. Owing to this October 21, 1976, reproduction was taking unique habitat, and the uniqueness of the fish place, indicating the fishes apparent adoption of itself, Devil's Hole was designated as a disjunct their new environment. ' Numbers in brackets identify references in the bibliography. APPLICATION but highly fluctuating population of Tryonia now exists within the refugium. Elmid beetles and The results and conclusions in this report will be planaria are, however, absent. Significant of interest to anyone working with desert fishes numbers of other aquatic insects are present. Of and/or endangered fish species in particular. particular importance are the dragonfly larvae Unfortunately, increased human need for land which at times are numerous. (and water) coupled with the restricted range of many desert fishes has threatened some of the endemic species. This has resulted in an CONCLUSIONS increased interest in fish refugia. With the design of the Hoover Dam refugium being incorporated The following general conclusions resulted from for other endangered fish species; the Pahrump the Hoover Dam refugium studies: killifish, Empetrichthys I. latos, for example; it is necessary to determine the effectiveness of this refugium as quickly as possible. Results of this 1. The Hoover Dam refugium population of study will also be important in determining the Cyprinodon diabolis has become the first future status of the Devil's Hole pupfish established population of the fish outside of (Cyprinodon diabolis). Devil's Hole. 2. Population fluctuations in the Hoover Dam SUMMARY refugium are similar to those observed in Devil's Hole, with lowest numbers observed in This report attempts to examine the status of the late winter and highest numbers in August Hoover Dam refugium population of Cyprinodon through October. diabolis by comparing community structure and complexity, population fluctuations, sex ratio 3. During the sampling period, population data, morphometrics, and meristics of the Hoover levels varied from a high of 69 during October Dam refugium population to the original Devil's 1 976 to a low of 48 in February 1977. Hole population, the source of the transplanted fish (fig. 1). Research reported herein was 4. The male:female sex ratio in the refugium conducted from October 1975 through is highly variable, ranging from 2.92:1 to March 1977. 0.75:1. Monthly population counts showed that 5. Standard length of the refugium fluctuations of pupfish numbers observed in the population has increased to a mean of Hoover Dam refugium were similar to those 25.1 mm (millimetres) compared to a mean of noted in