REC-ERC-77-11

OBSERVATIONS ON THE STATUS OF THE DEVIL'S HOLE 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 J. E. Deacon of the University of Nevada is thanked for his comprehensive review of this manuscript and the use of unpublished population data from Devil's Hole.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 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 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" . During the past 35 years, man's activities the pupfish by ordering a water level which have apparently caused the of four would allow the pupfish to survive and species and six subspecies of fish within reproduce successfully. However, in the early , 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 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 Devil's Hole, with lowest numbers 1 9 mm in Devil's Hole. occuring in late winter and highest numbers in late summer and early fall. The number of fish in 6. Mean values of predorsal and anal to the refugium ranged from 48 to 69. Sex ratios are caudal length are very similar for the refugium highly variable, as they are in Devil's Hole. and Devil's Hole populations. Morphometric examination revealed significant 7. Mean values of greatest body depth, differences between the Hoover Dam refugium greatest body width, head length, and least and Devil's Hole populations in five of seven measurements taken. An overall increase in caudal peduncle depth all differed significantly length was particularly evident. between the two populations.

Community diversity has increased within the 8. Meristic examinations showed Hoover Dam refugium since the initial insignificant variation between the two introduction of the green alga Spirogyra, the populations. hydrobiid snail Tryonia, elmid beetles Stenelmis, and planaria Dugesia, from Devil's Hole. Algal 9. Community diversity has increased in the diversity has increased from the single species refugium since the initial introduction of algae originally planted to at least seven. An often large, and invertebrates from Devil's Hole.

2 10. Predation by dragonfly larvae may pose Morphometric and meristic counts were made a problem for the refugium population. as described for cyprinodonts by Miller [5]. Measurements were made with precision dial 11. The Hoover Dam refugium has been calipers to the nearest 0.1 mm. All counts and successful as a temporary environment for the measurements were taken from live specimens Devil's Hole pupfish, however, the at the refugium. Eleven fish were examined for environment which Devil's Hole provides is morphometric and meristic characters. In some unique and probably cannot be permanently fin ray counts, less than 11 fish were examined. duplicated. The necessity of making these counts and measurements on live fish of course raises questions regarding their comparability with DESCRIPTION OF THE preserved specimens. This approach was taken HOOVER DAM REFUGIUM because of restrictions on the collecting permit.

The Hoover Dam refugium was constructed in RESULTS August 1 972 and is located less than 1 km (kilometre) below Hoover Dam in Clark County, Nev. on land administered by the Bureau of During the period from October 1 975 through Reclamation (fig. 2). The refugium is March 1 977, population numbers ranged from a approximately 2 by 6 m and ranges from 1 to 3 m low of 48 in February 1 977 to a high of 69 in in depth (fig. 3). October 1 976. This fluctuation corresponds well with that displayed by Cyprinodon diabolis m Water for the refugium is provided by a nearby Devil's Hole where in 1 976, the lowest in February and the hot spring which flows at 40 °C (fig. 4). Within population estimate was 1 80 highest was 410 in September (fig. 6). On the refugium, water temperature is maintained March 1 4, 1974, the Hoover Dam refugium near 33 °C by controlling the rate of flow into the population was estimated at between and refugium. In summer months, the flow of hot 1 94 204. After the initial introduction of fish in water is increased. Water enters the refugium at October 1 972, the population underwent an the deep end and exits via an outlfow weir near explosion in numbers which resulted in the March the surface (fig. 5). 1 974 estimate [7]. In November 1 974, the population had decreased to an estimated 110 to 117, and by October 1 975, there was a further METHODS reduction to 62 fish. However, since October 1 975, the population has apparently stabilized. Monthly population counts were made at the Hoover Dam refugium. Counting procedures During population counts, the sex ratio of the involved partitioning the refugium into seven population was examined. Monthly male:female sections. In each section, the following sex ratios proved to be highly variable, ranging categories of fish were counted on at least two from 2.92:1 to 0.75:1 (fig. 7). During most of the occasions (the number of occasions depending year, there are slightly more males than females. upon the consistency of the counts): males, females, juveniles, and all fish. The average Reproduction occurs throughout the year in the counts of males, females, and juveniles were Hoover Dam refugium with highest reproductive added to any observed larvae to arrive at a final activity from late May through August. Juveniles total count which appears in the tables. The (fish 1 5 mm or less in length) comprised counts of "all fish" were used only as a approximately a third of the total fish observed in comparison. Beginning in January 1 976, a scuba June (20 of 63), July (22 of 63), and August (21 diver was employed during the population of 66) of 1 976. Lowest numbers of juveniles counts. By chasing the fish out otthe deep end, observed was in February 1 977 (1 of 48). The the diver enabled more accurate and consistent greatest abundance of larval fishes was seen in counts to be made at the surface. Through the May through August. described counting procedure, sex ratios of all adult individuals (those longer than 1 5 mm Community diversity has increased within the length) were determined. Hoover Dam refugium. Originally in October

3 1 972, hydrobiid snails. Tryonia; elmid beetles, caudal length were similar in both populations. Stenelmis; green algae. Spirogyra; and planaria, Meristic data, seeming less susceptable to Dugesia, were planted into the refugium from change, showed little difference between the Devil's Hole. Examination of the algae during the two populations (table 2). fall of 1976 revealed the presence of six genera. Dominant algae included the green, Spirogyra, and the blue-green, Mastigocladus laminosa DISCUSSION OF FISH REFUGIA (fig. 8). Two other blue-greens, Oscillatoria and to a lesser extent Aphanothece, were present. Attached to Mastigocladusand Oscillatoria were Recent deterioration of habitats and introduction the diatoms, Achnanthes and Cymbella. The of exotic fishes has led to reduced populations of hydrobiid snail, Tryonia, exists as a viable, highly many native fishes. The Death Valley fishes of fluctuating population within the refugium. The eastern California and southwestern Nevada in snails become omnipresent within the refugium particular, have been under ever-increasing from March through August. In winter months, pressures due to increased use and development the snail population is reduced to a mere of the area. It is here, in the Death Valley system, remnant of its summer numbers, with most where interest in fish refugia has often been individuals on rocks in the deep end of the focused. refugium. Elmid beetles and planaria failed to become established within the refugium, Refugia for endangered Death Valley fishes exist perhaps because of the absence of shallow, in a myriad of forms dependent upon land and sloping substrates within the refugium. The water availability and the requirements of the refugium walls are vertical and the shallowest fishes involved. Completibn of the depth is 1 m. The addition of a declining shelf, Native Fish Sanctuary in October 1969 provided or the simple rearrangement of substrate, might a 2.3 hectare natural refugium in Fish Slough, provide a suitable niche for these invertebrates. Owens Valley, including the Owens pupfish, Various aquatic insects inhabit the refugium. Cyprinodon radiosus;a distinctive speckled dace, Dragonfly larvae, a known fish-fish egg predator, Rhinichthys osculus; the Tui chub, occur in the refugium. It is not uncommon to Gila bicolor snyderi; and the Owens sucker, remove these larvae from the waters of the Catostomus fumeiventris [6]. This type of natural refugium during the monthly population counts. refugium located in the same basin in which the Normally, dragonfly larvae would not pose a fish are endemic to is preferred. However, threat to a fish population; however, with the low conditions do not always permit the numbers of fish in winter and spring, even limited establishment of such a refugium. This was the predation could be significant. Such larvae do case when the Hoover Dam refugium site was not exist in Devil's Hole. chosen. This "cement tank" type of refugium should be considered only as a last resort. With During October 1 976, morphometric and this type of refugium, continuous surveillance and meristic data were gathered at the Hoover Dam management by qualified personnel is often refugium. These data were compared to those necessitated. Refugia are not substitutes for the gathered by Miller [5] on the Devil's Hole native fishes original habitat, but could act as population. Morphometric measurements showed an overall increase in body size of C. "insurance" against loss of a population. diabolisin the refugium (table 1). Standard length increased from a mean of 19 mm in Devil's Hole Some fish populations exist in highly unique to a mean of 25.2 mm in the refugium. A habitats which are nearly impossible or not maximum length of 31.5 mm was observed for practical to reproduce elsewhere; Devil's Hole a refugium female (larger fish were seen but were represents such a habitat. The Hoover Dam not sampled). The proportion of body depth to refugium provides insurance against loss of the standard length was greater in the refugium Devil's Hole pupfish but does not provide a population. Similar results were observed for replacement for Devil's Hole itself, because body width and caudal peduncle depth. The different environments select for different proportion of head length to standard length was characters, resulting in genetic drift of the Hoover less in the refugium population than in the Devil's Dam population away from the Devil's Hole Hole population. Predorsal length and anal to population.

4 BIBLIOGRAPHY

[1] Miller, R. R. "Man and the Changing Fish Fauna of the American Southwest," Pap. Mich. Acad. Sci., Arts, Lett. 46: 365-404, 1961.

[2] Pister, E. P. "Desert Fishes and Their Habitats," Trans. Amer. Fish. Soc., 103(3): 531-540, 1974.

[3] U.S. Dept. of Interior. "Threatened Wildlife of the United States," Bur. Sport Fish. Wild. Resource Publ. 114 Wash., D.C., March, 1973.

[4] James, C. J. "Aspects of the Ecology of the Devil's Hole Pupfish, Cyprinodon diabolis Wales," Unpubl. M.S. Thesis, University of Nevada-L.V., 1969.

[5] Miller, R. R. "The Cyprindodont Fishes of the Death Valley System of Eastern California and Southeastern Nevada," Misc. Publ. Mus. Zool. Un iv. Mich., 68: 1-155, 1948.

[6] Miller, R. R. and E. P. Pister. "Management of the Owens Pupfish, Cyprinodon radiosus, in Mono County, California," Trans. Amer. Fish. Soc., 100(3): 502-509, 1971.

[7] Williams, J. E. "1975 Status Report on the Devil's Hole Pupfish, Cyprinodon diabolis, at the Hoover Dam Refugium," in, Preceedings of the Seventh Annual Symposium of the Desert Fishes Council, in press.

5 Figure 1.—Underwater photograph of Cyprinodon diabolis in the Hoover Dam refugium. Males are blue with black fin banding; females appear as a straw-green color. Photo P45-D-77921, P45-D-77925, and P45-D-77926

6 Figure 2.—The Hoover Dam refugium located just below Hoover Dam. Shown in the foreground, covered by screens. Photo P45-D-77920

7 5.79 m •

T I „Z/• Th 0 I ouTFLOW

-1 — / — JL A. „I. A. .a.

/1 ----Inflow pipe 1.75 m 1-,

Figure 3.-Longitudinal profile of the Hoover Dam refugium.

8 Figure 4.-The tapped hot springs being piped to the refugium. Photo P45-D-77923

9 Figure 5.—The outflow box (left) of the Hoover Dam refugium. Photo P45-D-77922

10 80 • N 400 \ / N / N / N N...,

60 AL 300 / V) , V V 0 ,

ct _J \ , a. ,.../ 40 . \ 200 0 a_ HOLE POPULATION SIZE) cc Hoover Dam Refugium -- — —Devil's Hole 0 20 100 0

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR 1 975 1 976 1 977 OCTOBER 1 975 THROUGH MARCH 1977 SAMPLING INTERVALS

Figure 6.—Comparison of monthly population fluctuations from Hoover Dam refugium and Devil's Hole populations of Cyprinodon diabolis. Refugium (solid line) and Devil's Hole (dashed line) data were collected from October 1975 to February 1977.

11 3:1

/ \ I \ / ‘\ 2:1 / X /

r'• 4 / / / \.

\ , \ V

Hoover Darn Refug urn — Devi I 's Hole

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY 1 975 1 976 1 977 SAMPLING INTERVALS

Figure 7.—Comparison of sex ratio fluctuations in Hoover Dam refugium and Devil's Hole populations. Refugium (solid line) and Devil's Hole (dashed line) data were gathered from October 1975 to March 1977 and October 1967 to August 1 968, respectively. Devil's Hole data from James [4].

1 2 Figure 8.-The shallow end of the refugium showing substrate and associated algal mats of Mastigocladus laminosa. Photo P45-D-77924

1 3 Table 1.—Morphometric comparison of Hoover Dam refugium and Devil's Hole populations. Refugium data were gathered in October 1976. Devil's Hole data from Miller (5).

Population Sex No. Standard length Body dimensions in thousandths of standard length: range (mean) ( mm) Predorsal Anal to caudal Body Body Head Peduncle range mean length length depth width length depth Hoover Dam M 4 20.5-29.9 25.2 559-702 317-378 361- 204- 288- 167-186 (606) (349) 401 235 334 (178) (386) (225) (316) Hoover Dam F 7 16.2-31.5 25.0 546-691 277-395 313- 200- 294- 154-177 (632) (330) 399 295 385 (167) (359) (246) (334) Devil's Hole M & F 34 14-28 19 335- — — 375 — (354) Devil's Hole M 10-18 — 601-654 329-355 309- 226- 159-177 (631) (343) 407 255 — (165) (355) (237) Devil's Hole F 10-12 — 617-645 315-332 304- 220- 150-165 (631) (325) 353 249 — (157) (329) (236) Table 2.—Meristic comparison of Hoover Dam refugium and Devil's Hole populations. Refugium data were gathered in October 1976. Devil's Hole data from Miller (5).

Hoover Dam Devil's Hole

Range Mean Range Mean Dorsal rays 11 11.0 1 0-13 11.13 Anal rays 11-12 11.5 1 0-12 11.24 Caudal rays 14-18 15.2 13-20 16.83 Pectoral rays 1 4-19 16.5 14-18 16.86 Pelvic rays 0 0.0 0-6 0.02

1 5