Download REC-ERC-77-11 OBSERVATIONS ON THE STATUS OF THE

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
UNITED STATES DEPARTMENT OF THE INTERIOR
SI METRIC
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unpublished population data from Devil's Hole.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
Application
...........................................................................................................
Summary ...............................................................................................................
Conclusions
...........................................................................................................
Description of the Hoover Dam refugium
Methods
...............................................................................................................
Results
Discussion of fish refugia
Bibliography
1
2
2
2
3
3
3
4
5
TABLES
Table
1
2
Morphometric comparison of Hoover Dam refugium and Devil's Hole
populations
........................................................................
Meristic comparison of Hoover Dam refugium and Devil's Hole
populations
14
15
FIGURES
Figure
1
2
3
4
5
6
7
8
Underwater photograph of Cyprinodon diabolis in the Hoover Dam
6
refugium
......................................................................................................................................
7
The Hoover Dam refugium located just below Hoover Dam ...........................
Longitudinal profile of the Hoover Dam refugium
........................................................
8
9
The tapped hot springs being piped to the refugium
......10
The outflow box (left) of the Hoover Dam refugium
Comparison of monthly population fluctuations from Hoover Dam
11
refugium and Devil's Hole populations of Cyprinodon diabolis ...................
Comparison of sex ratio fluctuations in Hoover Dam refugium and
.... 12
Devil's Hole populations
The shallow end of the refugium showing substrate and associated
13
algal mats of Mastigocladus lamiriosa
INTRODUCTION
Miller [1], in observing the fact that only about
1 00 fish species occur naturally in the United
States west of the Rocky Mountains, described
this fauna as depauperate, characterized by
relicts, monotypic genera, and large amounts of
endemism. In recent years, this unique and
specialized fish fauna has come under
considerable pressure from the introduction and
establishment of exotic fish species and a
reduction in habitat, usually via human demand
on the water supply [1, 2].
This problem has become particularly intense in
the southwestern United States where
agricultural pumping and diversion of
watercourses coupled with the establishment of
exotic fish species is threatening many native
fishes. During the past 35 years, man's activities
have apparently caused the extinction of four
species and six subspecies of fish within
California, Nevada, and Arizona [2]. Additionally,
50 species of fish, including the Devil's Hole
pupfish, within the eight Great Basin states and
northern Mexico are listed by the Department of
the Interior as threatened or endangered [3].
The one species which has received the most
publicity and in many ways has spearheaded
endangered species recovery work is the Devil's
Hole pupfish, Cyprinodon diabolis. The Devil's
Hole pupfish, until the recent transplant into the
Hoover Dam refugium, was restricted to a single
spring source in Ash Meadows, Nye County, Nev.
This single spring, named Devil's Hole, is located
approximately 15 m (metres) below the land
surface in a collapsed cave. Devil's Hole is part of
an underground water cavern system which is
known to exceed 100 m in depth. While the
cavern system is extensive, the pupfish use a very
small portion of it. A small 2- by 3-m shelf area
near the surface was found to be the site of
virtually all pupfish reproductive and feeding
activity [4].
Devil's Hole is, according to the National Park
Service, the most restricted habitat of any
vertebrate species in the world. Owing to this
unique habitat, and the uniqueness of the fish
itself, Devil's Hole was designated as a disjunct
' Numbers in brackets identify references in the
bibliography.
portion of the Death Valley National Monument
in 1952.
During the 1960's, agricultural development,
with its associated pumping of underground
water supplies, began affecting Devil's Hole by
lowering the water level on the critical shelf area.
When the relationship between pumping of
ground water and the falling water level in Devil's
Hole, and between the falling water level and
reduced pupfish reproduction was established,
the Department of the Interior requested that
pumping be stopped from four nearby wells. The
request was ignored; so in July 1973, the
Department of Interior requested the
Department of Justice to initiate litigation to
prevent the continued withdrawal of ground
water by pumping. This battle led to the U.S.
Supreme Court where, in 1976, the justices
upheld a lower court decision which "favored"
the pupfish by ordering a water level which
would allow the pupfish to survive and
reproduce successfully. However, in the early
1 970's (and presently for that matter), the
survival of the pupfish in Devil's Hole was in
doubt, therefore, a search began for a possible
transplant site. In 1971, a spring was located
below Hoover Darn which appeared to have a
temperature similar to the water of Devil's Hole,
33 °C. By August 1972, a triparty agreement
between the U.S. Fish and Wildlife Service, the
Bureau of Reclamation, and the Nevada
Department of Fish and Game resulted in the
completion of a water-filled cement pool, known
as the Hoover Dam refugium.
In September 1972, substrate material,
planarians Dugesia, hydrobiid snails Tryonia,
elmid beetles Stenelmis, and the green algae
Spirogyra, all from Devil's Hole, were placed in
the Hoover Dam refugium. On October 2, 1972,
seven Devil's Hole pupfish were placed in the
refugium. A 96-hour bioassay period was
initiated to examine the pupfish in their new
home. Two pupfish were lost shortly after
transfer. However, the remaining five apparently
thrived, so 20 additional fish were transplanted
into the refugium on October 13, 1976. One
dead pupfish was removed two days later. On
October 21, 1976, reproduction was taking
place, indicating the fishes apparent adoption of
their new environment.
but highly fluctuating population of Tryonia now
exists within the refugium. Elmid beetles and
planaria are, however, absent. Significant
numbers of other aquatic insects are present. Of
particular importance are the dragonfly larvae
which at times are numerous.
APPLICATION
The results and conclusions in this report will be
of interest to anyone working with desert fishes
and/or endangered fish species in particular.
Unfortunately, increased human need for land
(and water) coupled with the restricted range of
many desert fishes has threatened some of the
endemic species. This has resulted in an
increased interest in fish refugia. With the design
of the Hoover Dam refugium being incorporated
for other endangered fish species; the Pahrump
killifish, Empetrichthys I. latos, for example; it is
necessary to determine the effectiveness of this
refugium as quickly as possible. Results of this
study will also be important in determining the
future status of the Devil's Hole pupfish
(Cyprinodon diabolis).
CONCLUSIONS
The following general conclusions resulted from
the Hoover Dam refugium studies:
1. The Hoover Dam refugium population of
Cyprinodon diabolis has become the first
established population of the fish outside of
Devil's Hole.
2. Population fluctuations in the Hoover Dam
refugium are similar to those observed in
Devil's Hole, with lowest numbers observed in
late winter and highest numbers in August
through October.
SUMMARY
This report attempts to examine the status of the
Hoover Dam refugium population of Cyprinodon
diabolis by comparing community structure and
complexity, population fluctuations, sex ratio
data, morphometrics, and meristics of the Hoover
Dam refugium population to the original Devil's
Hole population, the source of the transplanted
fish (fig. 1). Research reported herein was
conducted from October 1975 through
March 1977.
3. During the sampling period, population
levels varied from a high of 69 during October
1 976 to a low of 48 in February 1977.
4. The male:female sex ratio in the refugium
is highly variable, ranging from 2.92:1 to
0.75:1.
Monthly population counts showed that
fluctuations of pupfish numbers observed in the
Hoover Dam refugium were similar to those
noted in Devil's Hole, with lowest numbers
occuring in late winter and highest numbers in
late summer and early fall. The number of fish in
the refugium ranged from 48 to 69. Sex ratios are
highly variable, as they are in Devil's Hole.
6. Mean values of predorsal and anal to
caudal length are very similar for the refugium
and Devil's Hole populations.
Morphometric examination revealed significant
differences between the Hoover Dam refugium
and Devil's Hole populations in five of seven
measurements taken. An overall increase in
length was particularly evident.
7. Mean values of greatest body depth,
greatest body width, head length, and least
caudal peduncle depth all differed significantly
between the two populations.
5. Standard length of the refugium
population has increased to a mean of
25.1 mm (millimetres) compared to a mean of
1 9 mm in Devil's Hole.
8.
Meristic examinations showed
insignificant variation between the two
populations.
Community diversity has increased within the
Hoover Dam refugium since the initial
introduction of the green alga Spirogyra, the
hydrobiid snail Tryonia, elmid beetles Stenelmis,
and planaria Dugesia, from Devil's Hole. Algal
diversity has increased from the single species
originally planted to at least seven. An often large,
9. Community diversity has increased in the
refugium since the initial introduction of algae
and invertebrates from Devil's Hole.
2
Morphometric and meristic counts were made
as described for cyprinodonts by Miller [5].
Measurements were made with precision dial
calipers to the nearest 0.1 mm. All counts and
measurements were taken from live specimens
at the refugium. Eleven fish were examined for
morphometric and meristic characters. In some
fin ray counts, less than 11 fish were examined.
The necessity of making these counts and
measurements on live fish of course raises
questions regarding their comparability with
preserved specimens. This approach was taken
because of restrictions on the collecting permit.
10. Predation by dragonfly larvae may pose
a problem for the refugium population.
11.
The Hoover Dam refugium has been
successful as a temporary environment for the
Devil's Hole pupfish, however, the
environment which Devil's Hole provides is
unique and probably cannot be permanently
duplicated.
DESCRIPTION OF THE
HOOVER DAM REFUGIUM
The Hoover Dam refugium was constructed in
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
Reclamation (fig. 2). The refugium is
approximately 2 by 6 m and ranges from 1 to 3 m
in depth (fig. 3).
RESULTS
During the period from October 1 975 through
March 1 977, population numbers ranged from a
low of 48 in February 1 977 to a high of 69 in
October 1 976. This fluctuation corresponds well
with that displayed by Cyprinodon diabolis m
Devil's Hole where in 1 976, the lowest
population estimate was 1 80 in February and the
highest was 410 in September (fig. 6). On
March 1 4, 1974, the Hoover Dam refugium
population was estimated at between 1 94 and
204. After the initial introduction of fish in
October 1 972, the population underwent an
explosion in numbers which resulted in the March
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
reduction to 62 fish. However, since October
1 975, the population has apparently stabilized.
Water for the refugium is provided by a nearby
hot spring which flows at 40 °C (fig. 4). Within
the refugium, water temperature is maintained
near 33 °C by controlling the rate of flow into the
refugium. In summer months, the flow of hot
water is increased. Water enters the refugium at
the deep end and exits via an outlfow weir near
the surface (fig. 5).
METHODS
Monthly population counts were made at the
Hoover Dam refugium. Counting procedures
involved partitioning the refugium into seven
sections. In each section, the following
categories of fish were counted on at least two
occasions (the number of occasions depending
upon the consistency of the counts): males,
females, juveniles, and all fish. The average
counts of males, females, and juveniles were
added to any observed larvae to arrive at a final
total count which appears in the tables. The
counts of "all fish" were used only as a
comparison. Beginning in January 1 976, a scuba
diver was employed during the population
counts. By chasing the fish out otthe deep end,
the diver enabled more accurate and consistent
counts to be made at the surface. Through the
described counting procedure, sex ratios of all
adult individuals (those longer than 1 5 mm
length) were determined.
During population counts, the sex ratio of the
population was examined. Monthly male:female
sex ratios proved to be highly variable, ranging
from 2.92:1 to 0.75:1 (fig. 7). During most of the
year, there are slightly more males than females.
Reproduction occurs throughout the year in the
Hoover Dam refugium with highest reproductive
activity from late May through August. Juveniles
(fish 1 5 mm or less in length) comprised
approximately a third of the total fish observed in
June (20 of 63), July (22 of 63), and August (21
of 66) of 1 976. Lowest numbers of juveniles
observed was in February 1 977 (1 of 48). The
greatest abundance of larval fishes was seen in
May through August.
Community diversity has increased within the
Hoover Dam refugium. Originally in October
3
1 972, hydrobiid snails. Tryonia; elmid beetles,
Stenelmis; green algae. Spirogyra; and planaria,
Dugesia, were planted into the refugium from
Devil's Hole. Examination of the algae during the
fall of 1976 revealed the presence of six genera.
Dominant algae included the green, Spirogyra,
and the blue-green, Mastigocladus laminosa
(fig. 8). Two other blue-greens, Oscillatoria and
to a lesser extent Aphanothece, were present.
Attached to Mastigocladusand Oscillatoria were
the diatoms, Achnanthes and Cymbella. The
hydrobiid snail, Tryonia, exists as a viable, highly
fluctuating population within the refugium. The
snails become omnipresent within the refugium
from March through August. In winter months,
the snail population is reduced to a mere
remnant of its summer numbers, with most
individuals on rocks in the deep end of the
refugium. Elmid beetles and planaria failed to
become established within the refugium,
perhaps because of the absence of shallow,
sloping substrates within the refugium. The
refugium walls are vertical and the shallowest
depth is 1 m. The addition of a declining shelf,
or the simple rearrangement of substrate, might
provide a suitable niche for these invertebrates.
Various aquatic insects inhabit the refugium.
Dragonfly larvae, a known fish-fish egg predator,
occur in the refugium. It is not uncommon to
remove these larvae from the waters of the
refugium during the monthly population counts.
Normally, dragonfly larvae would not pose a
threat to a fish population; however, with the low
numbers of fish in winter and spring, even limited
predation could be significant. Such larvae do
not exist in Devil's Hole.
caudal length were similar in both populations.
Meristic data, seeming less susceptable to
change, showed little difference between the
two populations (table 2).
DISCUSSION OF FISH REFUGIA
Recent deterioration of habitats and introduction
of exotic fishes has led to reduced populations of
many native fishes. The Death Valley fishes of
eastern California and southwestern Nevada in
particular, have been under ever-increasing
pressures due to increased use and development
of the area. It is here, in the Death Valley system,
where interest in fish refugia has often been
focused.
Refugia for endangered Death Valley fishes exist
in a myriad of forms dependent upon land and
water availability and the requirements of the
fishes involved. Completibn of the Owens Valley
Native Fish Sanctuary in October 1969 provided
a 2.3 hectare natural refugium in Fish Slough,
Owens Valley, including the Owens pupfish,
Cyprinodon radiosus;a distinctive speckled dace,
Rhinichthys osculus; the Owens River Tui chub,
Gila bicolor snyderi; and the Owens sucker,
Catostomus fumeiventris [6]. This type of natural
refugium located in the same basin in which the
fish are endemic to is preferred. However,
conditions do not always permit the
establishment of such a refugium. This was the
case when the Hoover Dam refugium site was
chosen. This "cement tank" type of refugium
should be considered only as a last resort. With
this type of refugium, continuous surveillance and
management by qualified personnel is often
necessitated. Refugia are not substitutes for the
native fishes original habitat, but could act as
"insurance" against loss of a population.
During October 1 976, morphometric and
meristic data were gathered at the Hoover Dam
refugium. These data were compared to those
gathered by Miller [5] on the Devil's Hole
population. Morphometric measurements
showed an overall increase in body size of C.
diabolisin the refugium (table 1). Standard length
increased from a mean of 19 mm in Devil's Hole
to a mean of 25.2 mm in the refugium. A
maximum length of 31.5 mm was observed for
a refugium female (larger fish were seen but were
not sampled). The proportion of body depth to
standard length was greater in the refugium
population. Similar results were observed for
body width and caudal peduncle depth. The
proportion of head length to standard length was
less in the refugium population than in the Devil's
Hole population. Predorsal length and anal to
Some fish populations exist in highly unique
habitats which are nearly impossible or not
practical to reproduce elsewhere; Devil's Hole
represents such a habitat. The Hoover Dam
refugium provides insurance against loss of the
Devil's Hole pupfish but does not provide a
replacement for Devil's Hole itself, because
different environments select for different
characters, resulting in genetic drift of the Hoover
Dam population away from the Devil's Hole
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.
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.
[5]
[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
0
I
JL
—
A.
•
Z/•
Th
ouTFLOW
„
„I.
-1
A./ .a.
—
/1
1-,
1.75 m
Figure 3.-Longitudinal profile of the Hoover Dam refugium.
8
Inflow pipe
----
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
60
AL
,,
/
V)
0
\.
ct
_J
a.
0 40
a_
cc
,
V
V
\
,.../
Hoover Dam
-- — —Devil's Hole
0
300
200
HOLE POPULATION SIZE)
N...,
Refugium
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].
12
Figure 8.-The shallow end of the refugium showing substrate and
associated algal mats of Mastigocladus laminosa. Photo P45-D-77924
13
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
( mm)
range
mean
Body dimensions in thousandths of standard length: range (mean)
Predorsal
length
Anal to caudal
length
Body
depth
Body
width
Head
length
Peduncle
depth
Hoover Dam
M
4
20.5-29.9
25.2
559-702
(606)
317-378
(349)
361401
(386)
204235
(225)
288334
(316)
167-186
(178)
Hoover Dam
F
7
16.2-31.5
25.0
546-691
(632)
277-395
(330)
313399
(359)
200295
(246)
294385
(334)
154-177
(167)
Devil's Hole
M&F
34
14-28
19
—
—
335375
(354)
Devil's Hole
Devil's Hole
M
F
10-18
10-12
—
—
—
601-654
(631)
329-355
(343)
309407
(355)
226255
(237)
—
159-177
(165)
617-645
(631)
315-332
(325)
304353
(329)
220249
(236)
—
150-165
(157)
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).
Devil's Hole
Hoover Dam
Dorsal rays
Anal rays
Caudal rays
Pectoral rays
Pelvic rays
Range
Mean
Range
Mean
11
11-12
14-18
1 4-19
0
11.0
11.5
15.2
16.5
0.0
1 0-13
1 0-12
13-20
14-18
0-6
11.13
11.24
16.83
16.86
0.02
15