Devil's Hole Pupfish (Cyprinodon diabolis): An Endangered But Resilient Prehistoric Species Struggles to Survive

Cyprinodon diabolis is commonly known as the Devils Hole pupfish. They are minuscule fish, having a maximum length of less than one inch (25 millimeters) and averaging around 0.75 inches (19 millimeters) in length. Males have iridescent silvery blue coloring that shimmers as they swim. Females are colored yellow brown. They are a short-lived species, with a lifespan of approximately one year. Pupfish reach maturity within two to four months after hatching.

Devils Hole pupfish are classed as an endemic species (Greek: ἐν, en, “in” + δῆμος, demos, “people, district”) because they are found only in a specific geographic range. In fact, they are named after that location, which is a cavepool in Devils Hole cavern in Nye County, southwestern Nevada (36°25′31″ North, 116°17′28″ East). This limestone cavern is located, at an altitude of 2,400 feet (732 meters) above sea level, in a hilly range of the Amargosa Desert within the Ash Meadows National Wildlife Refuge, a 23,000 acre (9,300 hectares) sanctuary created in 1984.

Devils Hole opened over 60,000 years ago onto desert terrain as a tectonic (Latin: tectonicus, "building") cave, a secondary cave which is created by some kind of geological force after surrounding rocks have completed their formation. Dense layers of calcite that coat the cavern’s walls, especially in a nearby, separate, air-filled chamber, Brown's Room, have been invaluable in providing scientists with a 500,000-year record of temperature and other climatic variations. The 100 feet by 30 feet (30 by 9 meters) elongated rectangular outline of Devils Hole, oriented lengthwise northeast to southwest on the arid landscape, leads downwards to the warm watery depths of the vast aquifer that lies unsuspectingly underneath the dry external environment.

The geothermal (Greek: γη, ge, or γαια, gaia, "earth" + θέρμη, therme, "heat") pool, fed by the regional, south central Nevada aquifer, surfaces about 50 feet (15 meters) below the opening of Devils Hole cavern. The surface of Devils Hole pool is 10 by 65 feet (about 3 to 20 meters). Its depth far surpasses its surface measurements, for it burrows to unexplored depths, well below 500 feet (about 152 meters), branching into an endless, intricate network of caverns. The bottom has never been reached.

Devils Hole pool is a remnant of the prehistoric Death Valley Lake System, an extensive lake and riverine system in the area that was reduced to about thirty isolated springs and seeps with the most recent recession of the water table about 12,000 years ago during the late Pleistocene (Greek: πλεῖστος, pleistos, "most" + καινός, kainos, "new") Epoch. This aquifer contains paleowater (Greek: παλαιός, palaios, “old”) or fossil groundwater, which is a non-renewable resource as fossil aquifers, with low replenishment from precipitation, have a recharge rate that is low or even zero, with their dependence on snow melt and precipitation. Rainfall replenishment from the Spring Mountains ranges annually from around 4 inches (10 centimeters) at lower elevations to around 20 inches (50 centimeters) at the crest of the range.

The precise habitat of Cyprinodon diabolis is situated within the upper 80 feet (24 meters) of the part of Devil's Hole cavern that receives daylight, which permeates there for less than four hours per day in the summer (June, July, August) and not at all during December and January. Feeding and spawning primarily take place on a submerged limestone shelf, 10 feet by 16 feet (3 by 4.9 meters), shallowly covered by water near the south end of the pool's surface. A lower shelf, completely immersed by 16 to 30 feet (5 to 9 meters) of water, slopes downward into the cave and does not serve as main living quarters for this species that is diurnal (Latin: diēs, "day"), that is, active during the daytime.

Filamentous green algae (genus Spirogyra) and diatoms (genus Denticula) are the primary food source for Cyprinodon diabolis. The shelf is the only location in the pool that provides the mix of adequate direct sunlight with nutrient concentration (supplied by droppings from roosting or nesting barn owls, Tyto alba) and sufficient water that is requisite for algal photosynthesis. Peak spawning, from April to mid-June, coincides with peak algal growth. During spawning, the female deposits on this algal cushion four to five eggs, which are then fertilized by the male.

The temperature in this species' habitat ranges from 90° to 98° Fahrenheit (32° to 36.5° Celsius). Variations reflect time of day, amount of direct sunlight, and yearly seasons. Deeper expanses typically settle at 92.3° Fahrenheit (34° C).

With such a restricted habitat, Cyprinodon diabolis may be seen to lead a precarious existence. Severe threats to their habitat may have a devastating impact on their population. As such, conservationist-ichthyologists (Greek: ἰχθύς, ikhthus, "fish" + λόγος, logos, "study") Carl Leavitt Hubbs (October 19, 1894–June 30, 1979) and Robert Rush Miller (April 23, 1916-February 10, 2003) recommended in the 1940s that Devil's Hole be included as a detached unit of the Death Valley National Monument (now known as Death Valley National Park).

Presidential Proclamation No. 2961: For the sake of "a peculiar race of desert fish"

On January 17, 1952, the 40 acre (16 hectares) tract surrounding Devil's Hole was withdrawn from the public domain through Proclamation No. 2961 by President Harry Truman, acting under the American Antiquities Act of 1906 (16 U.S.C. § 431-433), which authorizes presidential designation as national monuments

". . .objects of historic or scientific interest that are situated upon the lands owned or controlled by the Government of the United States. . ."

The Proclamation noted the cavern's tectonic origin and limestone construction as well as its

"remarkable underground pool. . . . a unique subsurface remnant of the prehistoric chain of lakes which, in Pleistocene times, formed the Death Valley Lake System. . ."

The Proclamation then acknowledged that the integrality of the subterranean pool

". . .to the hydrographic history of the Death Valley region is further confirmed by the presence in this pool of a peculiar race of desert fish, and zoologists have demonstrated that this race of fish, which is found nowhere else in the world, evolved only after the gradual drying up of the Death Valley Lake System isolated this fish population from the original ancestral stock that, in Pleistocene times, was common to the entire region. . ."

The Proclamation placed the Devil's Hole tract under the management and direction of the National Park Service, an agency of the U.S. Department of the Interior that was created on August 25, 1916 under the National Park Service Organic Act (16 U.S.C. § 1-4). Additionally, Devils Hole was fenced off, and access was limited to the National Park Service.

In 1962 the U.S. Geological Survey installed a copper marker as a hydrologic gage to track water levels in Devil's Hole. According to their records, the level remained relatively stable at 1.2 feet below the marker. As long as the water level remains within three feet or less of the marker, most of the rock shelf is submerged so algae grows and Cyprinodon diabolis has no worries.

Emblematic of concern over this minuscule species' viability, Cyprinodon diabolis benefited from the Endangered Species Preservation Act of 1966, appearing in the first listing of endangered fishes, which was released on March 11, 1967.

Cappaert v. United States: U.S. Supreme Court about water rights for a vanishing species

Beginning in 1968, from March to October, Spring Meadows Ranch, a cattle ranch of about 12,000 acres owned by Francis Leo Cappaert and Marilyn I. Cappaert of Vicksburg, Mississippi, began pumping groundwater from a well, located about 2.5 miles from Devil's Hole, that drew on the same aquifer. Thereafter, water levels began dipping in Devil's Hole, from 2.3 feet below the marker in 1969 to:

• 3.17 feet in 1970;
• 3.48 feet in 1971;
• 3.93 feet in 1972.

In April 1970, in accordance with Nevada law, Spring Meadows Ranch filed an application with State Engineer Roland D. Westergard for permits concerning changes in water use of some of their wells. The National Park Service requested either denial of the permits or postponement in lieu of identifying Spring Meadows' wells that affect Devils Hole. State Engineer Westergard rejected postponement and, denying the existence of federal water rights or the possible adverse effects on the water table, as well as extolling the public interest derived from the ranch's increased economic development, decided to issue the permits.

In August 1971 the United States filed for an injunction through the U.S. District Court for the District of Nevada to restrict the ranch from pumping, except for domestic purposes, from six specific wells proximitous to Devil's Hole. On June 2, 1972 the complaint was amended to add two more wells. On April 9, 1974, the District Court enjoined any pumping that lowered the water level in Devil's Hole to three feet below the marker.

The Cappaerts appealed the case to the Court of Appeals for the Ninth Circuit, which affirmed the District Court's decision in their opinion dated December 4, 1974.

The case then went to the U.S. Supreme Court, which agreed to hear the issue of water rights. The highest court in the land then affirmed in a unanimous ruling on June 7, 1976, the previous decisions of the two lower courts. The opinion, delivered by 15th U.S. Supreme Court Chief Justice Warren Earl Burger (September 17, 1907–June 25, 1995), cited the "special protection" specifically afforded to Devil's Hole pool in President Truman's Proclamation and held that

". . .as of 1952, when the United States reserved Devil's Hole, it acquired by reservation water rights in unappropriated appurtenant water sufficient to maintain the level of the pool to preserve its scientific value, and thereby implement Proclamation No. 2961."

The case was remanded back to the district court for an evidentiary hearing to determine the specific terms of the injunction. On March 24, 1978, the district court issued its final order permanently enjoining the ranch

". . .except for domestic purposes. . .to limit the pumping from underground waters from wells. . .now existing or hereafter drilled. . .to the extent required to achieve and to maintain at Devil's Hole, Death Valley National Monument, a daily mean water level of 2.7 feet below the copper washer. . ."

While establishing the minimum water level at 2.7 feet (0.82 meters), the district court has the jurisdiction to raise the water level requirement in response to changes that render the determined level insufficient.

Ash Meadows National Wildlife Refuge: Buffering Devils Hole

On June 18, 1984, the Ash Meadows National Refuge was created as a wildlife sanctuary. The Refuge sprawls over 23,000 acres (9,300 hectares) at a distance of about 90 miles (140 kilometers) to the west-northwest of the ever-expanding Las Vegas. Its acreage represents the area of impact, which was determined to be the extent within which groundwater withdrawals, through irrigation and other pumping activities, would incontrovertibly reduce the water level in Devils Hole.

That expanse had been purchased from the farm corporation in 1977 by developers who planned to build a subdivision of 30,000 residential lots. Meanwhile concern over the plight of Cyprinodon diabolis kept rising, and in the early 1980s increasing attention was directed to the dozens of other unique plant and animal species indigenous to this terrain. The Nature Conservancy intervened to purchase the land from the developers and then resold it to the U.S. Fish and Wildlife Service.

The Refuge wraps around three sides of Devils Hole, while the north side is bordered by U.S. Bureau of Land Management property.

Devils Hole Pupfish Recovery Plan: Artificial refugia for backup populations

As a species with only one natural population endemic to a severely restricted geographic area within a delicately specific ecosystem (Greek: οἶκος, oikos, "home" + σύστημα, sustēma, "organized whole, body"), the Devils Hole pupfish is never eligible for delistment (removal) according to the Endangered Species Act of 1973 (16 U.S.C. § 1531 et seq.). Therefore, the recovery plan aims for downlisting, that is, reclassed from endangered down to threatened. Recovery criteria require a stable wild population of 300 individuals in winter and 700 in late autumn as well as two captive (not wild) populations in offsite refugia.

A concrete tank replicating the Devils Hole ecosystem was designed as an artificial refugium (Latin: refugium, "a taking refuge" [from re-, "back" + fugere, "to flee" + -ium, "place for"]) to propagate backup populations of Cyprinodon diabolis outside of their fragile native habitat. The first refugium was established at Hoover Dam in 1972.

Two more refugia, comprising the U.S. Fish and Wildlife Service's Amargosa Valley Pupfish Station, were established near Devils Hole within the Ash Meadows National Wildlife Refuge in 1980 at School Springs (now no longer operational) and in 1991 at Point of Rocks. Unfortunately, both of these populations became hybridized as a result of breeding with a related endangered species, Ash Meadows Amargosa pupfish (Cyprinodon nevadensis mionectes), that slipped into the refugia.

Population transfers occur as a strategy to refine captive habitats. Thus, on May 2, 2006, eighty hybridized pupfish (40 females, 20 males, 20 juveniles) were transferred from Point of Rocks Refuge, with half going to Willow Beach National Fish Hatchery in Arizona, about 11 miles downriver from Hoover Dam, and the other half to a refugium in Shark Reef Aquarium at Mandalay Bay Hotel and Casino on the Las Vegas Strip.

On May 18, 2006 populations were shifted as part of a strategy for integrating wild and captive populations. Two males were transferred from Devils Hole to Shark Reef and were joined there by two females, who arrived there from Hoover Dam Refuge. Five postlarvae, that is, recently hatched fish, practically invisible at 0.27 to 0.35 inches (7 to 9 millimeters), were relocated to Willow Beach. After these transfers, thirty-six adult Cyprinodon diabolis remained in Devils Hole.

Population surveys: Small fish, small numbers

The Devil's Hole community undergoes seasonal fluctuations in population, whereby spring numbers are low after a winter decline and autumn numbers increase.

The first underwater population survey was conducted in November 1954 and yielded a count of approximately 300 individuals.

Since regular population surveys were initiated in 1972, the Cyprinodon diabolis population has never approached the desired minimum of 700 in the late autumn. Surveys over the next two decades stabilized at an average of 324 individuals. A high of 582 was reached in the September 1994 survey. Beginning in the late 1990s a downward trend set in so that an average of 275 in 1997 dropped drastically in August and September 2004 with the loss of one-third of the population during two flash floods and further dips to 84 in November 2005 and to only thirty-eight in April 2006. Fall surveys enumerated 85 pupfish in 2006 and 92 in 2007.

Since 2007 population estimates have been evincing an upward swing. The fall 2008 estimate of 127 individuals represented a double achievement: the first triple digit estimate since 2004 and the first three year upward trend since 1996.

As mandated by the agency's General Management Plan of 2002, the National Park Service now conducts biannual population surveys in April and October. Surveys entail a surface count plus a count covering a descent down to about 100 feet (about 30 meters) by divers.

In April 2011 the population was estimated at 104.

Devils Hole: Sliding water levels

Water levels in Devils Hole remained basically stable during the 45,000 year period from the creation of the fissured skylight that opened up the cavepool 60,000 years ago up until about the end of the last glaciation about 15,000 years ago. During that seemingly halcyon time, the water level was about 16 feet (5 meters) higher than the current level of about 49.2 feet (15 meters) from the opening.

An important natural influence upon water level is wrought by earthquakes, whether local or at a distance.

On April 4, 2010, U.S. Geological Survey cameras fortuitiously caught the sloshing turbulence in Devils Hole cavepool induced by the shockwaves tickling the Mojave Desert that were generated by the epicenter of the El Mayor-Cucapah earthquake, at a distance of 300 miles south near Mexicali in Baja California. The earthquake struck for about 1.5 minutes at 3:40 p.m. Pacific Daylight Time, but the pool shuddered for around 15 minutes. Water splashed up to drench the cameras which were located four feet above the waterline.

It is thought that the pupfish, which quickly were hidden by sediment stirred up from their home ledge, sought temporary shelter in deeper waters. The effect on Cyprinodon diabolis could be likened to swimming in the heart of a tsunami, being battered by wave after raging wave.

Cyprinodon diabolis: As sensitive as canaries in coal mines

Ambre Chaudoin, a graduate student in fisheries conservation and management at the University of Arizona, researches the intricate dynamics of Cyprinodon diabolis and their ecosystem in a study conducted by U.S.G.S. Arizona Fish and Wildlife Cooperative Research Unit. Twice monthly she travels to Devils Hole from Tucson with Olin Feuerbacher, senior research specialist for the Cooperative, for equipment checks and for data downloads. In describing the fragile microhabitat required by Cyprinodon diabolis and the complex macrosystem which impacts the pool through even such factors as remote earthquakes, Ambre equates the pupfish to canaries (Serinus canaria) in coal mines. With their heightened sensitivity to toxic gases such as carbon monoxide and methane, canaries served as early warning systems to miners, often saving human lives at the expense of their own.

The delicate nuances of their habitat makes Cyprinodon diabolis sensitive to change, whether effected by humans or by nature. Devils Hole has served as their tiny universe for untold ages. Their struggle to survive natural and manmade calamities poignantly stretches across the last half of the twentieth century and into this current century.

Hopefully, the same unassuming resilience that Cyprinodon diabolis has displayed from prehistoric to modern times, especially as evidenced by their recent, wise escape into the depths from the Devils Hole tsunami, will enable them to elude extinction as well.

My special thanks to:

• National Park Service Devils Hole Dive Team for their underwater photograph of Devils Hole;
• The U.S. Fish and Wildlife Service for photographs of Devils Hole pupfish, aerial view of Devils Hole, Hoover Dam refugium, and Willow Beach National Fish Hatchery, as well as for their Devils Hole location map and sectional drawing of Devils Hole cave system;
• U.S. Geological Survey photographs by Olin Feuerbacher of Devils Hole pupfish and Devils Hole;
• U.S. Geological Survey/Ambre Chaudoin YouTube video of Devils Hole "tsunami";
• pbs/YouTube for the Nature segment, "Life in Death Valley: Devil's Hole Pupfish"

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This hub is dedicated to the Devils Hole Pupfish and to the people and organizations who strive for Cyprinodon diabolis' recovery.

Bonar, Scott A. The Conservation Professional’s Guide to Working with People. Washington DC: Island Press, 2007.

Devils Hole Site Plan: Environmental Assessment July 2009. Pahrump, NV: Death Valley National Park, 2009.

Lewis Center for Educational Research. Devils Hole Pupfish: Looking Into Its Past to Discover Its Future. Academy for Academic Excellence. http://hegel.lewiscenter.org/users/mhuffine/subprojects/Student%20Led%20Research/pupworld/index.php (Last accessed June 2, 2011)

Minckley, Charles O., and James E. Deacon. “Foods of the Devil’s Hole Pupfish, Cyprinodon diabolis (Cyprinodontidae).” Southwestern Naturalist 20(1): 105-111 (1975).

Riggs, Alan C., and James E. Deacon. Connectivity in Desert Aquatic Ecosystems: The Devils Hole Story.” In: Conference Proceedings: Spring-Fed Wetlands: Important Scientific and Cultural Resources of the Intermountain Region, May 7-9, 2002, Las Vegas, Nevada. Desert Research Institute.

Shepard, William D., Dean W. Blinn, Ray J. Hoffman, and Paul T. Kantz. “Algae of Devils Hole, Nevada, Death Valley National Park.” Western North American Naturalist 60 (4): 410-419 (2000).

Stolte, Daniel. “UA ‘tsunami’ video sheds light on struggling pupfish.” UANews. University of Arizona Office of University Communications, May 10, 2010. http://ali.opi.arizona.edu/node/31886 (Last accessed June 2, 2011)

Szabo, Barney J., Peter T. Kolesar, Alan C. Riggs, Issac J. Winograd, and Kenneth R. Ludwig. “Paleoclimatic inferences from a 120,000-yr calcite record of water-table fluctuations in Browns Room of Devils Hole, Nevada.” Quaternary Research 41 (1): 59-69 (January 1994).

U.S. Fish and Wildlife Service. Recovery Plan for the Endangered and Threatened Species of Ash Meadows, Nevada. Portland: U.S.F.W.S., 1990.

Westenburg, Craig L. Water Resources Data for the Devils Hole Area, Nye County, Nevada, July 1978-September 1988. Open File Report 90-381. Carson City: U.S. Department of the Interior, 1993.

Wullschleger, John G., and William P. Van Liew. “Devils Hole revisited: Why are pupfish numbers and water level dropping again?” ParkScience 23(2): 26-30 (Fall 2005)

Copyright Thursday, June 2, 2011 by Derdriu