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US Fish & Wildlife Service FieldNotes

PACIFIC SOUTHWEST REGION: New Home for the Next Generation of Devils Hole Pupfish

Region 8, December 11, 2013
The 100,000 gallon replica tank of Devils Hole.
The 100,000 gallon replica tank of Devils Hole. - Photo Credit: n/a
The Ash Meadows Fish Conservation Facility staff search for eggs in carpet fibers.
The Ash Meadows Fish Conservation Facility staff search for eggs in carpet fibers. - Photo Credit: n/a
Adult Devils Hole pupfish in Devils Hole.
Adult Devils Hole pupfish in Devils Hole. - Photo Credit: n/a

By Cindy Sandoval

Ninety miles west of the shows on the Las Vegas strip there is a real life drama playing out at Devils Hole as biologists race to save the endangered Devils Hole pupfish (Cyprinodon diabolis). Devils Hole, an underwater cave in the Nevada desert, is located within Ash Meadows National Wildlife Refuge.

The U.S. Fish and Wildlife Service (Service) recently built a facility to conduct research and establish a backup or refuge population of the rare Devils Hole pupfish. The Ash Meadows Fish Conservation Facility located less than a mile from Devils Hole was funded through the income of federal land sales with a cost of approximately 4.5 million dollars. The state of the art facility has a 100,000 gallon concrete tank replica of Devils Hole and a propagation room with numerous aquariums where the first captive raised generation of pupfish will grow up.

The Devils Hole pupfish is one of the rarest fish in the world and it exists only in Devils Hole, a desert spring and underwater cave that is deeper than 400 feet. The pupfish is an inch-long, iridescent blue fish that lives in water that is nearly 93 degrees Fahrenheit year-round. In the wild, a pupfish will spend most of its life in the top 80 feet of the cavern. Spawning habitat for the fish is among the smallest in the world and consists mainly of an 8 foot wide by 18 foot long rock shallow shelf where algae and aquatic invertebrate abundance, the primary prey of pupfish, changes seasonally based on the intensity and duration of sunlight.

The shimmering fish was first listed as endangered in 1967 due to the threat of habitat loss as local water demands in the Mojave Desert increased. Water levels were so low at times it almost completely exposed the shallow shelf reducing the amount of spawning habitat, which prompted the Department of Interior, and other conservation organizations such as the Desert Fishes Council to seek an injunction to halt groundwater pumping in the area around Devils Hole. This limit on water use, which reached all the way up to the Supreme Court, set a precedent for reserving groundwater for an endangered species.

Since the Devils Hole pupfish was listed as endangered the population has been closely monitored. This short-lived species (approximately one year) has a natural high and low cycle, with the fall population decreasing by 35-65 percent in the spring due to natural die-off. When bi-annual population counts using SCUBA and surface counters began in 1972, fall fish counts were estimated near 500 pupfish. From the late 1970’s through 1996, the population appeared to be relatively stable. However in 1997, counts started on a downward trend for unknown reasons.

In fall 2012, 75 pupfish were observed and this year’s spring and fall counts resulted in all-time low population count with 35 and 65 fish, respectively. These low population numbers are cause for concern for many environmental and conservation organizations. “The Devils Hole pupfish is an indicator species, a proverbial canary in the coal mine. Not only is it our duty to try to save this unique species whose existence has been jeopardized by habitat alteration, but its continued existence has implications far beyond itself. As an indicator species, it is a means to learn more about factors affecting species--our natural resources--which is particularly important in the face of the ever-increasing human population and other changes such as global climate change,” said Ambre Chaudoin, Propagation Support Specialist, with the Great Basin Institute.

Living at the edge of their physiological limits, wild Devils Hole pupfish are subjected to a combination of conditions that would be lethal for most other species of fish, including high temperatures, low dissolved oxygen levels, and seasonal light and algal production changes. In order to create a refuge population of these unique fish and to further knowledge of how these fish survive when so many others would perish, the new facility was specifically designed for studying and raising Devils Hole pupfish with the capability to manipulate conditions to replicate their natural environments.

The replica refuge tank is an in-ground tank with a variety of cutting edge equipment to allow manipulation and monitoring of a variety of conditions such as water level, water quality, and sunlight duration. The replica tank is approximately 22 feet deep and includes two shelves and a cavern environment to provide the primary spawning and feeding habitats similar to Devils Hole. The refuge tank design went as far as to build the tank in an atrium like structure with adjustable louvers to be able to manipulate sunlight in the artificial habitat and make it similar to that found at Devils Hole all times of the year.

As impressive as the large refuge tank’s complex array of computers and auto-dialer alarms is, it was ultimately the Devils Hole pupfish eggs that made the facility a success. Working closely with the National Park Service and the Nevada Department of Wildlife, the Service started to transport Devils Hole pupfish eggs in August 2013 to determine if the eggs could be successfully hatched in captivity.

Eggs are currently only removed from Devils Hole during periods where research has shown that natural larval fish survival is low. Monitoring by National Park Service and others has shown that there is a natural surge in spawning in the spring and fall. However this research also shows that while spawning continues through the winter, those eggs being deposited do not survive to adulthood, suggesting that egg collection during this period can be done without adversely affecting the wild population.

“Collecting eggs from Devils Hole has allowed us to utilize the best available science to hatch eggs and rear fish in captivity and most of the methods we are using were developed at the University of Arizona-Tucson over the past few years by Olin Fuerbacher, who is now the facility’s aquaculturist. Establishing a refuge population of Devils Hole pupfish at the Facility will allow us to test several hypotheses as to why their population has declined in Devils Hole,” said Darrick Weissenfluh Ash Meadows Fish Conservation Facility manager.

With the adult fish being an inch in length, one can imagine how small the pupfish eggs are. To collect the tiny eggs that are approximately 0.04” (1 mm) in size, biologists at the new facility place a piece of pre-sterilized store bought carpet and yarn on top of a tile measuring about 1 foot square on the Devils Hole shallow shelf. The carpet is soaked and sterilized to remove any glue and chemicals that could harm the remaining population of the endangered pupfish in their natural habitat. The carpet spawning mats remain in Devils Hole for up to a week before they are removed and transported back to the facility’s propagation room.

"Once at the fish facility, staff gently fan and brush the carpets with their hands to dislodge the delicate eggs, a total of 48 eggs have been collected thus far and approximately half of them were fertile. Of the fertile eggs, 25 have hatched, and 21 have continued to survive. The oldest fish are a month old and have grown to approximately 0.6 (15 mm) in length, “ added Weissenfluh.

Aquaculturist Olin Fuerbacher with the Great Basin Institute believes that this refuge population holds the potential for understanding what makes the fish special and understand the populations recent decline. "If this fish goes extinct, so does our opportunity to learn what it might teach us," Fuerbacher said. 

If all goes according to plan, this next generation of Devils Hole pupfish at the facility should reach adulthood in two or three months and the gender of each fish will become apparent. The Service will continue to adapt and improve egg collection and propagation techniques to expand the facility’s Devils Hole pupfish population and will continue to provide management with vital information that will help bring back this species from the brink of extinction.

Cindy Sandoval is a Pathways intern in external affairs at the Pacific Southwest Regional Office in Sacramento, Calif.

Contact Info: Cynthia Sandoval, 916-978-6159, cynthia_d_sandoval@fws.gov