Devils Hole a detached unit of Death Valley National Park, located within Ash Meadows National Wildlife Refuge

Devils Hole pupfish

By Jeannie Stafford
Nevada Fish and Wildlife Office
The Devils Hole pupfish (Cyprinodon diabolis) was listed as endangered in 1967. This iridescent blue inch-long fish’s only natural habitat is in the 93 degree waters of Devils Hole, which is a detached unit of Death Valley National Park.  Although the cavern is over 400 feet deep, the pupfish are believed to spawn exclusively on a shallow rock shelf just under the water’s surface. Endemic species with limited distribution like the Devils Hole pupfish are at greatest risk of extinction since they do not have the flexibility to change locations to adapt to changing environments. 

This short-lived species (approximately one year) has a natural high and low cycle, with the population in the fall being larger than that in the spring due to natural die-off during the winter months.  However, the population of Devils Hole pupfish has not exceeded 553 individuals since population surveys began in 1972. 

From the late1970’s through 1996, the population appeared to be relatively stable with an average population size of 324 individuals.  In 1997, the fall population surveys started to indicate a downward trend for unknown reasons.  The population from 1997 to 2004 declined from an average of 275 individuals to 171 fish.  In August and September 2004, two separate rainfall events deposited 1.66 cubic meters of sediment on the main spawning shelf, for a loss of approximately 54 percent of pupfish spawning habitat. Subsequent multi-agency initiated restoration efforts are believed to have restored much of this habitat on the shelf. The adult population count conducted in November 2005 indicated a population of 84 individuals, and an April 2006 population count indicated an adult population of 38 individuals, the lowest count on record.  A dive survey in September 2006 resulted in 85 adult pupfish within Devils Hole indicating the pupfish were recruiting and reproducing in their natural environment.

Devils Hole Pupfish Management Actions

Increasing the population size of Devils Hole pupfish and establishing a population outside of Devils Hole is complicated and the situation is compounded by the small founder population, short lifespan, limited genetic diversity, and the difficulty of rearing them in captivity.  Managers and scientists are working collaboratively to identify the factors that contribute to successful propagation of pure Devils Hole pupfish and to understand how these factors interrelate.  

Decisions have been carefully and deliberately made to try and increase the size of the single wild Devils Hole pupfish population and establish a viable population outside of Devils Hole. Directors and Managers from the U.S. Fish and Wildlife Service, the National Park Service, and the Nevada Department of Wildlife participated in a formal decision making process (known as structured decision making) on August 2006, to make difficult decisions on future actions to reverse the decline of the Devils Hole pupfish. 

In order to understand how to propagate this pupfish in aquaria, techniques recommended by experts from across the United States and Mexico were tested using a hybridized Devils Hole pupfish at Willow Beach National Fish Hatchery and the Shark Reef Aquarium at Mandalay Bay Casino and Resort.  Although those efforts proved successful, propagation and maintaining the pure Devils Hole pupfish in captivity has had limited success. 

In 2006, agencies partnered with Shark Reef at Mandalay Bay to help with propagation techniques of the pure Devils Hole pupfish and moved Devils Hole pupfish from Devils Hole and Hoover Dam Refuge.  The facility currently maintains a healthy population of hybridized pupfish but propagation efforts with the pure Devils Hole pupfish were not successful.   In August, managers decided to move forward with backcrossing of the female hybrids with one pure Devils Hole pupfish male.  The male died later that year prior to successful propagation.  

Hoover Dam Refuge, which had previously been successful in rearing Devils Hole Pupfish in captivity, developed an exotic snail infestation in the summer of 2006 along with a decline in numbers of a captive population of Devils Hole pupfish.  Managers, with recommendations from scientists, moved all Devils Hole pupfish existing outside of Devils Hole (except one male at Shark Reef at Mandalay Bay) to one location; Willow Beach National Fish Hatchery.  

Dr. Arcadio Valdes, a pupfish expert from Mexico, assisted in propagating and monitoring the Devils Hole pupfish transferred to Willow Beach National Fish Hatchery.  These efforts produced the first successful propagation of pure Devils Hole pupfish in aquaria and three of those pupfish are surviving today.  The pure Devils Hole pupfish transferred to the facility, however, developed late stage lymphosarcoma and nephrocalcinosis and later died.

In December 2006, 12 Devils Hole pupfish were transferred to a refurbished refugium at Point of Rocks.  Three of those pupfish survived and in March 2006, a juvenile was located indicating successful reproduction.

As of April 10, 2007, there are six Devils Hole pupfish existing outside of Devils Hole; three reared at Willow Beach National Fish Hatchery, and two transferred from Devils Hole to Point of Rocks Refugium in December 2006 plus the juvenile.    

Supplemental feeding within Devils Hole began in January 2006 in response to poor fish health conditions observed.   This supplemental feeding appears to have increased the strength and vigor of the Devils Hole fish.  There are fewer signs of malnourishment and regular spawning (pursuit/chasing) activities have been observed.   The next few months will be the most productive period for the Devils Hole pupfish.  It is hoped that with the supplemental feeding they are going into this period healthier than in past springs. This will hopefully lead to a more successful spawning and reproduction of young pupfish before next winter.

Larval pupfish surveys were initiated in February 2007 and have been conducted every other week.  Initial results have been encouraging with a good number of larvae counted during earlier surveys and larvae numbers increasing through the most recent count.

In March 2006, a group of scientists was convened at Death Valley National Park to discuss long-term monitoring approaches at Devils Hole.  These scientists represented a diverse array of academic specialties such as hydrology, limnology, genetics, and fish population ecology.  With the help of these experts, a long-term monitoring strategy for Devils Hole is being drafted that will act to guide efforts to understand the ecosystem processes affecting the Devils Hole pupfish population.

In addition to continuation of adult and larval pupfish counts, efforts are being pursued in cooperation with the Desert Research Institute to understand energy and nutrient dynamics in Devils Hole.  These basic processes can act to regulate ecosystems from the bottom up and are, therefore, of primary importance to each component of the food web, including the Devils Hole pupfish.

Summary of Devils Hole Pupfish Relocation

Devils Hole Pupfish Transferred from Devils Hole

Devils Hole Pupfish Transferred from Hoover Dam Refuge

Date	Devils Hole Pupfish Transferred	Transferred T
5/18/06	2 females	Shark Reef at Mandalay Bay
6/15/06	2 males	Shark Reef at Mandalay Bay
8/9/06	1 female	Shark Reef at Mandalay Bay
8/9/06	4 males  3 females	Willow Beach National Fish Hatchery
9/6/06	4 males  5 females	Willow Beach National Fish Hatchery
Total Transferred	10 males  11 females                      (21 total)

Devils Hole Pupfish Transferred from Shark Reef at Mandalay Bay

Date	Devils Hole Pupfish Transferred	Transferred T
9/6/06	1 female	Willow Beach National Fish Hatchery
Total Transferred	0 males      1 female                          ( 1 total)

Current Devils Hole Pupfish Population Information

Date	Location	Male	Female	Juvenile	Total
4/2/07	Hoover Dam Refuge	0	0	0	0
4/10/07	Point of Rocks Refugium	1	1	1	3
4/2/07	Shark Reef at Mandalay Bay	0	0	0	0
4/2/07	Willow Beach National Fish Hatchery	2	1	0	3

 

9/23/06	Devils Hole-Adult Survey				85
3/1/07	Devils Hole-Larval Survey			6	6
4/14/07	Devils Hole – Adult Survey				38