B.L. MCLAUGHLIN / Special to the PVT Looking for pupfish, divers enter Devils Hole in Ash Meadows National Wildlife Refuge. Numbers appear to be up this year. Advertisement

ASH MEADOWS -- On the clear, cool Saturday morning of April 5, at Devils Hole, a diver pulling on his wetsuit called out, "Thanks for warming the suits," as he prepared for the spring count of Nye's rarest residents, the Devils Hole Pupfish.

The suits had been frozen the night before, to prevent the introduction of any outside contaminants.

Devils Hole is the only place in the world this particular species of fish is known to exist. With the tiny blue fish numbering fewer than 100 at any count during recent years, and less than 40 in the spring counts of the last two years, no one is taking any chances.

The numbers have always fluctuated to an extent, but for a still unknown reason, beginning in the mid 1990s, the numbers began to decline year by year.

In 2004, an unexpected heavy rain caused researchers' fish traps stored in the area to wash into the hole, trapping many of the fish, and reducing their numbers by half. By the spring of last year, the numbers had apparently stabilized, but at a near-low 38.

Here is the biggest mystery of Devils Hole -- what has happened to cause the gradual decline of the once flourishing pupfish?

Have they, like the two foolish divers the hole was named for, just disappeared into some unknown fate, or has there been some change in their environment that has affected them badly?

Many possibilities have been considered. Is global warming an issue - could the pool be too warm now, or too warm at night?

Are the fish too inbred - have they developed genetic weaknesses?

Has the type of algae growing on the 78-square-foot breeding shelf of the pool changed? Is it less nourishing? Is there simply less algae?

A barn owl used to nest very close to the pool, and contributed organic matter to the pool in the form of coughed-up owl pellets - small wads of fur and animal bones.

A different barn owl swooped high over the counting party's heads as they descended the steep, rocky slope to the pool - but this one nests farther away. Too far away to contribute?

Have the high fences put up to protect the delicate habitat somehow prevented the entrance of another contributing species? Could the fences have caused blockages of natural water flow, and the nutrients and minerals brought in by it, as they stopped rolling rocks and other materials?

Could there be a connection between the endangered status of the pupfish and the endangered status of the bats that seasonally inhabit Devils Hole 2?

The nearby cave's pool has no sunlight, no algae and no fish, but may connect to the pupfish's pool. Several of Saturday's divers did a preliminary exploration of Devils Hole 2 on Friday but were unable to prove a connection.

According to Mike Bower of the National Park Service, a fish biologist assigned to the Devils Hole Pupfish Recovery project, trying to find answers to the plight of the pupfish has "been a real lesson" in "the need to do proactive research and proactive monitoring."

Monitoring in the past, when pupfish numbers were high, was generally only of water temperature and water level. Now, when answers might be found by comparisons with past data, the data is not there.

The number of fish found in the spring has always been significantly less than in the fall, due primarily, researchers believe, to the more abundant sunlight during the summer, which promotes the growth of the algae the fish need to survive. The fall count in even the worst year was over 80.

This known fact prompted the researchers, even as they continued to search for answers to the dilemma, to begin a feeding program for the endangered pupfish.

A food was found that was very close to the pupfish's natural diet, and the team of Park Service, U.S. Fish and Wildlife, and Nevada Department of Wildlife scientists began feeding it to the Devils Hole fish in early 2007.

The 38 pupfish counted that spring appeared to be a good sign -- the population had remained stable. By fall, numbers were slightly higher than the previous year, up from 88 to 95.

So the mood on this April Saturday was hopeful. Ten minutes after the divers had carefully entered the water for their hour-long dive, Bower, Kevin Wilson of the Park Service, and Sean Harris of NDOW lined up on the temporary walk above the breeding shelf for a count of the surface pupfish. After three counts, they had determined 15 were in their area.

The first report from the divers was encouraging. As opposed to several years earlier, when the fish appeared thin, said Hillyard, "I saw a lot of fat fish."

The official result for the spring 2008 count of pupfish at Devils Hole is 45 -- seven more than last spring.

Paul Barrett of the Fish and Wildlife Service, pointed out that while this is a small increase in numbers, it is also an increase of 18 percent. Both Bower and Barrett emphasize that any gains will be small, because pupfish do not produce large numbers of offspring.

The consortium of scientists has recently introduced a new device to the Devils Hole pool -- a sort of floating protective cage for the pupfish larvae (young fish).

If they are successful in cultivating algae in the prototype enclosure, the researchers will cautiously begin introducing eggs and larvae into it, hoping to give the young pupfish one more means of protection in their journey to adulthood, and the species a better chance to survive.