FURNACE CREEK, Calif. – Scientists were cautiously optimistic during the annual Devil’s Hole Workshop here Thursday about the Devil’s Hole pupfish population.
A spring count of 92 fish was taken on April 4-5. The boost in the pupfish population was partially credited to recovery efforts undertaken last year.
Researchers collected 60 eggs last summer for the new Ash Meadows Fish Conservation Facility in another attempt to create a captive pupfish breeding population. Previous attempts failed at Hoover Dam in 1972 and Point of Rocks in 1990.
“Almost half of them did hatch and survive and are still alive. We are optimistic about things on that front as well as the front of seeing more fish in Devil’s Hole last spring, cautiously optimistic into the future,” said Bailey Gaines, a researcher on the pupfish program with Death Valley National Park.
The pupfish, Cyprinodon diabolis, have been counted every year in the spring and fall since 1972. The spring counts are typically lower than the fall. Three scuba divers descend part way into the 550-foot hole, the fish live on the shelves nearer the surface. Counts from the three divers are averaged. Gaines admitted they can’t know exactly how many pupfish are in Devil’s Hole but use the average to determine their relative abundance as a comparison with past years.
“We’re cautiously optimistic, 92 fish is what our official number was last spring. That’s more than anybody expected. We’re very pleased but we’re also very cautious with that number as well as to whether or not this is a trend we can rely on,” Gaines said.
Scientists were alarmed the species may be on the brink of extinction when only 35 pupfish were counted in April 2013. The fall 2013 count, when there are typically higher numbers of pupfish, was 65 fish.
“We got a little bit nervous in 2013 after a spring count of 35 fish,” Gaines said. That number was similar in a June 2013 interim count. “We got even a little more on edge after that point.”
“Everybody was a little on edge wondering what to do next, low numbers in spring, low numbers in June, very little ELS (early life stage) fish, very little recruitment. What do we do?” he asked.
The University of California, Berkeley performed an assessment on the risk of extinction to evaluate different management options. Gaines said they evaluated the risk of not doing anything and leaving the fish as they were in low numbers.
Gaines said that even raised the question: “Was Devil’s Hole just not a suitable habitat for them any more?”
The analysis told researchers the wild population could sustain a take of two adult pupfish from the native population for propagation at the fish conservation facility without a negative impact. But they elected to harvest eggs instead.
The temperature of the water at the 110,000-gallon tank is kept at a slightly-less stressful temperature of 93 degrees at Devil’s Hole, with slightly more oxygen content than levels at Devil’s Hole, which were described as near lethal levels for fish.
Gaines said cover packets were placed above a shelf at Devil’s Hole in response to disturbance events in winter 2012-13 in which much of the algae community was removed. That would also help reduce any possible predation of the fish, Gaines said.
They also modified the supplemental feeding of the pupfish, which has been taking place since the winter of 2006-07 in response to an unhealthy, emaciated appearance of some fish. They are being fed Rio Grande silvery meadow chow with a flaky appearance similar to what’s fed aquarium fish.
More egg collections are planned in June. A worker at the fish conservation facility said their efforts are also focusing on overall fish health and maintaining genetic diversity.