Endangered Devils Hole pupfish population at 25-year-high

(NPS) - National Park Service biologists are reporting increased numbers of one of the world’s rarest fishes.

Scientists counted 191 Devils Hole pupfish, which is the most fish observed during annual spring season counts in 25 years. This is good news for the critically endangered fish living in Death Valley National Park.

Devils Hole pupfish live in the smallest habitat of any vertebrate species on the planet. Devils Hole is a deep, water-filled cavern located near Ash Meadows National Wildlife Refuge in Nye County. The fish live in the upper 80 feet of the cave and depend on the 11-foot by 16-feet sun-lit shallow shelf at the cavern’s entrance for food and spawning.

The remnants of Hurricane Hilary affected Devils Hole in August 2023. While flooding can have negative effects on the fish in the short-term, Hilary mostly benefited the fishes’ ecosystem by adding nutrients that washed off the surrounding land surface in a fine layer of clay and silt.

Devils Hole pupfish are counted every spring and fall, using standard protocols. This year’s spring count was done April 6 and 7. Scientists used SCUBA to dive as deep as 100 feet to count fish. As the same time, other scientists count fish on the shallow shelf at the water surface.

Before the mid-1990s, scientists counted about 200-250 Devils Hole pupfish each spring. For about 20 years, the population dropped to an average of around 90 fish, with an all-time low of 35 fish in 2013.

Population counts in recent years have been higher. 191 observable pupfish were counted in April 2024, which is the highest spring count recorded since March 1999.