One of the most endangered fish species on the planet, one that inhabits a tiny, water-filled canyon, has experienced a population boom. National Park Service biologists recently surveyed the Devils Hole pupfish colony in Death Valley National Park and counted 263 individuals, the highest number recorded in 19 years.
This tally follows a 7.6 magnitude earthquake in Mexico that caused 4ft waves in Devils Hole on September 19. Pupfish are counted using visual dive and surface counters. The lapping waves washed away algae, invertebrates and other organic matter from a shallow shelf that pupfish use for food and spawning. This made it easier for biologists to see and count pupfish from the surface. Scientists using scuba diving have also counted pupfish at greater depths.
Devils Hole pupfish (Cyprinodon diabolis) live within the upper 80 feet of a cavern filled with deep water and a sunlit shallow plateau at the entrance to the cave, making them the smallest range of vertebrate species on the planet, according to the Park Service. Devils Hole is an isolated unit of Death Valley National Park, adjacent to Ash Meadows National Wildlife Refuge in Nye County, Nevada. Staff from the US Fish and Wildlife Service, Nevada Department of Wildlife, and National Park Service are cooperating to manage this critically endangered species.
Population size is estimated by counting fish throughout its habitat, with standard counting protocols. Scientists dive to count fish in the cavern, starting at depths less than 100 feet. Simultaneously, other scientists count the fish on the shallow shelf at the surface of the waters. The final tally includes both surface and underwater fish. The official result, 263 observable pupfish, is the highest fall count since September 2003.
Before the 1990s, the population was around 400 to 500 pupfish in the fall. However, pupfish numbers have been particularly low over the past two decades, averaging just 90 fish.
A return to higher numbers of pupfish at this time of year could signal significant changes in the ecosystem. Kevin Wilson, aquatic ecologist for Death Valley National Park, manages resources at Devils Hole and says “recent high counts in the spring and fall show the importance of maintaining long-term data as we are working to find out what has changed.”
Brandon Senger, supervising fisheries biologist for the Nevada Department of Wildlife, has been doing dive counts at Devils Hole since 2014 and noted, “I’ve never seen the population this robust before. Fish of all size classes were abundant. counted more fish at one level than we had in total in previous counts.”
Other biologists on site noted that the fish appeared in remarkable condition and were very active. Many pairs of courting and spawning pupfish were seen during the count. Jennifer Gumm, who manages the Ash Meadows Fish Conservation Facility for the US Fish and Wildlife Service, said “earthquake-induced spawning is a fascinating aspect of this species’ behavior.”
Having more pupfish in Devils Hole also affects the direction and focus of species recovery. This week’s tally continues an overall fall increase over the past nine years from an all-time low of 35 fish.
Michael Schwemm, senior fish biologist for the US Fish and Wildlife Service, said: “It’s exciting to see the numbers steadily increasing over the past few years. The current trend, especially in this highly variable population, clearly shows that habitat conditions have changed significantly since the lowest counts, and we are excited about future directions for research and recovery.
The next pupfish count will take place in the spring of 2023.