Is Lack of Adequate Food a Bottleneck to Survival of Devils Hole Pupfish Larvae?
USFWS, NPS, Nevada Division of Wildlife
September 2008 to September 2011
The Devils Hole pupfish Cyprinidon diabolis is a relic of the last ice age; stranded as receding glacial lakes moved across a drying and warming landscape. Found in a single limestone fissure in Death Valley National Park, the Devils Hole Pupfish has survived in its current location — perhaps the smallest vertebrate distribution in the world — for the last 25,000 years. The Devils Hole pupfish itself is an iridescent blue, 2.5mm-long fish that lacks pelvic fins. The spring-fed Devils Hole remains a constant 33°C, and contains approximately 2 ppm dissolved oxygen. Recent, dramatic declines in the Devils Hole pupfish population have raised concerns over the future of the species. As there are no remaining refugia for pure-strain pupfish outside of Devils Hole, the possibility of extinction has become quite real. Previous lack of success for rearing fish in laboratory settings coupled with low egg viability further complicate recovery efforts. Census divers and scientists associated with the Devils Hole program have reported sighting larval pupfish on the stone shelf, as well as adult fish throughout the upper reaches of the water column. However, there are few reports of middle-age class fish, and with numbers of adults that are significantly lower than previous years, it seems that many larval fish are simply not surviving to the adult age class. To identify if food bottlenecks to larval growth and survival are currently occurring in Devils Hole, we will compare treatments designed to represent the most important constituents of the algal and invertebrate assemblages from the 1970's and from 2001, as well as a flake food that is currently being used in supplemental feeding of the pupfish. Hybrid pupfish eggs will be collected, hatched, and larvae will be raised on Spirogyra, cyanobacteria, ostracods, amphipods, diatoms, or flake food through two weeks post-hatch. Invertebrates will be gut-loaded with either Spirogyra or cyanobacteria. Survival and weight will be measured in order to determine the most important constituents of the Devils Hole community. Field and laboratory work on this project is underway.