The shallow thermal regime of Devils Hole, Death Valley National Park

Abstract

Lay Abstract Devils Hole is an open, water‐filled fault in Ash Meadows National Wildlife Refuge that is home to the world's only population of endangered Devils Hole pupfish (Cyprinodon diabolis). In 1995, the population of Devils Hole pupfish began to decline, and to date no single cause for this decline has been identified. This article examines the influence of water temperature on the Devils Hole pupfish population by considering a part of the habitat that is critical to the pupfish's reproductive cycle: the shallow shelf at the south end of the pool. A mathematical model of the shallow shelf is used to examine the daily patterns of water flow and temperature change that result from the daily cycles of air temperature and solar radiation. The model matches well the data collected during this and other studies and shows that the shallow shelf of Devils Hole will respond to small changes in air temperature. Over the past 30 years, the southwestern United States has experienced an increase of up to 2 °C in average air temperature, and this increase has the potential to negatively affect the population of Devils Hole pupfish. The changes in local climate over this time period may have contributed to the decline of the Devils Hole pupfish population.

Phylogenetics support an ancient common origin of two scientific icons: Devils Hole and Devils Hole pupfish

“…All wild individuals of DHP live in this cavern and their only stable feeding and spawning ground is a small 3 × 6 m limestone shelf at the southern end of the pool (James ; Hausner et al . ). DHP is morphologically one of the most distinctive of the pupfish species (Wales ; Miller ) and is thought to have survived in this cavern, in complete isolation, for thousands of years (Deacon & Baugh ; Szabo et al .…”

“…Devils Hole is home to the Devils Hole pupfish (C. diabolis) (hereafter DHP) which may have the smallest geographic range of any known vertebrate species (Reid 2003;Hausner et al 2013). All wild individuals of DHP live in this cavern and their only stable feeding and spawning ground is a small 3 9 6 m limestone shelf at the southern end of the pool (James 1969;Hausner et al 2013).…”

Oxygen Consumption is Limited at an Ecologically Relevant Rearing Temperature in Pupfish Eggs

“…Following resolution of a legal battle over water rights that imperiled the species, the estimated population size of C. diabolis increased to a level of 200–500 adult fish (Andersen and Deacon, ; Riggs and Deacon, ). However, a gradual decline, beginning in 1996, brought the population to a low point of only 35 adult individuals in 2013 (Hausner et al., ). Although, the most recent census (April, 2016) found modest recovery with over 100 individuals counted, the species continues to be in a precarious situation.…”

“…Low recruitment of juveniles to the adult population could be a major factor in the recent population decline of C. diabolis (Hausner et al., ). Measured during acute exposure to increasing temperature, adult pupfish have a critical thermal maximum of ∼40°C (Brown and Feldmeth, ).…”

“…While successful recruitment is thought to take place mainly in the spring, some breeding takes place year round in Devils Hole and in other Ash Meadows springs (Shrode and Gerking, Riggs and Deacon, ; ). Depending on the time of year and spatial location in Devils Hole or other habitats, pupfish eggs may experience highly variable temperatures (Shrode and Gerking, ; Riggs and Deacon, ; Hausner et al, ). Unlike adult fish, developing eggs are unable to choose between different thermal environments until they hatch.…”