Devils hole pupfish
The Devils Hole pupfish (Cyprinodon diabolis) is a critically endangered species of the family Cyprinodontidae (pupfishes) found only in Devils Hole, a water-filled cavern in the US state of Nevada. It was first described as a species in 1930 and is most closely related to C. nevadensis and the Death Valley pupfish (C. salinus). The age of the species is unknown, with differing analyses offering ranges between one thousand and sixty thousand years. It is a small fish, with maximum lengths of up to 30 mm (1.2 in). Individuals vary in coloration based on age and sex: males are bright metallic blue while females and juveniles are more yellow. A defining trait of this species is its lack of pelvic fins. The pupfish consumes nearly every available food resource at Devils Hole, including beetles, snails, algae, and freshwater crustaceans, with diet varying throughout the year. It is preyed on by the predaceous diving beetle species Neoclypeodytes cinctellus, which was first observed in Devils Hole in 1999 or 2000. Reproduction occurs year-round, with spikes in the spring and fall. Females produce few eggs, though, and the survivorship from egg to adult is low. Individuals live 10–14 months.
Devils Hole is more than 130 m (430 ft) deep, though pupfish are only found in the upper 24 m (80 ft). The water is a constant temperature of 33 °C (91 °F) and dissolved oxygen levels are low. A small, shallowly submerged rock shelf provides critical feeding and spawning habitat for the pupfish. Nearby agricultural irrigation in the 1960s and 1970s caused the water to drop in Devils Hole, resulting in less and less of the shelf remaining submerged. Several court cases ensued, resulting in the Supreme Court case Cappaert v. United States, which determined that the preservation of Devils Hole as a National Monument in 1952 implicitly included preservation of adequate groundwater to maintain the scientific value of the pool and its fauna. Other threats faced by the species include flash floods, earthquakes, and vandalism.
As its entire native range is a single locality, efforts to create other populations have proceeded since the 1960s and 1970s, most of which have failed. Three refugia were created in 1972, 1973, and 1990, though all were closed by 2007 as a result of maintenance failures, hybridization, and small founder populations. In the early 2010s, an exact replica of the uppermost 6.7 m (22 ft) of Devils Hole was constructed at Ash Meadows Fish Conservation Facility, which was populated with eggs taken from Devils Hole in winter months when development into adults is unlikely. Efforts to conserve the wild population have included removing sediment from the shallow shelf, adding supplemental food, and installing fences and security cameras to keep unauthorized people away. Conservation efforts have been costly and divisive. During the legal battle over ground water in the 1960s and 1970s, bumper stickers were distributed that read "Kill the Pupfish" or "Save the Pupfish". Some have argued that the species should be allowed to go extinct, while others have said this would be akin to "bombing the Louvre to make way for a parking lot".: 76
Population counts are conducted twice a year, in the spring and fall, with the fall population usually much larger. Since 1972, population counts have peaked at around 550 individuals. The April 2013 count showed only 35 remaining in the wild, but by September 2022, the count showed a total of 263 observed wild pupfish. The Devils Hole pupfish has been listed as endangered by the US federal government since 1967 and critically endangered by the International Union for Conservation of Nature since 2014.
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DiurnalDiurnal animals are active during the daytime, with a period of sleeping or other inactivity at night. The timing of activity by an animal depends ...
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AlgivoreAn algivore is a common name for many bottom-dwelling or algae-eating species that feed on algae.
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OmnivoreAn omnivore is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and ani...
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HerbivoreA herbivore is an animal anatomically and physiologically adapted to eating plant material, for example, foliage, for the main component of its die...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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PolyandryPolygyny is a mating system in which one female lives and mates with multiple males but each male only mates with a single female.
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withThe Devils Hole pupfish is the smallest pupfish species in the genus Cyprinodon, with lengths up to 30 mm (1.2 in). The average length is 23 mm (0.9 in). Males and females differ in coloration. Males are overall dark brown with metallic blue on their sides. The margins of all fins are black, and the back has golden iridescence. Iridescence is particularly pronounced on the opercles (gill covers) which have a violet sheen on their posterior side. The iris is blue and also iridescent. Females and young are more yellow in color than the males. Females have yellowish-brown backs, and the margins of their pectoral and caudal fins are yellow, not black. The dorsal fin has a black margin like the males, however. Females' opercles are metallic green, and their eyes are tinted metallic blue. The young are overall colored as the females, though they have a faint vertical bar on their sides.
Individuals lack pelvic fins, though have been observed to grow them when raised in lower temperatures in captivity. Its dorsal fin has twelve rays, while each pectoral fin has seventeen rays. The caudal fin is convex in appearance and has twenty-eight rays, curving outward at the margin. Its lateral series (the number of scales from the back end of the opercle to the beginning of the tail) is twenty-seven scales. The scales are ctenoid, or toothed, on the outer margin.
Devils Hole and the pupfish are located in the Amargosa Desert ecosystem, in the Amargosa Valley, of southwestern Nevada, US, east of Death Valley and the Funeral Mountains and Amargosa Range. The Amargosa River is part of Devils Hole and the region's aquifer hydrology. Devils Hole is a water-filled cavern extending into a hillside. It is at an elevation of 730 m (2,400 ft) above sea level and the water is a constant temperature of 33 °C (91 °F). The surface area of Devils Hole is about 22 m long by 3.5 m wide (72 ft long by 11.5 ft wide). Its depth is at least 130 m (430 ft). Devils Hole "may be the smallest habitat in the world containing the entire population of a vertebrate species". Approximately 0.3 m (0.98 ft) deep on one end of Devils Hole is a small rock shelf of 3.5 by 5 m (11 by 16 ft). The dissolved oxygen of the water is 2.5–3.0 ppm up to around 22 m (72 ft) in depth, though the shallow shelf can have dissolved oxygen levels as high as 6.0–7.0 ppm in June and July.
Although pupfish have been found as deep as 24 metres (80 ft), their numbers are most dense above depths of 15 m (49 ft). They depend on the shallow shelf for spawning as well as for much of their diet which primarily consists of diatoms. Natural threats from flash floods to earthquakes have been known to disrupt this fragile ecosystem, but in the 1960s and 1970s, the major threat was groundwater depletion due to agricultural irrigation.
Research indicates that the annual population fluctuation is in response to the amount of algae on the shallow shelf, which is dependent on incoming solar radiation and nutrient levels. Nutrient availability may peak when the cave is used by barn owls as a roosting or nesting site, as their nutrient-rich pellets fall into the water.
The Devils Hole pupfish consumes a variety of food items representing nearly all possible food resources in Devils Hole. Its food resources include inorganic particulate matter; the algae Spirogyra and diatoms; the freshwater crustaceans Hyalella azteca and ostracods; protozoa; the beetle Stenelmis calida; the flatworm Girardia dorotocephala; and the freshwater snails Tryonia. The consumption of the various food resources varies seasonally, though inorganic particulate matter had a high frequency of occurrence in stomach contents year-round in one study. The inorganic particulate matter consists of primarily travertine, a form of limestone. The three most common food items for each season by frequency of occurrence were:
As Spirogyra was mostly found undigested in the stomach, the authors hypothesized that it was not important as a food resource, but rather as a foraging substrate. The inorganic particulate matter was thought to be incidentally consumed as well as a result of the fish's foraging strategy of bottom feeding and surface feeding.
Predators of the Devils Hole pupfish include the diving beetle species Neoclypeodytes cinctellus, which consumes its eggs and juveniles. N. cinctellus likely also preys on some of the same invertebrates as does the Devils Hole pupfish, meaning that it is a competitor as well as a predator. The diving beetle only recently became part of the ecosystem, and was first documented at Devils Hole in 1999 or 2000.
Although spawning year-round, spawning peaks from mid-February to mid-May with a smaller peak from July to September. Devils Hole pupfish females have low fecundity, which is the capacity to create offspring. The average female may only produce four or five mature ova (egg cells) each breeding season. Mature ova represent 10-20% of the total number of ova produced. During each spawn, a mature female is thought to produce only a single egg, which are only 1 mm (0.039 in) in diameter. In addition to its low fecundity, eggs have low hatching success and juveniles have low rates of survival. Individuals have a lifespan of 10–14 months.
Because the rock shelf upon which the fish feed and breed is susceptible to seismic activity, specialized behavior mitigates the impact of earthquakes. When a disturbance such as an earthquake occurs, it causes the fish to flee en masse into the depths,: 12:58 and begin a spawning event that may be out of season. During spawning brought upon by a disturbance, several males chase lone females until they become receptive, at which point the female allows one of the males to swim next to her. The female then lays an egg that the male immediately fertilizes.
The Devils Hole pupfish has daily and seasonal movement within the Hole. Around midday, when incoming sunlight is at its maximum intensity on the shallow shelf, the number of fish on the shelf decreases. This tendency to leave the shelf at midday is most pronounced April through September. From December to March, when the shallow shelf receives little if any direct sunlight at midday, the number of fish on the shelf increases as the day advances. In the summer months when the shelf receives the most sunlight, fish are overall less likely to use the shallow shelf.
Having adapted to an environment with low oxygen saturation, the Devils Hole pupfish has developed a behavior known as "paradoxical anaerobism". The fish enters a state of torpor, and has been known to forego breathing oxygen for up to two hours. As a byproduct of this alternate respiration method, the fish produces ethanol.: 17:52
The Devils Hole pupfish species is limited to a single site and highly susceptible to disturbance. In the 1970s, the species was threatened with groundwater depletion, as the withdrawal of groundwater lowered the water level of Devils Hole and limited their ability to spawn on the shallow shelf. After the groundwater withdrawal was limited, its population rebounded, but experienced a second decline from 1995 onward. The reasons for the second decline are unknown, but inbreeding depression, the loss of a prey species, changing algal and microbial communities, or shifting sediment dynamics have been hypothesized as potential factors. It could face threats in the future relating to climate change, as warming temperatures in the area are predicted to shorten the period of optimum recruitment, or the time when the next generation is produced and matures.
Large-scale earthquakes, such as the 2012 Guerrero–Oaxaca earthquake, the 2018 Gulf of Alaska earthquake, and the 2019 Ridgecrest earthquakes have caused standing waves known as seiches in Devils Hole, which can lead to an unseasonal spawning event due to the disruption of the pupfishes' environment. The waves caused by earthquakes can scour the algae from the rocks (as well as eggs and larvae), affecting the food supply and spawning grounds. Flash floods also disrupt the algae via debris swept into Devils Hole.
In addition to the indirect threat of groundwater depletion, human actions can impact the pupfish in other ways as well. A 2004 flash flood swept scientific monitoring equipment into Devils Hole, causing the deaths of an estimated eighty pupfish. In April 2016, three men broke into the Devils Hole protected area, destroying scientific equipment and wading onto the shallow shelf of Devils Hole, smashing pupfish eggs and larvae, as well as vomiting into the water.
Isolation over the course of thousands of years has led the Devils Hole pupfish to become what are believed to be one of the most inbred vertebrates on Earth, and the resulting high mutation load and genetic instability remains a potential long-term threat to the species as a whole.
Population surveys of the Devils Hole pupfish began in 1972. Population counts since then have been conducted using the same methods, with scuba diving researchers counting fish starting at depths of 30 m (100 ft) while researchers above the water count the individuals on the shallow shelf. From 1970 through 1996, the average population was 324. Population highs were recorded in 1980, 1990, and 1995 at counts of 541–548 individuals. Since 2005, the population at Devils Hole has been below 200 individuals, although the population fluctuates depending on the season. Low algae growth and other winter conditions cause spring populations to be 35–65% of the autumn population. The reasons for the decline of the population are unclear. A 2014 study ascertained that the Devils Hole pupfish had a 26–33% chance of becoming extinct in the next twenty years
In November 2005, divers counted just 84 individuals in the Devils Hole population, the same as the spring population, despite observations of egg-laying and juvenile fish during the summer. In 2007, between 38 and 42 fish were left in Devils Hole.
The pupfish count rose in the autumn of 2008 to 126, the first steady increase in more than 10 years. As of April 2013 U.S. Fish and Wildlife reported only 35 fish remain in their natural habitat, but increased to 92 when measured again in 2014. As of spring 2016, a periodic count found 115 of the fish living in the waters. In spring 2019, the pupfish population reached 136, the highest springtime population since 2003.
Population counts were suspended in 2020 due to the COVID-19 pandemic; however, egg collection for ex situ cultivation continued. Observers noted encouraging signs of population growth, and during the next count in April 2022, 175 pupfish were observed. The population has continued to grow, with 263 observed pupfish in September 2022.
