For one of the world's rarest fish, 2018 got off to a shaky start. Shortly after a powerful earthquake struck the Gulf of Alaska late last month, news began circulating that the seismic activity had caused the critically endangered Devils Hole pupfish to spawn out of season – thousands of miles away in their home near Nevada's Death Valley. Local experts, however, say certain details about that story have been misunderstood.
The Devils Hole pupfish (Cyprinodon diabolis) has been isolated in a single aquifer-fed pool in the northern Mojave Desert since retreating ice stranded the animals there over 10,000 years ago. And in that pool of hot, salty, 150-metre-deep water, the fish have remained for millennia – out of sight and mostly out of mind – while the world turned on.
Life in Devils Hole isn't easy. At around 90 degrees Fahrenheit (32°C), water in the pool is hotter than most marine fish can tolerate. Oxygen levels, meanwhile, can hit lethal lows, and food is often limited. And yet the pupfish survive in this mind-boggling micro-ecosystem, one of the smallest natural ranges known for any vertebrate.
Despite reigning supreme over such challenges, the Devils Hole pupfish has edged towards extinction in recent years: a rapidly shifting climate, groundwater pumping for irrigation, and still unclear impacts from other human activity have taken their toll. When population counts began in 1972, the pupfish population was about 550 strong; just 30 years later, that number had dwindled to 38. Today, the species is considered critically endangered at 110 to 130 observed individuals.
For a bit of perspective, science writer Jason Bittel points out that you could comfortably fit the entire pupfish population into a box cooler. "You'd probably even still have room left over for a case of beer," he wrote in a 2014 piece for OnEarth Magazine (which is a must-read for anyone interested in learning more about these rare fish, and why scientists want to save them).
For a population this small, any sudden environmental change can be devastating, so it's not surprising that news of the pupfish's recent "early spawning" caught the attention of conservation and science writers. A quick Google search will tell you that Devils Hole pupfish spawn in fall and spring, but Death Valley National Park aquatic ecologist Dr Kevin Wilson explains that's not entirely accurate.
Wilson notes that the fish actually spawn year-round; the spring and fall months, meanwhile, are typically their busiest "get busy" periods. That means at least some of the pupfish were already spawning before January's seismic upheaval.
"The misconception is that the earthquake 'started' the spawning," clarifies Wilson. "This is incorrect. Disturbance events like earthquakes and floods increase the spawning behaviour of the Devils Hole pupfish."
Male members of the species turn a stunning shade of blue during spawning, and park staff are now seeing an above-average number of sapphire studs in the wake of the quake.
If you're wondering how an earthquake in Alaska could boost fish breeding in a remote hole some 2,000 miles away in the desert, the answer lies deep underground. When an earthquake strikes, waves of energy ripple out from its epicentre. These seismic waves move through the Earth's surface and inner layers, and when they pass through an isolated body of water like Devils Hole, they cause some "sloshing". (This is comparable to how energy-driven waves can travel great distances to form tsunamis, though the latter are caused by up-down movement of the seafloor.)
The Alaskan quake caused the water level in Devils Hole to rise and fall by about a foot – a phenomenon known as a seismic seiche – and that change in their environment prompted more of the fish to spawn. However, suggestions that the rising water "tricked" the pupfish into thinking spring had arrived are incorrect. The water level in Devils Hole remains relatively stable throughout the year, which makes sense since Death Valley receives only around 60 mm of annual rainfall. The hole experiences two small peaks and troughs every 24 hours, much like the ocean's tides. These daily changes result in a water-level rise or fall of just six to eight inches, so it's likely the increased spawning was linked to the sudden, shaky disturbance caused by the earthquake, rather than a specific water level.
"The fish are curious and an innate reaction to disturbances is to increase spawning behaviour," he says. "This behaviour can be seen in other species after major floods in rivers."
Some scientists speculate that post-flood spawning has to do with boosted survival odds for offspring. Flooding can increase available habitat for fish fry, as well as bringing important nutrients like nitrogen and phosphorous into river systems, which can, in turn, make planktonic prey more abundant.
Other experts take a different view. Spawning during a flood does not seem worth the effort, they argue, since eggs and new hatchlings can become stranded quite easily when water levels return to normal. Instead, they see these disturbance-related spawning events as a population's last-ditch effort to reproduce in the face of danger. (If there's a chance of imminent death, you might as well send out a genetic contribution to ensure your line survives.)
Wilson, however, does not believe that Devils Hole will see any kind of lasting impact from the seiche. Spawning increases can follow even smaller habitat disturbances, like when scientists sample the substrate during routine environmental checkups.
Sometimes, though, a bit of habitat "turbulence" can be good for the denizens of Devils Hole. Back in 2012, an earthquake near Oaxaca, Mexico caused extreme "gurgling" in the pool. The resulting seiche waves washed over the upper rock shelf – the ledge on which most of the pupfish lay their eggs and congregate to feed on tasty algae – with enough force to clear it off.
While such events can temporarily limit the food available to the pupfish, and toss some of their eggs into the murky depths, Wilson thinks of them as something of an ecological "reset". In an interview with Scientific American after the Oaxaca earthquake, he noted that rare disturbances like these seiches can improve the pool's overall health over time.
At this point, it's too early to say whether the increased spawning activity will lead to an uptick in the number of pupfish in Devils Hole, but this seems unlikely. In fact, when food becomes scarce following a disturbance in the pool, pupfish occasionally turn to their own eggs or young for sustenance. Any "extras" that hatch in the coming months, therefore, might be gobbled up before algae levels have a chance to stabilise. We'll just have to wait and see.
"More people have walked on the moon than have witnessed the effects of an earthquake at Devils Hole," Wilson says.
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Top header image: Olin Feuerbacher/USFWS
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