In the US, an earthquake 3,200 km away triggers spawning in the world’s rarest fish

On January 23, a powerful 7.9 magnitude earthquake struck the northwest Pacific, rocking Alaska, United States.

More than 3,200 km away, the earthquake caused waves over 30 cm (1 foot) high in Devils Hole, a small water-filled limestone cave in the Death Valley National Park in Nevada. Devils Hole is the only known natural habitat of the incredibly rare Devils Hole pupfish (Cyprinodon diabolis).

“It’s crazy that distant earthquakes affect Devils Hole,” Kevin Wilson, aquatic ecologist for Death Valley National Park, said in a statement. “We have seen this a few times before, but it still amazes me.”

The earthquake-triggered waves set off a series of ripple effects on the critically endangered pupfish, considered the world’s rarest fish, and its habitat.

Spawning behaviour

Ambre Chaudoin, a biological science technician working at Devils Hole, for instance, observed the pupfish spawning immediately after the waves hit the pool, indicated by the females turning a drab olive brown that made the brilliant blue males stand out.

Such spawning is not out of the ordinary, though, Wilson told Mongabay. While pupfish spawning peaks in spring and early autumn, they do spawn year-round, especially after disturbances.

“Spawning behaviour increases after disturbance events such as earthquakes and floods. This is inherent in the pupfish,” Wilson said. “The increase in spawning activity occurs within several hours and can continue for several days. Several males will ‘chase’ a female for a certain amount of time and distance. Once the female is receptive, a single male will swim next to the female, they form an ‘s’ shape, and then the female lays an egg with the male fertilising it immediately.”

Food chain impact

The waves triggered by the earthquake will also have likely washed away some of the pupfish’s food, mostly algae, organic matter, and other invertebrates, the experts say. This is because the Devils Hole pupfish prefer to stay close to the pool’s surface – roughly the top 2 meters to 6 meters (6.6 feet to 19.7 feet) of the water column – and depend on this shallow shelf for their food and reproduction.

This shallow shelf is where most algae and other food sources grow, and the waves wash this food away and deposit them deeper inside. However, the biologists are hopeful that the food will rebound over time.

“Recolonisation of food materials depends on the time of year,” Wilson said. “Algae growth is greatest in late spring through early autumn when sunlight actually hits the water surface over the shallow shelf. During other times of the year, sunlight does not reach the shallow shelf because the water surface is 15 meters [49 feet] below the ground level.”

Some invertebrates like beetles and crustaceans will recolonise immediately, he added, while others like snails could take longer. “The short answer is that the recolonisation could take days to many weeks.”

Earthquakes can also “reset” the pupfish’s habitat, Wilson said. The earthquake-generated waves can wash off decomposing material from the shallow shelf, for example, and help create better conditions for the pupfish eggs to hatch.

“Earthquakes... can set up waves that clear the spawning shelf of the algae upon which the pupfish rely, however depending upon the time of year, the algae may regenerate quite rapidly,” Paul Barrett, a biologist who used to coordinate the Devils Hole pupfish recovery team at the United States Fish and Wildlife Service, explained after a 2010 earthquake triggered 1.2-meter (4-foot) waves in Devils Hole. “Furthermore, quakes can serve a useful purpose in shaking silt and other fine particles that have washed into Devils Hole off of the spawning shelf and into the deeper waters. This frees important space between the substrate particles where the Devils Hole pupfish larvae seek refuge.”

Critically endangered

The Devils Hole pupfish is currently listed as Critically Endangered on the International Union for Conservation of Nature Red List. In 2013, the tiny 2.5-cm (1-inch) fish was believed to be on the verge of extinction when pupfish populations dropped to a low of 35 observable individuals. Recent counts, however, estimate that there are about 115 to 130 pupfish surviving in Devils Hole today. The numbers are still low. But the pupfish populations have been relatively stable over the last few years, Wilson said.

“We are cautiously optimistic that the population will slowly increase over time,” he added. “We continue to monitor abiotic and biotic parameters that will hopefully provide us information on ecosystem processes and population dynamics of Devils Hole and the Devils Hole pupfish.”