Once Declared Extinct, Owens Pupfish Finds Fresh Hope in Long-Awaited New Habitat

In early April, just over 700 Owens pupfish were relocated by the California Department of Fish and Wildlife (CDFW) to River Spring Lakes Ecological Reserve in Owens Valley. The move is seen as a significant step forward for the rare North American fish, once declared extinct in 1940, that has been considered on “life-support” since it was re-discovered in 1964. 

“Prior to this most recent reintroduction project, [Owens pupfish] were occupying less than a quarter acre of habitat total, for a species that once occupied probably 200,000 acres or so of wetland marsh in 1900,” said Nick Buckmaster, an environmental scientist with CDFW. “We’ve reintroduced Owens pupfish to somewhere around 100 different locations in the Owens Valley before, with all but two of them having failed.”

A significant challenge for Owens pupfish, which only grow to about four or five inches, is that they are particularly prone to predation, especially from bass. 

“Pupfish did not evolve with a dominant fish predator, so there’s almost no predator avoidance behavior and that means pupfish are very easy for bass to eat and bass can eliminate pupfish very quickly,” Buckmaster said. “Unfortunately, following the introduction of bass to the Owens River System in 1917, over the next couple of decades the bass spread to almost every body of water and pupfish disappeared almost completely.”

A CDFW scientist at the River Spring Lakes Ecological Reserve – photo: California Department of Fish and Wildlife

Aside from bass, other threats have been known to hamper reintroduction projects of Owens pupfish in the past.

“[Reintroduction has] failed before because of non-native fish or invasive vegetation that will encroach on the open water habitat that pupfish need,” Buckmaster said. “Although if you total up the numbers that cause habitat or population loss, it comes down to like ⅓ bass, ⅓ invasive vegetation, and ⅓ unknown because for just some reason, the water quality wasn’t right or the temperature was too high.”

Despite these existing threats, Owens pupfish are seen as being uniquely resilient as a desert-fish species.

“They’re kind of the quintessential desert survivors as they can eat anything from blue-green algae, which is notoriously hard to digest, to tearing apart meat,” Buckmaster said. “They can tolerate water as cold as one degree centigrade, so right above freezing, to as hot as 40 degrees centigrade, which is almost over 100 degrees Fahrenheit. They can tolerate water that’s completely fresh or water more salty than seawater. So they’re incredibly tolerant of the environmental conditions that you can put them in, they really just have a couple of Achilles’ heels that keep them from being widespread.”

This new reintroduction project, however, differs from previous efforts due to the size and scale of their new habitat at River Spring Lakes Ecological Reserve. 

“This increases their occupied habitat and their population potential by five orders of magnitude,” Buckmaster explained. “[River Springs] is a long way from non-native species, so it’s a secure habitat. It’s got a very stable water supply, there’s no water development in that basin and it’s protected by conservation agencies. The Department of Fish and Wildlife owns a big part of the marsh and the Bureau of Land Management owns the other part, so there’s no private land development pressures. It’s really a rare win for a species that’s been limping along since 1969.”

Located between Mono Lake and Bishop, CA in the Upper Owens River Basin, River Spring Lakes Ecological Reserve is a terminal marsh system that creates a highly productive, wet saline environment that’s similar to what Owens pupfish occupied historically. 

The red dot marks the River Spring Lakes Ecological Reserve. Explore the area with this interactive map.


“[River Springs] is fed by a very stable, large, reoccurring spring that flows like a river out of the ground at the base of a salt flow. Depending on how much precipitation we’ve gotten, the amount of actual wet habitat available for pupfish fluctuates between about a mile and a half to two square miles, which is substantial for a species that has been subsisting more or less in pools the size of a bathtub for years,” according to Buckmaster.

Until recently, River Springs had been supporting a non-native population of hybridized Death Valley pupfish. They had been there since the 1940s, when the same University of Michigan researchers who would later rediscover the Owens pupfish moved the Death Valley subspecies from its Salt Creek and Saratoga Springs habitat in the Amargosa Basin over to River Springs.

“This was done to try to create a refuge of Death Valley pupfish because it was pre-Death Valley National Park and that area was looking at potential mining development and these are a very sensitive species,” Buckmaster said. “But today the Death Valley subspecies occupy 100% of their native range and their entire habitat is completely protected, so they’re considered to be one of the more stable species of native fish in eastern California. So we made a decision of prioritizing [the Owens pupfish] species that is in dire need of a secure habitat.”


Owens pupfish on the move – photo: California Department of Fish and Wildlife

The successful transfer of Owens pupfish to River Springs is the culmination of a five-year effort that began with a grant from the Fish and Wildlife Service. 

“We hired a crew and proceeded with removal of the non-native [Death Valley] pupfish, which was a multi-year process that involved manual removal and then sequential dewatering of the marsh system,” said Buckmaster. “It was extremely difficult because we ended up having to do it in the wintertime when temperatures were below zero degrees and we had a number of equipment failures. But at the end of the day, we pulled the non-native fish out and then waited a couple of years before introducing the Owens pupfish to the system just to make sure there was nothing left. So it was a marathon, but it seems to be worth it at this point.”

With the transfer now complete, it’s a matter of waiting to see how the Owens pupfish respond. But understanding their reproductive capabilities, the new and significantly larger habitat bodes well for them.

“Since reintroduction in April, we’ve seen spawning fish so they’re breeding successfully,” Buckmaster said. “This was a big move and now it’s really up to the pupfish to do their thing and make more pupfish. The pupfish are great as a recovery species, because if you put them in the right spot the females can breed 200 times a day for six months out of the year. That means they can double their population in something like a month and a half if you let them, so we don’t have to do anything at this point and it seems they’re doing fine.”

Owens pupfish in transit – photo: California Department of Fish and Wildlife

Before their transfer to River Springs, these 700-plus pupfish were subsisting in five different locations, where some of the Owens pupfish population still remain. Due to the small and isolated nature of these existing populations, the genetic diversity of the species has declined substantially. Consequently, the population now at River Springs is the first opportunity in nearly 100 years for the Owens pupfish to become genetically diverse again. 

“Historically, the Owens pupfish populations have been in these little habitats that we’ve had to create but are too small to support a genetically-viable population. So over time they lose alleles and genetic diversity, because there’s just not enough pupfish able to breed every year so this leads to an almost inbred population,” according to Buckmaster. “But now, they all have unique alleles so what that means is they’re all genetically different from each other. So for this new population, we pulled from all of those existing populations because essentially since 1969, they’ve been split up into all these little pockets and we needed to put them back together again to maximize the diversity and recreate the population of genetic diversity that Phil Pister rescued in 1969.””

Five years after their re-discovery in 1964, University of Michigan biologist Phil Pister essentially saved the Owens pupfish from the brink of a second declared extinction when his team realized their last habitat was drying up.

“It was a time when we were going through drought and a lot of the spring pools were starting to disappear,” said Buckmaster. “So at the 11th hour, Phil Pister went out and removed the last 800 pupfish from the drying habitat and moved them into a new habitat a couple of days later and essentially saved the species. Since then, the existing populations have been on life-support and largely isolated from each other.”

Consequently, a lot of value can be found in the successful reintroduction of the Owens pupfish to a new and significantly larger habitat within their historical range.

“From a scientific standpoint, they’re an interesting example of what happens when you isolate populations over time. There’s an ethical argument for preserving species of evolutionary significance or distinct lineage and Owens pupfish are incredibly unique in that way, too. Then there’s a moral obligation we have as humans who have dramatically altered the environment that we live in and Owens Valley is no different. We’ve introduced non-native fish, we’ve drained a lot of the marshes, we’ve changed the ecosystem out here dramatically and in the process of bending the environment to support our communities and meet our needs, we’ve almost eliminated a couple of species out here and so we have a responsibility to keep these other species on the planet around with us as we move forward,” Buckmaster explained.

As the CDFW looks to monitor this new Owens pupfish population moving forward, the future at least for now seems a little brighter for the fish once-popularized in Pister’s famous biological essay “Species in a Bucket.” 

“After a win like this, it’s very easy to be optimistic,” Buckmaster said. “We did a great job here, but there’s a lot of other wins that we can have for native species out in eastern California.” 

Scott King writes about science, the environment, and technology for the Ally. Support his work.


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