After three decades of costly recovery efforts, Utah Lake’s June suckers have rebounded from near extinction to a point at which the U.S. Fish and Wildlife Service has proposed downgrading the fish’s protection status from endangered to threatened.

An emergency captive-rearing program saved the large-bodied fish, but much work needs to be done to put the June sucker on a self-sustaining course, according to Mike Mills, a biologist who helps lead recovery efforts.

In a few months, Mills said, construction will begin on a project to re-create 300 acres of delta where the Provo River meets Utah Lake, providing crucial habitat for young suckers to survive the four years it takes to become spawning adults.

The once plentiful fish, which naturally inhabits only Utah Lake and its tributaries, became so rare by the 1990s that its survival seemed unlikely. The hatchery-rearing program has since enabled the number of spawning fish to reach 3,500, a tenfold jump from 1999, when a recovery plan was finalized, according to the proposed downlisting posted recently on the Federal Register.

Saving the fish from extinction is the result of partnerships across federal and state agencies, according to the service’s Mountain-Prairie regional director, Noreen Walsh.

“The improved status of the June sucker would not have been possible without the shared commitment to conservation from the Utah Division of Wildlife Resources and other partners,” Walsh said. “Our best chance for continued success in recovering species rests in the power of these long-term, collaborative partnerships.”

The move also cheered conservationists, who hailed the sucker’s rebound as a sign that the 1973 Endangered Species Act works to preserve habitat as well as save imperiled species — as Congress intended.

“This important law benefits not just species like the June sucker but people who depend on clean water," said Ryan Beam, a Utah-based conservation advocate for the Center for Biological Diversity. "If this hard work continues, maybe one day Utah Lake will once again shine clear.”

Among the West’s largest freshwater bodies, Utah Lake once teemed with millions of June suckers — so named for the month they spawn — which served as an important food source for Native Americans and later were harvested for fertilizer by Mormon settlers.

The fish’s population crashed in the 20th century from habitat loss and the proliferation of invasive carp and other introduced fish species. Agricultural and industrial runoff has also degraded the lake’s clear waters into a turbid, algae-infested mess.

(Chris Detrick | Tribune file photo) A newly released June Sucker swims in the Hobble Creek Wednesday, Nov. 12, 2008. The June Sucker Recovery Program unveiled its restoration of Hobble Creek in Springville and released the fish into the restored stream.

Adult suckers grow to up to 24 inches in length and weigh five pounds. They can live up to 40 years. They swim up the Provo River and other Utah Lake tributaries to spawn. After hatching, the larval suckers drift back down to the lake, but most die either en route or from lack of decent rearing habitat. Some wind up in the bellies of nonnative sport fish, such as largemouth bass, walleye and white bass.

Decades ago, a deep channel was dredged through the Provo’s flood plain, directing the river’s flow into the lake and eliminating a biologically rich delta, where young suckers once found sanctuary in dense vegetation growing in braided channels. Now, few young fish even reach the lake because the river’s flow slows drastically when it enters the artificial channel. The tiny suckers get stuck on the bottom and starve, according to Mills, who coordinates the June Sucker Recovery Program.

“It really acts as more of an arm of Utah Lake than a river, so there’s not enough velocity to push the larval fish out to the lake," said Mills. "It’s cold, stagnant water, whereas in the delta, things will be shallow, there’ll be vegetation, there will be warmer water, more food resources. It’s just a much more rich and dynamic environment.”

This lack of sucker survival resulted in what biologists call a “recruitment bottleneck,” where few young fish survive into adulthood.

“The delta [restoration project] is going to restore some of those habitat conditions that will give those larval fish a chance to grow and become adults,” Mills said. “That’s what’s missing in June sucker recovery — the ability of these fish to survive on their own and recruit into the adult population so that we’re not reliant on captive-reared individuals being stocked in the lake in order to keep the population up.”

Sucker recovery also has benefited from the large-scale removal of carp, which were introduced into the lake a century ago and flourished at the expense of native fish, including Bonneville cutthroat trout. These powerful bottom feeders root around the lake bed, wrecking the rooted vegetation that holds sediments in place and supports habitat.

The Utah Department of Natural Resources has pulled more than 13,000 tons of carp out of the lake between 2009 and 2017, resulting in habitat improvements that have increased survival rates for young suckers.

The state has established refuge populations of suckers at Red Butte Reservoir outside Salt Lake City and the Fisheries Experiment Station in Logan, and uses ponds in Box Elder County to grow hatchery fish before stocking them in Utah Lake. By 2017, some 800,000 subadult suckers have been released into the lake. Initially, 8-inch fish were released, but only 3% survived long enough to spawn, Mills said.

Four years ago, Mills’ program began keeping the hatchery fish longer.

“We try to raise them up to 12 inches. That’s been huge,” Mills said. “By increasing the size to 12 inches, we’re now looking at survival that’s approaching 30%, which is really good for an endangered species that’s captive-reared going into a wild environment.”

Now most of Utah’s Lake spawning suckers came from Red Butte or the Logan hatchery.

According to Mills, the June sucker would be the fourth endangered fish downlisted to threatened. The other three, all Oregon natives, were eventually delisted.

“This downlisting is saying, ‘Your captive-rearing program works. It’s been able to keep this population from declining,’” Mills said. “We have been on the right track, but this is no sign we have accomplished our group’s main goal. We are taking a minute to say, ‘Great,’ and focus right back on our projects.”