Endangered suckers may spawn near Rocky Point again after more than 40 years.

“1975 was probably the last time anyone saw suckers spawning there,” said Josh Rasmussen, a fish biologist for the U.S. Fish and Wildlife Service’s (USFWS) Klamath Falls office.

Early accounts from the 1800s suggest Lost River and shortnose suckers once lived and spawned throughout Upper Klamath Lake, but fish die-offs and poor survival rates led the species to be listed under the Endangered Species Act in 1988. According to the species’ Revised Recovery Plan, both sucker species face a high threat of extinction and are believed to have low recovery potential.

As part of a USFWS pilot program to reintroduce suckers throughout the lake, Rasmussen and two other USFWS employees are collecting thousands of inch-long sucker larvae from the Sprague and Williamson rivers. The immature fish — barely more than thin, translucent bodies with two black specks for eyes — are placed in coolers and transported to a floating dock off Rocky Point, near Harriman Springs and Crystal Creek, which are historical sucker spawning grounds.

The program’s goal is to imprint the rearing area in the suckers in the hopes they will return to spawn where they were raised, Rasmussen said. But after the suckers are released, it becomes a waiting game: many may not come back, and those that do, won’t do so for at least another three or four years.

“That’s what makes it difficult with the species. People want to see tangible results very quickly, but because of the ecology of the species, there’s not a lot we can do for the first four or five years of their life,” he said.

Tagging juveniles

According to Rasmussen, the 7,000 larvae that were released last week into three floating bays will remain there until September, when they become juvenile fish — about 4 or 5 inches long — and are large enough to be tagged with electronic transponders and released into the lake.

“I’m pretty confident we’ll be able to get the size fish we’re looking for in good numbers by the end of the year. That will open up a lot of other opportunities,” he said.

Rasmussen said scientists have two main theories as to why suckers stopped spawning throughout Upper Klamath Lake. The first is the species was overfished and not able to repopulate quickly enough to maintain healthy, reproducing populations.

“If that’s the case, it wouldn’t be very difficult to get the suckers to come back and start spawning again,” he said.

The second theory is something in the lake habitat changed and caused the fish to die out. Rasmussen said Lost River and shortnose suckers both have long life cycles and don’t become sexually mature adults until around 4 years old, although many live for another 30 years or more. Suckers that make it to adulthood have a 95 percent survival rate, while only 5 percent of first-year fish are expected to survive, he noted.

Dave Hewitt, a U.S. Geological Survey (USGS) fisheries biologist, said researchers are studying toxins released by algae, as well as oxygen-deficient periods caused by algae die-offs, for clues to the juvenile sucker disappearances. Hewitt said predators also may play a role in killing-off the young fish, but research supporting that hypothesis is limited.

“There are a number of theories, but nothing has risen to the top as the smoking gun,” he said.

Sucker survival

Rasmussen said the lake system is complex, making it difficult to understand what is affecting sucker survival. He said trials leading to the rearing program showed good results, but he also suspects poor water quality and oxygen deficiencies jeopardize juvenile suckers.

“If we notice things start to look bad, we’ll bring in some oxygen and supply oxygen to the cages during that period,” he said.

The three cages, or bays, attached to a floating dock are about 8-feet deep and covered with a mesh net to prevent predatory birds, like terns and grebes, from gobbling up the suckers. Rasmussen hopes maintaining water quality and limiting predation will improve their odds of survival.

“If I hit 50 percent, I would be ecstatic,” Rasmussen said.

Once the tagged suckers are released in September, electronic USGS antennas can pick up the fishes’ locations when they swim near underwater monitoring stations. Rasmussen anticipates the monitoring will help scientists learn more about what is killing the young suckers.

“Whether or not they’re going to come back, I have to believe we’re smart enough to figure it out,” he said.

ljarrell@heraldandnews.com; @LMJatHandN