KLAMATH FALLS — 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 more than 25 years ago.
As part a U.S. Fish and Wildlife Service effort to reintroduce endangered suckers, fish biologist Josh Rasmussen and two other USFWS employees collected thousands of inch-long sucker larvae from the Sprague and Williamson rivers, the Klamath Falls Herald and News reported.
The immature fish were placed in coolers and transported to a floating dock off Rocky Point, near Harriman Springs and Crystal Creek, historical sucker spawning grounds. The 7,000 larvae that were released last week into three floating bays will remain there until September, when they become juvenile fish and are large enough to be tagged with electronic transponders and released into the lake.
After the suckers are released, it becomes a waiting game. Some fish won’t come back. The ones that do won’t be back for another three or four years.
“That’s what makes it difficult with the species,” he said. “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.
Rasmussen said 1975 was probably the last time anyone saw suckers spawning near Rocky Point. He said scientists have two primary theories as to why suckers stopped spawning throughout Upper Klamath Lake — overfishing and a change in lake habitat.
Dave Hewitt, a U.S. Geological Survey 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.
“There are a number of theories, but nothing has risen to the top as the smoking gun,” he said.
Once the tagged suckers are released in September, electronic antennas can pick up the fishes’ locations when they swim near underwater monitoring stations. Rasmussen anticipates that will help scientists learn more about what is killing the young suckers.