Walleye feeding on conveyor belt of juvenile salmon

In the first steps of what could turn out to be a larger study, the Nez Perce Tribe found walleye in the Snake River may be consuming a concerning number of juvenile salmon.

The Nez Perce Department of Fisheries Resources Management placed a small-mesh gillnet near the mouth of the Tucannon River this spring.

“We caught 58 walleye in one quick set,” said Jason Vogel, research division director for the department. “Eight of those walleye, inside their guts, had PIT tags.”

Three of those eight tags were carried by endangered juvenile Snake River sockeye that had been gobbled up by the nonnative walleye. The others were a mix of hatchery and wild chinook.

Passive Integrated Transponder tags are about the size of a grain of rice. Fisheries managers inject them into the abdomens of hatchery fish and into some wild fish intercepted at fish sampling traps. The tags help fisheries managers track juvenile fish as they migrate to the ocean and adults when they return to fresh water.

Vogel said migrating juvenile salmon and Pacific lamprey serve up a veritable conveyor belt of prey for walleye. The tribe has funding for two to three years of work looking at the extent of predation on juvenile salmonids. He hopes the results will attract more money and the program can be expanded into a large-scale study and predator removal project.

The results from that one net set in front of the Tucannon may convince funding sources to back the work.

“We only PIT tag a certain number of fish, so every PIT tag represents a lot more,” he said.

He also noted the tags only stay in the predatory fish for a short time, 24 to 48 hours, before they progress through the digestive system and are expelled. That makes finding eight of them and three from sockeye that represent a much smaller percentage of juvenile salmon even more unlikely.

“That was really striking to us,” said Vogel. “Our analytical minds start to say these walleye are having a massive impact.”

Next year, Vogel said they will likely do several net sets near the mouth of the Tucannon River and other places that the first year of work has shown to be walleye and predation hot spots. The intent is to build a case for future funding and to remove the nonnative predatory fish caught in the nets.

“The tribe wants the salmon back. That is their culture. That is their heritage,” Vogel said. “We are alarmed by the continued decline of natural and hatchery fish and we are starting to throw more effort into predator removal.”