Survey raises questions about Metolius trout

A recent redband trout survey for the upper Metolius Basin raises both caution and optimism among fishery biologists.

The survey, authored by Fishery Biologist Bradley Houslet and released by Sisters Ranger District on July 20, clearly shows increased spawning success among "redbands," the local strain of rainbow trout.

But the timing and reasons for this increase pose interesting questions for biologists. One of the more intriguing is that the recent spawning success of wild redbands follows the cessation of stocking hatchery fish, which ended in 1995.

However, District Fishery Biologist Mike Riehle hesitates to draw definitive conclusions.

"We as scientists are conservative as to how we interpret (these) results," he added. "There are not a lot of past data for comparison."

Riehle said that "through years of stocking hatchery fish in the Metolius, a lot of these fish may survive to interbreed with wild fish."

So the question remains: How have historic hatchery releases impacted current numbers of wild redband trout in the Metolius River?

The redband trout is a "species of concern," according to Riehle. He explained that very few wild and native fish species remain that have not bred with hatchery fish.

"The redband is a native strain of rainbow trout found on the east side of Cascades," Riehle said. "It is separate from coastal and east side Klamath (rainbows)."

Releasing hatchery rainbows into the Metolius River apparently threatened the unique wild redbands with displacement.

"Hatchery fish are bred like cattle. They are bred at high rates and tend to be aggressive. They are raised in an enclosed area and have to compete in the raceways (of the hatchery)," he said.

While the aggressive hatchery fish can push the native trout from quality habitat in the river, genetically they have some disadvantages that make them less viable in the long run.

The hatchery fish "lose fitness genetically and behaviorally," Riehle said, giving them less chance of surviving in the wild.

When released into wild rivers and streams, these fish can also threaten the genetic viability of native strains such as the local redband.

So, it is possible that by discontinuing the release of hatchery fish, the number of native fish has a chance to rebound.

The Oregon Department of Fish and Wildlife (ODFW) has also documented genetic studies showing how hatchery fish can affect the health of wild populations, according to Acting District Fish Biologist Steve Marx with ODFW in Bend.

"(We) documented some decline in the resistance of wild fish to (a common) parasite due to interbreeding with hatchery fish," Marx explained. "The parasite will kill hatchery fish but wild fish normally have some resistance."

ODFW manages the Wizard Falls hatchery and has conducted redband studies whose results concur with those of the National Forest report.

"We developed a management plan based on the biology of the system," described Marx.

"We had a number of public meetings on different options considered for management, and the directive that came out of that was to manage for wild fish only."

In concert with their decision to halt stocking in the Metolius, ODFW also stopped stocking brook trout in the wilderness lakes of the basin.

Marx agrees with Riehle that it's too early to directly credit fish management programs for the redband's recovery. However, both agencies remain optimistic and will continue to monitor the success of this local strain of native rainbow trout.