Smolt kill on North Shore Streams

[DEADhead]

Update on the smolt kill from the Duluth News Tribune:

Field Reports: Heat blamed for rainbow trout die-off

COMPILED BY SAM COOK

NEWS TRIBUNE OUTDOORS WRITER

July's hot weather has taken a toll on young rainbow trout in the Lester and Knife rivers, according to Minnesota Department of Natural Resources officials.

About 400 to 500 of the yearling rainbows have died so far, said Don Schreiner, DNR Lake Superior area fisheries supervisor at French River. They began dying as early as the July 4 weekend.

Schreiner estimates at least 300 trout have died on the Knife and between 100 and 200 on the Lester.

The number of dead fish is small compared to the numbers stocked or reared naturally in the two streams. The Lester River takes an annual stocking of 42,500 yearling rainbows, and about 20,000 yearlings migrate down to Lake Superior from the Knife each summer, Schreiner said.

Similar die-offs have occurred about five years of the past 15, he said. The fish die as shallow areas of the river get too warm and the oxygen level drops.

"It's almost like a sauna where the sun heats up that water and the rock gets warm," Schreiner said.

Most yearling rainbows had successfully migrated to Lake Superior, although some may remain in deeper pools upstream.

Typically, the die-offs don't occur on streams farther northeast along the North Shore, Schreiner said. Those streams are fed in part by cooler groundwater and are also better shaded, he said.

Warm-weather events such as this, and streams freezing to the bottom in cold, relatively snowless winters, reduce the carrying capacity of North Shore streams, Schreiner said.

"People look at the streams in spring when they have a lot of water and think they have a lot of habitat," he said. "But it's times like this that the bottlenecks occur and habitat shrinks. That's what dictates the carrying capacity of the stream. This is crunch time."

He said more fish may die if warm weather persists into August.

[matthothand]

What a tragedy. Great post...though it saddens me.

[DEADhead]

No offense to Don or anything, since I think he does a good job managing, but I have to believe that there is a higher mortality rate on those rivers than what he stated. Just my opinion.

[Quickstrike]

I would agree, it's pretty bad up here. We needed the rain that the south shore got.