A southeastern Minnesota trout stream that suffered a major fish kill 15 months ago is bouncing back, according to a recent stream survey done by the Minnesota Department of Natural Resources.
In mid-October, staff from the DNR’s Lanesboro fisheries office conducted a fish population assessment on a portion of the South Branch Whitewater River northeast of Rochester. They found that the total brown trout population over the one-third mile segment they checked amounted to 41.28 pounds per acre, about a five-fold increase over what they sampled a year ago.
Last fall’s results still were down from the 70.18 pounds of brown trout sampled in April 2015. The drop occurred after a late July 2015 die-off of several thousand fish, including brown and rainbow trout, dace, white suckers and sculpin. State investigators were unable to pinpoint the exact cause of the fish kill, attributing it to a combination of conditions following heavy rain.
“We’re glad to see the South Branch recovering,” said Vaughn Snook, DNR Lanesboro area assistant fisheries supervisor. “Hopefully, by this time next year, we’ll be back to pre-incident levels, depending on weather and other environmental factors throughout the watershed.”
Brown trout populations in the South Branch Whitewater have fluctuated during the past 10 years. Variations appear related to spring precipitation, Snook said. Heavy rains in late March through April reduce the number of young brown trout that survive.
Based on 36 years of monitoring, a reasonable expectation for brown trout populations in that segment of the stream might be around 150 pounds per acre, a level last seen in 2012. In the early 2000s, brown trout in the South Branch Whitewater exceeded 200 pounds per acre. The stream has not been stocked with brown trout since 1989 because natural reproduction has continues to be sufficient to maintain a healthy population.
“Anglers shouldn’t think twice about not fishing,” Snook said. “The Whitewater’s south branch is on its way to recovery and the time to catch trout is now.”
More information about trout and trout streams in the Lanesboro area is available at www.mndnr.gov/areas/fisheries/lanesboro/management.html.