CROSS PLAINS, Wis. - Fishery biologists doing routine population monitoring work on Black Earth Creek downstream of Cross Plains have documented a drop in fish populations from South Valley Road downstream about 0.8 miles. On-stream reports from early season trout anglers support this observation.
"We can't say with any certainty what the cause of the drop might be," said Scot Stewart, the Department of Natural Resources district fishery supervisor. "There are several possibilities including the very cold winter, an unknown runoff event of some kind or even last year's floods which greatly reduced the size of the 2013 year-class of fish in the creek. We simply don't have any solid evidence that points to any one clear cause.
"The good news is that this creek has high quality trout habitat, is very productive, and will recover naturally in two to three years. We can say this with confidence because we've experienced fish kills here before and the creek has recovered nicely within the two to three year timeframe."
Even some of the possible causes are somewhat lacking in probability say fishery experts. A sustained and very cold winter would make a runoff event less likely and there is no record of any such event taking place. A single reduced year class alone would not completely explain the preliminary estimate of a 70 percent drop in fish population in this stretch of stream.
"Winter is a stressful time of year for trout in streams, and this past winter was colder and longer than what we typically experience," said Matt Mitro, a DNR cold-water fish research scientist. "Our monitoring of water temperatures in nearby streams showed near-freezing temperatures from early December through March in areas of streams away from springs. Trout streams are usually not that cold for that length of time."
Biologists have already taken steps to ease the impact to the popular stream fishery by stocking 300 surplus wild brown trout from brood stock and additional rainbow trout into the affected stretch of stream.
Biologists will continue routine seasonal population monitoring in the area but will add some additional summertime monitoring as current work schedules allow.
"We've worked to build populations in this outstanding stream but something has happened," adds Stewart, "we don't know what, but we've taken action to soften the impact to anglers and we expect the stream to fully recover as it has done in the past."