This story also appeared in Mountain Journal The only thing more unpredictable than anglers fibbing about the size of their catch is how they decide where to catch it. The latter changed this June with the release of TroutCast, an internet tool th at both predicts water conditions in Montana trout streams and also shows how future fish populations may grow or shrink. In the process, it may upend longstanding strategies for improving the state’s $1.5 billion angling economy. “This shows you in real time how stressful conditions are occurring across Montana, so it shows you where you want to go fish,” said Tim Cline, assistant professor of cold-water fish ecology at Montana State University in Bozeman. “And by having all this population data and flow mechanics publicly available, we can show how water supply drives fish production. People can understand just how valuable water is.” Fishing, especially trout fishing, feeds both the economy and sense of identity in Greater Yellowstone. The state’s native cutthroat and bull trout species both teeter on the edge of environmental distress, while its non-native but prolific rainbow, brown and brook trout depend on cold, clean water to thrive. Consistently hotter summers and increasing agricultural irrigation demands have stressed the trout world to the point that closures and access restrictions have become routine. The website has two primary features: management forecasts and population forecasts. The management predictions use streamflow- and temperature-gauge data from the U.S. Geological Survey along with the National Oceanic and Atmospheric Administration’s National Integrated Drought Information System to predict the possibility that a river or basin might exceed management thresholds. Water that’s too warm or too low can trigger “hoot owl” restrictions which limit anglers to early-morning hours of river access. The tool can look ahead one to four weeks. The TroutCast tool shows how predicted streamflow and temperature levels may trigger fishing restrictions in Montana Rivers. It also combines long-term fishing population records with streamflow forecasts to project how trout numbers may rise or fall in high or low water conditions. Credit: USGS TroutCast’s population forecast page combines that water data into a more complex set of Montana Fish, Wildlife and Parks fish census records dating back to the 1970s. It aims to tell if brown or rainbow trout numbers at particular sites are increasing, holding stable or decreasing compared to the previous one, five or 10 years. “We all know fish need water,” Clint Muhlfeld, director of the USGS Northern Rocky Mountain Science Center, told Mountain Journal. “TroutCast is able to quantify how much water is necessary to sustain or rebuild these populations. We can quantify what a cubic foot per second of water means to the carrying capacity of fish across the state. That’s a whole new thing.” And it’s taking hold. Cline and Muhlfeld were showing the website to colleagues at Trout Unlimited a few weeks ago when someone mentioned that recent improvements on a Ruby River dam near Virginia City might add an extra 20 cfs to the flow. Cline showed how the website’s population archives find the Ruby can support 384 fish per mile at its current streamflow of 140 cfs. Bumping that up to 160 cfs would nearly double that number to 784 fish per mile. But local circumstances matter, and the same inputs sometimes produce different outcomes. The website’s interactive population graphing tool shows most rivers receive the hoped-for census increase as water levels rise. Other rivers do the exact opposite, forecasting population declines as flows increase. Cline told Mountain Journal the divergent results reflect the nuances of individual rivers. In cases where more water results in fewer fish, he said, the extra flow likely comes from a dam flood-control release that washes away egg spawning beds. A June 8 check of the Madison River near West Yellowstone shows the reach is likely to experience both low flows and high temperatures in the next one to four weeks. Anglers can use these reports to help choose what rivers to fish for best conditions. Credit: USGS Combining decades of water and fish census data might also revolutionize how fisheries managers, hydropower operators and irrigators think about helping trout. The usual pattern has been to enjoy the wet years and scramble to find extra water in drought years. Those scrambles include paying farmers to divert their irrigation water back into the rivers, or restricting and closing access to anglers. The population trend data suggests a different management strategy. Muhlfeld said rather than attempt to preserve fish numbers in dry times, it could be more productive to boost populations when the water is plentiful. “It’s better to bank a surplus rather than try to stop a decline,” he said. “Some rivers, especially ones that are heavily irrigated like the Big Hole, those populations are walking a tightrope. They’re barely replacing themselves. But if we focus on the wet years as a way to build the populations back up, those populations can really respond significantly. That makes them more resilient during drought.” TroutCast has been a collaborative project five years in the making, drawing on resources from USGS, Montana State University and Montana Department of Fish, Wildlife and Parks. As the site develops a user track record, future versions will roll out for Idaho and Wyoming rivers.  In addition to helping anglers plan their next outing, it may also improve the way people consider the most precious resource in the West. “This transforms the way we think about drought and the value of water,” Muhlfeld said. “It allows us to move from a reactive mode of management to a proactive mode.” The post New web tool lets fish predict river conditions appeared first on Montana Free Press. ...read more read less