The Montana State University graduate student caught more than 34,000 fish in Eastern Montana last year, and he's out there again this year. He has pulled in everything from perch to suckers. He has caught 25-inch channel catfish and one-inch minnows.
"I like to brag about it to people," Mullen joked, adding that he is studying for his master's degree in fisheries management and returned 99.9 percent of the fish to the water. He carried the rest to MSU to verify their species.
Mullen is researching five prairie streams that flow directly into the Yellowstone River and examining the fish to see how their groupings change with the season and location in the stream. The streams are Cedar Creek and Cabin Creek near Glendive, O'Fallon near Terry, North Sunday near Miles City and Sweeney near Forsyth. Sweeney is the smallest stream, and O'Fallon is the largest.
His net-and-release project started last June and will run two years, said Mullen who is working mostly on private land. So far, he has noticed that the closer he is to the Yellowstone River, the more species he finds.
"As you move upstream, species drop out and you get less diversity," Mullen said. "Sometimes upper sites have a greater abundance of fish, but they are definitely lower in species richness."
Mullen has also learned that stream width, water flow and streambed substrate seem to be the most important factors in how and where the fish assemble. Stonecats, for example, generally swim around cobbles and boulders.
Hoping to help stream managers and add to the general body of knowledge about prairie streams, Mullen returns to Eastern Montana every spring, summer, fall and winter. He samples up to 10 sites per stream by walking on one bank while a technician walks on the other. They pull a seine net through the water between them, then stop after 300 meters to empty the fish into buckets, identify, count and measure the fish. They also record information like stream widths, amount of flow, water quality, dissolved oxygen levels and pH levels.
Mullen said he has found 24 species of fish so far, 19 of them native to Montana. One surprise was finding yellow perch. Another was fishing the lower side of Cedar Creek and catching only two western silvery minnows all summer but more than 100 in the fall.
"I think it's due to maybe a combination of factors," Mullen theorized. "In the fall, the fish may have grown large enough to be retained by the mesh of the net."
Eastern Montana also had a big snowstorm last fall, he said. When the snow melted, it resulted in high flows that could have attracted the western silvery minnow and other fish that normally swim in the Yellowstone. One of Mullen's goals is seeing how the fish that swim in the Yellowstone use the five tributaries.
"A lot of the work that's been done on prairie streams is gathering baseline data," said Mullen whose advisors are Bob Bramblett and Christopher Guy of the Montana Cooperative Fishery Research Unit at MSU.
Bramblett said many Eastern Montana streams were never sampled until recently; prairie streams weren't a priority compared to streams that held game fish. However, Bramblett and his students have so far found 49 species of fish in the prairie streams of Eastern Montana. Thirty of those species were native to Montana. Nineteen were introduced.
Mullen, a native of Maine, said he likes fishing in the streams and lakes around Bozeman, but his project has given him an appreciation for the prairie streams, too.
"It's a pretty neat system," he said. "There's a lot of diversity."
Evelyn Boswell, (406) 994-5135 or firstname.lastname@example.org