Large trout numbers decline in Madison River

“Town Crier” newsletter – Briefs from the Region (1) – 6/3/20

According to the Bozeman Daily Chronicle, the number of large brown and rainbow trout in the upper Madison River has declined below 20-year averages. Travis Horton, Region 3 Fisheries manager for Fish, Wildlife and Parks in Bozeman told the Chronicle, “It’s been good to excellent recruitment for quite a while, but the adults aren’t there,” where recruitment, in an ecological context, is defined by an increase of a natural population via the arrival of new animals, through migration or birth. According to the FWP’s report, the estimated number of brown and rainbow trout larger than 6 inches declines by about 40 percent from 2018 to 2019 in the Pine Butte Section, with mortality of 2-year-old fish and older increasing for unknown reasons; at the Varney Bridge section, brown trout are at 81 percent of the 20-year average and the rainbow trout population was down 55 percent, leveling at 72 percent of the 20-year average. One prominent theory is a thermal change, where warmer temps speed growth but shorten lifespans, and the Madison River has shown a trend “toward higher maximum annual temperatures since 2011.” Fisheries’ staff on regional rivers like the Beaverhead and Ruby have reported similar declines, particularly in brown trout populations. Additionally, fishing in warmer temps can increase the stress placed on a landed fish, at times proving fatal; FWP requests anglers to avoid fishing during the hottest moments of the day, especially where a 2017 FWP study showed 69 percent of Madison River anglers were nonresidents—sparking ire and debate over tentative regulations to curb overcrowding.