During the month of September, 2021, The Idaho Department of Fish and Game along with staff and volunteers from Friends of the Teton River conducted fisheries population surveys on the Teton River in Teton Valley and on the South Fork of the Teton River West of Rexburg. These population surveys provide valuable information to track fish populations through time, which is especially informational this summer after experiencing low flows and warm water temperatures in the Teton River.
Preliminary analysis of this year’s populations survey shows a few noteworthy trends in the population dynamics of trout in the Teton River. Fisheries managers and FTR found that total abundance of trout is consistent with 10-year averages. Unfortunately, since record high abundances in 2017, trout numbers have been in decline. FTR is encouraged to see that this year’s low flows and warm temperatures did not have a population level impact on total trout abundance when compared to the 10-year average. Lastly, Brown trout populations continue to grow in the Teton Watershed, adding to challenges for native Yellowstone Cutthroat trout.
Over the past four years there has been a decreasing trend in Yellowstone Cutthroat trout (YCT) at all electrofishing sites. That trend has come after historic YCT abundance in 2017. Rainbow trout populations increased slightly in two of the three study reaches and Brook trout numbers decreased.Brown trout numbers were up in the South Fork of the Teton River and in the Teton River at the Breckenridge monitoring site (downstream of Packsaddle Bridge). The Breckenridge monitoring site on the upper Teton has seen a steady and concerning increase in Brown trout. In 2013 Idaho Fish and Game estimated that the Brown trout population was 23 fish per mile. Since that survey in 2013 Brown trout numbers have increased, the population is now estimated at 192 Brown trout per mile in 2021. Rising numbers of Brown trout add another challenge to native YCT populations that are already impacted by hybridization with Rainbow trout and competition with Brook Trout. Brown trout are known to prey on YCT, and compete with native fish species for habitat and food. Based on evidence from other watersheds in the region we believe that Brown trout could directly outcompete YCT, leading to the collapse of the YCT population in the Teton.
It is FTR’s mission to restore and conserve the Teton River Watershed, ensuring a lasting legacy of clean water, healthy streams, and a vibrant wild fishery. By continuing to work with the community on YCT conservation projects including stream restoration, flow restoration, fish passage restoration and screening canals, FTR is making a tangible positive impact on the Teton River fishery. Furthermore, FTR is focused on better understanding the Brown trout population in the valley, and will work with IDFG to create a management plan for the growing Brown trout population. It is FTR’s intention to do everything possible to restore and conserve the Yellowstone Cutthroat trout populations in the Teton Watershed.