Glacier National Park Native Fish Population and Lake Fisheries Monitoring, Program Report 2016

Downs, Christopher; McCubbins, Jonathan

Native Fish Population Abstract: In 2009, Glacier National Park (GNP) began development of a monitoring program for native salmonids inhabiting park streams. The intent of the program is to establish baseline abundance levels in a variety of park waters to serve as useful benchmarks for monitoring changes in populations over time. We continued this work through 2016, sampling in three waterbodies. We conducted snorkel surveys on Mineral and Upper McDonald (Middle Fork Flathead drainage) creeks. Trap netting was conducted in Slide and Red Eagle Lakes and Sherburne Reservoir. We noted presence or absence along with relative abundance of amphibians in our surveys. In general, the largest threat currently facing migratory native fish species on the east side of the park is the unscreened St. Mary River irrigation diversion near Babb, part of the Milk River Irrigation Project. Other threats include non-native species (walleye) found in the St. Mary River downstream of the U.S./Canada border. The most significant threat to native fish on the west side of the park comes from invasive species, such as rainbow, brook, and lake trout. However, management and conservation of native fish in the North and Middle forks of the Flathead River remains complicated due to the presence of migratory and resident populations of native salmonids, and expanding distribution of invasive fish species. Lake Fisheries Monitoring Abstract: We sampled Lower Quartz, Harrison and Saint Mary lakes in GNP in 2016 to characterize and assess fish communities and trends occurring within the fish communities over time. We used sinking multi-filament experimental mesh gill nets, set overnight, to sample all lakes from late July through late August, when the lakes were thermally stratified. Relative abundance of most species have remained stable when compared to historical sampling. Decline in bull trout relative abundance has been occurring since introduced lake trout migrated from downstream areas into each of these three lakes. Following the dramatic decline in bull trout abundance throughout the 1970’s and 1980’s, bull trout have remained at extremely low numbers when compared to historic abundance estimates. Although vastly reduced in numbers, bull trout persist within all three of the lakes sampled in 2016.