Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Montana Fishery Project

Quantifying Brown Trout and Lake Trout predation on Burbot and Mountain Whitefish

July 2019 - June 2023


Participating Agencies

  • Wyoming Game and Fish

Purpose and Need: Burbot and Mountain Whitefish are important native sportfish species in Wyoming, with Burbot classified as a Species of Greatest Conservation Need (ranked as Native Species Status 3; WGFD 2017). Additionally, Underwood et al. (2015) revealed that genetic differentiation exists among Wind River tributary drainage Burbot stocks. Thus, the Torrey Creek drainage Burbot stock that occurs in Torrey Creek and Trail, Ring, and Torrey lakes is a high conservation priority (Figure 1). Managers have been concerned with the declines in Ring Lake Burbot since the 1990s. Burbot catch rate was higher in Ring Lake than four other Wind River drainage lakes from 1967 to 1969, and six other drainage lakes from 1995 to 1996 (Miller 1970a, 1970b; Krueger and Hubert 1997). Conversely, Ring Lake Burbot catch rate in trammel nets was lower than six of seven other drainage lakes from 2007 to 2008 and lowest among six drainage lakes from 2011 to 2013 (Abrahamse 2009; Lewandoski 2015). Additionally, spring 2018 Burbot catch rate in fyke nets was only 0.02/hour, compared to 0.22/hour in 1995 to 1996 (Krueger 1996; unpublished data). Hubert et al. (2008) also estimated that Ring Lake Burbot survival decreased from 77% in 1969-1970 to 56% in 1995-1996. Exploitation was not the cause of decreased Burbot numbers in Ring Lake (Lewandoski et al. 2017). Thus, the cause(s) of the decline in Ring Lake Burbot abundance remains unknown. Less is known about Mountain Whitefish in the Torrey Creek drainage. Whitefish abundance in Torrey Lake has been consistently low since the early 1950s. Only one mountain Whitefish was captured during 11 gill-net sampling events from 1954 through 1977, and zero were captured during nine gill-net and five trammel-net sampling events from 1980 through 2017 (Connell 1978; WGFD unpublished data). Conversely, high numbers of Mountain Whitefish have been captured in Trail Lake during the same time period, with the most recent sampling event producing a gill-net catch rate of 0.94 fish/hour (WGFD 2018). Available data suggest Ring Lake numbers have decreased since the late 1960s. Connell (1977) reported that gill net catch rate of Mountain Whitefish in Ring Lake averaged 0.29 fish/hour during five sampling events from 1954 through 1970, whereas catch rate during three sampling events from 1998 through 2017 averaged 0.07 fish/hour (WGFD unpublished data). Additionally, no Mountain Whitefish were captured in trammel nets (which are likely a more efficient sampling gear because of a smaller mesh size than the gill nets) during sampling events in 2005 and 2017 (WGFD unpublished data). A possible cause of the decline in Ring Lake Burbot and Mountain Whitefish abundance that needs further research is the introduction of Brown Trout and Lake Trout. Lake Trout were first stocked in 1937 and Brown Trout likely entered the drainage in the late 1940s or early 1950s (Connell 1977; Connell 1978). The origin of Brown Trout in the drainage is unknown. Immigration from the Wind River was the most likely source. Brown Trout stocking may have also occurred; however, no stocking records exist. Although no sampling data exist for the 17-year period after Lake Trout were first stocked, trend data indicate a gradual decrease in Burbot and Mountain Whitefish abundance in Ring Lake after Brown Trout became established. Brown Trout predation on Burbot was confirmed in the autumn of 2017 in Torrey Creek upstream from Ring Lake (WGFD 2018). Although sample size was small (n = 6 stomachs), Burbot occurred in 33% of Brown Trout stomachs (WGFD 2018). Torrey Creek upstream of Ring and Trail lakes are known Burbot spawning and nursery areas, and managers are concerned that fall-migrating Brown Trout into Torrey Creek may reduce Burbot recruitment through predation (Bjorn 1939; Williams 1959; Miller 1970a; Miller 1970b; Glaid et al. 2016). Mangers also suspect that Brown Trout predation on Mountain Whitefish migrating downstream from Trail Lake may be the cause of low numbers of Mountain Whitefish in Ring Lake. Goal: To estimate the predatory influence of Brown Trout and Lake Trout on the Burbot population and Mountain Whitefish in the Torrey Creek drainage