Lake trout (Salvelinus namaycush) suppression for bull trout (Salvelinus confluentus) recovery in Flathead Lake, Montana, North America

Abstract

Non-native lake trout Salvelinus namaycush displaced native bull trout Salvelinus confluentus in Flathead Lake, Montana, USA, after 1984, when Mysis diluviana became abundant following its introduction in upstream lakes in 1968-1976. We developed a simulation model to determine the fishing mortality rate on lake trout that would enable bull trout recovery. Model simulations indicated that suppression of adult lake trout by 75% from current abundance would reduce predation on bull trout by 90%. Current removals of lake trout through incentivized fishing contests has not been sufficient to suppress lake trout abundance estimated by markrecapture or indexed by stratified-random gill netting. In contrast, size structure, body condition, mortality, and maturity are changing consistent with a densitydependent reduction in lake trout abundance. Population modeling indicated total fishing effort would need to increase 3-fold to reduce adult lake trout population density by 75%. We conclude that increased fishing effort would suppress lake trout population density and predation on juvenile bull trout, and thereby enable higher abundance of adult bull trout in Flathead Lake and its tributaries.

The role of Salvelinus in contemporary studies of evolution, trophic ecology and anthropogenic change

“…Thus, predation may have a strong structuring effect on fish populations in subarctic lake ecosystems. Salvelinus seem well suited to study the effects from predation as piscivory among charrs ranges from cannibalism, via intraspecific predation, to highly piscivorous species such as Lake charr populations (Amundsen, 2016;Bryce et al, 2016;Hansen et al, 2016a, b;Knudsen et al, 2016b).…”

“…Non-native Lake trout displaced native Bull trout (S. confluentus) in Flathead Lake, Montana when Mysis diluviana became abundant following its introduction into the lake watershed. To understand the possible consequences of proposed management actions aimed at restoring native Bull trout populations, Hansen et al (2016a) developed a simulation model to determine how increased fishing mortality on Lake trout might enable Bull trout recovery, noting that significant increases in fishing effort would be required to reduce Lake trout populations enough to effect the ecological release of Bull trout from Lake trout predation pressure. Modelling experiments such as these can provide useful descriptive data relating cause to effect.…”

Organic Pellet Decomposition Induces Mortality of Lake Trout Embryos in Yellowstone Lake

“…; Hansen et al. ; Fredenberg et al. ) could be enhanced by use of pellets to induce embryo mortality because spawning sites are known in many of these lakes (e.g., Dux et al.…”

Optimal harvesting policy of an inland fishery resource under incomplete information

“…The problem is serious for more complicated models . Problems in fishery resource management are not the exception . Nøstbakken and Conrad reviewed uncertainties encountered in bio‐economic modeling, focusing on dynamic programming as the central tool for their resolution.…”

“…[5][6][7] Problems in fishery resource management are not the exception. [8][9][10][11] Nøstbakken and Conrad 12 reviewed uncertainties encountered in bio-economic modeling, focusing on dynamic programming as the central tool for their resolution. Trade-offs between costs and benefits of fishery resource management can be formulated in this context.…”