Modeling Brook Trout Carrying Capacity in Owhi Lake, Washington, Using Bioenergetics

Abstract

AbstractThe management of fish populations often requires an understanding of how density‐dependent effects influence population dynamics. In systems where natural populations are supplemented with stocking, the question of “how much food is available” becomes increasingly important. One typical approach for assessing density‐dependent interactions is to identify disparities between fish consumption rates and food availability. The objective of our study was to determine whether seasonal lake prey production could support Brook Trout Salvelinus fontinalis consumption demand in Owhi Lake, Washington, at observed abundances. Brook Trout were collected seasonally from 2015 to 2017 to obtain information on length, weight, age, diet, growth, and mortality. Population abundance was estimated in summer by using hydroacoustic surveys. Littoral invertebrates and pelagic zooplankton were collected concurrently with fish to enumerate biomass and production. Bioenergetics modeling was used to estimate prey consumption by Brook Trout. In conjunction with supply–demand comparisons, we used growth efficiencies and maximum consumption rates to further identify potential seasonal and annual food limitations. Our results suggest that prey production could support Brook Trout consumption demand for all years, but littoral invertebrate consumption was close to or exceeded prey production in summer and fall 2017. Growth efficiency was lowest and maximum consumption rates were highest in summer 2017 relative to all other seasons and years. In addition to observed diet switching from littoral invertebrates to zooplankton in summer 2016 and 2017, we concluded that lower growth efficiencies, lower annual survival rates, and increased consumption rates were influenced by littoral invertebrate production. The Owhi Lake Brook Trout stocking program may require adaptive management (i.e., annual evaluations) to balance natural recruitment.