Modeling Brook Trout carrying capacity in Owhi Lake, Washington using bioenergetics
Primary author: Timothy Taylor
Co-author(s): Benjamin Cross; Barry Moore
Faculty sponsor: Barry C. Moore
Primary college/unit: Agricultural, Human and Natural Resource Sciences
The 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 identifying disparities between fish consumption rates and food availability. The objective of our study was to determine if seasonal lake prey production could support Brook Trout consumption demands 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 summers 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 for Brook Trout. In conjunction with supply-demand comparisons, we used growth efficiencies and maximum consumption rates to further identify potential season and annual food limitations. Our results suggest that prey production could support Brook Trout consumption demands for all years, but littoral invertebrate consumption was near to, or exceeded, prey production in summer and fall 2017. Growth efficiency was lowest and maximum consumption rates were highest in summer 2017 compared to all seasons and years. In addition to observed diet switching in summer 2016 and 2017 from littoral invertebrates to zooplankton, we concluded that lower growth efficiencies, lower annual survival rates, and increased consumption rates were influenced by littoral invertebrate production.