Carrying Capacity: A Concept for Guiding Brook Trout Stocking on Owhi Lake, Washington

Carrying capacity is a concept that connotes the maximum population level that can be sustained in a system with finite resources (i.e. food and space). Carrying capacity is particularly important to fisheries managers who must balance stocking rates with population dynamics within the context of available habitat and food resources in order to sustain sport or sustenance fisheries. We estimated a baseline carrying capacity for Brook Trout (Salvelinus fontinalis) in Owhi Lake, WA. Owhi Lake provides an excellent test case for carrying capacity as Brook Trout is the only harbored fish species. Previous studies have quantified their prey consumption, including crayfish, macroinvertebrates, and zooplankton. We used the program Fish Bioenergetics 3.0 to identify trout energy requirements and monitored dissolved oxygen and temperature variations using water profiles to quantify available habitat. To quantify prey availability, crayfish were collected using minnow traps and SCUBA surveys. Zooplankton densities were quantified using profile collections; littoral invertebrates were quantified using D-frame kick nets. We estimated total available energy using prey densities and caloric values to estimate short-term carrying capacity of the lake. We will use our models to examine varying stocking regimens and plan on future studies to refine the model parameters and predictive power.