Research Project Begins Lake Trout Population Study

The Idaho Department of Fish and Game is beginning a comprehensive study of the lake trout population in Priest Lake. The cooperative project with the University Of Idaho College Of Natural Resources and the Kalispel Tribe comes on the heels of an energetic public debate about long-term management of the lake's sport fishery. The research will focus on estimating the number of lake trout currently in Priest Lake as well as key characteristics, such as growth and survival rates and food habits. To capture trout for the population estimate, large-scale commercial netting equipment will be used, similar to that being used in Lake Pend Oreille. From March through May, deep-water trap nets and short-duration set gillnets will be used to capture, measure and mark lake trout with an individually numbered tag. Though a small number of fish will be sacrificed for age and stomach analysis, as many marked fish as possible will be released back to the lake unharmed. The research project is the beginning of an effort to develop a more complete understanding of the Priest Lake fishery - to include zooplankton, kokanee, Mysis shrimp and lake trout. Ultimately, the information will be used to help develop a long-term management plan for Priest Lake. Historically, Priest and Upper Priest lakes both provided popular sport fisheries for native cutthroat and bull trout. Kokanee were introduced in the 1930s and 1940s. They not only provided an abundant food source for bull trout, they rapidly became the most popular sport fish, supporting a harvest of 50,000 to100,000 fish and 15,000 angler days every year. The popular cutthroat, bull trout and kokanee fisheries lasted through the 1970s but abruptly collapsed in the 1980s when the population of lake trout exploded after the introduction of Mysis shrimp. Through the 1980s millions of kokanee fry and hundreds of thousands of cutthroat fingerlings were stocked in Priest Lake and its tributaries in an effort to overcome the predation impact of lake trout. The efforts were unsuccessful. The fishery shifted from a diverse yield and trophy fishery to one dominated by lake trout. Though popular with some anglers, overall participation in the fishery declined by a third to a half since the 1950s, despite a near tripling in the area's human population over the same period. The average size of lake trout declined over the years as anglers targeted lake trout, and the prey base disappeared. In the 1970s, the lightly harvested population, about 200 fish per year, resulted in lake trout averaging about 20 pounds, and the 57_-pound state record lake trout was caught in 1971. By 1983, annual harvest increased to almost 5,000, but average size declined to 4 pounds. Annual harvest was nearly 30,000 lake trout by 2003, but the average weight was only 2.1 pounds. Fish and Game has adopted a variety of rules in response to the declining size of lake trout. Restricting harvest, however, had little impact, and tagging studies show the decrease in size is a function of poor growth rates rather than harvest. Though lake trout grow well to 14-16 inches feeding on Mysis shrimp, growth rates of mature lake trout, 18-20 inches, are typically less than a half inch per year. Without abundant prey fish in the system, growth rates are insufficient to produce many trophy size fish, regardless of rules. Angler opinions about management direction for Priest Lake have been split since the collapse of kokanee in the late 1970s and domination of the fishery by lake trout. Many anglers would like to see restoration of a cutthroat, bull trout and kokanee fishery, while others prefer sticking with lake trout. Others pin hopes on the idea that a balance between kokanee and lake trout is feasible. Regardless of the ultimate management direction set for the lake fishery, the lake trout population estimate will be a tremendously valuable piece of information. Fish and Game will be scheduling a public meeting in late February to discuss the project and answer questions anglers may have.