Self-sustainability of trout populations in currently-stocked alpine lakes in Californi's Sierra Nevada
Trout are often stocked into alpine lakes based on the assumption that resident trout populations are not self-sustaining and would go extinct without regular stocking. However, this assumption has not been rigorously tested. The objectives of our study were to (1) estimate the proportion of currently-stocked alpine lakes in California’s Sierra Nevada (USA) that contain self-sustaining trout populations, (2) identify the characteristics of lakes associated with self-sustainability, and (3) quantify the effects of stocking termination on trout density and individual growth rates in self-sustaining populations. We surveyed trout populations in 95 John Muir Wilderness (JMW) lakes before and after a 4-8 year stocking halt and 111 Sequoia/Kings Canyon National Park (SEKI) lakes after a ≥ 20 year stocking hiatus. Seventy-two percent of JMW study lakes and 66% of SEKI study lakes contained self-sustaining trout populations based on evidence of successful recruitment during the no-stocking period. Regression analysis identified spawning habitat area and lake elevation as significant factors influencing trout population persistence. Trout populations in lakes with >2.1 m2 of spawning habitat and located at elevations <3520 m were nearly always self-sustaining. For self-sustaining populations, the termination of stocking did not result in significant changes in population density or individual growth rates. We conclude that most trout stocking in Sierra Nevada alpine lakes could be permanently halted without negatively impacting these fisheries.