Simulating Supplementation Strategies for Restoring and Maintaining Stream Resident Cutthroat Trout Populations

Many interior populations of cutthroat trout Oncorhynchus clarki are at increased risk for extinction because of small population size and the limited length of habitable streams. Further, many of these streams cannot be altered to provide adequate conditions for population persistence. I constructed a stage-based stochastic population matrix model to (1) evaluate reintroduction strategies for streams capable of population restoration and (2) evaluate the feasibility of maintaining populations through periodic supplemental stocking. In general, stocking adults reduced extinction risk more than did stocking comparable numbers of age-0 fish, subadults, or subadults plus adults. Moreover, the greater the numbers of fish stocked, the greater the decrease in extinction risk. When reintroducing populations for restoration, stocking at least 250 adults (10% of the carrying capacity) in a one-time reintroduction event was as effective in achieving population persistence as stocking multiple times over several years. In contrast, the use of age-0 fish or subadults required either repeated stocking over multiple years or adding large numbers of fish relative to the carrying capacity. The persistence of restored populations did not differ substantially between the multiple-year stocking strategies when fish were added during years 1, 2, and 3 or during years 1, 3, and 5. Simulations of supplemental stocking showed that even very small populations were persistent when stocked with as few as 10 adults every 10–20 years. The results of the simulation model indicate that supplementing populations may be an effective conservation strategy to achieve long-term population persistence if no other options for expanding population capacity exist.