Open-population models provide an alternative trout monitoring method in the upper Yellowstone River, Montana

Abstract

Objective. Long-term monitoring programs typically require standardization to evaluate changes in fish populations over time. However, incorporating new methods into long-term monitoring programs may become increasingly important as climate change affects sampling conditions. In the upper Yellowstone River, Montana, biologists have monitored trout abundance using closed-population, Lincoln–Petersen mark–recapture methods since 1978. In the past two decades, changes in the hydrologic regime have prevented monitoring from occurring annually. Methods. We investigated the feasibility of individually marking trout and using the POPAN formulation of the Jolly–Seber model to estimate the abundance and survival of three trout species in the upper Yellowstone River as an alternative to historical monitoring methods. When using this modeling framework, annual sampling can be conducted in a reduced time period, allowing monitoring to be adapted to changing environmental conditions. Results. Analysis of a 3-year empirical data set provided estimates of abundance and survival for most sites and species. Simulations indicated that POPAN models produced unbiased estimates of demographic parameters when detection probability was 0.20 or greater, and the precision of estimates increased as detection probability and apparent survival increased. Conclusions. Using POPAN models to analyze mark–recapture data from individually marked fish may provide a feasible alternative for monitoring trout populations in the upper Yellowstone River. Although further evaluation of monitoring methods as data collection continues is warranted, open-population models show promise as a useful tool for monitoring the trout fishery in the Yellowstone River and in rivers across Montana.