Estimating disperser abundance using open population models that incorporate data from continuous detection passive integrated transponder arrays

Abstract

Autonomous passive integrated transponder (PIT) tag antenna systems continuously detect individually marked organisms at one or more fixed points over long time periods. Estimating abundance using data from autonomous antennas can be challenging because these systems do not detect unmarked individuals. Here we pair PIT antenna data from a tributary with mark–recapture sampling data in a mainstem river to estimate the number of fish moving from the mainstem to the tributary. We then use our model to estimate abundance of non-native rainbow trout (Oncorhynchus mykiss) that move from the Colorado River to the Little Colorado River, the latter of which is important spawning and rearing habitat for federally endangered humpback chub (Gila cypha). We estimate that 226 rainbow trout (95% confidence interval: 127–370) entered the Little Colorado River from October 2013 to April 2014. We discuss the challenges of incorporating detections from autonomous PIT antenna systems into mark–recapture population models, particularly in regards to using information about spatial location to estimate movement and detection probabilities.