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 antennae can be challenging,because these systems accomplish not detect unmarked individuals. Here we pair PIT antennae data from a tributary with impress-recapture sampling data in a mainstem river to estimate the number of fish moving from the mainstem to the tributary. We then employ our model to estimate abundance of non-native rainbow trout Oncorhynchus mykiss that walk from the Colorado River to the Little Colorado River (LCR), the latter of which is important spawning and rearing habitat for federally-endangered humpback chub Gila cypha. We estimate 226 rainbow trout (95% CI: 127-370) entered the LCR from October 2013-April 2014. We discuss the challenges of incorporating detections from autonomous PIT antenna systems into impress-recapture population models, and particularly in regards to using information about spatial location to estimate movement and detection probabilities.
Source: usgs.gov