Keeping it classy: classification of live fish and ghost PIT tags detected with a mobile PIT tag interrogation system using an innovative analytical approach

Abstract

The ability of PIT tag data to improve demographic parameter estimates has led to the rapid advancement of PIT tag systems. However, ghost tags create uncertainty about detected tag status (i.e., live fish or ghost tag) when using mobile interrogation systems. We developed a method to differentiate between live fish and ghost tags using a random forest classification model with a novel data input structure based on known fate PIT tag detections in the San Juan River, NM, CO, and UT, USA. We used our model to classify detected tags with an overall error rate of 6.8% (1.6% ghost tags error rate and 21.8% live fish error rate). The important variables for classification were related to distance moved and response to flood flows; however, habitat variables did not appear to influence model accuracy. Our results and approach allow the use of mobile detection data with confidence and allow for greater accuracy in movement, distribution, and habitat use studies, potentially helping identify influential management actions improving our ability to conserve and recover endangered fish.

Incorporating antenna detections into abundance estimates of fish

“…The assumptions of each of our approaches include: 1) all fish in the same state (i.e., size bin) in the sampling area have equal physical capture probabilities, 2) all marked fish in the same state in the sampling area have equal antenna detection probabilities, 3) antenna detections occur in discrete time, 4) only live fish are detected with antennas so that ghost tags are absent (Bond et al 2019;Stout et al 2020), and 5) antenna detections and physical captures are independent.…”