Remote PIT tag detections improve precision of mark-recapture parameter estimates for Humpback Chub Gila cypha in the Upper Colorado River Basin.

Authors: Zachary Ahrens, Brian Hines, Travis Francis, Kevin Bestgen, Gary White, David Speas

Year: 2024

Abstract

Precise estimation of population size and demographic rates is critical to monitoring, conservation planning, and management of rare species. Mark-recapture techniques using passive integrated transponder (PIT) tags to mark individual fish and analytical software in Program MARK to model population parameters are now well established and commonly used. Recently, portable submersible PIT antennas have enabled researchers to use PIT technology as a detection method in difficult to sample environments, which allows recognition of a marked animal in the study area in the absence of a physical capture. We incorporated five years of remote PIT detections from portable submersible antennas into sampling and analysis of two complementary Humpback Chub monitoring datasets obtained from 1998 to 2021. The PIT detections improved probability of capture estimates, yielding narrower confidence intervals and reduced coefficients of variation for estimates of abundance using Robust Design closed capture models. Increased detections also allowed for more complex survival estimate modeling. Improved precision in estimates allowed discernment of temporal population trends on a finer scale than in years preceding use of submersible antennas. These results demonstrate the value of portable submersible PIT detectors for monitoring desert fishes in general, and provide valuable insights for specific applications in other settings.