Integrating PIT technology into gear evaluation in an unregulated desert tributary

Abstract

Fish characteristics and behavioral response to gear influences catchability. Monitoring of native fishes including bluehead Sucker Catostomus discobolus, flannelmouth Sucker Catostomus latippinis, and the endangered humpback chub Gila cypha occurs throughout the Grand Canyon and its tributaries. To quantify species-specific conditional capture probability (p^ ; probability of capturing an individual fish being conditional on the individual occupying the site), we placed a flat plate passive integrated transponder (PIT) antenna 1.5 m downstream from a hoop net and processed fish during monitoring activities for three years (2011–2013). The capture probability was conditional on fish presence as determined by PIT tag detection from the flat plate antenna. We used logistic regression to test for effects of trap response, and a non-parametric bootstrap routine was used to evaluate differences in p^ among years and fish species. Pooled p^ was similar between humpback chub (mean = 0.10, 95% CIs = 0.04–0.20) and flannelmouth sucker (mean = 0.13, 95% CIs = 0.05–0.26), while bluehead sucker were never recaptured (p^ = 0). Integrating antennas into gear evaluation has broad implications to other systems as this approach could be used to standardize catch rate estimates among different passive entrapment gears of various sizes, and among different habitat types. Obtaining catchability estimates among gear types is useful when assessing modifications to long-term monitoring programs and key to stock assessment. Here, we integrated PIT tags and antennas into gear evaluation to quantify conditional capture probability, and provided a test-of-concept for larger, broader studies that can use the underlying principles and techniques shared in this study.