Hoop net capture efficiencies of previously pit tagged fish using submersible antenna detections

Authors: Pilar Rinker, David Ward, Michael Pillow

Year: 2024

Abstract

Hoop netting is a common sampling technique used in the Grand Canyon which detects species that are not commonly captured using typical boat electrofishing methods. The US Fish and Wildlife Service uses hoop nets on an annual basis to sample Humpback Chub, Gila cypha, and Flannelmouth Sucker, Catostomus latipinnis, populations throughout the Canyon to track population trends and abundance. During our regular monitoring, we deployed four sets of paired baited hoop nets and baited submersible antennas to evaluate capture efficiency. Each pair was deployed within the same eddy separated by enough space that the antenna would not scan fish within the hoop net. We restricted the analysis to those fish that were recaptures, previously pit tagged, because that is the population of fish that is available for detection using antennas. Upon preliminary analysis, we found that 47.8% of the fish captured in hoop nets were also detected on antennas which may suggest the capture efficiency of pit tagged fish in hoops nets is high. However, only 12.2% of the unique fish that were detected on antennas were also captured in hoop nets. The antennas detected more previously pit tagged fish than hoop nets. This suggests that there may be behavioral differences amongst the pit tagged population that may be attributed to size, species, or becoming trap-happy or trap-shy.