Low‐level infection of parasitic copepods on Rainbow Trout does not affect vulnerability to angling or short‐term survival following catch‐and‐release angling

Abstract Parasitic copepods, or “gill lice,” can negatively impact fish hosts resulting in reduction in fitness and increased probability of mortality. The purpose of our study was to determine the effect of Salmincola californiensis on the vulnerability of Rainbow Trout to recreational angling and short‐term survival after being caught and released. We compared the prevalence and intensity of infection of S. californiensis on Rainbow Trout caught while angling and with a backpack electrofisher in May and October 2020 in Birch Creek, Idaho. In October, we also conducted a stress test (i.e. air exposure treatment) on trout caught by angling to determine the effects of parasitic copepods on short‐term survival of Rainbow Trout in a catch‐and‐release fishery. Infection with S. californiensis did not influence the vulnerability of Rainbow Trout to angling. After adjusting for sample size and size distribution, prevalence of infection in May was 48.3% for Rainbow Trout caught while electrofishing compared to 49.3% for Rainbow Trout caught while angling. In October, prevalence of infection was 41.2% for Rainbow Trout caught while electrofishing compared to 41.8% for Rainbow Trout caught while angling. We did not find a difference in short‐term survival of infected and uninfected Rainbow Trout after the stress test (4 ‐7 days after the test). We did not observe consequences of infection by parasitic copepods on vulnerability to angling or short‐term survival of Rainbow Trout in Birch Creek. However, conditions (i.e. low‐level of infection and relatively small fish) may not have been conducive to detecting differences in performance metrics; further testing at higher intensity of infection and with larger fish may uncover negative impacts of parasitic copepods on Rainbow Trout.