Using distribution and movement of invasive channel catfish Ictalurus punctatus in the San Juan River to inform removal efforts
Invasive channel catfish ( Ictalurus punctatus ) pose threats to native fishes through predation and competition. A channel catfish removal program in the San Juan River was implemented in the 1990s, but exploitation was insufficient to cause population declines. Because knowledge of movement timing and spatial aggregations of channel catfish could inform future removal efforts and increase exploitation rates, we used active and passive radio telemetry in 2023 and 2024 and mark-recapture data from 2011–2015 to assess seasonal patterns in their distribution and movement. Additionally, spawning periodicity was identified through water temperature and activity data recovered from adults implanted with archival transmitters and by estimating back-calculated spawning dates obtained via otoliths pulled from young-of-year fish. We observed limited upstream movement ( n = 25/528 radio-tagged fish > 10 river kilometers) prior to daily mean water temperatures reaching 21°C followed by upstream movement after water temperatures exceeded 21°C. Generalized linear mixed models suggested a positive relationship between movement rates and total length and a modal relationship between movement rates and water temperature with a predicted maximum movement at 20.8°C. Movement rates of females were predicted to be 2.4x greater than males. Mark-recapture data confirmed limited movement with an upstream bias during summer. Modal activity patterns observed in 10 of 12 archive-tagged fish peaked at an average of 21.3°C. We found little evidence of aggregations, but synchronized upstream movement likely cued by water temperatures ~ 21°C may provide the opportunity for resource managers to use passive sampling techniques to target channel catfish during upstream spawning movements.