Effects of flow-training on physiological performance and post-stocking movement and survival of hatchery-reared endangered Colorado Pikeminnow in the San Juan River

Abstract

Colorado Pikeminnow (Ptychocheilus lucius) in the San Juan River depend heavily on stocking, yet retention and recruitment remain below species recovery goals. We evaluated whether increasing hatchery flow-training velocities would improve physiological performance, post-stocking apparent survival, and retention of stocked fish. Fish were reared in control raceways under low static flow or in treatment raceways exposed to higher static and pulsed flows across three stocking cohorts. We assessed oxygen consumption using intermittent flow respirometry, estimated apparent survival from radio telemetry and PIT tag detections, and modeled downstream detection probability and movement rates. Flow training produced inconsistent physiological responses across stocking cohorts. Radio telemetry indicated no meaningful treatment effect on apparent survival during the first five weeks post-stocking. PIT-tag based models similarly showed little treatment difference in fall stockings, but in a spring stocking flow-trained fish had approximately 7% higher early apparent survival and 88% more expected fish remaining by the end of the 90-day period. Downstream dispersal was strongly correlated with season with spring-stocked fish less likely to be detected downstream than fall-stocked fish. Flow-trained fish stocked during a high flow event in fall 2024 were 15% less likely than controls to be detected at lower arrays. Overall, flow training alone did not produce a consistent survival advantage, and stocking season and environmental conditions explained more variation than treatment. These findings suggest that considering an interaction between stocking season and flow training may provide the greatest management benefit.