Movement and Growth of Juvenile Colorado Pikeminnows in the San Juan River, Colorado, New Mexico, and Utah

Understanding patterns of animal distribution and abundance based on their movements is important to identify the habitats and factors that maximize growth and reproductive success. Despite stocking age‐0 hatchery‐reared Colorado Pikeminnow Ptychocheilus lucius for over 10 years in the San Juan River of Colorado, New Mexico, and Utah, the population consists primarily of stocked juveniles; adults remain rare. We investigated seasonal movement and growth of juvenile Colorado Pikeminnows in the San Juan River from 2009 to 2012 to inform recovery efforts throughout the Colorado River basin. Our results indicated fish made long‐distance upstream movements from spring to summer while moving back downstream over winter. Seasonal movements may be associated with maximizing growth along longitudinal and seasonal temperature regimes. Length‐at‐age relationships reveal Colorado Pikeminnows in the San Juan River were larger than individuals of the same age in other populations in the upper Colorado River basin. While warmer water temperatures may have played some role in the larger lengths at age we observed, the hatchery‐reared fish that are stocked at age 0 are probably larger than their wild‐spawned counterparts of the same age. Variation in growth rates among size‐classes indicates small Colorado Pikeminnows (<200 mm TL) had slower growth rates than larger individuals in the San Juan River, suggesting a possible resource limitation for smaller juvenile fish. Understanding how seasonal movement and growth of all life stages of Colorado Pikeminnow interact with modified river systems will be important for population conservation and recovery efforts in the upper Colorado River basin.