How mobile are fish populations? Diel movement, population turnover, and site fidelity in suckers

Abstract

Movement of organisms is an important mechanism controlling an array of processes within ecosystems. Recent analyses suggest that movement is composed of individual displacement (distance moved by individuals) and turnover (proportion of individuals moving). Turnover of individuals is important because it influences population size and structure, as well as interactions among individuals and different species within a habitat. We used stationary antennas and passive integrated transponders tags to monitor individual habitat use, turnover, and displacement of Sonora suckers (Catostomus insignis) and desert suckers (Catostomus clarkii) in the West Fork Gila River, New Mexico, USA. Many tagged fish used our focal stationary antenna reach, but only a subset was consistently present. Population size and turnover rates were variable from day to day. Although some individuals spent the majority of their time within the focal reach, most made extended departures (one or more days) from their home pools. Many individuals displayed fidelity to a particular habitat despite forays elsewhere, returning to the focal reach throughout the study. Diel or short-term movements may explain high turnover rates typically observed and, combined with high site fidelity, may result in the misclassification of individuals as sedentary, despite frequent, potentially short-term, movements into other habitats.