An Evaluation of the Efficacy of a Targeted Supplemental Stocking Using a Multistate Capture–Recapture Model

Abstract

AbstractStocking is a management tool that provides fish directly to anglers and can partly address concerns over low catch rates. Although stocking is recognized as an effective management tool for addressing low catch rates, stocking fish represents a considerable investment. Stocking may not be a viable option if fish do not persist within targeted areas, are not accessible to anglers, or pose a potential risk to sensitive species. The goal of this study was to assess the survivorship, movement, and persistence of stocked Rainbow Trout Oncorhynchus mykiss (RBT) within the walk‐in section of Lees Ferry, Colorado River, Arizona, in order to evaluate the efficacy of targeted stocking for this fishery. To meet this goal, we used acoustic telemetry to monitor stocked trout and assess movement out of the management area. A multistate model was used to distill spatiotemporal telemetry data into a multinomial state response, the spatial zones of our study area, to evaluate the efficacy of targeted stocking. The estimated 3‐month survival of RBT that remained within the walk‐in section without transitioning was 37.3–68.1% based on the 95% confidence interval (CI). Persistence of RBT, which accounts for fish movement, within the walk‐in section after 3 months was estimated to be 29.6–33.5% of the original stocked population. Three‐month transition rates downstream out of the walk‐in section (95% CI = 12.8–15.8%) were higher than upstream transition rates out of the walk‐in section (95% CI = 7.7–10.0%). These findings suggest that targeted stocking can effectively supplement the fishery at the walk‐in section of Lees Ferry based on the relatively high persistence of stocked RBT within the targeted area. However, managers will need to weigh stocking densities, transition probabilities, and catch rate goals to determine an acceptable level of risk to the native populations while addressing management goals.