Benefits of stocking fewer but larger individuals with implications for native fish recovery

Abstract

Artificial propagation is commonly used to reduce extinction risk for native, imperiled fish species. Thus, identifying stocking strategies that most effectively augment adult abundance is a critical aspect of successful adaptive management. The threatened June sucker ( Chasmistes liorus) , endemic to Utah Lake, UT, USA, experienced major declines in abundance following extensive ecosystem degredation. Over 800 000 June sucker were stocked from hatcheries, grow-out ponds, and refuge populations from 1990–2019 across a range of sizes and seasons. Here, we evaluated post-stocking survival of June sucker using a Cormack–Jolly–Seber model with three covariates: size at stocking, origin, and season. Survival was positively correlated with size at stocking, with evidence of a possible size-selective predation threshold between 200 and 300 mm, and spring stocking appeared to produce higher survival rates than summer or fall. We also compared cost and benefit for stocking hatchery-origin June sucker at different sizes, finding that stocking fewer but larger (age-2) individuals was more cost-effective than stocking more but smaller (age-1) individuals. Our results highlight operational changes that can help maximize the efficacy of native fish hatchery programs.