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

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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.

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