Evaluation of floating basket incubators for instream reintroductions of fish at early life stages

ABSTRACT Objective Anthropogenic disturbances led to the decline and extirpation of Arctic Grayling Thymallus arcticus populations in the continental United States, prompting renewed interest in restoration via early life stage stocking. Remote site incubators (RSIs) have been used successfully to support instream egg incubation, but their dependence on relatively steep stream gradients limits applicability in low-gradient systems, such as those in Michigan’s Lower Peninsula. We evaluated the performance of a novel, low-cost floating basket incubator (FBI) as an alternative rearing device for low-gradient streams targeted for Arctic Grayling reintroduction. Methods We compared egg-to-fry survival of Rainbow Trout Oncorhynchus mykiss, Brook Trout Salvelinus fontinalis, and Walleye Sander vitreus in paired RSI and FBI deployments across hatchery and field settings. To statistically analyze results, we used random-effects meta-analysis, one-way ANOVAs, and generalized linear models. Results A random-effects meta-analysis indicated similar survival between incubator types, with the difference in survival (i.e., RSI − FBI) averaging 2.97 percentage points (95% CI = −3.15 to 9.09). Despite slightly lower survival relative to RSIs, the FBIs had four times more egg capacity per unit, required significantly less labor and material to deploy, and functioned with minimal maintenance in low-velocity stream environments. Using generalized linear models, we identified stream location and percent fungus as the strongest predictors of Rainbow Trout egg survival in FBIs. Conclusions Our results support the use of FBIs for Arctic Grayling restoration in low-gradient systems by offering a scalable, efficient, and field-deployable tool for instream incubation, with performance comparable to that of traditional RSIs under typical field conditions.