Using Radiotelemetry to Inform and Guide Muskellunge Culture and Stocking Techniques in Spirit Lake, Iowa

Abstract Agencies commonly stock Muskellunge Esox masquinongy to maintain or augment populations throughout much of North America. Muskellunge poststocking survival is variable, and adult populations are vulnerable to periodic lapses in recruitment. Radiotelemetry evaluated whether changes in stocking techniques caused recruitment declines of spring-stocked yearling Muskellunge in Spirit Lake, Iowa, or whether total length, condition, or 10-d dispersal influenced poststocking survival. The workers fitted hatchery-reared Muskellunge (38–40 fish; n = 78 fish in total) with radio transmitters and stocked in May 2016–2017 by using one of two techniques: 1) fish stocked immediately following 6-h transport in a hatchery distribution truck with Edwards treatment–laden water or 2) fish provided 36-h recovery period after a hauling event and then stocked. Radiotelemetry revealed that stocking techniques did not influence Muskellunge survival or dispersal, but survival significantly improved for fish stocked at larger sizes. Using this information, production techniques in 2018–2019 included an additional 33–40-d rearing period for Muskellunge less than 330 mm when measured for total length in mid-May. We radiotagged a subset of these fish (14–16 fish/y; n = 30 fish total), and survival improved to more than 73.4%. Subsequent application of telemetry was via a side-by-side comparison in 2020 for greater than or equal to 330-mm Muskellunge fitted with radio transmitters and stocked in May (n = 17 fish) and those reared using the grow-out procedure and stocked in June (n = 21 fish). Both cohorts experienced poor survival (39.2–56.1%), resulting from both fish and great blue heron Ardea herodias predation, despite large differences in dispersal. Regardless of stocking technique, this study identified that most mortality occurred within the first 25 d poststocking. These results indicate that Muskellunge populations in natural lakes would benefit from a better understanding of poststocking survival and stocking practices that minimize predator threats during this critical period.