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AUTHORS: Jonathan Meerbeek, DJ Vogeler - Iowa Department of Natural Resources
ABSTRACT: Muskellunge angling opportunities in Iowa are a direct result of stocking since natural reproduction is extremely limited. The Iowa Department of Natural Resources (DNR) maintains these fisheries via stocking yearling Muskellunge. Recently, adult populations in some lakes have decreased, despite increased stocking rates and frequencies. Current mark-recapture studies found that stocked yearling survival has decreased precipitously as well. Transportation stress and predation are thought to be partially responsible for poor yearling Muskellunge survival. For example, in an effort to prevent the spread of zebra mussels, the Iowa DNR treats all water that leaves their hatchery facilities with the Edwards Treatment procedure. This additional treatment in conjunction with extended transport time may have direct and indirect effects on stocked yearling Muskellunge survival. The objective of this project was to evaluate post-stocking survival of stocked yearling Muskellunge in Spirit Lake, Iowa and to compare cohort survival via three stocking techniques: (1) stocked directly at ramp; (2) transported to holding tanks at Spirit Lake Hatchery and allowed to recover for 36 hours prior to being stocked at boat ramp; (3) transported off-shore via boat and stocked. Twenty Muskellunge yearlings (mean TL = 12.9”) from each stocking technique were implanted with radio tags and fish were tracked periodically up to 108 days post-stocking. All yearling Muskellunge stocked from the ramp experienced low Initial mortality (2.4%). Fish stocked offshore were difficult to detect via radio telemetry and initial mortality could not be estimated. Known mortality over 100-d was 10%, 35%, and 20% for direct, hatchery holdover, and offshore stocked fish, respectively. Overall, short-term (100-d) mortality was at least 22%. A logistic regression model found that total length at time of stocking significantly influenced yearling Muskellunge survival. Based on these data, production techniques that result in larger fish size will benefit Muskellunge populations in Iowa.
