AbstractMuskellunge Esox masquinongy fisheries in Ohio are maintained through annual stocking of advanced fingerlings (25–30 cm) at nine reservoirs. Voluntary angler catch reporting is the principal method for monitoring (stocking and angling success) these fisheries. During 1960–2007, anglers reported catching over 47,000 Muskellunge by mailing catch cards to the Ohio Department of Natural Resources, Division of Wildlife. In 2008, a new online catch reporting system, the Muskie Angler Log (MAL), was launched. Designed in collaboration with anglers, the MAL provides important fishery data to biologists while also serving as a fishing resource for anglers. Anglers who use the MAL can view, summarize, and download their personal catches, review reservoir‐specific stocking records and catch histories, and examine recent catch details that are voluntarily shared by other anglers. Catch data from the MAL is vital to the Ohio Department of Natural Resources, Division of Wildlife for characterizing fisheries, tracking fishery performance (numbers and sizes), leveraging Muskellunge management decisions, and supporting Muskellunge‐specific research. Total reported catches in the MAL have increased over time, with most (six of nine) reservoirs showing increased or stable trends in reported catches. Despite increasing catch reports, annual angler participation in the MAL has declined, which could reduce the effectiveness of the system in monitoring these fisheries. It is not known whether this trend represents an actual decline in participation or is a function of the periodicity in catches among anglers. We modeled the change in the population size (λ) of anglers participating in the MAL using a mark–recapture method (Pradel model). Overall, the modeling indicated that the population of anglers using the MAL has declined since 2008, with the number of anglers belonging to a Muskellunge fishing club declining slower than that for nonclub members. Intervention methods promoting and incentivizing the use of the MAL will be required to assure that the MAL provides the necessary data for managing Muskellunge.