Estimates of recreational fishing effort and catch are needed to inform fisheries management, but such estimates can be challenging to obtain. We combined a zig-zag line transect survey of buoys, a fisheries enforcement survey and a drone survey to estimate recreational effort in the open-access trap fishery for signal crayfish (Pacifastacus leniusculus) in the sixth largest lake in Europe, Lake V & auml;ttern, Sweden. Using supporting variables such as size of nearby ports and bathymetry, our model-assisted estimate of total effort was 6400 (+/- 4300 CI) buoys during the three-weekend season. Using the frequency of buoys to traps as a constant, the total number of crayfish traps was estimated to be 25,500 (+/- 17,000 CI). The sampling design and methods presented are useful for ecologists and resource managers to design future multi-source surveys of recreational trap fishing effort
