Illegal fishing has detrimental environmental and social impacts, but these effects are difficult to mitigate without reliable estimates of fisher non-compliance. Methods used by fisheries managers to estimate illegal fishing often require indirect estimation of poaching using biological, economic or sociological indicators. This study presents a unique application of the randomized response technique (RRT) for direct estimation of non-compliance in fisheries to the Northern California recreational red abalone (Haliotis rufescens) fishery. An anonymous paper-based compliance and sociodemographic survey of recreational fishers in Sonoma and Mendocino Counties estimated 29% non-compliance with the daily take limit, 23% with the minimum size limit, 19% with licensing laws and 15% with the annual take limit. RRT results also indicated how different sociodemographic characteristics related to non-compliance. Visitors had higher non-compliance rates than local fishers for all regulations except daily take limits, which an estimated 72% of locals violated versus 18% of visitors. High fisher awareness of regulations, fisher age, income and fishing experience did not appear to influence illegal take. RRT is a powerful tool which can aid conservation managers in prioritizing action.