Recognition of the importance of recreational fisheries requires an appropriate survey design to collect data that is representative of the catch. This study describes a probability-based, access-point survey to collect biological data from catches of western rock lobster (Panulirus cygnus) retained by boat-based recreational fishers in Western Australia, involving substantial spatiotemporal differences across the distribution of the species and recreational fishery. Carapace length and body weight were recorded for retained lobsters at fifteen latitudinally-separated boat ramps across three fishing seasons (2015/16-2017/18). The spatiotemporal scope of the survey differed between years to determine a long-term, cost-effective design to evaluate the mean body weight of retained lobsters. Current funding allows for six (3 weekday/weekend) to eight (4 weekday/weekend) shifts per site per month. Confidence intervals (95%) for bootstrapped mean body weight did not differ between spatial and temporal subsets of data. This provided strong evidence that future monitoring of the mean body weight of P. cygnus retained by recreational fishers in WA can coincide with sites and months with greatest fishing activity. This facilitated a cost-effective annual survey, with a recommendation to conduct occasional, comprehensive, probability-based surveys to detect longer-term biological changes. This approach could be applied in other low-participation recreational fisheries.