BACKGROUND: Understanding job tasks and estimating occupational exposures is difficult for self-employed or autonomous workers, who tend to be dispersed, with no fixed workplace, employment records, or historical exposure measurements. METHODS: We used ethnographic methods to collect work information for southern commercial fishermen. Major activities were mapped using the seasonal round, an anthropological tool that records activities of groups whose lifeways depend on natural cycles. RESULTS: Fishermen's work schedules depended on boat size, gear, market fluctuations, and regulations, as well as season. The seasonal round guided the analysis of qualitative data on annual cycles of activities increasing understanding of exposures and their variation. CONCLUSIONS: Combined with detailed exposure information this framework for organizing and categorizing seasonal activities could improve accuracy of exposure information and guide quantitative analysis in work settings that challenge standard exposure assessment methods.