In assessing fisheries, effort information can often be a limiting factor. This is true of well documented legal fishing fleets, and even more so of illegal, unreported, and unregulated (IUU) fleets. We studied the insular Colombian Caribbean spiny lobster fishery to see if economic conditions have influenced fishing effort in the observed fleet. We have catch per unit effort data from the diver- and trap-based industrial fishing vessels with Colombian permits spanning a period of light fishing, expansion, stock collapse, and recent signs of rebuilding. Economic data were available on the costs of fishing and expected revenues over the past 15 years. We performed a regression analysis of various measures of fishing effort on expected costs of fishing and on expected revenue per unit effort. Effort measures included annual participation (a binary variable), trips per season, and days per trip. Expected costs of fishing were calculated by accounting for a wide range of factors, but fuel price drove annual variability. Expected revenues per unit effort were determined by multiplying the price of lobster by last seasons fleet-specific catch per unit effort, both of which varied from year to year. Our results indicate that boats were more likely to participate and take more trips per year when fishing costs were lower and expected revenue per unit effort were higher. Trips were also longer when costs were lower. Our results imply that economic conditions may be crucial in determining fishing pressure, and provide insight for better modeling of IUU fishing.