An index of risk of co-occurrence between marine mammals and watercraft: Example of the Florida manatee

► We developed statistical models to predict the distribution of boats and manatees. ► We derived an index of risk of co-occurrence. ► Accounting for imperfect detection of manatees was important. ► We evaluated the influence of key covariates on manatee and boat distribution. ► Estimating manatee-boat co-occurrence is useful for the optimal design of speed zones.