Among others who point to environmental variability and managerial uncertainty as causes of fishery collapse, Roughgarden and Smith (1996) argue that three sources of uncertainty are important for fisheries management: variability in fish dynamics, inaccurate stock size estimates, and inaccurate implementation of harvest quotas. We develop a bioeconomic model with these three sources of uncertainty, and solve for optimal escapement based on measurements of fish stock in a discrete-time model. Among other results we find: (1) when uncertainties are high, we generally reject the constant-escapement rule advocated in much of the existing literature, (2) inaccurate stock estimation affects policy in a fundamentally different way than the other sources of uncertainty, and (3) the optimal policy leads to significantly higher commercial profits and lower extinction risk than the optimal constant-escapement policy (by 42% and 56%, respectively).