A simulation study to evaluate impacts of uncertainty on the assessment of American lobster fishery in the Gulf of Maine

The status of the American lobster (Homarus americanus) in the Gulf of Maine (GOM) has been assessed for the last two decades by comparing an estimated current fishing mortality rate for females (F_cur) with a deterministically estimated biological reference point, F_10%. The most recent assessment determined that GOM had exceeded the F_10% for every year calculated, although in this time landings and abundance have doubled. The current policy does not consider uncertainty in the assessment. This study evaluates the impacts of uncertainty in F_10% and F_cur on the status assessment of lobster fishery. Using a Monte Carlo simulation approach, we found that the status assessment would be influenced by uncertainties in estimating F_10% and F_cur, and by the choice of decision confidence level reflecting the level of risk managers would like to take. A large uncertainty in F_cur and F_10% and a high decision confidence level reduce the likelihood of defining the stock as overfished, and vice versa. Our results suggest that the probability of lobster overfishing may be less than previously thought, and that uncertainty in F_cur and F_10% should be quantified and considered in determining the status of the GOM lobster stock.