ASSESSING UNCERTAINTY AND RISK IN EXPLOITED MARINE POPULATIONS

The assessment and management of exploited fish and invertebrate popul ations is subject to several types of uncertainty. This uncertainty tr anslates into risk to the population in the development and implementa tion of fishery management advice. Here, we define risk as the probabi lity that exploitation rates will exceed a threshold level where long term sustainability of the stock is threatened. We distinguish among s everal sources of error or uncertainty due to (a) stochasticity in dem ographic rates and processes, particularly in survival rates during th e early life stages; (b) measurement error resulting from sampling var iation in the determination of population parameters or in model estim ation; and (c) the lack of complete information on population and ecos ystem dynamics. The first represents a form of aleatory uncertainty wh ile the latter two factors represent forms of epistemic uncertainty. T o illustrate these points, we evaluate the recent status of the George s Bank cod stock in a risk assessment framework. Short term stochastic projections are made accounting for uncertainty in population size an d for random variability in the number of young surviving to enter the fishery. We show that recent declines in this cod stock can be attrib uted to exploitation rates that have substantially exceeded sustainabl e levels. Published by Elsevier Science Limited.