A theory for optimal monitoring of marine reserves

Leah R. Gerber,* Maria Beger, Michael A. McCarthy and Hugh P. Possingham Ecology, Evolution and Environmental Sciences, Arizona State University, College and University Dr, Tempe, AZ 852871501, USA The Ecology Centre, School of Integrative Biology, The University of Queensland, Brisbane 4072, Australia Australian Research Centre for Urban Ecology, Royal Botanic Gardens Melbourne, c/o The School of Botany, The University of Melbourne, Parkville VIC 3010, Australia *Correspondence: E-mail: [email protected] Abstract Monitoring of marine reserves has traditionally focused on the task of rejecting the null hypothesis that marine reserves have no impact on the population and community structure of harvested populations. We consider the role of monitoring of marine reserves to gain information needed for management decisions. In particular we use a decision theoretic framework to answer the question: how long should we monitor the recovery of an over-fished stock to determine the fraction of that stock to reserve? This exposes a natural tension between the cost (in terms of time and money) of additional monitoring, and the benefit of more accurately parameterizing a population model for the stock, that in turn leads to a better decision about the optimal size for the reserve with respect to harvesting. We found that the optimal monitoring time frame is rarely more than 5 years. A higher economic discount rate decreased the optimal monitoring time frame, making the expected benefit of more certainty about parameters in the system negligible compared with the expected gain from earlier exploitation.