Toward sustainable management of small cetacean fisheries around Japan Hiroshi OKAMURA,* Toshihide IWASAKI AND Tomio MIYASHITA National Research Institute of Far Seas Fisheries, Fisheries Research Agency,Yokohama, Kanagawa 236-8648, Japan ABSTRACT: The management of Japanese domestic fisheries for small cetaceans has been based on a traditional approach that involves only the best set of assumptions and data. However, uncer- tainty, which is pervasive and inevitable for most fisheries resources, often leads the traditional approach to serious failure. Here is presented the basic framework of a simulation-based approach with a simple Bayesian method that is applicable to Japanese fisheries for small cetaceans. For illustration, the simulation model was applied to Dall’s porpoise data in order to investigate the robustness of several management procedures against uncertainty. The simulation showed that the current management procedure, based on only the best values, could fail to manage the stocks at a considerably high probability. However, the use of the conservative management procedure, potential biological removal, permits the sustainable harvesting of Dall’s porpoise for at least 100 years into the future, even under uncertainty. In conjunction with a firm structure for implementation of management procedures, the spread of simulation-based approaches will quickly enable successful sustainable management of small cetaceans. KEY WORDS: Bayesian approach, conditioning, Dall’s porpoise, operating model, PBR, Phocoenoides dalli, simulation. INTRODUCTION The exploitation of whale populations was a matter of controversy during the 1970s and 1980s. 1,2 The International Whaling Commission (IWC) intro- duced a blanket moratorium on commercial whaling in 1982, which came into force in the 1985–1986 season. This moratorium did not include small cetacean fisheries, and the Japanese government has granted annual catch quotas for these fisheries. 2 The current Japanese catch quotas (before 2007) were determined based on stock assessments that considered the best set of abun- dance estimates and assumptions for the biologi- cal parameters. For example, the increasing rate, which is regarded as the maximum sustainable yield (MSY) rate or one-half the maximum theoretical productivity rate of the population, was assumed at 4% for Dall’s porpoises. The catch quotas for Dall’s porpoises were calculated using the increasing rate multiplied by the best abun- dance estimates of the stocks obtained from sight- ing surveys. Unfortunately, the information on the fisheries resource is generally subject to various uncertain- ties. 3 Fisheries management based only on ‘best’ estimates does not effectively include these uncer- tainties and often leads to serious failure. 1,3 We must recognize the importance of uncertainty and the need to develop a management procedure that is robust to uncertainty. Fisheries management typically begins with a discussion about the management objectives, fol- lowed by their specification and prioritization. The only way to determine whether the manage- ment objectives will be satisfied using some man- agement procedures is to test the robustness of the procedure using a simulation modeling approach with operating models that span the range of plausible uncertainty. 1 These simulations enable us to select the best management proce- dure(s) that are robust to uncertainty, by taking into account the trade-offs among conflicting objectives. In addition, they are very helpful in *Corresponding author: Tel: 81-45-788-7514. Fax: 81-45-788-5004. Email: okamura@fra.affrc.go.jp Received 16 October 2007. Accepted 24 January 2008. FISHERIES SCIENCE 2008; 74: 718–729 © 2008 Japanese Society of Fisheries Science doi:10.1111/j.1444-2906.2008.01582.x