Estimation of the optimal regulation size considering bid price increase with growth in size selectable coral reef fisheries

Size regulation is one of the most common and effective fisheries management strategies to increase future catch for coastal fishes. In this study, the optimal regulation size of the Pacific steephead parrotfish Chlorurus microrhinos was estimated considering bid price increase with growth as well as fish growth rate, natural mortality, and fishing mortality for the species in Okinawa, southern Japan. The optimal regulation size leading to the maximum future catch on a weight basis was estimated to be 30.6 cm fork length (FL), by which a 4.2% increase in catch was predicted. On the other hand, the optimal regulation size leading the maximum future revenue on a financial basis was estimated to be 32.9 cm FL, by which 9.0% revenue increase was predicted. This difference was from the increase of unit price (yen/kg) of individual fish with growth. To establish a size regulation in local fisheries, optimal regulation size and its effect should be estimated on a financial basis, and this will enable information that is more readily understandable for local fishers. Current regulation size of C. microrhinos in the Yaeyama region of Okinawa is 25 cm FL and should be increased to 30 or 35 cm FL for effective stock management.