© 2005 International Council for the Exploration of the Sea
Evaluation of current and alternative fisheries management scenarios based on spawning-per-recruit (SPR), revenue-per-recruit (RPR), and yield-per-recruit (YPR) diagrams
Division of Fish Population Dynamics, Ocean Research Institute, The University of Tokyo Minamidai 1-15-1, Nakano-ku, Tokyo, 164-8639 Japan
*tel: +81 3 5351 6495; fax: +81 3 5351 6492. e-mail: katukawa{at}ori.u-tokyo.ac.jp.
Spawning-per-recruit (SPR) and yield-per-recruit (YPR) analyses are widely used in stock assessments of exploited fish populations. In decision-making for fisheries management, the trade-off between fisheries production (YPR) and stock reproduction (SPR) is important. The general outputs of SPR and YPR analysis, such as single variate plots with contour lines or optimal harvest strategies estimated by numerical optimization, are inappropriate in obtaining an overview of the trade-off. This paper introduces a diagram that expresses graphically the bivariate trade-off between YPR and SPR. The method was applied to chub mackerel (Scomber japonicus) data, and two management scenarios were compared using the SPR–YPR diagram. Differences between YPR and revenue-per-recruit (RPR) were also considered. The results showed that: (i) current estimated fishing mortality is suggestive of growth-overfishing, and there is room for improving SPR and YPR simultaneously; (ii) increasing the age at first capture is more effective than effort control; (iii) management strategies that maximize landing weight or revenue are significantly different. The management strategy that maximizes landing weight, when considered from the viewpoint of maximizing revenue, results in growth-overfishing.
Keywords: chub mackerel, revenue per recruit (RPR), size-dependent price, spawning per recruit (SPR), yield per recruit (YPR)
Received 14 May 2004; accepted 5 February 2005.