What stock-per recruit target can be applied to Japanese fisheries resources under large uncertainties in the stock-recruitment relationship?

Abstract

Maximum sustainable yield reference points (MSY-RPs) are usually calculated assuming spawner-recruitment relationships (SRR) and population dynamics of the stock. However, due to the difficulty of estimating SRR, the uncertainty in MSY-RPs is often too large to be put into practice. Therefore, based on the concept of maximum–minimum yield (MMY), fishing mortality (F) that gives %SPR (spawner biomass per recruitment [SPR] at a given F relative to SPR in the absence of fishing) of 30–50% (F_30-50%SPR) is often used as a proxy of F_MSY (F that maximizes the long-term catch). In this study, we estimated ${F}_{\%{\mathrm{SPR}}_{{\text{MMY}}}}$ (F expected to produce %SPR at MMY) for 30 stocks of Japanese fishery resources based on the life-history parameters of the stocks and steepness assumptions derived from meta-analysis. Our results showed that %SPR_MMY ranged from 23% to 62% (excluding 86% of Scomberomorus niphonius), depending on the stock and the assumed steepness scenario. If the fish were caught under ${F}_{\%{\mathrm{SPR}}_{{\text{MMY}}}}$, at least 70% of the MSY could be expected in Japanese fishery resources. When compared with the %SPR_MSY for the 15 stocks estimated through Japanese fishery stock assessment, %SPR_MMY were similar, or often larger. %SPR_MMY can be considered a precautionary value, reflecting the uncertainty of SRR.