Age, growth, mortality, and yield-per-recruit of red spotted grouper Epinephelus akaara in the central Seto Inland Sea, Japan

The red spotted grouper Epinephelus akaara is important for commercial and recreational fishing in the coastal waters of East Asia. In Japan, approximately 850,000 juveniles are released annually for stock enhancement, and the catch in several release areas has increased. Life-history traits are important for fisheries management and stocking programmers. The age, growth, and mortality of fish collected from the central Seto Inland Sea from June 2012 to November 2014 were examined using 1022 sectioned sagittal otoliths, and the yield-per-recruit (YPR) was calculated. The opaque zones in the otoliths were confirmed to be annuli, formed mainly between June and July. The oldest fish was 16 years old. The percentage of those between two and five years was approximately 80%, whereas that of more than ten years was only 0.6%. The five parameters von Bertalanffy growth equation was calculated as: TLt = 390 {1 - 0.23[(t - 3.78)(2 )+ 1](-1)}{1 - exp [-0.34 (t + 0.28)]}, where TLt is the total length (mm) at t (year). The total, natural, and fishing mortality rates were calculated to be 0.80, 0.24-0.31 and 0.49-0.56 year(-1), respectively. The YPR analysis indicated that the current fishing mortality rate (F-current) was higher than F-0.1 and F-max, and that increasing the age at first capture is more effective than decreasing F for increasing the YPR. These results provide important information for fisheries management and the stocking of E. akaara.

Automated summary

This study analyzed the ecological characteristics of the red spotted grouper, including age, growth, and mortality. The results showed a wide age distribution for the species, with a low percentage of individuals over 10 years old. Calculating the yield-per-recruit, it was found that increasing the age at first capture is more effective in increasing the yield. These findings provide important insights for fisheries management and stocking programs.