This study researched the population of ecological characteristics of the goldeyes rockfish Sebasetes thompsoni sampled by gill net in the Ulleungdo area from February 2013 to February 2014 in order to assess the current stock status and provide scientific advice for management implementation. The instantaneous coefficient of total mortality (Z) was 0.78/year and the survival rate (S) was 0.459. The instantaneous coefficient of natural mortality (M) was 0.461/year. Based on the estimates of Z and M, the instantaneous coefficient of fishing mortality (F) was 0.318/year. The age at first capture (tc) was 4.41/years. Current Yield-per-recruit (YPR) was 30.83 g, and fishing mortality at maximum YPR (Fmax) and fishing mortality corresponding to 10% of the maximum slope in YPR curve (F0.1) were 3.257/year and 0.673/year, respectively. F35% and F40%, indicating fishing mortalities at 35% and 40% of maximum Spawning biomass-per-recruit (SBPR), were 0.619/year and 0.509/year, respectively. Based on the biological reference points, fishing mortality at overfished threshold yield (FOTY) was calculated as 0.509/year. Current SBPR/SBPRMSY was 1.313 above 1.0, which means ‘not overfishe,’ while current F/FOTY was 0.629 below 1.0, which indicates ‘not overfishing.’ In conclusion, the current status of goldeyes rockfish was located in green zone (i.e., not overfished and not overfishing) according to the revised Kobe plot.

Yield per recruit model is the most popular method for fisheries stock assessment. However, stock assessment using yield per recruit model can lead to recruitment overfishing as this model only considers the maximum yield per recruit without spawning biomass for reproduction. For this reason, spawning biomass per recruit model which reveals variations of spawning stock biomass per fishing mortality (F) and age at first capture (tc) is considered as more proper method for stock assessment. There are mainly two methods for spawning biomass per recruit model known as age specific selectivity method and knife– edged selectivity method. In the knife–edged selectivity method, the spawning biomass per recruit has been often calculated using biomass per recruit value by multiplying the maturity ratio of the recruited age. But the maturity ratio in the previous method was not considered properly in previous studies. Therefore, a new method of the knife–edged selectivity model was suggested in this study using a weighted average of the maturity ratio for ages from the first capture to the lifespan. The optimum fishing mortality in terms of F35% which was obtained from the new method was compared to the old method for small yellow croaker stock in Korea. The value of F35% using the new knife–edged selectivity model was 0.302/year and the value using the old model was 0.349/year. However, the value of F35% using the age specific selectivity model was estimated as 0.320/year which was closer to the value from the new knife–edged selectivity model.

This study was performed to estimate biomass and to provide management plan through population ecological characteristics, including survival rate, instantaneous coefficient of natural and fishing mortalities, and age at first capture of Flathead grey mullet, Mugil cephalus, in the coastal waters of Yeosu. Survival rate (S) of the flathead grey mullet was 3.671. The instantaneous coefficients of natural mortality (M) and fishing mortality (F) was estimated to be 0.325 /year, 0.962 /year for flathead grey mullet. Also fist capure age of flathead grey mullet was 3.61year. The current biomass of the flathead grey mullet in the study area was estimated to be 19.6 M/T and F0.1 and F40% were estimated 0.340 /year, 0.225 /year. For the stock assessment result, flathead grey mullet was not overfished but overfishing.