Yield per recruitment evaluation of Oratosquilla oratoria in coastal waters of Shandong

In order to complement the basic biological information of Oratosquilla oratoria and provide managers with scientific guidance and theoretical basis, based on the size composition data of O. oratoria obtained from fishery independent surveys from 2016 to 2017 in coastal waters of Shandong Peninsula, this study estimated the growth and mortality parameters of O. oratoria. A length-structure yield per recruitment model was used to assess the population dynamics and management strategy of the species. A total of 5 028 individuals were caught, from which the length-weight relationship was derived as W=0.014 5L^2.88, showing a negative allometric growth pattern. Asymptotic body length and growth coefficient estimated by ELEFAN were L_∞=19.87 cm and K=0.62 a⁻¹, respectively. The growth rate of O. oratoria showed remarkable seasonal oscillation, the highest in October and the lowest in April, and the amplitude of the seasonal oscillation (C) was 0.76. The total mortality (Z) estimated by length-converted catch curve was 3.24 a⁻¹, and the natural mortality (M) estimated by several estimators ranged from 0.75 to 1.27 a⁻¹. Accordingly, the fishing mortality (F) ranged from 1.96 to 2.49 a⁻¹, and the mean exploitation rate was 0.67. Results of YPR model showed that with the F increasing, YPR tended to increase at first, and then decrease. Biological reference points F_0.1 and F_max were 0.92 a⁻¹ and 1.88 a⁻¹, respectively. This study shows that O. oratoria stock is over-exploited. In order to maintain stock and fishery of O. oratoria, fishing pressure needs to be reduced and length at first capture should be increased.