Growth, mortality and optimum catchable size of Bombay duck (Harpadon nehereus) in the Wentai fishing ground, East China Sea

Some traditional fishery resources in the East China Sea have showed an apparent decline trend over years and therefore, those subordinate economic species, such as Harpadon nehereus, have gradually became dominant species, which also has important economic value and plays a key role in local eco-system. During the period from November 2015 to August 2016, a total of 2611 samples of H. nehereus were collected in the Wentai fishing ground. Based on the length information recorded, an ELEFAN I technique was used to estimate growth and mortality parameters of H. nehereus, and an incomplete β function dynamic pool model was adopted to determine the catchable size and evaluate the exploitation conditions for H. nehereusresources. The results show that: the length-weight relationships of H. nehereus in the Wentai fishing ground was W=0.000 5L^3.87 (R²=0.906 7), and this relationship was insignificantly different between females and males. The parameters of Von Bertalanffy Growth function for H. nehereus were L_∞=32.13 cm, K=0.39 and t₀=–0.69, with the inflexion for body weight growth estimated at 2.78 years. The total mortality coefficient calculated with linear catch curve based on body length structure was 2.55, and the natural mortality coefficient estimated by Pauly’s empirical equation was 0.66. Meanwhile, the fishing mortality coefficient was found to be 1.89 and the exploitation rate was 0.74. The dynamic pool model indicated the age of capture and the first catchable size should be increased, and the first catchable age and the corresponding capture length should be set at 1.15 years, and 16.5 cm, respectively.