GROWTH, MORTALITY AND EVALUATION OF RESOURCE UTILIZATION FOR TWO SALANGIDAE, PROTOSALANX HYALOCRANIUS AND NEOSALANX TAIHUENSIS IN HONGZE LAKE

Two Salangidae, Protosalanx hyalocranius (Abbott, 1901) and Neosalanx taihuensis (Chen, 1956) were sampled monthly from July 2015 to June 2016 in Hongze Lake. Catch per Unit Effort (CPUE) was estimated for these two species as the number of individuals or weight of each species collected per km² of water area; growth and mortality parameters were estimated for both populations. The equilibrium output model was used to evaluate the appropriate onset timing of fishing to achieve the highest yield per-recruitment and to establish an optimized fishery management scheme. The spawner biomass per-recruitment (SBR) model was constructed to assess the fishing effects under two different fishery management schemes, the current one and the optimized one based on the equilibrium output model. Ranges of the body length and body weight for P. hyalocranius were 20.39—182.68 mm and 0.10—34.79 g, respectively; this fish had two rapid growth periods, from April to June and from August to November; the most fitted growth function was the von Bertalanffy equation, L_t=173.35×1–e^{–1.972(t–0.092)}; fishing mortality and natural mortality coefficients for the population were estimated as 8.583/year and 3.292/year, respectively. Ranges of the body length and body weight for N. taihuensis were 20.4—82.7 mm and 0.04—3.40 g, respectively; this fish showed a relatively constant growth rate from April through November; the most fitted growth function was the Logistic equation, L_t=66.82/1+e^{–5.386(t–0.124)}; fishing mortality and natural mortality coefficients for the populations were estimated as 7.006/year and 1.146/year, respectively. The current fishing management protocol on Salangidae in Hongze Lake has a banned fishing season between January 1 and August 8. Fishing is open for one week in mid-May. The equilibrium output model showed that the sum of yield per-recruitment for both species could reach the highest value when the banned fishing season is extended for 20 days, with the closure of one week fishing period in May and the onset of fishing period on August 29. Results of the SBR model showed that the SBR residues for P. hyalocranius were 20.23% and 36.72% of the unexploited state under the current protocol and the adjusted protocol, respectively, and those for N. taihuensis were 7.50% and 12.86%, respectively. In conclusion, the adjusted management protocol could effectively reduce fishing pressure for P. hyalocranius, but not for N. taihuensis.