Impacts of the El Niño event on the population dynamics of Ommastrephes bartramii in the Northwest Pacific Ocean

Ommastrephes bartramii is one of the important and significant economic species in the Northwest Pacific Ocean, and the variation in biomass is susceptible to the climate change, such as El Niño. In this study, we assumed that the oceanic Niño index (ONI) affected the parameters, including intrinsic rate of growth (r), carrying capacity (K), respectively and simultaneously, of population dynamics model for O. bartramii. Thus, four surplus production models, Schaefer’s model of surplus production (SP) and three environmentally dependent surplus production (EDSP) models (E_r-EDSP, E_K-EDSP and E_r-E_K-EDSP) were developed to evaluate the trend of the stock dynamics of O. bartramii in the Northwest Pacific. The results showed that the Deviance Information Criterion (DIC) values of three EDSP models were less than the DIC value of SP model. Moreover, the E_r-E_K-EDSP with the smallest DIC value served as the optimal model. The estimated Maximum Sustainable Yield (MSY) value was 39.26×10⁴ tons. From 1994 to 2017, the fishing mortality rate (F_t) of O. bartramii was far lower than the target mortality rate (F_tar) and the fishing mortality rate at the level of MSY (F_MSY). In 2017, the stock resources of O. bartramii in the Northwest Pacific Ocean were less than the corresponding resources at the level of MSY (B_MSY). Currently, the O. bartramii stock in the Northwest Pacific is being overfished or was being overfished. The conclusion could be used for sustainable development and management of O. bartramii in the Northwest Pacific Ocean.