Climate-induced habitat suitability variations of chub mackerel Scomber japonicus in the East China Sea

Chub mackerel Scomber japonicas is an economically important fish species, extensively distributed in the East China Sea, the Yellow Sea and the Sea of Japan. Climate variability has strong impacts on its habitat. In this study, an integrated habitat suitability index (HSI) model was constructed to examine habitat suitability of S. japonicas in the East China Sea, and evaluate the relationship with the El Nino and La Nina events, with three crucial environmental variables (sea surface temperature (SST), sea surface height (SSH) and net primary production (NPP)) as predictors. The HSI model was developed using data over 2006-2013 and validated using data in 2014 and 2015. Results showed that the HSI model with the best model performance yielded robust predictions of habitat suitability for S. japonicas. The decreasing catch and CPUE (catch per unit effort) of S. japonicus during 2006-2015 were highly consistent with substantial shrinkage of suitable and optimal habitats, and enlargement of normal and poor habitats. Similar movement pattern was also found between the latitudinal gravity centers of fishing effort for S. japonicas fishery and the gravity centers of potential habitat. In addition, spatial correlation analysis indicated that the HSI value was significantly positively related to the SST anomaly (SSTA) and negatively correlated with the SSH anomaly (SSHA) and NPP anomaly (NPPA), on the main fishing ground between 25 degrees-30 degrees N and 120 degrees-130 degrees E. Furthermore, various intensity of the El Nino and La Nina event may lead to different variations in the habitat suitability of S. japonicus. Comparing to the very strong El Nino, the moderate El Nitio events would yield rising SSTA and lowing SSHA and NPPA, leading to dramatically enlarged suitable habitat of S. japonicas. The habitat quality in La Nina events with different intensity depended on the local environmental variability on the fishing ground. Our findings suggested that the El Nino and La Nina events prominently affected the habitat suitability of S. japonicas in the East China Sea. However, the impacts varied with the intensity of each anomalous climatic event.