Comparison of habitat suitability index models for purpleback flying squid (Sthenoteuthis oualaniensis) in the open South China sea

Abstract

Fisheries resources in inshore regions of the South China Sea (SCS) have been depleted by overfishing. Purpleback flying squid (Sthenoteuthis oualaniensis) fishery is considered as a potential resource in the open SCS. However, little is known about their optimal habitat. Here, habitat suitability index (HSI) models were constructed using the external envelope and arithmetic mean methods to identify optimal habitats of purpleback flying squid. The matched fishery and environmental data (sea surface temperature, sea surface height anomaly, and ocean net primary productivity data) were collected from 2010 to 2014 in the open SCS. We calculated catch per unit effort (CPUE) and fishing effort to estimate the suitability index. The estimated suitable ranges for sea surface temperature, sea surface height anomaly, and net primary productivity were 27.1-30.4 °C, 0-0.15 cm, and 236.2-492.8 mg C/m2 d based on the HSI model incorporating fishing effort. The corresponding suitable ranges estimated by the HSI model incorporating CPUE were 27.4-30.7 °C, 0.03-0.18 cm, and 238.4-475.5 mg C/m2 d, respectively. When HSI values for 2014 were >0.6, the HSI model based on fishing effort explained 72.6% of the fishing effort and the average CPUE was 4.29 t/d. The HSI model based on CPUE explained 66.39% of the fishing effort for 2014 and the average CPUE was 4.23 t/d. The accuracy of the forecasting model based on fishing effort was higher than that based on CPUE. This HSI model can be used to aid in the management and conservation of purpleback flying squid in the SCS.