Modeling habitat of skipjack tuna of free swimming school in Western and Central Pacific Ocean based on MaxEnt model

Due to the negative effects of extensive use of drifting artificial fish aggregating devices (FADs) on tuna stocks, tuna purse seine fishing has become a development trend towards catching free swimming school, so it is necessary to specifically study the habitat use of free swimming school of skipjack tuna (Katsuwonus pelamis). In this study, we used monthly tuna fishery data from the Western and Central Pacific Fisheries Commission (WCPFC) from 2016 to 2020, different layers of water temperature (SST, Temp₂₀₀), sea surface salinity (SSS), dissolved oxygen concentration (DO₀, DO₅₀, DO₂₀₀), east-west current velocity (EV), north-south current velocity (NV), mixed layer depth (MLD), chlorophyll a concentration (CHL₀, CHL₅₀, CHL₁₀₀, CHL₂₀₀), and a total of 13 environmental variables by Maximum Entropy (MaxEnt) model to simulate the habitat distribution of the free swimming school and their monthly variation patterns. The results show that the AUC and sensitivity values of both the test and training set of the model were greater than 0.90, and the true skill statistics values were greater than 0.80, indicating that the model has strong predictive ability and can be used for the habitat suitability modeling of skipjack tuna. SST and DO₂₀₀ were the key factors affecting the habitat preference of free swimming school, with the optimal ranges of 30−31  ℃ and 114−153 mmol·m⁻³, respectively. During the survey period, the highly suitable habitat for free swimming school was mainly near the waters of Papua New Guinea and Solomon Islands, with a large variation in the range extending eastward in different periods, and the difference in longitude reached 6°. The results provide references for the prediction of the central fishing ground of free swimming school of skipjack tuna by Chinese tuna purse seine fleet.