The relationship between the temporal-spatial distribution of fishing ground of yellowfin tuna ( Thunnus albacares ) and themocline characteristics in the tropic Indian Ocean

Based on the monthly themocline characteristic parameters of tropic Indian Ocean obtained by the Argo profile data from China Argo Real-time Data Center (CARDC), along with the longline fisheries data of yellowfin tuna (Thunnus albacares) provided by the Indian Ocean Tuna Commission (IOTC), the spatial overlay maps of the average monthly at themocline characteristic parameters and CPUE value of yellowfin tuna were plotted to analyze the relationship between the fishing grounds distribution of yellowfin tuna and themocline characteristics parameters. The seasonal variety of the upper bound depth, temperature and the lower boundary depth and the fishing ground distribution of yellowfin tuna were found from the analysis results. Meanwhile, the relationship between the fishing ground distribution of yellowfin tuna and the seasonal variety of the themocline were remarkable. During the northeast monsoon, the range of the upper boundary depth in the higher value of CPUE fishing area was 30-50m, and the CPUE value was lower where the upper boundary was over than 70m. While the upper boundary depth was more than 120m during the southwest monsoon. The lower boundary depth in the higher value of CPUE fishing area was less than 200m during the northeast monsoon, while that was over than 300m during the southwest monsoon. During the northeast monsoon, the upper boundary temperature was more than 25 degree C and the CPUE value was generally lower in the area with the temperature less than 24 degree C, while that during the southwest monsoon ranged wildly, extended to 22 degree C, and the CPUE value was lower under 22 degree C.Based on the frequency analysis and empirical cumulative distribution function (ECDF), the optimum range of the upper boundary temperature and depth were 25-29 degree C and 30-70m, respectively, while that of lower boundary temperature and depth were 13-16 degree C and 140-200m, respectively. The results were trusted test by K-S test.