The relationship between the thermocline features and the rate of fishing success for free school caught by the tuna purse seiner in the Western and Central Pacific Ocean

Abstract:

The thermocline featuress are related to fishing success of surface tuna fishery, however, the thermocline is varied with the change of areas and seasons, so the impact of thermocline on the fishing operations is also different. The present study analyzed the thermocline features in the fishing ground of Chinese tuna purse seiner fleet operating in the Western and Central Pacific Ocean and explored the relationship between local thermocline feature and rate of fishing success for tuna purse seiners with combining to sinking depth of purse seine measured at the sea and the correpondent fishing information. The results showed that (1) the upper depths of thermocline for 91.2 percent settings were over 100 m in the survey, so the deeper upper depth of thermocline were the important features of thermocline in the fishing ground. (2) the 95% confidence intervals for maximum sinking depth of gear, the upper depth of thermocline, and sinking depth of purse seine within the thermocline ranged from 185.0 to 197.8 m, from 146.0 to 158.3 m and from 34.3 m to 44.0 m, respectively. (3) Correlation analysis showed that there is no significant correlation between rate of fishing success and thermocline (P>0.05), and the possible reason was that the deeper upper depth of thermocline in the local fishing ground allow targeted fish to escape in the larger space before they come close to the thermocline, so what in the sharp temperature gradient of thermocline lost the effect to obstruct the fish.