sinking depth and sinking speed of tuna purse seines. We attached a micro-temperature and depth recorder (10 TDR-2050) to a purse seine on the “JINHUI NO.6” vessel (Shanghai Pelagic Fishing Company) and collected data from 23 sets in the Western and Central Pacific Ocean (WCPO) between October and December 2006. The sinking depth did not achieve the theoretical maximum sinking depth, instead accounting for 51.4% of the maximum stretched height (311.1m) of the netting. The relationship between ) for the mid section of leadline can be described using the formula:+ =0.998 3). The sinking speed differed among the sections of the lead line. The fastest sinking speed was recorded at the back wing end, followed by the mid section and the bulk. The sinking speed decreased with depth, the deeper the sinking depth of leadline, the lower the sinking speed. Fluctuations in the confidence interval of the average sinking speed of leadline followed a pattern of large-small-large as the depth increased. The relationship between the sinking speed () at the mid part of leadline can be described using the formula: −4 = 0.986 7). Our observations provide insight into ways to improve sinking performance in tuna purse seines and a reference for fishing operations.