金枪鱼围网沉降性能对自由鱼群捕获率的影响

The relationship between purse seine sinking performance and fishing success for free swimming tuna schools

本研究分析了2006-2012年中国金枪鱼围网船队89个网次的沉降性能与捕获率之间的关系,结果表明：（1）网具中部最大沉降深度的95％置信区间为195.3～209.3 m,网具中部平均沉降速度的95％置信区间为0.181～0.192 m/s; （2）海上测定的数据显示,不同沉降速度组对应的捕获率具有显著性差异（P＜0.1）,捕获率随着沉降速度的增加明显上升（20.0％～66.7％）,而捕获率在不同沉降深度组间呈现出无规律的变化;（3）Logistic回归全模型的筛选结果表明,虽然沉降深度（D）的回归系数差异不显著（P＞0.1）,但投网成功的概率与沉降速度（回关系紧密（P＜0.1）,模型预测的不同沉降速度所对应的捕获率也与实际观察结果相吻合.由此建议在今后研究中应致力于提高网具沉降速度而非增加网具沉降深度.

We evaluated the relationship between the rate of fishing success and the sinking performance of purse seines operated by a Chinese tuna purse seine fleet from 2006 to 2012. The 95% confidence intervals for maximum sinking depth （D） and average sinking speed （S） of the middle part of gear ranged from 195.3 m to 209.3 m and from 0.181 rn/s to 0.192 m/s, respectively. The data obtained from at-sea observations indicate there is a significant difference in the fishing success among the different sinking speeds. Fishing success increased rapidly from 20.0% to 66.7% with an increase in the sinking speed. However, there was no relationship between fishing success and sinking depth. An initial run of the full logistic regression model revealed that the sinking depth is not a significant factor of fishing success （P〉0.01）, i.e. the probability of fishing success depends only on the sinking speed of the fishing gear. Moreover, fishing successes at different speeds predicted by the model were similar to the at-sea observations. Our results suggest that more effort should be made to accelerating the sinking speed but not deepen the sinking depth of fishing gear.