三疣梭子蟹对蟹笼网目和刚性矩形逃逸口的逃逸行为比较

Comparison of escape behavior of Portunus trituberculatus between meshes opening and rigid rectangular escape vent in crab pots

为了解东海近海蟹笼逃逸口类型对三疣梭子蟹(Portunus trituberculatus)逃逸行为的影响,使用红外水下摄像装备,对入笼的三疣梭子蟹在不同行为阶段对安装于侧网靠近笼底一侧的刚性矩形逃逸口(高40mm×宽200mm)和网目逃逸口(由2个位置较低的40mm×60mm和1个位置较高的60mm×60mm破目构成)的行为反应进行观察。根据三疣梭子蟹探索、发现并接近、穿越企图和穿越逃逸口个体连续行为的4个阶段观察结果显示:相比刚性矩形逃逸口,三疣梭子蟹在网目逃逸口实验蟹笼中的探索行为持续时间更长;在笼底探索的个体能定位、发现并接近2种不同类型逃逸口,但发现并接近网目逃逸口时距离入笼的平均时间(P<0.01)和平均次数(P=0.061)均大于刚性矩形逃逸口;发现约85%接近逃逸口的三疣梭子蟹企图穿越逃逸口,且在逃逸口类型之间没有显著差异;三疣梭子蟹在网目逃逸口前停留了更长的时间(P=0.006),且这一时间显著影响着个体是否企图逃逸的行为。所有个体均采用侧身姿态穿越逃逸口,对于刚性矩形逃逸口,个体甲高与逃逸口高度的关系是决定个体能否成功逃逸的关键因素;对于网目逃逸口,个体优先尝试穿越较低逃逸口,并最终全部逃逸。实验结果表明网目逃逸口可以作为蟹笼渔具逃逸装置,生物可降解材料应用可成为缓解蟹笼幽灵捕捞问题的技术手段之一。

In order to understand the effect of escape opening type on the escaping behavior of Portunus trituberculatus in crab pots, the response behavior of crabs pre-stocked in pots to rigid rectangular escape vent with 40 mm height×200 mm width and meshes escape openings composed of two 40 mm×60 mm meshes in lower position and one 60 mm×60 mm mesh in higher position was observed and recorded in tank by infrared underwater camera. Both escape opening were located at the bottom edge of side panels. According to behavioral characteristics of crab behaviors, the continuous response behavior of P. trituberculatus to pots and escape openings was divided into four stages: search, detect and approach, attempt to pass, and pass through the escape openings. The video recording of the response behavior showed that, compared with those in the experimental pot with rigid rectangular escape opening, pre-stocked P. trituberculatus in pot with meshes escape opening explored more frequently and persistently. Crabs could locate, detect and approach the escape opening readily in their search behavior at the floor of pots, regardless of type of escape opening. However, the average number of times and duration of approaching the meshes escape openings were greater than those of approaching the escape rigid escape vent(P< 0.001 for average duration and P=0.061 for average number of times). For crabs approaching openings, nearly 85% of them attempted to pass through openings and no significant difference in attempt to pass through between different opening types was detected. Duration of stay in front of the escape openings of P. trituberculatus, which was considered as a significant factor influencing the attempt to pass thorough, was significantly longer(P=0.006) for meshes escape openings than that for rigid rectangular escape vent. All crabs walked sideways through escape openings, so whether crabs could pass through an rigid escape vent depended upon the relationship between carapace depth and opening height of rigid escape vent. As for the meshes escape openings, crabs preferred to pass through the lower opening and eventually succeeded in escaping. Nevertheless, the effective releasing crabs of meshes escape openings suggested that the mesh opening could be used as an effective escape device and the usage of biodegradable netting panel would be one of the technical measures to alleviate ghost fishing effect when pots were lost in crab pot fisheries.