南海灯光罩网渔业中点斑原海豚的声波驱赶

Acoustic deterrent of pantropical spotted dolphins(Stenella attenuata) from light-falling net fisheries in the South China Sea

灯光罩网是南海外海的一种主要捕捞方式,夜晚作业时点斑原海豚(Stenellaattenuata)常常聚集在渔船周围进行捕食活动,导致被网具兼捕死亡。本研究研发宽带声波驱豚系统,分别于2019年5月19日和28日在南海进行海上试验,确定了驱赶点斑原海豚的有效频段,定量评估了驱豚效果。研究结果表明:1~10 kHz的线性调频信号对点斑原海豚有一定的驱赶作用。2次试验系统开启前的海豚单体信号数目小于开启后,而离船平均间距大于开启后,即海豚远离了调查船;5月28日试验时,系统开启后3个阈值均没有检测到疑似单体信号,即在离船120 m范围内,无点斑原海豚存在。系统开启前后20min,垂直声学映像中各单元格的平均NASC值存在显著性差异(P<0.05),且开启前的NASC要小于开启后。通过海上试验,本研究验证了宽带声波驱豚系统的有效性,初步确定了驱赶点斑原海豚的有效声波频段与脉冲模式,然而本研究还有一些不足之处,需要进行更多的试验予以完善,以便于未来的推广应用。

The use of light-falling nets is an important fishing method in the South China Sea. Pantropical spotted dolphins(Stenella attenuata) often gather around fishing vessels using light-falling nets for predatory activities at night, leading to accidental injuries and even death. In this study, we used a wide-band acoustic system to deter pantropical spotted dolphins from the fishing vessels. After two tests, the effective deterrent frequency was determined, and the deterrent effect was quantitatively evaluated. The results indicate that a 1–10 kHz linear frequency modulation signal could deter pantropical spotted dolphins. The number of dolphin signals and the average distance between dolphins and vessels were greater after the signal launch. On May 28, no suspected dolphin signals were detected at the three thresholds. In addition, by analyzing and comparing the nautical area scattering coefficient(NASC) value of each cell in the vertical acoustic ecogram, we found that there were significant differences in the NASC values of each cell before and after the dolphin deterrent was applied(P<0.05), and the mean NASC value was larger after the deterrent was used. This study has verified the effectiveness of a wide-band acoustic dolphin deterrent system, and established a preliminary protection method for the pantropical spotted dolphin in the light-falling net fisheries in the South China Sea. However, this study has some limitations, and further studies are needed to improve this method in the future.