南极南奥克尼群岛2017年春季南极磷虾资源声学评估

Acoustic estimation of Euphausia superba in the South Orkney Islands in austral spring 2017

南极磷虾(Euphausia superba)为南大洋中上层生态系统的关键种,对其生物量的研究有助于更准确地掌握磷虾的生态和分布信息。基于2017年我国南极磷虾声学调查采集的断面回波映像,应用声学回波后处理软件(Echoview),评估了南奥克尼群岛周边水域的磷虾生物量。该海域磷虾体长范围为25.50～49.21mm,平均体长为(33.01±4.06) mm;其中雌性平均体长为(33.15±3.90) mm,雄性平均体长为(32.68±4.43) mm,雌、雄磷虾体长无显著性差异。本海域声学映像可分为1338个积分单元,最大单元磷虾密度为554.07 g/m^2,最小单元密度值为0 g/m^2。调查海域磷虾分布不均匀,87.90%的积分单元无磷虾生物量。磷虾平均密度为71.01g/m^2,总生物量为1.77×106 t,密度差异系数为97.4%。磷虾主要分布在水深<200 m的南奥克尼群岛大陆架海域,群岛东侧磷虾生物量多于西侧。积分单元中磷虾密度大于450 g/m^2但小于600 g/m^2的有2个,群岛东西两侧各1个;密度值大于300 g/m^2但小于450 g/m^2的积分单元有6个, 5个位于群岛东侧。远离群岛的2个断面(1, 9)和调查海域中心的2个断面(5, 6)磷虾生物量较少。本海域磷虾的昼夜垂直移动对磷虾生物量评估也无影响。磷虾白天聚集在60～180 m水层,随着时间推移,磷虾逐渐向上或向下移动。光照强度是触发磷虾白天下沉、夜晚上浮的因素之一。

Antarctic krill(Euphausia superba) is a key species in the Southern Ocean ecosystem, and knowledge regarding its biomass is essential to understand the ecology and distribution of krill. The acoustic data was collected across extensive gradients in the South Orkney Islands on the commercial fishing vessel Long Teng. Krill targets were identified in acoustic data using a multi-frequency identification window and converted to krill density using the Stochastic Distorted-Wave Born Approximation target strength model. The average krill length was(33.01±4.06) mm, with a maximum length of 49.21 mm and a minimum length of 25.50 mm. There was no significant difference between male and female krill length. The whole ecogram could be divided into 1338 integration units, of which 586 units were in daytime and 752 units were at night. The maximum krill density was554.07 g/m^2 and the minimum density was 0 g/m^2. The Antarctic krill were mainly aggregated, with 87.90% integration units having no biomass. There was no significant difference in diurnal NASC and Sv values of the 9 transects, which suggested that the diurnal vertical movement had no effect on the estimation of krill biomass. The average krill density was 71.01 g/m^2 and the total biomass was 1.77×106 t in this area. The krill were mainly aggregated in a 60–180 m water depth range in the daytime, and gradually moved upwards or downwards at night.Light intensity is one of the factors that influence the krill diurnal vertical movement. However, a proportion of the Antarctic krill sunk to deeper waters at night, which may be to prey on the deep-water food. The results of this study provide abundant information on krill distribution in this area and basic data for current feedback on the krill resource management of CCAMLR. In future, the research on the correlation between krill biomass and external factors(environmental factors, predators) can help us understand the population structures more accurately and predict the distribution of krill resources.