Krill swarms observed along transects 7 to 11 during the BROKE-West voyage

This is data describing acoustically observed krill swarms that was used in the Bestley et al. (2017) paper 'Predicting krill swarm characteristics important for marine predators foraging off East Antarctica' (http://onlinelibrary.wiley.com/doi/10.1111/ecog.03080/full). Abstract of the paper presented here:Open ocean predator-prey interactions are often difficult to interpret because of a lack of information on prey fields at scales relevant to predator behaviour. Hence, there is strong interest in identifying the biological and physical factors influencing the distribution and abundance of prey species, which may be of broad predictive use for conservation planning and evaluating effects of environmental change. This study focuses on a key Southern Ocean prey species, Antarctic krill Euphausia superba, using acoustic observations of individual swarms (aggregations) from a large-scale survey off East Antarctica. We developed two sets of statistical models describing swarm characteristics, one set using underway survey data for the explanatory variables, and the other using their satellite remotely sensed analogues. While survey data are in situ and contemporaneous with the swarm data, remotely sensed data are all that is available for prediction and inference about prey distribution in other areas or at other times. The fitted models showed that the primary biophysical influences on krill swarm characteristics included daylight (solar elevation/radiation) and proximity to the Antarctic continental slope, but there were also complex relationships with current velocities and gradients. Overall model performance was similar regardless of whether underway or remotely sensed predictors were used. We applied the latter models to generate regional-scale spatial predictions using a 10-yr remotely-sensed time series. This retrospective modelling identified areas off east Antarctica where relatively dense krill swarms were consistently predicted during austral mid-summers, which may underpin key foraging areas for marine predators. Spatiotemporal predictions along Antarctic predator satellite tracks, from independent studies, illustrate the potential for uptake into further quantitative modelling of predator movements and foraging. The approach is widely applicable to other krill-dependent ecosystems, and our findings are relevant to similar efforts examining biophysical linkages elsewhere in the Southern Ocean and beyond.This comma separated variable (CSV) file contains the krill swarm data used in:Bestley, S., Raymond, B., Gales, N.J., Harcourt, R.G., Hindell, M.A., Jonsen, I.D., Nicol, S., Peron, C., Sumner, M.D., Weimerskirch, H. and Wotherspoon, S.J., Cox, M.J. (2017). Predicting krill swarm characteristics important for marine predators foraging off East Antarctica. Ecography.The column descriptions are:Depth_mean_m = (units m) mean depth of a krill swarmDate = (YYYYMMDD) observation date (UTC)Time = (HH:mm:ss.ss) observation time (UTC)Lat = (dd.ddddd) latitudeLon = (ddd.ddddd) longitudetransect = BROKE West transect number 7 to 11 (see Fig. 1, Bestley et al. 2017)denVolgm3 = (units g wet mass m-3) internal krill swarm density in gram wet mass per cubic metre.

本数据集收录了经声学观测得到的磷虾群（krill swarms）数据，相关数据曾被用于Bestley等人2017年发表的论文《预测南极东部海域近海海洋捕食者觅食所需的关键磷虾群特征》（论文链接：http://onlinelibrary.wiley.com/doi/10.1111/ecog.03080/full）。

以下为该论文的摘要：
公海海域的捕食者-猎物相互作用往往难以解析，原因在于缺乏与捕食者行为尺度相匹配的猎物场相关数据。因此，学界亟需明确影响猎物种群分布与丰度的生物与物理因子，这类研究可广泛应用于保护规划制定以及环境变化影响评估工作。本研究聚焦南大洋关键猎物种群——南极大磷虾（Antarctic krill, Euphausia superba），使用了南极东部海域大规模声学调查获取的单个磷虾群（聚集体）观测数据。研究团队构建了两组用于描述磷虾群特征的统计模型：一组以随航调查数据作为解释变量，另一组则采用卫星遥感替代数据作为解释变量。随航调查数据属于原位同步观测数据，可与磷虾群数据匹配使用；而在其他区域或时段开展猎物分布预测与推断时，则仅能获取卫星遥感数据。拟合后的模型结果显示，影响磷虾群特征的核心生物物理因子包括光照条件（太阳高度角/太阳辐射）以及与南极大陆坡的距离，同时洋流流速与流速梯度也与磷虾群特征存在复杂关联。无论采用随航调查还是遥感预测变量，模型整体性能均无显著差异。研究团队基于10年的遥感时间序列数据，使用后一组模型生成了区域尺度的空间预测结果。本次回顾性建模明确了南极东部海域的部分区域，在南半球仲夏时节该区域始终存在高密度磷虾群，这一区域或为海洋捕食者的核心觅食场。基于独立研究得到的南极捕食者卫星追踪轨迹生成的时空预测结果，表明该模型可进一步应用于捕食者移动与觅食行为的定量建模研究。本研究方法可广泛推广至其他依赖磷虾的生态系统，研究结果也可为南大洋乃至全球其他区域的生物物理关联相关研究提供参考。

本逗号分隔值（CSV, comma separated variable）文件包含了上述论文中使用的磷虾群数据，论文完整信息如下：Bestley, S., Raymond, B., Gales, N.J., Harcourt, R.G., Hindell, M.A., Jonsen, I.D., Nicol, S., Peron, C., Sumner, M.D., Weimerskirch, H.、Wotherspoon, S.J. 与Cox, M.J.（2017），《预测南极东部海域近海海洋捕食者觅食所需的关键磷虾群特征》，发表于《Ecography》期刊。

各字段说明如下：
1. Depth_mean_m：单位为米（m），指磷虾群的平均深度
2. Date：格式为YYYYMMDD，指观测日期（协调世界时UTC）
3. Time：格式为HH:mm:ss.ss，指观测时间（协调世界时UTC）
4. Lat：格式为dd.ddddd，指纬度
5. Lon：格式为ddd.ddddd，指经度
6. transect：指BROKE West调查样带编号7至11（详见Bestley等人2017年论文图1）
7. denVolgm3：单位为克湿重每立方米（g·m⁻³），指磷虾群内部的湿重密度