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 swarm
Date = (YYYYMMDD) observation date (UTC)
Time = (HH:mm:ss.ss) observation time (UTC)
Lat = (dd.ddddd) latitude
Lon = (ddd.ddddd) longitude
transect = 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.

本数据集用于描述声学观测得到的磷虾群，相关数据被应用于Bestley等人（2017）发表的论文《南极东部海域近海海洋捕食者觅食所需磷虾群特征预测》（英文原文：Predicting krill swarm characteristics important for marine predators foraging off East Antarctica，论文链接：http://onlinelibrary.wiley.com/doi/10.1111/ecog.03080/full）。

论文摘要如下：
由于缺乏与捕食者行为尺度相匹配的猎物场信息，开阔海域捕食者-猎物相互作用的研究往往难以阐释。因此，学界迫切需要明确影响猎物物种分布与丰度的生物及物理因子，这可为保护规划及评估环境变化影响提供广泛的预测依据。本研究聚焦南大洋关键猎物物种——南极磷虾（Euphausia superba），利用南极东部海域大尺度调查中获取的单个磷虾群（聚集体）声学观测数据。我们构建了两套描述磷虾群特征的统计模型：第一套以走航调查数据作为解释变量，第二套则采用卫星遥感的替代变量。尽管走航数据为与磷虾群数据同步获取的原位观测数据，但在对其他区域或时段的猎物分布进行预测与推断时，遥感数据是唯一可用的数据源。拟合后的模型显示，影响磷虾群特征的主要生物物理因子包括光照条件（太阳高度角/辐射量）以及与南极大陆坡的距离，同时其与海流速度及梯度间存在复杂关联。无论采用走航预测变量还是遥感预测变量，模型整体性能均相近。我们将基于遥感变量的模型应用于10年遥感时间序列数据，生成了区域尺度的空间预测结果。此项回顾性建模识别出南极东部近海区域，在南半球仲夏期间持续形成相对密集的磷虾群，这些区域可能是海洋捕食者的核心觅食区。基于独立研究获得的南极捕食者卫星追踪轨迹生成的时空预测结果表明，该方法可进一步应用于捕食者移动与觅食的定量化建模。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）文件包含该研究使用的磷虾群数据，相关文献引用为：
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.

各列说明如下：
- Depth_mean_m：单位为米（m），指磷虾群的平均深度
- Date：格式为YYYYMMDD，指观测日期（协调世界时UTC）
- Time：格式为HH:mm:ss.ss，指观测时间（协调世界时UTC）
- Lat：格式为dd.ddddd，指纬度
- Lon：格式为ddd.ddddd，指经度
- transect：指BROKE West航段编号7至11（详见Bestley等人2017年论文图1）
- denVolgm3：单位为克湿重每立方米（g湿重·m⁻³），指磷虾群内部的种群密度