Single- and multi-beam echosounder assessment of Antarctic krill aggregations

Acoustic backscatter measurements from aggregations of Antarctic krill were collected over two field seasons (2006 and 2007) in the waters north of Livingston Island using two 5.5‐m inflatable vessels. One was equipped with a dual‐frequency (38‐ and 200‐kHz) single‐beam echosounder, while the other used a 200‐kHz multi‐beam system. In addition to independent survey operations, both vessels participated in joint survey operations where the two boats followed the same trackline separated by a small distance (10–40 m). These data allow us to compare how the two echosounder systems “see” the same (or very similar) krill aggregations. During 2006, some tracklines were also occupied by a large (300‐ft) vessel although vessel separation distances were larger during these operations. The combination of measurements from single‐ and multi‐beam echosounders (and nearby net tows) provides the opportunity to characterize krill aggregation size, shape, numerical density, and overall biomass. Observations of krill pred...