Ocean glider based, acoustic detection of Antarctic krill (UK Antarctic Science)

The interdisciplinary and multi-institute GENTOO (Gliders: Excellent New Tools for Observing the Ocean) project undertook a cruise to the northwestern Weddell Sea in early 2012. During the cruise net samples, acoustic transects and CTD casts were undertaken. In addition surface drifters and three ocean gliders (iRobot Seagliders) were deployed. One of the gliders was fitted with a bespoke 120 kHz single-beam, calibratable echo sounder, an instrument appropriate for detecting the presence and measuring the biomass of Antarctic krill (Euphausia superba) by means of measuring mean volume backscatter. Antarctic krill are a key species in the ecosystem of the Southern Ocean where they are consumed by a very large numbers of higher trophic level predators. The Weddell Sea is a potentially important area of spawning of Antarctic krill with juvenile stages exploiting the winter ice habitat before being advected into the Scotia Sea when the ice retreats. Understanding the distribution of krill in the Weddell Sea is problematic, however, due to the difficulty and expense of accessing this remote and often ice-covered region and the limited seasonal window of Antarctic operations. The development of sophisticated autonomous vehicle offers the possibility for long deployments, spanning several months and remote monitoring via satellite telemetry of collected data. We discuss the calibration of the echo sounder using known targets and the validation of krill swarm identification by mounting the echo sounder on a net. The analysis of the acoustic data collected during the glider deployment is presented and we consider the potential and challenges of using Seagliders as platforms for estimating krill biomass and advective flux in Antarctic waters.