Sounding out zooplankton: using autonomous wideband echosounders to characterise polar ecosystems

Krill and copepods (zooplankton, small marine organisms) are ubiquitous within the world's oceans, and play a key role in polar marine foodwebs as food for higher trophic levels, including fisheries, and for carbon cycling. Yet we are still challenged to measure their abundance and distribution accurately and the challenge gets harder at larger temporal and spatial scales. Acoustic methods are used widely for estimating fish and plankton abundance and distribution, but there is ambiguity in the interpretation of acoustic data to species identification.

New wideband acoustic technology offers a potential way to characterise a range of sound scatterers including zooplankton by measuring acoustic responses continuously across a wide frequency range, increasing the amount of information available for spectral characterization of targets. In addition, compressed pulse processing can increase the temporal- and range-resolution, enabling enhanced feature extraction from within organism aggregations (e.g. krill swarms).

This project will use these next generation wideband autonomous echosounders, deployed vertically, in autonomous mode on moorings, and on autonomous vehicles to examine krill and copepod identification and distribution in polar waters and in a test-bed in Loch Etive, Scotland.
The student will develop methods for identifying krill and copepod echoes within wideband acoustic data, and make novel observations of the distribution of copepods and krill within aggregations and swarms.

They will analyse existing data from moored echosounders to examine high range resolution acoustic data from within Antarctic krill swarms. Using their species identification techniques to identify krill, they will examine intra-swarm behavior. Additional research opportunities may include analyzing acoustic data from an Autonomous Underwater Vehicle deployment (e.g. echosounder mounted on Autosub and deployed within the Weddell Sea), where the student will examine vehicle behaviour and its influence on wideband species identification, or the association of zooplankton with sea ice, exploring the mechanisms and patterns of variability in zooplankton distribution.

Where possible the student will also collect new data from vertical deployments of the wideband echosounder with concurrent net sampling. We identify two opportunities for this, 1) with supervisors at SAMS, Oban as part of ongoing funded projects into zooplankton physiology/behavior and 2) during one of BAS' fieldwork campaigns (Southern Ocean), learning key practical skills. They will use net samples to parameterize acoustic scattering models to describe key taxa, comparing modelled target strength frequency response curves with observed data to validate wideband species identification.

The NEXUSS CDT provides state-of-the-art, highly experiential training in the application and development of cutting-edge Smart and Autonomous Observing Systems for the environmental sciences, alongside comprehensive personal and professional development. There will be extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial / government / policy partners. They will be registered at SAMS, part of the University of the Highlands and Islands where they will be primarily based. However they will also be hosted at BAS and on occasion where necessary for training, St Andrews. At SAMS, the student will become part of a vibrant PhD community and supported and mentored by an experienced thesis panel. In this way the student will experience research and work life at both Universities and a government research centre. They will have access to a comprehensive suite of specific and generic training.