The bio-acoustic sub-facility collects underway active acoustic data while vessels are transiting ocean basins (Kloser et al., 2009). These bio-acoustic data provide an indicator of abundance, distribution and behaviour of mid-trophic level organisms (macro-zooplankton and micronekton communities ~2 to 20 cm length including small fish, crustaceans, squids and gelatinous organisms) needed for ecosystem-based fisheries management, marine planning and monitoring impacts of climate change and variability.

These mid-trophic level organisms are a key link between the primary producers and smaller zooplankton and higher predators in marine food webs. The largest portion of this fauna inhabits depths below 200 m with some of these organisms undertaking diel vertical migrations (DVM) to feed on near-surface zooplankton at night and returning to depth at dawns, thus actively transporting carbon from the surface waters to the deep-ocean and linking epipelagic and deep-water food chains.

Despite the enormous pelagic realm these organisms occupy and their pivotal role in the functioning of ecosystems linking biogeochemistry to the distribution and abundance of predators they remain one of the least known components of the ecosystem.

Coupled ocean-biogeochemical-population models have identified a gap in knowledge of this area (Lehodey et al., 2010; Smith et al., 2011). Ecosystem models need observations on the distribution and abundance of these micronekton mid-trophic functional groups at shelf and basin scale to validate predictions, but there are very few observations in southern hemisphere waters (Lehodey et al., 2014).

These sparse observations come from a variety of sampling devices of limited spatial and temporal extent making it difficult to compare biomass estimates or determine the value of the data as an ecological indicator. The bioacoustics program is improving this situation with 161,793 km of data collected and processed between 2010 and 2014.

The Bio-Acoustic sub-facility is part of several major international efforts to sample the world's oceans. CLimate Impacts on Oceanic TOp Predators (CLIOTOP) program  is a ten-year programme implemented under the international research programmes GLOBEC (2005 to 2009) and IMBER (2010 to 2014), two components of the International Geosphere-Biosphere Programme (Handegard et al., 2009).

CLIOTOP focuses on oceanic top predators within their ecosystems and is based on a worldwide comparative approach among regions, oceans and species. It requires a substantive international collaborative effort to identify, characterise, monitor and model the key processes involved in the dynamics of oceanic pelagic ecosystems in a context of both climate variability and change and intensive fishing of top predators (e.g. Lehodey et al. 2008 (Fig. 2).

The goal is to improve knowledge and to develop a reliable predictive capacity combining observation and modelling for single species and ecosystem dynamics at short, medium and long term scales. It is proposed that observational platforms equipped with multi-frequency acoustics will provide data for identification and quantification of marine life on a global scale, and reliably transfer data to the users. It is envisaged that this will be achieved through a combination of existing components and expertise (e.g. Argo buoys, vessels of opportunity, moorings, etc.) capable of large scale monitoring of mid-trophic level prey organisms, their horizontal and vertical size-resolved distribution and abundance in the pelagic environment.

Similarly other international groups are focused on this area of work are the ICES Working Group Fisheries Acoustic Science and Technology, which provides key advice on standard protocols for calibration and data processing through its working and study groups. Calibration of acoustic instruments and standard processing protocols have been developed in this area over a number of years and published as cooperative research reports.

This group meets annually to advance the science of bio-acoustics and further develop and check protocols. Likewise the CCAMLR sub group ASAM meets to discuss specific issues of bio-acoustic surveys in the Southern Oceans. The Southern Ocean Network of Acoustics (SONA) group has been formed to coordinate data collections in the southern hemisphere.

Instrumentation and Data

The Bio-acoustics subfacility involves the use of echosounders, at single and multiple frequencies, on research, large fishing and geophysical survey vessels to estimate mid-trophic level organism distribution and abundance around the Australian Exclusive Economic Zone (EEZ) shelf, slope and oceanic environments. The primary data-type recorded from the vessel-mounted echosounder systems is georeferenced calibrated water column volume backscatter, Sv [dB re 1 m-1].

A number of vessels are participating in the bio-acoustics program depending on location and availability (5-10). Some of the vessels are commercial fishing vessels that have agreed to record data during transits to and from fishing grounds, while others are scientific research vessels collecting underway acoustic data during transits and science operations. All vessels collect 38 kHz acoustic data from either Simrad EK60, ES60 or ES70 echosounders. In all cases the 38 kHz echosounders are connected to Simrad ES38B transducers.  The RV Aurora Australis and the now ceased RV Southern Surveyor collect concurrent acoustic data at 12, 120 and 200 kHz.

The new CSIRO Marine National Facility vessel RV Investigator is the latest vessel to join the program and collects data with Simrad EK60 split beam echosounders at 38, 70, 120, 200 and 333 KHz.

The bio-acoustics sub-facility delivers delayed mode data of calibrated acoustic volume backscatter at 38 kHz (as well as 12, 18, 120 and 200 kHz where available) at a spatial resolution of 10 m depth by 1 km long, down to a nominal depth of 1000 m. Processing of the data is described in Ryan et al. (2015).