Acoustic Monitoring

Acoustic surveys have been conducted at various scales since the 1980s. CCAMLR Members conduct acoustic surveys to estimate krill biomass. In an acoustic survey an acoustic transponder, usually located underneath a ship, sends a sound signal downwards into the water column, and when it encounters organisms a reflected signal is detected by receivers on the ship. The strength of the reflection can be analysed to determine the quantity of krill beneath the ship. 

There have been many localised acoustic surveys and four large scale coordinated international acoustic surveys since 1979. 

During the First International Biomass Experiment in 1979/1980 (FIBEX), 11 ships undertook coordinated acoustic surveys to map the large-scale distribution of Antarctic krill in the Atlantic and Indian Ocean sectors of the Southern Ocean. The Second International BIOMASS Experiment (SIBEX), during 1985 and 1986, investigated temporal changes in krill distribution and abundance focusing on the Antarctic Peninsula region. 

The CCAMLR 2000 Survey was the first large-scale, multinational, multi-ship survey using standardised protocols. It was conducted over a 32-day period, providing a comprehensive snapshot of the oceanography, zooplankton, krill, and higher predator biomass and distribution for the Scotia Sea and Antarctic Peninsula region at that time. The innovative transect design sampled only during the hours of daylight provided a comprehensive and robust estimate of 60 million tonnes of krill biomass in Statistical Area 48 (the ‘Atlantic sector’), where most krill fishing occurs.

In 2019 another large scale survey was organised. The 2019 Area 48 Krill Survey undertook approximately 13,600 kilometres of transects in the Atlantic sector in the same area as the  earlier 2000 survey. The krill standing stock for the Area 48 was estimated to be 62.6 million tonnes. The highest mean krill densities were found in the South Orkney Islands stratum (93.2 g.m-2 above the water column) and the lowest in the South Georgia Island stratum (6.4 g.m-2).

The collection and analysis of acoustic data is now routine and includes inputs from both scientific and commercial vessels in Antarctic waters, and from the more frequent small scale surveys as well as less frequent large scale surveys. In 2015, an instruction manual for the collection of acoustic data from fishing vessels was developed and the data collected by fishing vessels along defined CCAMLR transects are maintained by the CCAMLR Secretariat. The use of fishing vessels to undertake regular acoustic surveys within management strata will support more accurate and frequent biomass estimates to inform CCAMLR’s revised krill fishery management approach in Subareas 48.1 to 48.4.