AERD Acoustics

AERD Acousitcs

Non-invasive ecosystem monitoring

krillAntarctic krill (Euphausia superba, Dana) are among the most abundant animal in the Antarctic. However, in a habitat roughly the size of England, finding them can be difficult. These important and sometimes elusive animals are the primary prey item for all of the major predators in the Southern Ocean – including humans.

The Antarctic Ecosystem Research Division (AERD) has used acoustic monitoring of the productive waters around the South Shetland Islands to find and count these elusive animals since 1992, both on their daily migrations up and down through the water column and on their long-term migrations that follow the regional currents.

By tracking krill, the AERD is able to determine their relative annual abundance, dispersion, and population density. Combined with biological and physical oceanographic data, these acoustically-determined krill population patterns allow US scientists to understand how krill interact with their environment, and will help determine which environmental changes might impact their population size.

Krill NASC values 2007-2008Each year the AERD surveys the waters surrounding the South Shetland Islands, covering more than 120,000 km2 between January and March. During that time, acoustic data is collected by AERD biologist Anthony Cossio, using a series of four high-tech fish finders operating at different frequencies. These acoustic instruments send and receive signals through the water column every two seconds. When a signal bounces off an animal in the water column that signal is counted. Using the different frequencies AERD biologists can determine which signals are from krill and which signals are from other animals in the water column below the ship.

These acoustic data, processed under the supervision of Dr. Christian Reiss, reveal the secrets of krill location and their numbers – information that allows U.S. and international scientists, all part of an International Fishing Treaty, to make informed decisions about the best ways to sustainably use this precious resource.CCAMLR meeting

Completed on an annual basis, these surveys have become a critical element of the krill management decision-making process. Because these surveys have been completed annually for almost 20 years, AERD scientists are also able draw comparisons to annual changes in environmental conditions on a long-term scale. With the significant changes in the Antarctic environment occurring owing to global climate change, AERD data are a critical component of NOAAs Climate Change Program. The international community that utilizes Antarctic resources has come to rely heavily on the information provided by these acoustic surveys to monitor the effects of the krill fishery on this economically vital population, and to link these effects to changes in land-based predator populations like seals, penguins, and great whales.

For technical information, please contact Dr. Christian Reiss or the AERD at the Southwest Fisheries Science Center, La Jolla, CA.