IMIS

The Aurora Australis Voyage 7 had five objectives:

• to define the distribution patterns and abundance of krill in the krill dominated continental shelf area of the Prydz Bay region;
• to define the krill population structure within this area and the distribution pattern of developmental stages, especially spawning females;
• to define the distribution patterns and composition of the other two principal communities, neritic and oceanic, which border the krill dominated community;
• to specifically determine the zooplankton composition within the main feeding area of Adélie Penguins from Béchervaise Island monitoring site, Mawson;
• to record and analyse various physical and biological processes, eg. Salinity, temperature, ice and phytoplankton, to determine how these parameters affect the observed distribution patterns.

Surveys of krill and other zooplankton were taken in Prydz Bay, Antarctica between January and February 1993. At each station, rectangular midwater trawls and CTDs/bottle casts were made. During the program, echosounders and echointegrators were operating to provide krill abundance and distribution data, in addition to that from the RMT trawls. Initial analysis has shown that Euphausia crystallorophias dominates the neritic community on the shelf, while Euphausia superba was found not to occur in high abundance in the central Prydz Bay area between 70 and 78 degrees East. This dataset is a subset of the full cruise. Only four of the scheduled sites were not sampled due to heavy pack ice cover (9-10/10), in the areas of Four Ladies Bank and Cape Darnley. Sections of the study areas were previously sampled for zooplankton in 1990/91, and hydroacoustic data were also previously sampled in 1990/91 and 1991/92. A minimum of 88 stations were planned, approximately 30 nautical miles apart in latitude and longitude. Sites between 67 and 78 degrees East were also sampled during 1990/91. The 0-200m water layer was routinely sampled at each station by a downward oblique haul using a rectangular midwater trawl (RMT) 1+8 net. CTD or bottle casts were made to 200m normally, to sample phytoplankton and record physical oceanographic profiles. Hydroacoustic data were obtained using echosounders and echointegrators operating at 38kHz, 120kHz and 200kHz. Hydroacoustic data were also collected during 1990/91 and 1991/92. CTD data and zooplankton data were collected at each station to maintain consistency.