Nella Dan: FIBEX Cruise - Hydroacoustic krill survey data

Full description

This dataset contains hydroacoustic results from the First International Biomass Experiment (FIBEX) cruise of the Nella Dan. This cruise is the first in a series of six cruises, performing a long term survey of krill and other zooplankton distribution and abundance. FIBEX was an international project, done in co-operation with Japan, South Africa and France. Fourteen transects were made by Australia off Antarctica in the Australian sector (Mawson to Davis region) and Prydz Bay in January to March 1981, covering a survey area of 1.09x10^6 square kilometers. Quantitative and geographic krill distribution, abundance, mean and variance of the krill weight density, and total krill biomass were obtained. The standing stock of krill for the Prydz Bay region was calculated at the second workshop to be approximately 1.3 million tonnes, or 1.6 million tonnes if extrapolated over the survey area of the SIBEX II cruise. Temperature, nutrient and salinty data were also obtained, as well as trawl results. Summary results are listed in the documentation.

A scanned copy of the acoustics log book from the voyage is available for download from the provided URL.

Lineage

Progress Code: completed

Statement: This voyage is one of six which are studying the abundance and disribution of Euphausia superba and other zooplankton. This provides a good coverage of the area at varying season times and conditions. Ship-board instrumentation: A Simrad echosounding system was used, comprising of an EK-38 echosounder operating at 38 kHz, and EK-120 echosounder operating at 120 kHz, a QD echointegrator and grey scale chart recorders. The EK-38 was only used intermittently. The echosounder transducers were hull mounted approximately 6m below the surface. The towed transducer system was deployed at a nominal depth of 30m. Data collection: Fourteen transects were made, eleven in an east-west direction, parallel to the mean direction of the prevailing ocean currents and to the continental shelf, and three in a north-south direction. The 120kHz echosounder was run continuously while MV Nella Dan was in the study area. The QD integrator was set to integrate 8 depth layers between 1m and 200m below the transducer. The effective integration range was 7-206m. The echointegrator output, including the mean volume backscatter strength for each of the eight layers, was recorded on paper tape at the end of each 1 nautical mile integration interval. The mean target strength of krill were calculated from the lengths of the individual krill. Post-cruise processing: Acoustic data were processed on a VAX 11/750 computer. Mean density and variance of the mean were estimated using the ratio estimator, a process adopted at the second post-FIBEX acoustic workshop. Biomass was estimated for an area defined by a box drawn around the transects and extended on two sides by half the mean spacing between the transects. Mean krill biomass, variance of the biomass, and 95% confidence limits about the mean were calculated from the estimated mean and variance of the krill surface density. Please see the documentation reference for further details, and theoretical information. Data are logically consistent, as oceanographic data (CTD measurements) and water collections for phytoplankton pigment analysis were also obtained at the same sampling sites as the krill and zooplankton hauls and acoustic surveys. East-west transects were used for eleven of the fourteen transects on this cruise. It was decided that north-south transects were more effective, and these were used for the two following voyages. Cruise track was determined systematically before the commencement of the cruise, to eliminate any bias.