CCAMLR

A method is described for calculating indices of sea ice distribution from digital data distributed by the National Snow and Ice Data Centre, Colorado, USA. Data consist of an image of the Antarctic, made up of 312x332 pixels, each having a dimension of 25x25km, for every day in the year. Primary data of the distance of sea ice from CEMP sites, the northerly position of the sea ice edge, and the percentage ice cover in subareas, are entered into the CCAMLR database. Indices of ice cover are calculated from these primary data. The techniques used are validated against alternative known data.

The potential of multi-frequency acoustic technology for quantifying fish and plankton is widely recognized. At a U.S. GLOBEC workshop in 1991, one of the considered problems was measuring macrozooplankton and micronekton. It was concluded that in order to survey animals in the size range 0.5-5 cm, it would be expedient to use at least three and perhaps as many as 8-10 frequencies in the range 38-420 kHz. Here, a specific design is evaluated: ten more or less standard, approximately logarithmically spaced frequencies are chosen. Each frequency represents the resonant condition of a circular piston transducer with 10-deg beamwidth. The performance of this system is assessed through the maximum detection range of single targets, assuming transmission near the cavitation limit but consistent with dynamic strength and heat generation in ceramic elements, isotropic ambient noise, and detection threshold of 20 dB. Target strength is treated as a parameter, with investigated values from -130 to -50 dB. Performance assessment for a volumetric distribution of scatterers is similarly treated.

Design of sondes for in situ measurement of zooplankton or other scatterers requires choosing among alternative transducer geometries. This contribution addresses the problem of choosing between cylindrical and circular piston transducers by comparing the performance of the two according to the principle that the acoustically active areas be equal. Computations are performed with the actual dimensions of six fabricated cylindrical transducers, whose beam patterns have been measured by the manufacturer at a total of 11 frequencies spanning the range 27-710 kHz. Nominal power levels assigned to the cylindrical transducers are also used for both transducer types. Comparison of theoretically computed beam patterns with measurement gives confidence in the radiation model, which is used to compute the directivity index and on-axis sensitivity loss due to curvature of the cylindrical transducers, referred to as the curvature loss. Under identical conditions of excitation, isotropic ambient noise, and detection threshold of 20 dB, the active sonar equation is exercised to estimate the maximum detection range of both single targets and multiple targets distributed throughout the sampling volume. In every single case, the performance of the equal-area circular piston is superior to that of the corresponding cylindrical transducer. This is directly attributable to differences in directivity index and curvature loss. Other, pragmatic considerations argue for the choice of the circular piston transducer over the cylindrical transducer. Three problems requiring future treatment are identified.

On the ground of materials collected by biologists-observers from October 1989 to June 1990 near the South Orkney Islands the growth of males and females are characterized according to size groups, distinguished using the probability paper. Seven size groups both for males and females were distiguished. The growth period for the males continued from October to April, and from October to February for the females. The increment for this period was the same for both sexes and had about 8–9 mm in length. The males’ one day increments were 0.046–0.076, and for the females – 0.065–0.074 mm. It is supposed that krill don’t reach the age of 5 years.

Experiments on estimation of krill transport by a current and its distribution characteristics variability were carried out within a local ground of Subarea 48.3 in the fleet operation area. It is shown that krill transport by wat4er flow across the fishing ground results in variation of fished krill aggregations distribution, and thus, in unstable indices of fishing vessels activity. During the the period of observations (29.05.91–03.06.19) at variable krill distribution characteristics due to outside transport of different krill population modifications across the investigation area, the variation coefficient of catch per a houl of BMRT type vessel amount to V = 0.7, that of a trawl catchability V = 0.197, the variation coefficient of krill biomass within the fishing ground V = 0.6, and a variation coefficient of possible catch per fishing day ( over 24 hours ) is only V = 0.13. At considerable variations of krill distribution characteristics daily catch of vessels with higly efficient technological equipment appears slightly sensitive to the fishery conditions variations. The other index of a vessel operation, such as catch per an hour haul , is more sensitive.