CCAMLR

Larval fishes were obtained from 0-50 m bongo net and stratified 0-200 m Nansen net samples collected in the western Bransfield Strait region during four RACER program cruises, December, 1986, through March, 1987. Three nototheniid species, Nototheniops larseni, Notothenia gibberifrons, and Trematomus scotti, numerically dominated the total catch. Two typically abundant species in this area, Pleuragramma antarcticum and Notothenia kempi, were relatively uncommon. Depth related catch differences appear to be responsible for substantial shifts in species abundance relations between the two types of net hauls. Gear differences, the restricted geographical coverage, and between year variability in hydrographic conditions may explain species dominance differences between the RACER samples and prior surveys in the Antarctic Peninsula area.
Largest abundances occurred during January in the vicinity of Gerlache Strait and island shelf areas; larvae were infrequently collected in Drake Passage waters. Individual species demonstrated different distributional patterns suggesting that water mass influence, larval depth distribution, and behavioral differences may be involved.
Estimated January-March growth rates for Nototheniops larseni (0.06 mm day-1) and Trematomus scotti (0.05 mm day-1) are similar but low compared to that of Notothenia gibberifrons (0.12 mm day-1).

Field research activities conducted aboard the NOAA Ship Surveyor during the 1989 austral summer in waters adjacent to the Antarctic Peninsula and South Georgia are described. Operations included 1) ice seal studies in Gerlache Strait, 2) ichthyoplankton survey around South Georgia, 3) benthic survey for fish and invertebrates around South Georgia, 4) measurements of air and surface water C02 content, 5) detailed bathymetric mapping, 6) pelagic bird and marine mammal observations, 7) sampling for fish age and growth studies, 8) hydroacoustic survey for krill around Elephant and King George Islands, 9) net sampling for krill in association with the hydroacoustic survey, 10) sampling for larval krill and associated measurements of sea surface temperature and chlorophyll-a, 11) observations of bird densities associated with krill distribution, and 12) collection of cephlapod specimens.

The hydroacoustic survey found a high krill abundance in the Elephant Island area (a “superswarm" not unlike 1981) and a very low abundance in the King George Island area compared to last years survey. The total biomass in the vicinity of Elephant Island estimated from 200 kHz survey data was 940 k tons with only 34 k tons in the King George Island/Bransfield Strait. The survey results apply to 6,057 nm2 near Elephant Island and 5,454 nm2 in the Bransfield Strait. The “superswarm” was estimated to contain 975 k tons of krill and covered approximately 200 nm2.

The selection of a survey area of sufficient size to acount for the migratory behavior of krill and based on evaluating the variance structure of sampling within the area from a time-series of data from 1981, 1984 and 1978-1989 permitted resolution of inter-year differences in standing stock. The two units of sub-area within the site exhibit different patterns of annual distribution, but the combined total standing stock has a consistent variance to mean biomass relationship that appears relatively uniform from year to year. Using only sub-area biomass leads to an ambiguous interpretation of the data as to whether high or law standing stock is due to low production (ie. "good" year vs. “bad” year) or differential effects of migration. Using the total of both sub-areas the survey area can be shown to exhibit high standing stock (greater than 2 million tons) years, moderate standing stock (approximately 1 million tons) years, and low standing stock (less than 1/2 million ton) years. The size of the total area (200 m by 200 nm) can be adequately surveyed in 10 to 14 days and covers sufficient area to probably encompasses the migratory range of a single group of krill within the period of observation and with a predominant origin of individuals from the Weddell Sea. The size of the area and the approach taken to evaluate it may have broader utility in establishing similar survey areas at other localities in the Antarctic.

The distribution of krill (Euphausia superba) concentrations derived from Japanese krill fishing and minke whaling (Balaenoptera acutorostrata) data was investigated in relation to bottom topography, sea-ice and hydrographic features. Data were from the Indian, Pacific and western Atlantic sectors. In early summer (December) the areas of operation for both fisheries were affected by the latitudinal position and shape of the pack-ice edge. Harvesting was frequently conducted in the vicinity of a more southerly positioned pack-ice edge. Whaling was also undertaken in the embayments created by the pack-ice edge. When the ice-edge was at its southernmost limit (January- March), krill fishing data indicated that harvestable areas were associated with the continental and insular shelf breaks, not the pack-ice edge. Minke whaling data also suggested that not only sea-ice but also topographical features such as the continental shelf break and various banks may be important factors affecting minke whale distribution. Krill harvesting areas in the vicinity of the shelf breaks were often coincident with hydrographic fronts. These frontal features, by accompanying convergence or by coupling with krill specific behavior, were speculated to induce the formation of krill concentrations. The concentration of E. superba around a bank on the Ross Sea shelf is suggested on the basis of extreme high concentration of minke whales and their food composition