CCAMLR

This paper describes the usefulness of satellite ocean color remote sensing in the Antarctic Ocean by making a comparison between CZCS chlorophyll images and ship-measured chlorophyll concentrations in the sea area off Enderby Land, Antarctica. In addition, some characteristics of the chlorophyll distribution in the Antarctic Ocean are briefly explained by means of the three-month(January-March) composite images.

The main aims of CCAMLR are reviewed in an essay which discusses the advances in the effectiveness of harvesting, arising from developments in science and technology in comparison with the requirements of science to provide information for rational management. It is concluded that co-operation is essential between fishermen and scientists to ensure the provision of the data needed to test hypotheses related to the functioning of the Southern Ocean ecosystem. Although currently co-operation is fairly good it would be improved by an increased spirit of trust between the various parties.

Data from the FIBEX acoustic survey in the West Atlantic sector have been re-examined to check the consistency of krill abundance estimates derived from different survey vessels. There is a good level of consistency between the results from four of the vessels, Itzumi, Dr Eduardo L Holmberg, Odysee and Walther Herwig. While there is an error factor due to the combination of data collected at 50kHz (Walther Herwig survey) with data collected at 120 kHz (all other vessels), it is concluded that this does not materially affect on the estimated biomass.
The data from the Profesor Siedlecki survey do not provide estimates that are consistent with the other surveys. The authors can find no explanation for this difference.

Foregut contents of the Antarctic krill Euphausia superba Dana which were collected in the South Georgia area in austral winter, 12 July ~ 4 August 1992 were observed. A total of 130 individuals (adults: 78, subadults: 49, juveniles: 3) which were caught by krill trawling from various depths were examined in this study. The foregut contents of the krill consisted of various fragments of crustacean zooplankton in 77 individuals out of 130 examined. Among the fragments a portion of the pereiopods of krill was found from all specimens examined. Although the obtained materials were geographically confined to the South Georgian waters, which was free from fast ice throughout the year, the results might imply that E. superba seemed to seasonally switch their food source: E. superba demonstrated herbivorous food habits during the rich phytoplankton bloom, but might change to carnivorous habits in the fall and winter. Strong cannibalistic food habits during austral winter as found in this study are considered to be important aspects for the population dynamics of krill.

The implications between a regional and whole distribution of the Antarctic krill, Euphausia superba DANA, and its environmental gradients in the summer season were considered. In order to find out the relationship between the geographical distribution of E. superba and its oceanographical gradients, an environmental index was introduced. The environmental index was the integrated value of water temperature from the surface to 200m in depth Z. As the results, the area of the high concentration of E. superba coincided with the area of low values of Q 200 chiefly falling in the range from 0°C to –1.5°C where showed the thick Winter Water, especially the area of the Slope Water and the Shelf Water south of the Antarctic Divergence zone.

Annual primary production of ice algae and phytoplankton under fast ice near Syowa Station (69°00'S, 39°35'E), Antarctica, was estimated. Mean daily production in each month from February 1983 to January 1984 was calculated with a mathematical model based on measured parameters of solar radiation, day length, attenuation coefficients of snow, ice and water, chlorophyll a standing stock, quantum yield for photosynthesis etc. Solar radiation measured at Syowa Station ranged from 0 E m-2 h-1 in June to 13.3 E m-2 h-1 in December. Relative light intensity estimated at the bottom of sea ice during the year ranged from 0 to 6.5% of incident solar radiation, due to attenuation with snow and ice. Maximum daily production of ice algae (34 mgC m-2 day-1) and phytoplankton (450 mgC m-2 day-1) was reached in December and in February, respectively. The estimated annual production of ice algae and phytoplankton was 3.5 and 17 gC m-2, respectively. These results indicate that summer phytoplankton production contributed remarkably to the primary production in the coastal ice-covered area near Syowa Station.

Relationship between food environment and maturity of krill around the South Shetland Islands is discussed. Data during 91/92 austral summer shows that when chlorophyll concentration in fraction larger than 2um was high, feeding activity of krill was also high in the natural environment. 5 years data from commercial krill trawlers indicates that percentages of occurrence of gravid female was high when the feeding activity of the krill was high through out the season.
Therefore, interannual fluctuations of maturity populations are governed by the food environment, the phytoplankton stock in the size fraction larger 1 in krill namely by than 2um.

During 1979 to 1991, relationship between the size of Antarctic krill and the extent of the sea ice in the sea area around the South Shetland Islands are described. Mean size of krill near the coastal zone appeared to be small in summer season just after a strong ice extent had occurred. This implies that strong recruitment of small size krill had occurred just after the season with the strong ice extent. Interannual fluctuations of the ice extent are known to relate with the strength of the Antarctic circumpolar trough. Therefore, it could be suggested climate and ecology of krill populations are closely related.

This paper summaries Japanese krill catch data during austral summer in 1991/92 season. A main fishing ground was persistently formed north of the Livingston island. CPUEs show the highest values at the height of summer (late January - late March). Krill with modal lengths of 41-45 mm were dominant in catches, ca. 5mm smaller than those for the previous season.

Acoustic methods appear to be the best way to estimate Antarctic krill abundance directly. Information on body orientation, however, is needed to obtain reliable krill acoustic target strength (TS) values, since TS varies with body orientation. Krill body orientation was measured in an aquarium aboard the R. V. Kaiyo Maru. Average body orientation was 45.6° (SD = 19.6°, N= 67), which was slightly less than that when animals were hovering, 49.7° (SD=7.5°, N=50). Such an acute angle of elevation would tend to reduce the reflected echo intensity when compared to animals swimming horizontally.
Although mature females with marked swelling of the cephalothorax were not included in the experiment, the center of mass was found to be situated more to the anterior than in males and immature females. The hovering orientation, which is close to average body orientation, of mature males and mature females was estimated on the basis of Kils’ model. Mature females with swollen cephalothorax demonstrated larger tilt angles relative to the horizontal plane than did males, as the center of mass is positioned more to the anterior and the pleopods are less developed in females. It is concluded that the orientation, and therefore TS, may differ according to the maturity stage composition of individual aggregations