CCAMLR

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

Aim of this document is to supply a short information of chlorophyll distribution patterns around the South Shetland Islands in the Antarctic survey of R/V the Kaiyo Maru from 13 December 1990 to 11 January 1991 (Leg I) and from 16 January to 11 February 1991 (Leg II). In the north of Livingston Island, high chlorophyll a concentration and low POC/chlorophyll a ratio in Leg II and low chlorophyll a concentration in Leg I suggest that phytoplankton bloom occurred in this area for about one month.

This document submits the basic information on the hydrographic flux in Statistical Area 58. Those are surface geostrophic flow in the whole of Statistical Area 58, and vertical distributions of geostrophic flow along 37° E, 75° E,114° E and 155° E.

A theoretical prolate spheroid liquid model is applied to predict the target strength (TS) of krill. Scattering patterns are shown to demonstrate orientation dependence of krill TS. Length-to- wavelength ratio (L/λ) dependencies of reduced (normalized by body length squared) target strength are shown for some orientation distributions. The results can explain well-organized experimental results. The variability of the TS of krill is large where L/λ is larger than unity. Therefore, a frequency around 70 kHz is superior to 120 kHz which are ordinarily used for krill surveys.

Data from the Eduardo L Holmberg FIBEX survey have been re-examined for incorporation into the BIOMASS Database in the approved standardised format. The results indicate the krill were concentrated to the western end of the South Orkney Islands. Density values are consistent with those from other FIBEX surveys.

A numerical model is being developed for assessment of Euphausia superba in Antarctic Ocean, which consists of:
(1)calculation of three dimensional current field using CCSR version (developed by Dr. Yamanaka of Center of Climate System Research, University of Tokyo) of the three dimensional primitive equation for the ocean circulation developed originally at the GFDL, Princeton, NJ,
(2)calculation of spatial distribution of DIN (Dissolved Inorganic Nitrogen)
(3)calculation of spatial distribution of DON (Dissolved Organic Nitrogen),
(4)calculation of spatial distribution of Chl.a and
(5)calculation of spatial distributiion of Euphausia superba.
Our model will be capable of calculating the detailed spatial distribution of Euphausia superba by dividing the Antarctic Ocean into many grid points. It also takes into consideration the effects of fisheris.

Biogenic silica (BSi), lithogenic silica (LSi), particulate organic carbon (POC) and nitrogen (PON), and chlorophyll a (Chl a) were measured in the surface waters (