CCAMLR

Feeding behavior of Antarctic krill (Euphausia superba) on salps was observed through onboard experiments during 1994/95 Kaiyo Maru Antarctic Ocean research cruise. Feeding rate was more than 1 salp/krill/day. Among 4 items of ethanol extracts; salps, phytoplankton, krill, and polychaets, krill preferred salps best. This evidence implies that the substances extracted from salps were most attractive to krill. The result of our experiment might indicate a tight ecological relationship between krill and salps. Since salps have ability to ingest wide size range of particles, there might also be a possibility of link between microbial loop and krill through salps.

Observations on abundance of by-catch fishes were made during the austral summer months of 1995 (from 30 January to 18 February) on board F/V Niitaka Maru to the north of the South Shetland Islands. Among 78 hauls examined, a total of 97 specimens of fishes belonging to five species, Electrona antarctica, Electrona carlsbergi, Protomyctophum tenisoni, Krefftichthys anderssoni and Notolepis coatsi, were found in 20 trawl catches. Juvenile or adult notothenioid fishes were never found in a random sample of 50 kg of krill. Number of by-catch fishes ranged from 0 to 50 per 100 kg of krill catch and total wet weight of by-catch fishes also ranged from 0 to 248.2 g per 100 kg of krill catch. Abundance of by-catch fishes was higher in krill hauls with the low catch rates.

Distribution and biomass of salps and Antarctic krill (Euphausia superba) were investigated near the South Shetland Islands during austral summer 1990-1991. Salp biomass ranged between 0 and 556 mgC•m-3 and was greatest at a station in the Bransfield Strait in late December 1990. Salp biomass was lower than that of E. superba. Two species of salps; Salpa thompsoni and Ihlea racovitzai were found, and the former was dominant numerically. Spatial distribution and generation composition of these two species was different. Spatial distributions of salps and E. superba did not overlap particularly so the January-February period. While E. superba was found mainly in the coastal area which showed high-chlorophyll a values, salps exhibited high biomass in the oceanic area with low chlorophyll a concentrations. Predation by salps on small krill and the competitive removal of food by them, are discussed as potential reasons for the relatively low abundance of E. superba at the stations where salps were present in great numbers.

This paper demonstrated the relationship between sea-level air pressure gradients in Drake Passage and krill recruitment variabiIlty. Years of high pressure gradients coincided with the years of good krill recruitment, and vice versa.

On the processes to investigate a proper model for understanding the processes that govern the biochemical cycle in Antarctic Ocean, we made a research plan as follows: (1) to develop an OGCM (Ocean General Circulation Model) (2) to develop a one dimensional ecosystem model that can be applied to primary production in Antarctic Ocean (3) to develop an ecosystem model able to describe krill ecology (4) to develop a numerical model to couple the OGCM and ecosystem models (5) to develop a numerical model including the effect of marine mammal consumption and catch of krill (6) to develop the integrated model with the above 5 items.
This year, we have developed a three dimensional regional model off King George Island and Livingstone Island to connect the OGCM developed by CCSR (Center for Climate System Research, University of Tokyo).

This paper summarizes Japanese krill catch data during austral summer in 1993/94 season. Main fishing grounds were persistently formed in the north of Livingston Island throughout the season, and the west of Elephant Island from April to May. CPUEs showed the highest values at the height of summer (early February - early March) in the north of Livingston Island, and April at the west of Elephant Island. Krill with a modal length of 41-45mm were dominant in catches, almost same as the previous season.

The seventh Antarctic research cruise by the R/V Kaiyo Maru of the Japanese Fisheries Agency was conducted in the southwest of the Scotia Sea, especially in the vicinity of the South Shetland Islands from December 1994 to February 1995. The main objective of the seventh research was an oceanographic and ecological survey in relation to the distribution and abundance of the Antarctic krill (Euphausia superba). This document introduces an outline of the contents enforced by the research. Detailed analytical studies are currently in progress.

Water flows in harvestable areas for Antarctic krill (Euphausia superba) on the continental slope and shelf of the South Shetland Islands were examined based on drifting buoy data. Convergent complex eddies were observed in harvestable areas on the shelf, while shear current was observed in those on the slope. Large-scale movements of the buoys suggest krill flux from the South Shetlands into South Georgia or the South Orkneys.