CCAMLR

The effectiveness of a split-beam echosounder system to delineate single scatterers and accurately measure in-situ target strengths (TS) is dramatically enhanced (98.2 -99.4%) by combining synchronized signals from two or more adjacent split-beam transducers of different frequencies. The accuracy of the method was determined through controlled test tank experiments using multiple standard spheres and 38 and 120 kHz split-beam transducers. Furthermore, by utilizing the angular position information from one of the split-beam transducers, additional corresponding TS measurements can be collected with juxtaposed single-beam transducers. Both methods were utilized to extract in-situ TS measurements of Antarctic scatterers simultaneously at 38, 120, and 200 kHz. Differences in the resulting TS measurements provided information about the identity of constituents in a mixed species assembly.

Catch Per Unit Effort data are presented from krill fishing operations in CCAMLR Subareas 48.1 , 48.2, 48.3 for the period 1975/76 to 1987/88. Comparisons are carried out between Subareas in single years, between years on a Subarea and Area basis, and between oceanic and shelf regions. Results show that the CPUE may differ between Subareas, years and shelf/oceanic regions. Obviously, a consistent pattern of CPUE values does not occur over time for the entire area. High average CPUE were observed in the years 1975/76 and 1980/81, wheras the lowest CPUE occurred in Subarea 48.3 in 1977/78. The validity of the CPUE index is discussed as an indicator for krill abundance/biomass and caution is expressed in this regard. Depending on the circumstances a CPUE index may seriously under- or overestimate the amount of krill available in a Statistical Subarea. Overall length frequency distributions from commercial fishing operations in general tend to show little interannual variation, because several factors influence the representativeness of krill smaller 35 mm in the catches.

A CCAMLR Ecosystem Monitoring Program (CEMP) was initiated at Bouvet0ya, South Atlantic Ocean, during an expedition to the island from 9 December 1996 to 22 February 1997. A research station was established at the CEMP site, Nyrøysa, on the western coast of the island. Species included in the monitoring program are the Chinstrap Penguin, Macaroni Penguin and Antarctic Fur Seal.
Preliminary results from the first season of CEMP monitoring (parameters A3, A4, A5, A6, A8, A9, C1 and C2) are reported together with results from other CEMP-re1ated work (entanglement of fur seals, and diving behaviour and population changes of penguins and fur seals). The population of Chinstrap Penguins at Nyrøysa has declined sharply since the last count in 1989/90. The population of Macaroni Penguins has shown a more moderate decline, whereas the population of Antarctic Fur Seals has grown dramatically since the last visit.

A CCAMLR Ecosystem Monitoring Program (CEMP) has been initiated by Norway at Bouvetøya, South Atlantic Ocean. A permanent research station was established at the CEMP site, Nyrøysa, on the western coast of the island during the 1996/97 field season. Species included in the monitoring program are the Chinstrap Penguin, Macaroni Penguin and Antarctic Fur Seal. During the first field season (1996/97), monitoring of the following parameters were initiated for the two species of penguins: Breeding population size (A3), Age-specific annual survival and recruitment (A4), Duration of foraging trips (A5), Breeding success (A6), Chick diet (A8) and Breeding chronology (A9). For the Antarctic Fur Seal, the program includes monitoring of Duration of cow foraging/attendance cycles (C1) and Pup growth (C2).

As an indicator of body fat condition, interannual variability in girth of minke whales (Balaenoptera acutorostrata) was analyzed in relation to sea-ice extent, stomach-content mass and distribution of minke whales in Antarctic Areas IV (70° -130° E) and V (130° E-170°W) from 1989/90 to 1994/95. Of the six years included in the study, two were categorized as years of poor body fat condition, and three as years of good condition. Estimated body weight gain during the feeding season in poor years was 25 % lower than in good years. The relationship between girth and stomach content mass in the ice-edge zone suggests that girth can be a useful indicator of food availability. In Areas IV and V, krill (Euphausia superba) was the dominant prey species, but in the southern part of the Ross Sea (in Area V), E. crystallorophias was the dominant prey species. Distribution of minke whales showed a greater interannual variability in Area V than in Area IV, reflecting a greater degree of variability in sea-ice extent in Area V. In Area V, in a year of high sea-ice extent, the krill-rich slope region in the western zone was covered by ice. This may have led to poor food availability and resulted in a very low density of minke whales along the ice-edger The Ross Sea zone was an area of low food supply throughout the study period. Paradoxically, this zone always contained numerous minke whales, especially pregnant females.

The consumption of Antarctic krill (Euphausia superba) by the southern minke whale (Balaenoptera acutorostrata) in Areas IV and V of the Antarctic was estimated from diurnal change in the forestomach content mass, standard metabolism and the body mass increase methods based on JARPA (the Japanese Whale Research Program Under Special Permit in the Antarctic) data. Estimates of the daily food consumption rate obtained from the three methods ranged from 3 to 4 %. Consumption estimates during austral summer in Areas IV and V were 14.7 - 17.8 x 105 t and 63.2 - 77.0 x 105 t, respectively. The values in Area IV were equivalent to roughly one - fourth of a total estimate biomass of krill in Area IV. Consumption in Area V by minke whales was an order of magnitude greater than the estimated consumption by adelie penguins and crabeater seals. These results indicate the importance of minke whales to the ecosystems in Areas IV and V during the austral summer.

During December 1996 the Elephant Island standard grid was surveyed for krill and salps. Krill and salps were present at almost all of the stations, other epipelagic zooplankton species were relatively scarce. Maximum krill density exceeded 7350 juvenile krill per 1000 m3. In general krill density was much higher than in previous years. The krill stock was dominated by length classes around 35 mm, representing age group 2+ and the year-class 1994/95 (proportional recruitment R2 = 0.85). The year-class 1995/96, the present juvenile age group 1 +, does not repeat the very successful recruitment of the preceeding year-class. In December 1996 adult krill was mostly (68 %) found to be in the prespawning stage, indicating an average year for krill reprodution in this area, which is not the optimum starting point for a good recruitment of this year-class. At the same time the salp abundance was above average, but still one order of magnitude lower than in the salp bloom years 1992/93 and 1993/94.