CCAMLR

To estimate the abundance and distribution of Antarctic krill (Euphausia superba) in the vicinity of South Shetland Islands (SSI), a hydroacoustic/oceanographic survey was conducted by the R/V Onnuri from 9 to 19 January 2000. The acoustic data were obtained using a Simrad EK500 echosounder operating at 38, 120, and 200 kHz, from 8 transects comprising the South Shetland Islands (SSI) mesoscale box (total transect length = 459 nautical miles, area = 11,313 n mile2). Krill were collected with a Bongo net (mesh size: 0.333 mm, 0.505 mm) to determine their size composition and stage of development. In addition, Conductivity, Temperature and Depth (CTD) and on-station Acoustic Doppler Current Profiler (ADCP) were deployed to understand the physical structure of the water column at 11 stations.
The hydrography was differentiable between the offshore region and coastal area. Offshore stations showed the presence of ‘Winter Water’ in mid layer and Circumpolar Deep Water at greater depths. Offshore water and coastal water were also seen to the north and south of Elephant Island, respectively. ADCP results indicate the water flowing from the Bransfield Strait out to the offshore region around the east of King George Island.
The length-weight relationship of krill sampled during the survey was w = 0.0035*(L)3.2108 where w was the mass (mg) and L was the total length (mm) ; the median length was 50 mm. The conversion factor for integrated backscattering area to areal krill biomass density at 120 kHz was 0.1556. The mean density of krill near the SSI area was 12 g/m2 with a coefficient of variance (CV) of 14.5%. The mean density and CV in the Bransfield strait was 9 g/m2 and 20.3 %. Krill swarms of relatively high densities occurred to the north of Smith Island, north and east of King George Island and north and south of Elephant Island.

Research on water structure and dynamics, krill biomass assessment, biology and distribution were carried out in two standard boxes on the shelf and slope northwest and northeast of South Georgia. Eight hydroacoustic transects with hydrographic stations and RMT8+1 trawls were carried out in each box. Krill were distributed rather evenly throughout both boxes, but no dense concentrations were apparent. In the western box krill density was nearly 0.2 glm3 and in the eastern box was 1.8 - 4.7 glm3 • Juvenile krill of 30-36 mm length were observed in the shelf zone and larger specimens, including spawning and posts pawning females of 50 mm and larger, were distributed in slope zone and deep oceanic waters. According to these preliminary results, krill abundance on the South Georgia shelf in January 2000 was lower then usual and no concentrations suitable for commercial fishing were observed. Temperature and salinity measurements carried out on the standard hydrographic stations revealed oceanographic conditions were similar to the long term mean values. However on this survey we did not observe any of the usual gyres or eddies which lead to the formation and maintenance of krill concentrations.

The paper covers the-results of an acoustic estimation of distribution for krill and non-krill zooplankton within the area of South Sandwich Islands that has been obtained with multy-frequencies algorithms according to the data on survey by Russian vessel ATLANTIDA under CCAMLR Survey-2000. Distribution of acoustic characteristics for krill and non-krill fractions of antarctic zooplankton has been compared. It has been showed that within the field locations occupied by waters of the Weddell Sea and Frontal Zone of Weddell Gyral the bulk of zooplankton had been made of krill, while non-krill fraction dominated in water masses of the Antarctic Circumpolar Current.

Quickly studied and quantified were sources of uncertainty in the CCAMLR 2000 acoustical estimate of krill abundance in FAO statistical area 48. The variance in system calibration was evaluated in relation to the effects of variant water temperature and salinity on sound speed, sound absorption, and beam characteristics. Uncertainty in krill target strength (TS) was estimated using a distorted wave born approximation model of krill TS, fitted with measured distributions of animal lengths and orientations. The uncertainty in species delineation was also investigated through the same scattering model. The combined measurement and sampling variance was estimated from a simulation which assumed the three frequency measurements provided independent estimates of the krill biomass. The overall variance (1 1.33%) was little different from the sampling variance (1 1.38%). That is, the measurement variance may be negligible relative to the sampling variance due to the large number of measurements averaged to derive the ultimate biomass estimate. Some potential sources of bias were also explored. The latter (ie. stemming from uncertainties in target strength, species delineation, bubble attenuation, thresholding, area definition, etc.), may be more appreciable components of measurement uncertainty. Further studies are warranted.

Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is it’s aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella, the Australian sea lion, Neophoca cinerea, and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.5 times longer than the cADL, while New Zealand sea lions on average dove 1.4 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL (P

Spawning by Antarctic fish is generally considered to be seasonal and restricted to a brief period during the autumn and winter. Arising from this it has been assumed that the gonadal maturation cycle is also closely tracked to the time of year. The gonad maturation cycle of the mackerel icefish, Champsocephalus gunnari, was investigated using data collected during research surveys and from sampling the commercial fishery. Spawning appears to occur at the same time each year, but the timing of gonadal development is subject to a considerable inter-annual variation. The implications of this variation are discussed with respect to feeding conditions.

Mackerel icefish are widespread on the South Georgia shelf, Antarctica and have been subject to commercial fishing since the early 1970s. They are known to feed predominantly on krill. An index of condition which uses the ratio of the measured total mass to the estimated mass is show to provide a good indicator of local krill density. The index is likely to be little affected by the reproductive cycle unless there is high krill availability during the months around the spawning time and even then the effect is much less than the highest observed values The condition index responds rapidly to changes in hill density and therefore can provide indications of short term variations in krill availability. Condition index provides a useful proxy for krill density that is likely to be of considerable value in interpreting the results from ecosystem assessments such as that in progress under the auspices of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).