WG-KRILL-91

Estimation of krill target strength was made by ensonification of encaged live krill and using trawling-acoustic method . Ensonification of encaged live krill. For aggregations with mean lengths in the range (45,50) mm the mean single-krill target strengths are in the range (-68, -69) dB at 136 kHz. For aggregations with mean lengths in the range (43,47)mm the mean single-krill target Read More
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In-situ measurements of individual krill target strength are presented (modal value = -69db). Net samples obtained immediately before the experiment indicate that the animals were reproductively mature and averaged 47.44mm in length. Results agree well with recent predictions of acoustic target strength based on extrapolations of other field experiments using the bent cylinder model of sound Read More
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Since krill distributional data do show evidence of spatial correlation, estimators of abundance which attempt to model such effects (such as those based on Kriging) may provide improved abundance estimates from survey data. However, computer simulation studies are first required to test whether such estimators, and alternative possible survey designs, are indeed likely to provide improved Read More
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An observed distribution of Meganyctiphanes norvegica aggregations is used to examine the effects of krill swarm orientation and shape on the success of two proposed survey designs. The simulation involves a number of random paths of parallel or radially arranged transects passing through three distributions each of which is given 4 rotations. The results indicate that the coefficient of Read More
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Four Polish commercial trawlers participated in the krill fishery in 1990/91 season on the fishing grounds in statistical Sub-areas 48.2 and 48.3. In total 9 333.7 tonnes of krill were harvested. As the fishery data were not fully analysed yet no clear trends in catch-per-unit-effort for different fishing grounds during the season could be detected.

Method of estimation of krill drift velocity in water current,using repeated acoustic transects on rectangular polygon is discribed.Dimensions of polygon and frequency of acoustic observations have to be determined with taking into account distribution patterns of krill,its patchiness, between-swarm distance (BSD) and between-clusters distance (BCD).For ocean current velocity- 20 sm/sec,ship Read More
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Clarification of main tendencies of spatial changeability of size composition of E.superba was undertaken by means of comparision of various size groups of curstacean distribution in the region of the South Orkney islands and adjacent waters. Materials of 14 separte expeditions were used (Table 1), which cover 20-years period (from 1965 to 1985). Data on size composition of E.superba for each Read More
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To delineate zooplankton distribution and abundance in Bransfield Strait, in relation to hydrographic condition, a total of 29 sampling stations was occupied for the CTD casts and plankton towings in a systematic grid from December 29, 1989 to January 7, 1990. Comparisons of temperature and salinity distributions and T-S diagrams suggest that the cold and saline Weddell Sea water entered from Read More
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The theoretical basis underlying estimation of krill abundance using echo-integration and aggregation information are briefly described. The chief differences of the two approaches are highlighted. It is concluded that the echo-integration approach is superior for the estimation of regional krill abundance and its variance since it is easier to apply, requires less data analysis and does not Read More
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Midwater trawl catchability is variable depending both on fishing object behaviour and distributional pattern end trawl parameters. Data on trawl catchability distribution parameters and krill distributional pattern in the surveyed area enable to increase reliability of the biomass estimates.
Comparative analysis for catchability of fishery midwater trawls and small research trawls, when Read More
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Krill swarms were recorded acoustically along a 2340 Nm of the ice edge between Elephant Island and South Orkney Islands. Depth distributions and migration pattern were different for the three distinguished regions. It has been sugested that physical factors are the most important in both :horizontal and vertical krill distributions.

Physical characteristics of 437 krill aggregations detected acoustically in the area o£ S.0rkney are discribed.All swarm parameters were registered and processed automatically.The aggregations thickness and length (2.5 m and 10.4 m)were considerably smaller, then those published by. other authers. The aggregations were on average 2.2 km apart. It is shown that aggregation parameters depend in Read More
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The waters in the vicinity of the South Shetland Islands and Elephant Island were surveyed to investigate mechanisms for the formation of krill concentrations and to estimate acoustic biomass of krill in the 1990/91 austral summer. Main krill concentrations occurred in the shelf waters north of the islands, as usual. Tracks of drifting buoys (with curtain drogues at 30 m depth where krill Read More
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A net sampling survey for krill was carried out by RV ‘Meteor’ along the Antarctic Peninsula from 26 December 1989 to 14 January 1990. Results were compared with data of an identical survey with RV ‘Polarstern’ in 1987/88. Seasonal variation between summer and winter abundance/biomass data exceeded a factor of 35 times, while interannual variability between available surveys reached only a Read More
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The problem of acoustic abundance estimation is briefly reviewed. Under proper conditions, fish density can be measured with high accuracy along line transects. Observed variations in fish density consequently reflect biological variations, or inhomogeneity in spatial distribution. The particular problem of estimating fish abundance over an area from line-transect measurements of fish density Read More
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Length composition of krill in diurnal and night hauls of FV Lepus, off S. Orkneys in January and February 1991, generally show similar pattern. The proportion of bigger individuals of krill in night hauls was slightly higher than within diurnal hauls. CPUE values in February were higher than those in January. No larval fish were recorded in krill catches. Only few specimens of Electrona Read More
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This paper summarized the chilean catch data for 1991. Especial emphasis is given to the analysis of haul-by-haul data and its use in understanding small scale spatial distribution of fishing grounds. The results show that the krill fishery in subarea 48.1 is particularly intense near CEMP sites. Other uses of haul-by-haul data are suggestted.

The CCAMLR.AUS dataset available to the Subgroup on Survey Design was derived from a survey of Prydz Bay, Antarctica, in December 1990. Swarm length, depth, thickness, MVBS and interswarm length was calculated for swarms of euphausids encountered along a 78 km transect over the continental shelf close to the CEMP study site at Magnetic Island. The euphausid species was probably Euphausia Read More
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Observations are reported of icefish being taken as bycatch during krill fishing operations from a research vessel. The results indicate that the bycatch of fish in the commercial krill fishery may be significant in some areas of the South Georgia shelf. The problem is thought to be least in open ocean krill fishing.

A large-scale acoustic survey of zooplankton stocks of the waters around South Georgia was carried out during November and December 1981. The data have been analysed as a survey using various definitions of strata. The total biomass in the area of 155 786 km2 was estimated to be 1.8225 x 106 t (Coefficient of Variation = 9.5%). This gives an estimate of mean density throughout the region of 11 Read More
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Estimates are calculated for the parameter λ in the yield equation Y = λ M B0 for a kri11 fishery in which both the fishery and kri11 growth are seasonal. The criterion used for the calculations is that the probability that the kri11 spawning biomass drops below 20% of its average pre-exploitation level over a 20 year period of harvesting should not exceed l0%. The value of λ depends strongly Read More
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