Variability of krill biomass estimates in repeated mesoscale surveys in relation to CCAMLR-2000 Survey

One of the important problems in interpreting CCAMLR-2000 results is how they reflect the krill biomass status, is it high, medium or low at the present time. The comparative analysis of krill biomasses derived from trawl catches was carried out; retrospective data of three Soviet surveys, covering the main part of the CCAMLR-2000 area, were used: RV “Argus” (27.01.84-16.03.84) and RV “Evrika” (11.10.84-14.12.84 and 20.01.88-09.03.88). There were used similar gear (Isaak's Kidd Midwater Trawl) and methods of sampling, but sampling was carried out in the 0-100 m water layer instead 0-200 m in CCAMLR-2000. Krill biomass index calculated for the whole area of Soviet surveys doesn't reveal any significant changes, being in the limit of 15.3-20.3 g/m2. When assuming that changes of average weight density reflect biomass variability, it may be suggested that value of the total krill biomass in the area 48 is quite stable during last seventeen years. It is to be noted however that due to difference in layers sampled during CCAMLR-2000 and Soviet surveys, krill biomass derived from data collected in 80-s may be considered as overestimated comparing CCAMLR-2000 results, the rate of overestimation is unclear. If it is true and level of overestimation is considerably high, we have to admit increase in krill biomass since 80-s, however rate of this increase is impossible to determine on the present stage.