CCAMLR

Current velocity data from a single time realisation of the FRAM model are presented for particular areas of the Scotia Sea. The regions are based on the CCAMLR sub-areas and also include a more detailed area around South Georgia. Mean current velocities have been calculated for region boundaries over the upper 250m of the water column. These have been combined with estimates of krill density and standing stocks to consider the large scale flux of krill through the regions and estimate residence times

A methodology is described which when applied to data from an acoustic survey will yield mean krill density along an arbitrary section through the survey area, giving results compatible with the specifications given in wg-krill-93 Appendix D. A program written to calculate such sections is also described and example output displayed. A similar program calculates current speeds normal to a section given an oceanographic dataset of current direction and speed. The two programs produce compatible vectors of krill density and current speed along specified sections

Conditions for precise measurement of in situ fish target strength (TS) are empirically studied and two indexes are introduced for this purpose. One is the number of fish in the effective reverberation volume which contributes echo formation at a certain instant and the other is the percentage of the multiple echoes which is derived from a residual of the single echo extraction. With the decrease of both indexes measured target strength approach a certain asymptotic value which is admitted as reliable from the past study. This shows the existence of some threshold values and below these threshold values TS measurement will be successful. The effectiveness of both indexes is confirmed by the data set obtained from one large same fish school in the eastern shelf of Bering sea during the intership calibration between Japanese and U.S. vessels on 15 and 16 August 1991.

Published in J.Mar.Acoust.Soc.