A study of UK and Russian surveys using acoustics to augment trawling methods in shelf waters off South Georgia (Subarea 48.3)

In 2001/2002 Russian and UK vessels undertook surveys for icefish at South Georgia. Both used acoustic and trawl methods, and this paper uses both datasets to explore the similarities and differences between the surveys and discuss how much of the variation between the vessels was due to differences in the gear used and how much was due to natural spatial/temporal variability of the stock. The acoustic surveys indicated that icefish were not only located near to the seabed, but that a significant portion of icefish biomass was located in the water column. Thus the traditional approach of using bottom trawls to assess icefish standing stock has resulted in biased estimates below the true value: acoustic estimates are ~ 1.5 times greater This should be taken into account in the forthcoming stock assessment during WG-FSA–2002. These results show that the current observation system for the collection of data for icefish stock assessment should be changed to include regular acoustic surveys. This will improve the stock estimates of this species, and to achieve this we recommend the development of new survey designs and corresponding manuals.