ANALYSIS OF ICE-FISH (CHAMPSOCEPHALUS GUNNARI) SPATIAL DISTRIBUTION FOR OPTIMIZATION OF THE BOTTOM TRAWL SURVEY SAMPLING

Acoustic and trawl samples obtained in the near-bottom layers covered by bottom trawl surveys in the South Georgia area are analyzed. The high heterogeneity of horizontal and vertical fish distribution in the near-bottom layers within the surveyed area is shown. Influence of this fish distribution heterogeneity on trawl surveys efficiency and reliability is analyzed by simulating the impact on fish biomass estimates of varying headline height of bottom trawl and shifting trawl stations positions. Under example of Russian and UK bottom surveys carried out in the South Georgia area during season’s 2000 and 2002, it is shown that inter-seasons and inter-vessels differences between fish biomass estimates may be to a considerable degree stipulated by heterogeneity of fish distribution in the near-bottom layer relative to the trawl sampling strategy, including fishing gear operation zones (Russian trawl HEK-4M and UK trawl FP120) and the trawl station locations rather than by the variability of the stock state.