Demersal fish community structure, distribution and trophic relationships on the slope (depth range 200-1500 m) of the sub-Antarctic Prince Edward Islands and surrounding sea rises have been investigated during the pilot survey conducted in April 2001 onboard fishing vessel MV Ibis. A total of 56 fish taxa were collected during the survey, of which 43 were identified to species level, 8 to the genus level and 5 to the family level. Among identified taxa, 36 constituted new records for the area investigated. Total CPUE (catch per unit effort) during the survey ranged from 1.1 to 268.1 ind.h-1. Both average fish diversity and total CPUE positively correlated with the trawling depth. Overall, mean sampling depth and near-bottom temperature explained 56% of both total fish CPUE and diversity variation. The hierarchal analysis identified three distinct fish assemblages with very pronounced dominant species, which occupied different vertical zones with likely specific environmental characteristics. Major shifts in communities have occurred at 500-600 m and 800-900 m depth strata, which were probably augmented by the physical and biological vertical zonation. Analyses of diets of selected fish species showed that they are feeding generalists consuming predominantly pelagic, including epipelagic, and meso-/benthopelagic prey. Diet data on 6 species and stable isotopes of 22 fish species revealed that with a few exceptions most species occupy the fourth trophic level and are tertiary consumers. Wide variability in carbon isotopic signatures is discussed with respect of alternative (possible importance of high Antarctic and chemoautotrophic versus photoautotrophic sub-Antarctic primary production) organic matter sources at the base of deep-sea food webs.
Abstract:
Based on the analysis of data on the searching fishery on Antarctic toothfish (D. mawsoni) by the Russian fishing vessels "Yantar" and "Volna" in the seasons of 2002/03-2003/04 it has been obtained that the long-line catchability and size composition of fish depended on the fishing depth, bottom orography and sharp change in the depth, etc. In this relation, to determine the areas and depth of Antarctic toothfish concentration the need for extension of searching fishery area boundaries was proven with the use of passive fishing gears in the meso- and bathypelagial.. The constructions and schemes to set the vertical and combined vertical-bottom longlines.
