A review of Polish fishery and assessment of fish stock biomass off South Georgia
The review deals with the analysis of Polish catches off South Georgia in 1976-1982 and changes observed in the structure and biomass of the exploited fish stocks. Fisheries were carried out by 5-10 factory trawlers operating during the whole year with 2-3 month intervals, mostly in the Antarctic winter. In 1976-77, 1980/81 and 1981/82 the target species was Champsocephalus gunnari. In other years it was mixed fishery. The size of Polish catches depended more on the amount of fishing effort applied rather than on fish availability. The bulk of catches consisted of five species: Champsocephalus gunnari, Chaenocephalus aceratus, Pseudochaenichthys georgianus, Notothenia gibberifrons and N. rossii marrnorata. The statistical data on catch composition submitted by Poland to the FAO were corrected by proper separation of individual species in commercial catches.
The analyses of catch length and age composition revealed a similar pattern for most of the species. At the beginning of the fishery, the larger and older specimens were dominant in the catches. This situation changed in the late seventies when younger fish began to predominate. The data indicates that the average length and age of C. gunnari and N. rossii marmorata has approached a point at which they reach sexual maturity, and in some cases (e.g. Dissostichus eleginoides) has already gone beyond this point.
The material collected by observers on commercial vessels was used for fish biomass estimates by the "swept area" method. The estimates were obtained under the assumptions of an even fish distribution and 100% catchability of the trawl, and refer to the one-third section of the island shelf. These assumptions and other sources of errors are discussed. The biomass of fishable stocks in the first season of Polish catches was estimated at about 383,000 tons. Differences in the biomass of C. gunnari were the major factor influencing the magnitude of changes of the estimates in subsequent fishing seasons.