Analysis of changes in biomass of fish stocks in the South Georgia area in 1976/77-1986/87
The swept area method was used to estimate biomass density changes in the stocks of five fish species (Champsocephalus gunnari, Chaenocephalus aceratus, Pseudochaenichthys georgianus, Notothenia gibberifrons and Notothenia rossii marmorata) in the South Georgia area in the seasons 1976/77-1986/87. In most of the seasons analysed, the estimates covered a near-bottom layer in about 1/6 of the area of the island shelf.
Assessment results point to considerable variations in fish biomass density, in the studied period. Estimates of fish stocks biomass ranged from 43 to 158 thousand tons. The changes in the biomass level are first of all a result of periodical fluctuations in the biomass density of C. gunnari stock. High biomass density appeared with 2-4 year intervals after recruiting an abundant year-class to the exploited stock. The biomass of other bottom species is more stable, especially in the case of N. gibberifrons. Recently, an increase in the C. aceratus stock has been observed and, at the same time, there has been a gradual decline in the P. georgianus stock.