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 of 1916/77-1986/87. 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 thous.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 years intervals after recruiting an abundant year-class to the exploited stock. Biomass of other bottom species is more stable, especially in case of N.gibberifrons. Recently, an increase of the C.aceratus stock is observed and, at the same time, a gradual decline of the P.georgianus.