Age determination was carried out on Notothenia gibberifrons specimens collected at two localities of the South Shetland Islands (Low I. and Potter Cove, 25 De Mayo I./King George). Samples were composed by small and medium size fishes (14.8-38 cm of total length). Otolith and scale readings have been compared in 19 Potter specimens. In some of them scale readings resulted one year greater. This could arise from the difficulty to differentiate false from annual checks in scales. Age determination by otolith cross sections proved to be the most reliable method. Mean length data at age presented here for Low I. specimens were compared with previous published values. This confirmed that fishes from the Antarctic Peninsula Subarea smaller than those around South Georgia at the same age group. Likewise, our values are lower than the ones reported previously for specimens of South Bay, Palmer Archipelago. Possible reasons for these differences are discussed. It is expected that the Otoliths/Scales/Bones Exchange System established by CCAMLR will contribute to eliminate discrepancies on age and growth studies of Antarctic Fish.
Abstract:
Finfish have been harvested in the Atlantic sector of the Southern Ocean since the end of the 1960s by the Soviet Union mainly. Notothenia rossii marmorata was the target species in the first peak years 1969-71 which yielded about 500,000 tonnes in 2 seasons. Since 1975/76 fishing is mostly directed to the icefish Champsocephalus gunnari and to a lesser extent Patagonotothen brevicauda guntheri. Catches of C. gunnari peaked at about 240,000, 220,000 and 100,000 tonnes in 1976-78, 1982-84 and 1986-88.
N. rossii marmorat is the species mostly affected by the fishery. Stock size around South Georgia is less than 5 % of the pristine level at present. Recruitment has dropped since the second half of the 1970s. Simulation studies indicate that the stock size will only double within 10 years time at the present level of recruitment.
Stock size of C. gunnari, around South Georgia is largely dependent on the strength of the recruiting yearclass which also forms the bulk of catches in the fishery. Stocks of C. gunnari around the South Orkney Islands and in the Peninsula region seem to be heavily depleted by the fishery and are in need for conservation measures.
P. br. guntheri is the only species for which the fishery is unregulated so far. Stock size as well as recruitment indicate a downward trend. The level of conservation measures to be established for the stock is, however, dependent on the availability of the most recent catch compositions to obtain a better assessment of the actual state of the stock.
