Size variations associated with abundance changes in juvenile Notothenia rossii observed at Potter Cove, South Shetland Islands, since the end of the fishery in the area

Samp1es of fjord fish of the species N. rossii and N. neglecta collected at Potter Cove, King George/25 de Mayo Island, South Shetland Islands, from 1983 to 1991, allowed to study the previously reported abundance changes as a size-related process. The data were analyzed using a Nested ANOVA design to obtain variance components and expected values. An increase and then a decrease in the expected mean sizes of pre-recruit N. rossii was clearly observed along the whole sampling period. This was interpreted as a consequence of a significant reduction in the influx of the youngest age classes into inshore waters followed by the departure of the older (and more abundant) specimens offshore. These changes are strongly associated with the last significant catches of fin-fish in the Subarea 48.1 in 1979/80 and could also be related to the still undetermined incidental mortality of larvae and juvenile in the krill fishery. Not surprisingly, the analogous treatment of data of N. neglecta, a species with similar ecological habits in the fjords but not commercially fished, showed variations around the expected overall mean size without any significant trend. In addition, the 1991 abundance data of fjord N. rossii and N. gibberifrons relative to N. neglecta indicate low levels, similar to those already reported for the last three years in the same area.