Increase in relative abundance of fjord Notothenia rossii in Potter Cover, South Shetland Islands, after the decrease associated with commercial fishing in the area

A monitoring program of demersal fish in inshore sites of the South Shetland Islands has continued in Potter Cove from 1991 to 1999, covering a continuous sampling period of sixteen years and in Harmony Cove, Nelson Island, in the austral summer 1995/96. The decline in trammel net catches of fjord fishes of the species Notothenia rossii and Gobionotothen gibberifrons in relation to the non commercially fished Notothenia coriiceps, which was already reported for the period 1983-1990 in a previous study, is still evident. An increasing trend of N. rossii catches was observed, but the actual levels of relative abundance of this species and G. gibberifrons are well below those found in the early 80´s. These results are supported by our knowledge on the diet of the piscivorous Antarctic shag Phalacrocorax bransfieldensis in the South Shetland/Antarctic Peninsula area in this decade. The most likely explanation for the decrease in recruitment to the inshore sub-populations of N. rossii and G. gibberifrons in the last sixteen years is the effect of the offshore commercial fishery in the area in the late 1970s. This interpretation is consistent with the information on the historical offshore commercial fishing and with the results of scientific surveys in the area.