Long term variations in abundance and size composition of fjord Notothenia rossii, Gobionotothen gibberifrons and Notothenia coriiceps at potter cove, South Shetland Islands, after the 1978-1980 fishery in the area

ALESCIO, N. S.; MARSCHOFF, E,.R.; BARRERA ORO, E. R.

Buenos Aires

Conferencia; XXXI SCAR 4th Open Science Conference; 2010

SCAR (Scientific Committee on Antarctic Research)

Commercial fishing depleted demersal fish stocks off the South Shetland Islandsduring the late 1970s. We assessed long-term impacts to remaining fish by collectingsamples at Potter Cove during summer over a 28-yr period, 1983-2010. We report changesin size and abundance of the commercially exploited Notothenia rossii and Gobionotothengibberifrons relative to the ecologically similar but unexploited N. coriiceps. A sharp decline inN. rossii abundance during 1983 to 1991 corresponded to an increase in mean size between1983-84 and 1986-87, and is consistent with the duration of the species’ inshore phase (6-7yr). Subsequently, the abundance decreased with the entrance of weak cohorts into thepopulation, while modal age changed from 2-3 to 6-7 yr. Abundance and length data of G.gibberifrons, available from 1986, exhibited a similar pattern to that of N. rossii up to 1992.After a period of relative stability in mean size (1992-94), a sharp increase was associatedwith a continuous decline in relative abundance suggesting increasingly low recruitment. Thelength-frequency distribution of unexploited N. coriiceps through the whole period does notshow any trend in modal size nor in mean length. Abundance data of the three species fromoffshore surveys are consistent with a decrease and subsequent recovery of N. rossii, adecrease of G. gibberifrons and an increase of N. coriiceps. The concomitant decliningtrends observed in a fish predator’s population (Imperial cormorant Phalacrocorax spp.) isapparently explained by changes in inshore fish availability, owing to over-exploitation andnot climate/oceanographic change.