Long-term changes in the size composition of fjord Notothenia rossii, Gobionotothen gibberifrons and Notothenia coriiceps at Potter Cove, after the 1978–1980 fishery in the area

Fish samples collected through an overall period of 24 years at Potter Cove after the impact of the fishery in the area in 1978-80, allowed the comparison of the variations in mean annual lengths and density distributions of the commercially exploited species N. rossi and G. gibberrifrons with the ecologically similar but unexploited N. coriiceps. The sharp decline in the abundance of N. rossii reported for the period 1983 - 1991/2 is consistent with the increase in mean size observed between 1983 and 1986/7 and the duration of the inshore phase of the species, which is known to last for 6-7 years. In the following years, until 1991/92, the decreasing abundance is consistent with the entrance of low strength cohorts with the consequent reduction in mean size. The above interpretation is supported by the length distributions observed between 1982/83 and 1985/86, where the modal age changes from 2/3 to 6/7 years. After 1991/92 the densities, mean sizes and abundances do not depend on a single forcing event but on several interacting factors. The length data of G. gibberifrons, available from 1986, show a decrease until 1991/92, exhibiting a similar pattern to that of N. rossii. After a period of relative stability in mean sizes (1992-1994) a sharp increase is associated with a continuous decline in relative abundance suggesting that it is due to increasingly low recruitments. The length frequency distributions of N. coriiceps through the whole studied period do not show any definite change in modal size, nor a pattern in mean lengths as is the case with N. rossii and G. gibberifrons.