Biological characteristics of Antarctic fish stocks in the Southern Scotia Arc region

Commercial exploitation of finfish in the southern Scotia Arc took place from 1977/78 to 1989/90, with its heydays from 1977/78 to 1981/82. Except for Elephant Island, the state of fish stocks of the southern Scotia Arc region has found little attention until 1998 despite substantial catches in the first four years of the fishery and the possibility to sample these catches extensively. Scientific surveys were only conducted by Germany in 1985, and by Spain in 1987 and 1991. Recently, the US Antarctic Marine Living Resources Programme carried out two extensive surveys around Elephant Island and the lower South Shetland Islands in 1998 and around the South Orkney Islands in 1999. New data are presented on the species composition, species assemblages, length composition, length-weight relationships, length at sexual maturity and length at first spawning, gonado-somatic indices and oocyte diameter.
Lesser Antarctic species predominate in the fish fauna. Their species assemblages, however, differed to 55-60% from one shelf area to the other mostly due to differences in the occurrence of the abundant species on each shelf area and the increase in the number of high-Antarctic species in the South Orkney Islands. Length compositions and the proportion of large (=old) specimens in the populations provided no evidence for illegal fishing since the closure of the region some 10 years ago. Differences in length-weight relationships between areas are primarily due to differences in length compositions of the fish caught, but do not suggest substantial geographical differences in length to weight growth. Differences in estimates of length at sexual maturity and length at first spawning indicate that in some species final maturation of the gonads takes one year or more whereas in others gonad maturation is completed within one season. Length at sexual maturity and length at first spawning in C. gunnari is one year later on the southerly grounds than at South Georgia. The distribution of gonado-somatic indices in March suggested that L. squamifrons was at spawning while T. hansoni was already coming towards the end of the reproductive season. C. rastrospinosus and T. eulepidotus were close to spawning. Other species, such as N. rossii and P. georgianus spawn at least 1 - 2 months later than at South Georgia. Channichthyids except C. gunnari, and N. rossii and N. coriiceps have egg diameters of 4.3 – 5.2 mm at spawning. Trematomus species usually have egg diameters of 2.8 – 3.2 mm while species of the genera Gobionotothen and Lepidonotothen rarely exceed egg diameters of 2.0 mm. Measurements of oocyte diameters confirmed the findings on spawning time estimated from gonado-somatic indices.