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, and was in its heyday from 1977/78 to 1981/82. Except for Elephant Island, the state of fish stocks of the southern Scotia Arc region has been accorded little attention until 1998, despite substantial catches in the first four years of the fishery and ample opportunity to sample these catches. The only scientific surveys of these stocks during these years were conducted by Germany in 1985, and by Spain in 1987 and 1991. More recently, the US Antarctic Marine Living Resources (US AMLR) Program carried out two extensive surveys around Elephant Island and the lower South Shetland Islands in March 1998 and around the South Orkney Islands in March 1999. In this paper, the authors present new data on species composition, species groups, length compositions, length-weight relationships, length at sexual maturity and length at first spawning, gonadosomatic indices and oocyte diameter.
Lesser Antarctic or peri-Antarctic species predominated in the fish fauna. Species groups differed by up to 55-60% from one shelf area to the other, mostly due to differences in the abundance of the predominant 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 of illegal fishing since the closure of the region some 10 years ago. Differences in length-weight relationships between areas were primarily due to differences in length compositions of the fish caught, but did not suggest 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 was completed within one season. Length at sexual maturity and length at first spawning in Champsocephalus gunnari was one year later on the southerly grounds than at South Georgia. The distribution of gonadosomatic indices in March suggested that Lepidonontothen squamifrons was spawning while Trematomus hansoni was already coming to the end of its reproductive season. Chionodraco rastropinosus and Trematomus eulepiodus were close to spawning. Other species, such as Notothenia rossii and Pseudochaenichtyhys georgianus, spawn at least one to two months later than at South Georgia. Channichthyids (except C. gunnari), Notothenia rossii and Notothenia coriiceps have egg diameters of 4.3-5.2 mm at spawning. The Trematomus species investigated have egg diameters of 2.8-3.2 mm while in species of the genera Gobionotothen and Lepidonotothen, egg diameters rarely exceeded 2.0 mm. Measurements of oocyte diameters confirmed the findings on spawning time estimated from gonadosomatic indices.