CCAMLR

Samp1es of fjord fish of the species N. rossii and N. neglecta collected at Potter Cove, King George/25 de Mayo Island, South Shetland Islands, from 1983 to 1991, allowed to study the previously reported abundance changes as a size-related process. The data were analyzed using a Nested ANOVA design to obtain variance components and expected values. An increase and then a decrease in the expected mean sizes of pre-recruit N. rossii was clearly observed along the whole sampling period. This was interpreted as a consequence of a significant reduction in the influx of the youngest age classes into inshore waters followed by the departure of the older (and more abundant) specimens offshore. These changes are strongly associated with the last significant catches of fin-fish in the Subarea 48.1 in 1979/80 and could also be related to the still undetermined incidental mortality of larvae and juvenile in the krill fishery. Not surprisingly, the analogous treatment of data of N. neglecta, a species with similar ecological habits in the fjords but not commercially fished, showed variations around the expected overall mean size without any significant trend. In addition, the 1991 abundance data of fjord N. rossii and N. gibberifrons relative to N. neglecta indicate low levels, similar to those already reported for the last three years in the same area.

Existing antecedents are presented from technical publications concerning chilean fisheries of the patagonian toothfish Dissostichus eleginoides related with the selectivity of the type and size of hooks used in the longlines. Original data obtained during 1991 on the coast of Valdivia, South East Pacific, are added. The data show that the circle hooks are far more efficient that the right ones. The size frequency of the population collected with straight hooks No3 and 4 are not significatively different, being No 3 near 31 % more efficient than No 4. Different bait do not present significative differences. It is notorious that female proportion increases significatively in the catches, at the same time as the number of the straight hook increases (for example from 4 to 3) or when they change from straight to circle.

Capture statistic analyses from the different regions of Chile where fishery of patagonian toothfish (Bacalao de profundidad), Dissostichus eleginoides, has been developed are based in statistics published by the SERNAP (National Fishery Service). It shows that activity has lasted few years in each geographic region considered. As captures have decreased in the northern zone, the artisanal fleet has migrated towards south, concentrating actually in the X Region of Chile and we attract attention that, during the last years, a worrying by catch of factory boulterer vessels dedicated to the austral hake ( Merluccius australis ) have increased its captures in the most southern Region.

Dissostichus eleginoides is becoming an increasingly important species in the fisheries of the Southern Ocean. In Division 58.5.1, a directed trawl fishery has been in operation since 1984/85 and has expanded in the deep western sector of the Kerguelen shelf. This fishery harvests the sub-adult/adult part of the stock. Fishing effort and corresponding catches are very variable from one year to another and highly dependent on the harvestable resources of C. gunnari. Vital biological information for population dynamics, as well as demographic structures and trends observed in an abundance index are provided. Prospects for exploitation are discussed with respect to the development of fishing methods.

Feeding patterns of four Nototheniid, three Channichthyiid and two Bathydraconiid species were investigated and their daily diets were assessed from data obtained at a day-long station carded out in the Cosmonauts Sea (67°50 S - 41°25 E) in March 1988.
The type of food consumed by Chaenodraco wilsoni and Trematomus eulepidotus indicates that they are plankton-eaters as their diet comprised mainly of Euphausiids; T. centronotus is a benthophage feeding mainly on Gammarids and Polychaetas, T. hansoni is euriphagous while Dissostichus mawsoni, Cygnodraco mawsoni, Gymnodraco acuticeps, Chionodraco hamatus and Cryodraco antarcticus are predators which feed on juvenile Nototheniids and Myctophids.
Daily diet volumes of the species studied varied from 1 to 4% of their body weight while annual volumes ranged from 3 to 9 times their body weight. Mean annual diet volume of antarctic fish species was around 5 times their body weight.

Sexual maturation in the Mackerel Icefish, Champsocephalus gunnari, was studied by macroscopic examination of gonads. Evidence in support of the hypothesis that a proportion of mature fish fail to spawn was obtained. Histological examination of ovaries indicates that some ova were undergoing regression and resorption at least two months prior to the normal spawning date. It is concluded that the underlying cause is probably due to a shortage of krill, an important dietary item for Champsocephalus gunnari.

The results are presented of studying icefish vertical migration based on the data of R/V cruises during the seasons of 1982-83, 1983-84 and 1986-87, when this species was highly abundant on the South Georgia shelf. It is revealed that at day time the fish distributes near the bottom and the maximum catches were available at the middle of the light hours of the day. At twilight the fish concentrations migrate into the water column and the catches greatly decrease. The direct observations of icefish vertical migrations provided by means of hydroacoustic equipment are presented.