Borodin, R. and P. Kochkin (1988), Champsocephalus gunnari stock status in the South Georgia area

Data of age composition and fishing effort for 1976/77-1987/88 were used to analyse stock status and TAC for C. gunnari. Stock estimates were obtained using VPA with the following variations: mean F, Gamma methods, Pope and Shepherd method, using F regression on fishing effort and method of average weighted F.

For 1986/87 the values obtained by different methods differed considerably from each other, from 120 thousand tonnes (regression method) to 213 thousand tonnes (Pope-Shepherd method). For TAC prediction the stock size value was obtained by VPA with variations using F regression methods. The recruitment was taken at the lowest possible level for all these years (400 million specimens). Catch-per-unit-effort was also taken at the lowest level.

TAC was calculated for three possible situations:

(a) Fishing intensity (F) in a predicted period was equal to the average value of fishing mortality:

(b) For the predicted period fishing intensity was at the level of that in 1987/88;

(c) For the predicted period fishing intensity was F_0.1.

In the first two cases TAC=25-30 thousand tonnes and stock size does not change. For the third case TAC= 14-18 thousand tonnes and stock size increases. The analysis of the information shows that at the currently used value of stock size and even at the lowest possible recruitment levels and catch-per-unit-effort the present fishing regime does not lead to a decline in C. gunnari stock size.

McKenna, Jr., J.E. and S.B. Saila (1988), Results of fish stock assessment survey, South Georgia, December 1987 - January 1988

Commercial fish stocks around South Georgia have been declining since the early 1970's. A survey to monitor these stocks was carried out from December 1987 to January 1988. It complements earlier surveys in the same area and showed that most of the stocks are continuing to decline. Notothenia rossii is showing no signs of recovery and Champsocephalus gunnari is likely to continue declining in abundance.

Shust, K. and R. Borodin (1988), Notothenia (P.) guntheri stock status and TAC estimation in the area of Shag Rocks (Subarea 48.3)

Data on age composition of catches and fishing efforts for 1979/80-1987/88 were used to analyse N. guntheri stock status. On the basis of these data using VPA method with different adjustments stock estimates were obtained. Instantaneous natural mortality coefficient was M=0.7-0.9 (Atlantic Fisheries Research Institute data). To estimate terminal value of instantaneous fishing coefficient (F) different adjustments were used. Long term mean of F, Gamma method, Pope and Shepherd method, using F regression on fishing effort and using average weighted F. Prior to the beginning of fishery N. guntheri abundance was estimated as 227 thousand tonnes (using all the above mentioned methods). For 1986/87 the figure was only 102 thousand tonnes when calculation was done using regression equation and 160 thousand tonnes when the Gamma method was used (actual values of first and second age groups abundance were not taken into consideration). Of all these methods adjustments of F using the regression equation at which the correlation coefficients were the highest is the most preferable. Taking into consideration the fact that in the 1986/87 season the recruitment in the first age group was not abundance of N. guntheri in 1987/88 was 152 thousand tonnes. Then the following TAC values were obtained:

(a) Fishing intensity (F) in the predicted period is equal to the mean value of fishing mortality for the main commercially taken age groups (2-4 years);

(b) Fishing intensity in the predicted period is at the level of 1987/88;

(c) Fishing intensity in the predicted period is F_0.1.

In the first two cases TAC is 12.3-12.7 thousand tonnes and in the third case - 32.3 thousand tonnes. The analysis of estimations demonstrates that at the current level of fishing (1987/88) the size of the stock of N. guntheri will remain unchanged.

Ślósarczyk, W. and I. Wójcik (1988), Results of fish larvae sampling by means of fine-meshed samplers attached to a bottom trawl

Fine-meshed samplers were attached to the top of a bottom trawl in order to provide information on the composition, distribution and abundance of Antarctic fish larvae in the near-bottom zone, which is usually not sampled using plankton nets. The efficiency of various sized meshes for sampling larvae in the bottom zone and the resistance of the samplers to damage during trawl operations were observed. Number of fish caught by samplers constructed using 0.505 mm net were similar to those taken by samplers made using 12 mm net with 0.505 mm insets. The 12 mm net was, however, more vulnerable to damage. The nets were more effective in sampling when attached to the top of the trawl belly, not to the codend. A total of 12 fish species were recorded. The most common fishes caught were postlarval Nototheniidae, and among them Nototheniops larseni (9.3-20.5 mm). The abundance of postlarval fish was highest in the shallow (108-166 m), nearshore waters of the north eastern shelf of South Georgia. Low values of the abundance index, including most of zero catches, were recorded on the western and southwestern part of the island shelf. Differences observed between the species composition of samples taken in this study and samples which have been collected in the midwater zone during the summer in the South Georgia area are discussed.

Balguerías, E. (1988), Selectivity parameters for Notothenia gibberifrons Lönnberg, 1905 and Champsocephalus gunnari Lönnberg, 1905 obtained during “8611 ANTARCTICA [ANTARTIDA]” expedition

Mesh selectivity experiments for several finfish species were conducted during the Spanish Antarctic cruise “ANTARTIDA 8611” using the covered codend technique. This paper presents the results obtained for Notothenia gibberifrons and Champsocephalus gunnari. Selection factors calculated following different methods with a codend mesh of 68 mm were 2.87 for Notothenia gibberifrons and 3.10 for Champsocephalus gunnari.

Zaucha, J. (1988), Selectivity of standard Polish commercial trawl codends on Antarctic fishing grounds

Selectivity studies were carried out for two types of steelon codends used in commercial fishery, with a nominal mesh size A = 80 mm and A = 100 mm, made of double twines with a thickness of 4.2 mm. The studies covered 6 major fish species.

It appears from the study that Antarctic icefish and bumphead notothenia are subject to selection during trawling, although the effectiveness of this process - especially in the latter case - is not satisfactory.

Scotia Sea icefish, Chaenodraco wilsoni, and Chionodraco rastrospinosus exhibit a lower tendency to pass through meshes of the codend than Antarctic icefish and bumphead notothenia.

The solution to the problem of ensuring selectivity of codends at a sufficiently good level seems possible as a result of the application of webbing with permanently open meshes for codend construction.

The most difficult matter will be preparing a codend with proper selectivity properties for South Georgia icefish, because this species exhibits the smallest tendency to escape during the trawling among all the species studied.

Conclusions and observations were in some cases based on a relatively small amount of experimental material.

Further investigations of this problem are necessary since producing selective trawl gear for harvesting Antarctic fish seems crucial from the point of view of conservation of living fish resources on those fishing grounds.

Barrera-Oro, E. (1988), Age determination of Notothenia gibberifrons from the South Shetland Islands, Antarctic Peninsula subarea (Subarea 48.1)

Age determination was carried out on Notothenia gibberifrons specimens collected at two localities near the South Shetland Islands (Low I. and Potter Cove, 25 De Mayo/King George I.). Samples consisted of small and medium sized fish (total length - 14.8-38 cm). Otolith and scale readings have been compared in 19 Potter Cove specimens. In some cases scale readings gave a result of one year more. This could arise from the difficulty in differentiating between false and annual checks in scales. Age determination by otolith cross sections proved to be the most reliable method. Mean length data at age presented here for Low I. specimens were compared with previous published values. This confirmed that fish from the Antarctic Peninsula subarea are smaller than those in the same age group around South Georgia. Likewise, our values are lower than the ones reported previously for specimens of South Bay, Palmer Archipelago. Possible reasons for these differences are discussed. It is expected that the Otoliths/Scales/Bones Exchange System established by CCAMLR will help to eliminate discrepancies in age and growth studies of Antarctic fish.

Gordon, A.L. (1988), Physical oceanographic setting of the Siedlecki January 1987, South Shetland Island data set

In the vicinity of the northern tip of the Antarctic Peninsula, the Bransfield Straits and South Shetland Islands, cold polar waters from the Weddell Sea meet warmer circumpolar water from the Pacific Ocean. A series of fronts form which are collectively referred to as the Weddell-Scotia Confluence. Within the Confluence region the Weddell Gyre water is separated from the Pacific or Scotia Sea water by a zone of varied width (10 to 100 km) of water which can best be considered as continental margin water, advected into the region along the extreme western edge of the Weddell Gyre. It is relatively cold and low in salinity throughout the water column and prone to deep reach convective events, even as far north as the Bransfield Straits. Along the northern boundary of the Weddell-Scotia Confluence (the Scotia Front), where the Pacific water is encountered, there are indications of vigorous mixing processes of Bransfield Straits water (derived from the Weddell, with further local modification): an intrusive layer of Pacific derived relatively warm-salty water near 300 meters depth and deeper intrusions (500-1 500 meters; e.g. Siedlecki stations 217, 226, 231, 235, 236 and 250) of Pacific water, as the Scotia Front protrudes to the south, perhaps associated with mesoscale structures.

The Weddell-Scotia Confluence in the Bransfield Straits is associated with abundant krill populations. It is speculated that mixing of Weddell and Pacific waters near the tip of the Antarctic Peninsula is an important environmental feature related to this abundance.

Kock, K.-H. (1988), Preliminary results of a bottom trawl survey around Elephant Island in October and December 1987

A total of 40 bottom trawl hauls was carried out onboard RV Polarstern in October and December 1987. Preliminary results indicate rather stable stock compositions in Chaenocephalus aceratus, Notothenia gibberifrons and N. neglecta at least since February 1985. In N. rossii the proportion of larger (= older) fish in the catches increased. Composition of the catches of C. gunnari differed significantly from that in previous seasons which argues for an exchange with C. gunnari from other shelf areas of the Peninsula region.

Makarov, R.R. and K.P. Fedorov (1988), Large-scale peculiarities of phytocenosis species composition in the surface layer in the Antarctic Atlantic and Indian Ocean sectors

In surface phytoplankton samples (layer between 0 and 1 m) taken with a sampler towed by RV Professor Vize, Corethron criophilus dominated over vast areas within the distribution of the south peripheral waters and the centre of the Weddell Gyre. In the eastern Weddell Gyre a great change in the composition of phytoplankton species was registered. Variability in phytoplankton species composition occurred mainly in the Antarctic Convergence Zone. A seasonal shift in species composition was observed in the same regions (sub-Antarctic waters, the Convergence Zone proper, south periphery of the Antarctic Circumpolar Current). A great change in phytoplankton composition was also found near the continent (Alasheev Bay). During the observation season maximum biomass values of surface phytoplankton were registered in the south periphery of the Antarctic Circumpolar Current.

Maklygin, L.I., A.S. Fedorov, V.N. Shnar, Yu.A. Shulyakovsky, I.V. Krasovsky, Yu.D. Shuvaev and A.V. Kromsky (1988), Preliminary results of research activities of RV Evrika in the Scotia Sea in January-March 1988

In 1987/88 a multi-disciplinary survey was conducted of the Scotia Sea and adjacent waters, accompanied by regular trawlings with an Isaac-Kidd trawl. The waters off South Georgia in particular were surveyed twice. Research activities are part of the program implemented in areas of the Atlantic Sector of the Southern Ocean identified for monitoring by CCAMLR. During the observation season the zonal drift of waters of the Antarctic Circumpolar Current and Second Frontal Zone became stronger, causing the krill to drift eastwards. Krill concentrations were observed in the waters to the southeast of South Georgia where relatively small crustaceans of less than 35 mm dominated. In the east Scotia Sea a higher abundance of primary production was registered. The analysis of data on phytoplankton, zooplankton and krill (biological parameters) is now under way.

Williams, R. (1988), Australian research on Antarctic bird and seal diets

Many data on the diets of important vertebrate predator species in Prydz Bay and around the sub-Antarctic Heard and Macquarie Islands have been collected during the last seven years. Published and unpublished results are collated and summarised, and several important points emerge.

In Prydz Bay, on which is cantered the CCAMLR Ecosystem Monitoring Programme's priority study area, Euphausia superba forms a rather low proportion of the diet of most vertebrate predators. Euphausia crystallorophias and the fish Pleuragramma antarcticum are important in most diets, and many predators can switch between prey species. The use of these predators to monitor the state of prey populations is thus very limited, although continuing studies will be useful to assess the natural variability of the system.

Around the sub-Antarctic islands, the four penguin species feed more heavily on fish, especially myctophids, than at other comparable localities.