Shnar, V.N. and V.I. Shlibanov (1989), Hydrological conditions and characteristics of icefish (Channichthyidae) distribution on the South Georgia shelf in 1986/87

Some characteristics of spatial and temporal variability of the distribution of icefish (Channichthyidae) on the South Georgia shelf in relation to environmental conditions have been revealed from summaries and analyses of hydrographic, commercial fisheries and biological data for 1986/87.

Frolkina, Zh.A. and P. Gasyukov (1989), 1989/90 stock status and TAC assessment for Champsocephalus gunnari in Subarea 48.3 (South Georgia)

The 1989/90 stock status and TAC assessment for Champsocephalus gunnari in South Georgia Subarea (48.3) has been made using the biostatistic material for 1982/83 to 1987/88 collected by Soviet scientists. VPA tuning has been made by the Laurec-Shepherd method (1985) using standardized fishing effort. For the beginning of the 1989/90 fishing season, the stock was assessed at 130.2 thousand tonnes and the TAC at 23.6 thousand tonnes.

Frolkina, Zh.A. and R.S. Dorovskikh (1989), On assessment of Bertalanffy growth equation parameters and instantaneous natural mortality rate of South Georgia mackerel icefish

An analysis and summary of extensive published and unpublished data on size-weight and size-age composition of South Georgia mackerel icefish (Champsocephalus gunnari) for 1965 to 1987 is presented. The results enable the calculation of reliable weight-length equations for males and females by season and the verification of parameters for the Bertalanffy growth equation. Mean value of natural mortality rate was estimated at 0.55.

Frolkina, Zh.A. (1989), Methods of age determination for mackerel icefish (Champsocephalus gunnari Lönnberg 1905) from the South Georgia Island shelf

Radii of annual elements of otoliths of mackerel icefish (Champsocephalus gunnari) from the South Georgia shelf were determined by analyzing data on length frequency distribution of fish in catches simultaneously with otolith radii of fish taken in the period July to September. The latter was done using specimens from strictly defined age groups. It is suggested that the determined radii of annual elements of otolith could be used to adjust age assessments of fish longer than 30 cm having an enlarged otolith centre. An age/length key for the third quarter of the year was also calculated.

Kock, K.-H. (1989), Reproduction of the mackerel icefish (Champsocephalus gunnari) and its implications for fisheries management in the Atlantic sector of the Southern Ocean

Available information on key reproduction parameters of the mackerel icefish (Champsocephalus gunnari) has been reviewed and discussed in the light of existing conservation measures. Length at first spawning is approximately 25 cm around South Georgia and Kerguelen Islands, but approximately 35 cm around the South Orkney Islands and in the South Shetland Islands/Antarctic Peninsula region. Around South Georgia spawning takes place from March to May. Spawning around the South Orkney Islands and the South Shetland Islands probably occurs in June/July. Around South Georgia males start their spawning migration earlier than females. Fjords have been reported to be important spawning grounds. Fecundity is highest around South Georgia and Kerguelen but is decreasing towards higher latitudes.

Mesh size regulations presently in force offer very little protection to first spawners around South Georgia and juveniles and first spawners on the other South Atlantic fishing grounds. Spawning activities of C. gunnari and those of other exploited species could be best protected by the establishment of a permanent closed fishing season from 1 March to the end of each year's meeting of CCAMLR which is usually held in late October or early November.

Efanov, S.F., G.E. Bidenko and V.A. Boronin (1989), Trawl selectivity for Champsocephalus gunnari

Data on trawl selectivity for mackerel icefish (Champsocephalus gunnari L.), were collected in 1981 in the South Georgia area. The trawl bags tested were made of net webbing with 3.1 mm twine and 88.2 mm mesh size. Trawling speed was 3.5 knots. Icefish comprised 90 to 100% of catches. The logistic selectivity curves were calculated using the collected data. It was found that the selectivity factor for 88.2 mm mesh size was 2.81 and the 50% retention length was 24.8 mm (21.5 to 28.2 mm).

Köster, F.W. and K.-H. Kock (1989), Effects of different harvesting strategies on the mackerel icefish Champsocephalus gunnari around South Georgia

The effects of a number of harvesting strategies on the mackerel icefish (Champsocephalus gunnari) have been simulated for a period of 30 years. These were:

• different levels of constant fishing mortality (F_0.1, F_max, 2xF_max);
• harvesting constantly at 50% F_0.1 with F increasing three or five years after a good recruitment;
• pulse fishing at an interval of three years with no fishing in between; and
• changes in net selectivity resulting in a shift in partial recruitment.

For the projections, recruitment was assumed to follow the historical pattern.

Pulse fishing proved to be the least preferable harvesting alternative. In the absence of regular recruit surveys constant fishing at F_0.1 is most likely to be the most profitable and least risky harvesting strategy at present. The establishment of a regular recruit survey would offer the possibility of adjusting constant levels of fishing mortality to the strength of the incoming year class. An increase of F, however, should not occur earlier than four years after a good recruitment. A forward shift in partial recruitment values would not alter yield significantly when fishing at F_0.1 and F_max but would lead to a higher spawning stock biomass.

Shlibanov, V.I. (1989), 1989/1990 stock status and TAC assessment for Patagonotothen brevicauda guntheri in South Georgia subarea (48.3)

The 1989/90 stock status and TAC assessments for Patagonotothen brevicauda guntheri from the South Georgia subarea (48.3) have been made using biostatistical material for 1978/79 through 1988/89 collected by Soviet scientists. VPA tuning has been accomplished using the regression equation between fishing mortality and standardized fishing effort for each age-class. Stock has been assessed at 123.1 thousand tonnes with a TAC of 28.3 thousand tonnes for the initial period of 1989/90 fishing season.

Shlibanov, V.I. (1989), Growth and natural mortality of Patagonian rockcod (Patagonotothen guntheri shagensis) from Shag Rocks shelf

The parameters of Bertalanffy’s growth equation for Patagonian rockcod (Patagonotothen guntheri shagensis) were calculated by using age and length-weight data of research and fishery survey cruises in the Shag Rocks area from 1978 to 1986. The natural mortality rate was assessed by six different methods and was within a range of 0.63 to 1.06. The mean value of natural mortality M=0.8 was used in calculations and the optimal age and length for harvesting Patagonian rockcod were found to be 2.5 years and 12.6 cm.

Zaitsev, A.K. (1989), Growth and age/length structure of populations of Notothenia (Lepidonotothen) squamifrons (Nototheniidae) in various areas of the Indian sector of the Southern Ocean

Age, growth and age/length composition of populations of grey rockcod (Notothenia (Lepidonotothen) squamifrons), inhabiting areas of the Ob and Lena Banks and the Kerguelen Island Shelf, are presented in this paper. It was found that during the first years of life the linear growth rate is 3 to 5 cm per year. It decreases by a maximum of 1 cm during the last years of life. Maximum annual weight increments of 100 to 120 g at the banks and 153 to 188 g in the Kerguelen Island area were recorded for fish at age 6 to 12. Growth parameters were calculated according to Bertalanffy’s equation. The dynamics of age/length composition of catches are also examined in this paper. On the Ob and Lena Banks this composition is fairly stable but on the Kerguelen Shelf there is a tendency towards younger fish being more abundant.

Zaitsev, A.K. (1989), Natural mortality of grey rockcod (Notothenia squamifrons) in various areas of the Indian sector of the Southern Ocean

The rate of natural mortality of grey rockcod (Notothenia squamifrons) on the Ob and Lena Banks and the Kerguelen Shelf were determined using three independent methods. From the values obtained the means were taken to be the most reliable. These were 0.38, 0.36 and 0.33 for the above areas respectively. These values are comparable with those derived for most notothenioids.

Duhamel, G. (1989), Supplementary data on exploited stocks in Division 58.5.1 (Kerguelen)

The results of fishing cruises carried out from 1986/87 to 1988/89 in Division 58.5.1 (Kerguelen Island) have made possible a review of the status of the various harvested fish stocks. Since 1984, an average annual growth of 36% has been noted in the abundance of the juvenile section of the stock of Notothenia rossii, a species which is at present only fishable as a by-catch. The total biomass of the stock, however, remains very low according to the assessments carried out by the 1987 and 1988 scientific research cruises. The abundant 1985 cohort of Champsocephalus gunnari appeared in the shelf stock and it is from this cohort that the fishery achieved its good results in 1988/89, once the cohort had reached legal catch size. The value of the selected abundance index (catch per unit effort expressed in tonnes per fishing hour) is, however, lower than those observed for the two preceding cohorts (1979 and 1982) in a comparable period. The stock of Notothenia squamifrons shows a very low biomass value in 1987 and 1988. After a continuous reduction in average length since the creation of the EEZ, a slight increase has been recorded recently, accompanied by an increase in the abundance index, following a reduction in catch and fishing effort. This trend could well be reversed by too high a catch in 1988/89. Finally, it is not possible to accurately estimate the stock status of Dissostichus eleginoides because of the lack of recent fishery data.

Slosarczyk, W., E. Balguerias, K. Shust and S. Iglesias (1989), Evaluation of the results of trawl selectivity experiments by Poland, Spain and USSR in 1978/79, 1981/82 and 1986/87

Trawl selectivity for several species of Antarctic fish was evaluated taking into account additional data obtained by Poland, Spain and USSR during selectivity experiments in Statistical Area 48 in 1978/79, 1981/82 and 1986/87 seasons. These data comprise different characteristics of experimental codends, length frequency distribution of stocks sampled, catch rates and catch composition. Details of these data were analyzed and minimum mesh sizes for several species were calculated. It is recommended that introduction of these mesh sizes should be considered for commercial fishery in Statistical Area 48.

Kock, K.-H. (1989), Results of the CCAMLR Antarctic fish otoliths/scales/bones exchange system

An exchange system was established among Members of CCAMLR to compare age determinations for the same species among different laboratories. Four species were included in the exchange: Notothenia rossii, Champsocephalus gunnari, Notothenia gibberifrons and Pleuragramma antarcticum. The level of agreement in age determination was highest for scales of juvenile N. rossii and for otoliths of juvenile C. gunnari from South Georgia and lowest for scales of adult N. rossii and N. gibberifrons and otoliths of P. antarcticum. Agreement between otoliths and scales of individual N. gibberifrons was in the order of 50%. There was little indication that agreement between experienced investigators was higher than between experienced and less experienced ones.

Miller, D.G.M. (1989), Commercial krill fisheries in the Antarctic, 1973 to 1988

STATLANT data reported to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) are used to discern observable trends in catch and effort for the Antarctic krill (Euphausia superba) fishery between 1972/73 and 1987/88. The annual krill catch rose gradually to a peak of some 500 000 tonnes in 1981/82 before dropping to allow level in 1983/84 and stabilizing at about 400 000 tonnes thereafter. In terms of both catch and effort the Soviet and Japanese krill fisheries in Subareas 48.1, 48.2 and 48.3 prevail in the CCAMLR Convention Area. Monthly fishing patterns (November to April) are similar in all areas, except in Subarea 48.3 where fishing is predominantly confined to the winter months (April to August). Trends in the fishery with respect to independent estimates of krill abundance and minke whale (Balaenoptera acutorostrata) catches are discussed.

Mangel, M. (1989), Analysis and modelling of the Soviet Southern Ocean krill fleet, II: Estimating the number of concentrations and analytical justification for search data

In this paper, I show how data that are routinely collected by survey vessels can be used to estimate the number of concentrations of krill (Butterworth, 1988; Mangel, 1988) in a given region of the Southern Ocean. Sample computations are performed, using data collected by Soviet research/survey vessels in the early 1980s. These examples highlight the need for a navigational log as well as a fishing log in order to make accurate inferences. In the appendix, a method for correcting for the bias in the detection of concentrations is described.

Endo, Y. and T. Ichii (1989), CPUEs, body length and greenness of Antarctic krill during 1987/88 season in the fishing ground north of Livingston Island

In order to identify whether or not there was a marked change in two kinds of CPUEs, body length and greenness of krill during the fishing season, these parameters were examined for each 10-day period of the Japanese krill fishery in the northern waters of Livingston Island in the 1987/88 season. It appears that Japanese trawlers have not fished krill concentrations to the extent that a decrease in krill biomass in this area can be detected from these data. The percentages of “Egui” as an indicator of greenness of krill were too variable among trawlers to be an objective indicator at present.

Endo, Y. and Y. Shimadzu (1989), Size and density of krill layers fished by a Japanese trawler in the waters north of Livingston Island in January 1988

The size and density of fishable krill layers in the northern waters of Livingston Island were determined during the co-operative survey carried out by RV Kaiyo Maru and a Japanese trawler. The mean values of layer length, thickness and surface density were 3.25 km, 13.3 m and 228.0 g wet weight/m², respectively. The krill layers fished by the trawler during the co-operative survey were 44.5 times longer and 2.7 times thicker but 25% less dense than the typical swarms encountered during FIBEX surveys.

Ichii, T. and Y. Endo (1989), Brief comments on the simulation study made by Professor Butterworth on krill fishing by an individual Japanese trawler

In this paper, three essential questions are raised concerning the simulation study of the Japanese krill fishery carried out by Butterworth (1988). Firstly, the simulation study used krill distribution parameter values based on the FIBEX results, whereas Japanese vessels often operate on layers which are much larger than the swarms detected during FIBEX surveys. Since very little searching time is spent on layers, the utility of searching time data appears doubtful. Secondly, the utility of indices based on the sum of primary and secondary searching times (PST+SST) is also doubtful because SSTs are markedly dependent upon the type of products being produced, and the demand for each product varies substantially from one season to the next. Finally, attention is drawn to the unrealistic behaviour of the simulation model with respect to the values used for the minimum catch rate per overall elapsed time. It is suggested that an improvement in our knowledge of krill distribution is necessary before the routine implementation of searching time data collection is considered.

Croxall, J.P. (1989), Use of indices of predator status and performance in CCAMLR fishery management

This paper investigates how data on, or related to, reproductive performance of seabird and seal predators, collected as part of the CCAMLR Ecosystem Monitoring Program (CEMP) could be used in the management, by CCAMLR, of commercial fisheries. It reviews reasons why it is important for CCAMLR formally to use such data in its fishery management operations and discusses the constraints inherent in the CEMP data, both from predator monitoring and harvesting perspectives. An outline of a specific approach is provided, involving an assessment procedure and recommendations for management action. The three elements of the assessment are determining the magnitude and significance of changes in individual parameters, evaluating overall patterns of change within species, sites and areas and reviewing factors potentially influencing or correlated with the changes. The relative merits and feasibilities of recommendations for restrictions on the magnitude, timing and location of harvesting are reviewed, taking account of likely operational constraints on fisheries.

Marschoff, E. and B. González (1989), The use of analysis of penguin stomach contents in simultaneous study of prey and predator parameters

Size selectivity of krill by penguins is shown to be highly sensitive to the statistical assumptions made during the analysis of data. The nested ANOVA method is proposed as being the correct approach for analysis because lack of independence between krill specimens found in the stomach of a given penguin prevents the pooling of krill lengths from different samples. Samples taken in Bahía Esperanza were used to illustrate the different approaches to this analysis. A highly significant linear regression between krill size and time of sampling was found.

Full use of information obtained from analysis of penguin stomach contents requires block sampling designs. Replicating samples from the same penguin or studying portions of stomach samples at different stages of digestion are proposed as alternative methods.

Boveng, P. and J.L. Bengtson (1989), On the power to detect changes using the standard methods for monitoring parameters of predatory species

The CCAMLR guidelines (CCAMLR, 1989) for analyzing the statistical power to detect changes are applied using variance estimates from studies at the South Shetland Islands of lengths of first incubation shifts by penguins(Standard Method A2.1), duration of penguin foraging trips (A5.1), penguin breeding success (A6.1), penguin chick diet (A8.1), and fur seal foraging trip duration (C2.0). The other Standard Methods are not evaluated because the power analysis in the CCAMLR guidelines is inappropriate (fur seal pup growth rate C1.0), and/or because data from the studies considered here are insufficient for conducting power analyses (penguin arrival weight A1.1, trend in penguin population size A3.1, penguin demography A4.1, penguin fledging weight A7.1). Alternative forms for analyses of the power of Standard Methods A3.1, A5.1, C1.0, and C2.0 are proposed.

Boveng, P., J.L. Bengtson and M.E. Goebel (1989), Statistical power to detect changes in growth rates of Antarctic fur seal pups

Numerical simulations were used to investigate the power of methods for detecting changes (between years) in pup growth rates, the loss of power associated with obtaining weight samples on only three dates in a season, and potential means of increasing the power of the CCAMLR Ecosystem Monitoring Program Standard Method C1 (B). Using estimates of variance in pup weights obtained at Seal Island (60°59.5'S, 55°24.5'W), the simulations suggest that following the protocol of the Standard Method (50 pups of each sex, weighed on four dates at 28-day intervals) would result in the ability to detect a 17% change in the growth rate with a 10% chance of committing Type 1 or Type 2 errors. If only three samples(50 pups, 28-day intervals) are obtained, the detectable change increases to about 34% under the same conditions. Slight gains in power can be obtained in some cases, without increasing the total number of pups weighed in a season, by decreasing the time between weighings.

Whitehead, M.D. (1989), Sensitivity analysis for parameters of predatory species CCAMLR Ecosystem Monitoring Program

Following the request of the Scientific Committee of CCAMLR to conduct sensitivity analyses on existing data regarding predator breeding biology parameters, this report presents such a treatment of data obtained at the Magnetic Island Adélie penguin colony in Prydz Bay in the 1987/88 and 1988/89 breeding seasons.

The data on the following parameters were analyzed:

• adult weight on arrival at breeding colonies;
• duration of first incubation shift;
• duration of adult foraging trips;
• breeding success; and
• chick fledging weight.