CCAMLR

Methods for the calculation of the horizontal opening (swept area) of a bottom trawl are discussed. Details of the Scanmar trawl monitoring equipment used for making in situ measurements of horizontal opening and headline height of the FP-1 20 trawl during the 1993/94 UK fish stock assessment survey around South Georgia on the MV Cordella are provided. Empirical equations are derived for the calculation of horizontal opening from other, more easily obtained measurements, such as tow speed and trawI depth. A new multiple regression equation is compared to that used previously for the estimation of biomass parameters of the major fish species around South Georgia. The resulting difference in biomass estimates is of the order of a 1% to 5% increase, depending upon species.

A long lining stock depletion trial was undertaken by the Korean longliner Ihn Sung 66 in January 1994 in accordance with CCAMLR Conservation Measure 69/XII and the Experimental Protocol circulated by the Secretariat in COMM CIRC 93/50. The results of this experiment are presented. Leslie and DeLury methods are tested using simulations to determine the most appropriate method. The Leslie method is applied using a specialized Catch and Effort Data Analysis computer package (CEDA) to calculate local abundance. Various alternative error models are investigated to estimate confidence intervals for the local stock estimate. The initial population size was estimated to be 2914 fish. Assuming a fishable area of 50 nm2 this represented a density of 0.5kg/nm2 Suggestions are made for the design of future depletion experiments.

Traditional methods for estimating yield per recruit as a function of fishing mortality can result in inappropriate high estimates of yield that could lead to depletion of stocks because of widely varying recruitment patterns, overestimation of the abundance of the stock and age of the most recent survey. These problems are addressed in this paper by using stock projections to assess the probabilities of the stock of Electrona carlsbergi becoming depleted over a 20 year period. These projections have been undertaken using a generalised version of the CCAMLR Krill Yield Model. This is appropriate because this species has a number of similar attributes to krill, including population dynamics, behaviour and its importance as prey in the Antarctic ecosystem. The decision rules for determining yield adopted by Working Group on Krill were adopted for this analysis (where yield = γ.median pre-exploitation biomass): (i) choose γ1, so that the probability of the spawning biomass dropping below 20% of its pre-exploitation median level over a 20-year harvesting period is 10%; (ii) choose γ2, so that the median escapement over a 20-year period is 75%; (iii) select the lower of γ1 and γ2 as the level of γ for calculation of yield. The estimate of γ for a fishery targetting juvenile fish was 0.091.

The progress of the fishery for Dissostichus eleginoides in Subarea 48.3 in the 1993/94 season is described. Fishing took place around Shag rocks and South Georgia, being concentrated in 4 of the 5 experimental areas. CPUE for 1994 appears similar to that from previous years except for Chilean vessels.

As requested by the WG last year, the Secretariat circulated a list of software supported at the Secretariat with the Agendas and invitations to attend the working group. This document gives additional information on software and platforms available.

In 1991, the 0 age-class of C. gunnari were sampled at Shag Rocks on 18 January, off Possession Bay, South Georgia during 19-20 January and off much of the north-east coast of South Georgia between to 19 January to 19 February.
The size- frequency of fish at Shag Rocks contained two modes of 31-46mm and 55-87mm SL. however, off Possession Bay only one mode of 25-57mm SL was apparent. Fish in combined samples off the coast of South Georgia were 24-63mm SL. The mean and median sizes of the fish at these locations were all significantly (p The size difference between the larger size mode at Shag Rocks and those at South Georgia must be the result of different spawning seasons and/or egg development periods and/or growth rates. This suggests that there are two separate stocks of C. gunnari in a single CCAMLR statistical sub-area.
There is an apparent growth of around 0.76% SL d-1 (0.27mm SL d-1) for larvae on the South Georgia shelf which is comparable with previous reports of early growth in C. gunnari.

The diet composition and feeding intensity of mackerel icefish ( Champsocephalus gunnari) around Shag Rocks and the mainland of South Georgia was analyzed from 3,691 stomachs collected in January/February 1994. Main prey items were the amphipod hyperiid Themisto gaudichaudii, mysids (primarily Antarctomysis maxima), and krill (Euphausia superba) in the vicinity of South Georgia and T. gaudichaudii and Thysanoessa sp. around Shag Rocks.