CCAMLR

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.

Patagonian toothfish, Dissostichus eleginoides, spawn over the continental slope from July to September. Eggs have been observed primarily in the upper part of the water column over 2200-4400 m bottom depth. Embryos in stage III and IV of their embryonic development are described. Hatching is likely to occur in October/November. Scales do not start to form before the fish are 64-74 mm long.

Areas of seabed within 50m depth contours down to 100m and within 100m depth contours from 100 to 500m have been estimated from soundings obtained during plankton and bottom trawl surveys around Elephant Island (the northernmost island of the South Shetland Islands) from 1977/78 to 1992/93. The results are presented on a fine scale grid of 15’ lat x 30’ long.

Of 409 Notothenia coriiceps specimens tagged and released at Potter Cove, South Shetland Islands, in successive years from 1989 to 1992, 9 were recaptured at the same site after periods of 11-21 months. A comparison was carried out between the annuli found in scales removed before and after the period of liberty. In scales of those specimens recovered after 11-13 months, one extra annulus was laid down. The same analysis in one individual recovered after 21 months resulted in 2 extra closely spaced sclerites zones, which corresponded with an elapse of two winter seasons. The comparative analysis between scales taken at recapture and otolith cross sections of the same individual allowed a simultaneous counting of the annuli with good agreement. These results validate the principle of annual deposition of the annulus in scales and otoliths of N. coriiceps. A preliminary analysis of scales regenerated after release indicates that these observations are of value in validation studies.