CCAMLR

This paper presents a model of Sequential Population Analysis (SPA), based in catch at age data, for the evaluation of the state of the stock of Dissostichus eleginoides from the area 48.3 between 1992 to 1996. This, with the objective of knowing the results of management of this stock made under CCAMLR procedures. The model was programmed in a spreadsheet (Excel v.5) using the Solver function for the non-lineal calculus process. The application of this model, tuned by auxiliary information of effort, shows that the estimation of recruitment and the level of the TAG are extremely similar to those calculated by the WG-FSA in 1995 when F2/3 was applied, which allowed height level of spawning biomass per recruit escape. This event was even higher than that suggested by the rule of decision γl of CCAMLR. By other hand, the descent trends in Total, Fishable and Spawning Biomass showed a stabilization during the last year (1996) in relation to the previous ones. This result supports the idea that the use of the stochastic projections adopted by consensus last year, has produced an appropriate and promising assessment.

Data from individual trawls carried out by vessels operating in the krill fishery at South Georgia are examined and a range of descriptive measurements reflecting the operation of the fishery are produced. The measurements indicate that the krill fishery at South Georgia is geographically focussed, operating in a limited area along the shelf edge on the northern coast of the island. Each day a large number of trawls were undertaken by each ,vessel, with trawls being shorter in duration during the middle of the day. Daytime trawls were also generally deeper and produced a larger catch. Individual trawls were examined to establish the time required for each phase of the operation. The times associated with shooting and hauling the net were usually short and showed little variation, whereas the time associated with the actual trawl phase was longer and more variable. The distance between consecutive trawls was generally small, indicating that little effort was spent searching beyond the near neighbourhood. However, this phase of the operation took almost as long as the trawl itself and showed similar levels of variability. The range of measurements indicate that differences existed between years. Particular aspects of the variability are discussed in relation to the biology of krill, others are discussed in relation to the fishery operation.

The Polar Front (PF) forms the southern boundary to the Polar Frontal Zone (PFZ) along the northern edge of the Antarctic Circumpolar Current (ACC). In a number of areas the position of the PF (and thus the PFZ) is known to be influenced by topographic steering, while local bathymetry has also been implicated in the movement and retention of various associated mesoscale features. In this paper we examine the structure and position of the PF as it passes over the rugged bathymetry to the north of the Scotia Sea. Results are presented from an oceanographic transect crossing the PF to the northwest of South Georgia and from a pair of shorter transects south of the PF but north and east of the first. Associated with the PF was a narrow, high-speed flow embedded in broader, slower moving regions. This high-speed flow was found to have a geostrophic component of velocity that was slower than estimates for other regions of the PF. Comparisons with output from recent oceanographic models were found to be consistent with the physical observations. A second examination of the region after a period of 30 days suggested that the surface expression of the PF had shifted southward by approximately 35 km but that the PF was essentially in the same position over the southern edge of the Maurice Ewing Bank. An advanced very high resolution radiometer image taken during the cruise provided additional information about the position of the surface expression of the PF and the extent of mesoscale features that were present to the north of the study area. Immediately to the north of South Georgia, water in the eastward flow of the ACC meets colder, more saline water flowing west along the north coast of the island. The area where these two flows meet was found to be variable over the 30-day timescale of the cruise. This area is known to be of major biological significance, and variability in the local oceanography is possibly of crucial importance to many predator species breeding at the northern end of South Georgia.