This paper presents a flexible structure for a general yield model, which provides flexibility for assessing the influence of different patterns of growth, natural mortality, spawning and fishing on the estimates of yield per recruit. Also, it can be used to evaluate the performance of a stock under a specified catch regime. The model uses an adaptive Runge-Kutta procedure to evaluate stock trajectories and catch rates over a simulation period. In particular, this procedure calculates catches over each year by integrating a set of differential equations which incorporate functions that specify the rate of change or magnitude of parameters, such as growth, mortality, age dependent selectivity and seasonal patterns in fishing mortality, at specified time intervals during the year. This general approach also includes an option for a stock to experience a known catch history before the constant catch regime is introduced.

The survey comprised 48 bottom trawl hauls taken in subarea 48.3. About 80% of the hauls were intended as replicates of the position of hauls in the 1994 survey, allowing site by site comparison between both cruises. Of these, 20 hauls were located at less than 0.5 miles and 11 between 0.5 and 1.0 miles from those in the previous survey. Mean densities were obtained considering the spatial aggregation of stations in a nested ANOVA model. An increase over last year's values was observed in the density of several species, particularly Champsocephalus gunnari at the shelf of the South Georgia Islands. The age and size structure of this species in the whole subarea 48.3 is characterized the predominance of the younger fraction (below 4 years: 99.3% at the South Georgia Islands and 93.4 % at Shag Rocks). Along the cruise, 128 oceanographical stations were occupied. Oceanographical conditions were largely within the historical limits except for a the possible presence of a large eddy in the northern part of the Scotia Sea. Plankton samples contained krill more often than last year and an hydroacoustical survey for krill which covered a total of 800 nautical miles in the South Georgia shelf has shown the presence of krill aggregations in larger quantities than in last years survey.