Distribution characteristics of krill aggregations in the fishing ground off Coronation Island in the 1989/90 season
Distributional characteristics of krill aggregations in the Coronation Island fishing ground were examined in relation to environmental factors, the biological condition of krill and the performance of the fishery. Investigations were carried out from October 1989 to February 1990. An echo sounder was used to assess the characteristics of krill aggregations. Krill was harvested by standard midwater trawls with a horizontal mouth opening of 33 m. All common types of krill aggregations were recorded in the Coronation Island area over the observation period. From November to February scattered forms of krill tended to combine into larger aggregations. Wind force had no direct or indirect influence on the types of krill aggregations or their density. The increased temperature towards the end of the season, however, assisted the development of phytoplankton which in turn led to an increase in krill concentration. The biological parameters of krill examined (stages of maturity, sex ratio and krill size) varied according to aggregation type. The results obtained should be regarded as preliminary since they were based on data from one season only. Distributional characteristics of krill aggregations varied significantly over time. It was therefore recommended that CPUE simulation studies take into account the actual distributional features of targeted aggregations and the catchability rates of the trawls used at different times in the life of the fishery.