An attempt to derive a composite index of abundance from acoustic surveys and fishery data

Maps of krill (Euphausia superba) density derived from acoustic survey data and the distribution of fishing effort in the Chilean krill fishery indicate an area of high krill density wrapping around the northwestern end of Elephant Island during the austral summer of 1992. In this area, the distribution of catch-per-fishing-time and krill density (measured acoustically) show similar forms. Search time could not be used to estimate other aspects of krill distribution pattern because fishing operations are limited by processing efficiency rather than availability of krill. Analysis of the acoustic survey data suggested characteristic distribution pattern scales of 1.7 and 4 n.mile. Estimates of a composite index of krill abundance (SC-CCAMLR-VIII, 1989) were derived for two surveys from these data sets. In addition, the data suggest that the abundance of krill in the Elephant Island area can change rapidly, and when krill do come into to the area they are most often found in water 100m-500m depth along the shelf break north of Elephant Island, particularly in the area where it wraps around the western end of the island.