Determination of a statistically based survey area suitable for hydroacoustic stock assessment of Euphausia superba in the Elephant Island, King George Island, Bransfield Strait area

The selection of a survey area of sufficient size to acount for the migratory behavior of krill and based on evaluating the variance structure of sampling within the area from a time-series of data from 1981, 1984 and 1978-1989 permitted resolution of inter-year differences in standing stock. The two units of sub-area within the site exhibit different patterns of annual distribution, but the combined total standing stock has a consistent variance to mean biomass relationship that appears relatively uniform from year to year. Using only sub-area biomass leads to an ambiguous interpretation of the data as to whether high or law standing stock is due to low production (ie. "good" year vs. “bad” year) or differential effects of migration. Using the total of both sub-areas the survey area can be shown to exhibit high standing stock (greater than 2 million tons) years, moderate standing stock (approximately 1 million tons) years, and low standing stock (less than 1/2 million ton) years. The size of the total area (200 m by 200 nm) can be adequately surveyed in 10 to 14 days and covers sufficient area to probably encompasses the migratory range of a single group of krill within the period of observation and with a predominant origin of individuals from the Weddell Sea. The size of the area and the approach taken to evaluate it may have broader utility in establishing similar survey areas at other localities in the Antarctic.