CCAMLR

The distributional features and physical characteristics of some 1500 krill (Euphausia superba Dana) aggregations detected and sized acoustically in the south-west Indian Ocean are described. The aggregations were on average considerably smaller than elsewhere in the Antarctic. Aggregation biomass was log-normally distributed with a mean of 0.18 t. Only 3% of the aggregations were heavier than 1 t. The aggregations were on average 4.2 km apart along-track, and on 10 of the 15 survey days were randomly distributed, judged by a Chi-square test based on expected Poisson statistics. The distribution of aggregations heavier than 1 t, and of aggregations 20 km on either side of such aggregations was similarly judged to be random. These observations suggest widespread randomness throughout the survey area, which is consistent with the absence of pronounced hydrographic or topographic concentrating mechanisms in the region. On the 5 non-random days, aggregations were smaller than average and were clustered on a scale of I km, suggesting that they could have been in the process of fragmenting or amalgamating. Estimates of the mean nearest-neighbour distance were derived for the random distributions. It is suggested that these could be useful in the development of fisheries-dependent indices of krill abundance.

Polar Biology (in press)

In this paper, I show how data that are routinely collected by survey vessels can be used to estimate the number of Concentrations of krill (in the sense of Butterworth (1988), Mangel (1988)) in a given region of the southern ocean. Sample computations are performed, using data collected by Soviet research/survey vessels in the early 1980s. These examples highlight the need for a navigational log as well as a fishing log in order to make accurate inferences.