Krill Stocks

Many computations have been made of production and standing stock of krill, and most estimates of annual harvestable yield range from 100 to 150 million tonnes. These figures have been derived using a variety of approaches including the consumption of past and present stocks of whales (based on their length of residence in Antarctic waters, volume of stomach contents, and energy requirements); the consumption by other vertebrate predators; the catch rates of krill in plankton nets; and the proportion of primary production that is converted to krill.

However, there are no accurate data on the magnitude of either the standing stock or annual production of E. superba. It is popularly believed that krill stocks increased after whale stocks decreased. While there is indirect evidence that this occurred (e.g., increase in the population of winged birds, penguins and seals that feed on krill), direct evidence is lacking. Present techniques of estimating krill biomass directly from net hauls or by acoustic methods are subject to considerable variance because of the structure and highly irregular distribution of the swarms and the proportion of krill living outside the swarms. Such estimates may also be biased because of other factors; for example, large krill escape from most nets, and scientists lack information on the acoustic properties of krill, either individually or in swarms, which limits the accuracy of estimates based on use of an echosounder.

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