The longevity of krill is still a matter of controversy; however, there are indications that krill may live for more than four years. The traditional and often misleading method of determining krill age has been to examine the length frequency distribution of catches, regarding peaks in the histrogram as year-classes. Since krill moult and shrink in body size as an overwintering strategy, successive year-classes of mature krill can overlap, obscuring the length-age relationship. This method is being replaced by an innovative approach using lipofuscin, also called age pigment, which accumulates in the organism over time (Ettershank, 1984). The lipofuscin molecule is easily identified, since it is very large and characteristically fluorescent.

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