The control of the population size of krill has been related to predation (Marr, 1962; Laws, 1985; Murphy, 1995; Reid & Croxall, 2001) and to food resources within winter sea ice (Quetin et al., 1996; Siegel, 2000). Atkinson et al. (2004), analyzing the data of the stock and the span from 1926 to 2003, showed a direct link between annual krill density an sea-ice cover. This factor seems to be a dominant role not only in krill recruitment (Quetin et al., 1996; Siegel, 2000), but also in the population size (Atkinson et al., 2004). The link found with summer density of krill by Atkinson et al. (2004) was with ice cover the preceding winter. This lag period suggest the larval over-wintering as a key process affected by ice, larvae must be survive their first winter to recruit the following summer (Atkinson et al., 2004) and they need to double in length (Quetin et al., 1996) . Sufficient winter ice in the major spawning and nursery areas (the Antarctic Peninsula and Southern Scotia Arc, Marr, 1962; Quetin et al., 1996; Siegel, 2000; Hofmann & Hüsrevo?lu, 2003) affects krill density across a whole ocean basin. But the western Antarctic Peninsula is fastest warming area, and the winter sea ice duration is shortening (Parkinson, 2002). So the krill spawning and nursery areas are situated in region sensitive to environmental changes (Atkinson et al., 2004).
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