Krill Vertical Migrations in the Ross Sea

摘要

Krill vertical migrations in the Ross Sea were studied on the basis of three expeditions during the Antarctic summers of 1989/90, 1994/95 and 1997. Although there was no light change in the area during this time of a year krill did change its depth within a 24 hour cycle. The depth of krill swarms was averaged over two hour time intervals and approximated by the function H(t)=H_o + A_1 cos (2πt/T_1 +Φ_1) +A_2 cos (2πt/T_2+Φ_2), where H_o is the mean depth of krill, A_1 and A_2 are the amplitudes of migrations with periods of T_1=24 hour and T_2=12 hour accordingly,Φ_1 and Φ_2 are the phases of the migration, determining the time when migrations start. The migration pattern differed between years, with no migration in 1989/90, inverse migration in 1994 and classical migration in 1997. The amplitude of migrations was increasing with the length of individuals and with the latitude. The 24 hours periodicity was best pronounced for large adult krill, while for juvenes 12 hours cycle dominated.