MODELS OF THE EARLY LIFE-HISTORY OF EUPHAUSIA-SUPERBA .2. LAGRANGIAN CALCULATIONS

A three-dimensional time-dependent model of the circulation in the Bransfield Strait-South Shetland Islands region and a physiologically-based, temperature-dependent model of the descent-ascent behavior of the embryos and larvae of Euphausia superba were combined in a Lagrangian particle tracing model to simulate trajectories of krill embryos and larvae. The Lagrangian calculations show that: (1) surface flow is the primary factor influencing the final location of the embryo-larva particle: and (2) timing of krill spawning affects the eventual position of the feeding larvae. Seasonal changes in the wind stress field result in variability in direction and velocity of surface currents, which affects the embryo-larva trajectories. Conditions favourable for the transport of larvae to Bransfield Strait occur early in the spawning season. East of the Antarctic Peninsula larvae have a greater probability of entering Bransfield Strait if the krill embryos are released in mid-summer, January to February. Embryos released to the north of the South Shetland Islands. west of 62-degrees-W are transported into Drake Passage. Embryos released to the north of the South Shetland Islands and east of Livingston Island are transported westward where they can eventually enter Bransfield Strait. Krill larvae also are transported into Bransfield Strait from the Bellingshausen and Weddell Seas. The Lagrangian trajectories show that the western Bransfield Strait is a region of potentially high larval concentration due to transport from surrounding areas as well as local production. This is in agreement with observed krill larvae distributions, which show higher concentrations in this region.